1<?xml version="1.0" standalone="no"?> 2<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" 3"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" 4[ 5]> 6 7<article id="index"> 8 <articleinfo> 9 <title>D-Bus Specification</title> 10 <releaseinfo>Version 0.12</releaseinfo> 11 <date>7 November 2006</date> 12 <authorgroup> 13 <author> 14 <firstname>Havoc</firstname> 15 <surname>Pennington</surname> 16 <affiliation> 17 <orgname>Red Hat, Inc.</orgname> 18 <address> 19 <email>hp@pobox.com</email> 20 </address> 21 </affiliation> 22 </author> 23 <author> 24 <firstname>Anders</firstname> 25 <surname>Carlsson</surname> 26 <affiliation> 27 <orgname>CodeFactory AB</orgname> 28 <address> 29 <email>andersca@codefactory.se</email> 30 </address> 31 </affiliation> 32 </author> 33 <author> 34 <firstname>Alexander</firstname> 35 <surname>Larsson</surname> 36 <affiliation> 37 <orgname>Red Hat, Inc.</orgname> 38 <address> 39 <email>alexl@redhat.com</email> 40 </address> 41 </affiliation> 42 </author> 43 </authorgroup> 44 </articleinfo> 45 46 <sect1 id="introduction"> 47 <title>Introduction</title> 48 <para> 49 D-Bus is a system for low-latency, low-overhead, easy to use 50 interprocess communication (IPC). In more detail: 51 <itemizedlist> 52 <listitem> 53 <para> 54 D-Bus is <emphasis>low-latency</emphasis> because it is designed 55 to avoid round trips and allow asynchronous operation, much like 56 the X protocol. 57 </para> 58 </listitem> 59 <listitem> 60 <para> 61 D-Bus is <emphasis>low-overhead</emphasis> because it uses a 62 binary protocol, and does not have to convert to and from a text 63 format such as XML. Because D-Bus is intended for potentially 64 high-resolution same-machine IPC, not primarily for Internet IPC, 65 this is an interesting optimization. 66 </para> 67 </listitem> 68 <listitem> 69 <para> 70 D-Bus is <emphasis>easy to use</emphasis> because it works in terms 71 of <firstterm>messages</firstterm> rather than byte streams, and 72 automatically handles a lot of the hard IPC issues. Also, the D-Bus 73 library is designed to be wrapped in a way that lets developers use 74 their framework's existing object/type system, rather than learning 75 a new one specifically for IPC. 76 </para> 77 </listitem> 78 </itemizedlist> 79 </para> 80 81 <para> 82 The base D-Bus protocol is a one-to-one (peer-to-peer or client-server) 83 protocol, specified in <xref linkend="message-protocol"/>. That is, it is 84 a system for one application to talk to a single other 85 application. However, the primary intended application of the protocol is the 86 D-Bus <firstterm>message bus</firstterm>, specified in <xref 87 linkend="message-bus"/>. The message bus is a special application that 88 accepts connections from multiple other applications, and forwards 89 messages among them. 90 </para> 91 92 <para> 93 Uses of D-Bus include notification of system changes (notification of when 94 a camera is plugged in to a computer, or a new version of some software 95 has been installed), or desktop interoperability, for example a file 96 monitoring service or a configuration service. 97 </para> 98 99 <para> 100 D-Bus is designed for two specific use cases: 101 <itemizedlist> 102 <listitem> 103 <para> 104 A "system bus" for notifications from the system to user sessions, 105 and to allow the system to request input from user sessions. 106 </para> 107 </listitem> 108 <listitem> 109 <para> 110 A "session bus" used to implement desktop environments such as 111 GNOME and KDE. 112 </para> 113 </listitem> 114 </itemizedlist> 115 D-Bus is not intended to be a generic IPC system for any possible 116 application, and intentionally omits many features found in other 117 IPC systems for this reason. 118 </para> 119 120 <para> 121 At the same time, the bus daemons offer a number of features not found in 122 other IPC systems, such as single-owner "bus names" (similar to X 123 selections), on-demand startup of services, and security policies. 124 In many ways, these features are the primary motivation for developing 125 D-Bus; other systems would have sufficed if IPC were the only goal. 126 </para> 127 128 <para> 129 D-Bus may turn out to be useful in unanticipated applications, but future 130 versions of this spec and the reference implementation probably will not 131 incorporate features that interfere with the core use cases. 132 </para> 133 134 <para> 135 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 136 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 137 document are to be interpreted as described in RFC 2119. However, the 138 document could use a serious audit to be sure it makes sense to do 139 so. Also, they are not capitalized. 140 </para> 141 142 <sect2 id="stability"> 143 <title>Protocol and Specification Stability</title> 144 <para> 145 The D-Bus protocol is frozen (only compatible extensions are allowed) as 146 of November 8, 2006. However, this specification could still use a fair 147 bit of work to make interoperable reimplementation possible without 148 reference to the D-Bus reference implementation. Thus, this 149 specification is not marked 1.0. To mark it 1.0, we'd like to see 150 someone invest significant effort in clarifying the specification 151 language, and growing the specification to cover more aspects of the 152 reference implementation's behavior. 153 </para> 154 <para> 155 Until this work is complete, any attempt to reimplement D-Bus will 156 probably require looking at the reference implementation and/or asking 157 questions on the D-Bus mailing list about intended behavior. 158 Questions on the list are very welcome. 159 </para> 160 <para> 161 Nonetheless, this document should be a useful starting point and is 162 to our knowledge accurate, though incomplete. 163 </para> 164 </sect2> 165 166 </sect1> 167 168 <sect1 id="message-protocol"> 169 <title>Message Protocol</title> 170 171 <para> 172 A <firstterm>message</firstterm> consists of a 173 <firstterm>header</firstterm> and a <firstterm>body</firstterm>. If you 174 think of a message as a package, the header is the address, and the body 175 contains the package contents. The message delivery system uses the header 176 information to figure out where to send the message and how to interpret 177 it; the recipient interprets the body of the message. 178 </para> 179 180 <para> 181 The body of the message is made up of zero or more 182 <firstterm>arguments</firstterm>, which are typed values, such as an 183 integer or a byte array. 184 </para> 185 186 <para> 187 Both header and body use the same type system and format for 188 serializing data. Each type of value has a wire format. 189 Converting a value from some other representation into the wire 190 format is called <firstterm>marshaling</firstterm> and converting 191 it back from the wire format is <firstterm>unmarshaling</firstterm>. 192 </para> 193 194 <sect2 id="message-protocol-signatures"> 195 <title>Type Signatures</title> 196 197 <para> 198 The D-Bus protocol does not include type tags in the marshaled data; a 199 block of marshaled values must have a known <firstterm>type 200 signature</firstterm>. The type signature is made up of <firstterm>type 201 codes</firstterm>. A type code is an ASCII character representing the 202 type of a value. Because ASCII characters are used, the type signature 203 will always form a valid ASCII string. A simple string compare 204 determines whether two type signatures are equivalent. 205 </para> 206 207 <para> 208 As a simple example, the type code for 32-bit integer (<literal>INT32</literal>) is 209 the ASCII character 'i'. So the signature for a block of values 210 containing a single <literal>INT32</literal> would be: 211 <programlisting> 212 "i" 213 </programlisting> 214 A block of values containing two <literal>INT32</literal> would have this signature: 215 <programlisting> 216 "ii" 217 </programlisting> 218 </para> 219 220 <para> 221 All <firstterm>basic</firstterm> types work like 222 <literal>INT32</literal> in this example. To marshal and unmarshal 223 basic types, you simply read one value from the data 224 block corresponding to each type code in the signature. 225 In addition to basic types, there are four <firstterm>container</firstterm> 226 types: <literal>STRUCT</literal>, <literal>ARRAY</literal>, <literal>VARIANT</literal>, 227 and <literal>DICT_ENTRY</literal>. 228 </para> 229 230 <para> 231 <literal>STRUCT</literal> has a type code, ASCII character 'r', but this type 232 code does not appear in signatures. Instead, ASCII characters 233 '(' and ')' are used to mark the beginning and end of the struct. 234 So for example, a struct containing two integers would have this 235 signature: 236 <programlisting> 237 "(ii)" 238 </programlisting> 239 Structs can be nested, so for example a struct containing 240 an integer and another struct: 241 <programlisting> 242 "(i(ii))" 243 </programlisting> 244 The value block storing that struct would contain three integers; the 245 type signature allows you to distinguish "(i(ii))" from "((ii)i)" or 246 "(iii)" or "iii". 247 </para> 248 249 <para> 250 The <literal>STRUCT</literal> type code 'r' is not currently used in the D-Bus protocol, 251 but is useful in code that implements the protocol. This type code 252 is specified to allow such code to interoperate in non-protocol contexts. 253 </para> 254 255 <para> 256 <literal>ARRAY</literal> has ASCII character 'a' as type code. The array type code must be 257 followed by a <firstterm>single complete type</firstterm>. The single 258 complete type following the array is the type of each array element. So 259 the simple example is: 260 <programlisting> 261 "ai" 262 </programlisting> 263 which is an array of 32-bit integers. But an array can be of any type, 264 such as this array-of-struct-with-two-int32-fields: 265 <programlisting> 266 "a(ii)" 267 </programlisting> 268 Or this array of array of integer: 269 <programlisting> 270 "aai" 271 </programlisting> 272 </para> 273 274 <para> 275 The phrase <firstterm>single complete type</firstterm> deserves some 276 definition. A single complete type is a basic type code, a variant type code, 277 an array with its element type, or a struct with its fields. 278 So the following signatures are not single complete types: 279 <programlisting> 280 "aa" 281 </programlisting> 282 <programlisting> 283 "(ii" 284 </programlisting> 285 <programlisting> 286 "ii)" 287 </programlisting> 288 And the following signatures contain multiple complete types: 289 <programlisting> 290 "ii" 291 </programlisting> 292 <programlisting> 293 "aiai" 294 </programlisting> 295 <programlisting> 296 "(ii)(ii)" 297 </programlisting> 298 Note however that a single complete type may <emphasis>contain</emphasis> 299 multiple other single complete types. 300 </para> 301 302 <para> 303 <literal>VARIANT</literal> has ASCII character 'v' as its type code. A marshaled value of 304 type <literal>VARIANT</literal> will have the signature of a single complete type as part 305 of the <emphasis>value</emphasis>. This signature will be followed by a 306 marshaled value of that type. 307 </para> 308 309 <para> 310 A <literal>DICT_ENTRY</literal> works exactly like a struct, but rather 311 than parentheses it uses curly braces, and it has more restrictions. 312 The restrictions are: it occurs only as an array element type; it has 313 exactly two single complete types inside the curly braces; the first 314 single complete type (the "key") must be a basic type rather than a 315 container type. Implementations must not accept dict entries outside of 316 arrays, must not accept dict entries with zero, one, or more than two 317 fields, and must not accept dict entries with non-basic-typed keys. A 318 dict entry is always a key-value pair. 319 </para> 320 321 <para> 322 The first field in the <literal>DICT_ENTRY</literal> is always the key. 323 A message is considered corrupt if the same key occurs twice in the same 324 array of <literal>DICT_ENTRY</literal>. However, for performance reasons 325 implementations are not required to reject dicts with duplicate keys. 326 </para> 327 328 <para> 329 In most languages, an array of dict entry would be represented as a 330 map, hash table, or dict object. 331 </para> 332 333 <para> 334 The following table summarizes the D-Bus types. 335 <informaltable> 336 <tgroup cols="3"> 337 <thead> 338 <row> 339 <entry>Conventional Name</entry> 340 <entry>Code</entry> 341 <entry>Description</entry> 342 </row> 343 </thead> 344 <tbody> 345 <row> 346 <entry><literal>INVALID</literal></entry> 347 <entry>0 (ASCII NUL)</entry> 348 <entry>Not a valid type code, used to terminate signatures</entry> 349 </row><row> 350 <entry><literal>BYTE</literal></entry> 351 <entry>121 (ASCII 'y')</entry> 352 <entry>8-bit unsigned integer</entry> 353 </row><row> 354 <entry><literal>BOOLEAN</literal></entry> 355 <entry>98 (ASCII 'b')</entry> 356 <entry>Boolean value, 0 is <literal>FALSE</literal> and 1 is <literal>TRUE</literal>. Everything else is invalid.</entry> 357 </row><row> 358 <entry><literal>INT16</literal></entry> 359 <entry>110 (ASCII 'n')</entry> 360 <entry>16-bit signed integer</entry> 361 </row><row> 362 <entry><literal>UINT16</literal></entry> 363 <entry>113 (ASCII 'q')</entry> 364 <entry>16-bit unsigned integer</entry> 365 </row><row> 366 <entry><literal>INT32</literal></entry> 367 <entry>105 (ASCII 'i')</entry> 368 <entry>32-bit signed integer</entry> 369 </row><row> 370 <entry><literal>UINT32</literal></entry> 371 <entry>117 (ASCII 'u')</entry> 372 <entry>32-bit unsigned integer</entry> 373 </row><row> 374 <entry><literal>INT64</literal></entry> 375 <entry>120 (ASCII 'x')</entry> 376 <entry>64-bit signed integer</entry> 377 </row><row> 378 <entry><literal>UINT64</literal></entry> 379 <entry>116 (ASCII 't')</entry> 380 <entry>64-bit unsigned integer</entry> 381 </row><row> 382 <entry><literal>DOUBLE</literal></entry> 383 <entry>100 (ASCII 'd')</entry> 384 <entry>IEEE 754 double</entry> 385 </row><row> 386 <entry><literal>STRING</literal></entry> 387 <entry>115 (ASCII 's')</entry> 388 <entry>UTF-8 string (<emphasis>must</emphasis> be valid UTF-8). Must be nul terminated.</entry> 389 </row><row> 390 <entry><literal>OBJECT_PATH</literal></entry> 391 <entry>111 (ASCII 'o')</entry> 392 <entry>Name of an object instance</entry> 393 </row><row> 394 <entry><literal>SIGNATURE</literal></entry> 395 <entry>103 (ASCII 'g')</entry> 396 <entry>A type signature</entry> 397 </row><row> 398 <entry><literal>ARRAY</literal></entry> 399 <entry>97 (ASCII 'a')</entry> 400 <entry>Array</entry> 401 </row><row> 402 <entry><literal>STRUCT</literal></entry> 403 <entry>114 (ASCII 'r'), 40 (ASCII '('), 41 (ASCII ')')</entry> 404 <entry>Struct</entry> 405 </row><row> 406 <entry><literal>VARIANT</literal></entry> 407 <entry>118 (ASCII 'v') </entry> 408 <entry>Variant type (the type of the value is part of the value itself)</entry> 409 </row><row> 410 <entry><literal>DICT_ENTRY</literal></entry> 411 <entry>101 (ASCII 'e'), 123 (ASCII '{'), 125 (ASCII '}') </entry> 412 <entry>Entry in a dict or map (array of key-value pairs)</entry> 413 </row> 414 </tbody> 415 </tgroup> 416 </informaltable> 417 </para> 418 419 </sect2> 420 421 <sect2 id="message-protocol-marshaling"> 422 <title>Marshaling (Wire Format)</title> 423 424 <para> 425 Given a type signature, a block of bytes can be converted into typed 426 values. This section describes the format of the block of bytes. Byte 427 order and alignment issues are handled uniformly for all D-Bus types. 428 </para> 429 430 <para> 431 A block of bytes has an associated byte order. The byte order 432 has to be discovered in some way; for D-Bus messages, the 433 byte order is part of the message header as described in 434 <xref linkend="message-protocol-messages"/>. For now, assume 435 that the byte order is known to be either little endian or big 436 endian. 437 </para> 438 439 <para> 440 Each value in a block of bytes is aligned "naturally," for example 441 4-byte values are aligned to a 4-byte boundary, and 8-byte values to an 442 8-byte boundary. To properly align a value, <firstterm>alignment 443 padding</firstterm> may be necessary. The alignment padding must always 444 be the minimum required padding to properly align the following value; 445 and it must always be made up of nul bytes. The alignment padding must 446 not be left uninitialized (it can't contain garbage), and more padding 447 than required must not be used. 448 </para> 449 450 <para> 451 Given all this, the types are marshaled on the wire as follows: 452 <informaltable> 453 <tgroup cols="3"> 454 <thead> 455 <row> 456 <entry>Conventional Name</entry> 457 <entry>Encoding</entry> 458 <entry>Alignment</entry> 459 </row> 460 </thead> 461 <tbody> 462 <row> 463 <entry><literal>INVALID</literal></entry> 464 <entry>Not applicable; cannot be marshaled.</entry> 465 <entry>N/A</entry> 466 </row><row> 467 <entry><literal>BYTE</literal></entry> 468 <entry>A single 8-bit byte.</entry> 469 <entry>1</entry> 470 </row><row> 471 <entry><literal>BOOLEAN</literal></entry> 472 <entry>As for <literal>UINT32</literal>, but only 0 and 1 are valid values.</entry> 473 <entry>4</entry> 474 </row><row> 475 <entry><literal>INT16</literal></entry> 476 <entry>16-bit signed integer in the message's byte order.</entry> 477 <entry>2</entry> 478 </row><row> 479 <entry><literal>UINT16</literal></entry> 480 <entry>16-bit unsigned integer in the message's byte order.</entry> 481 <entry>2</entry> 482 </row><row> 483 <entry><literal>INT32</literal></entry> 484 <entry>32-bit signed integer in the message's byte order.</entry> 485 <entry>4</entry> 486 </row><row> 487 <entry><literal>UINT32</literal></entry> 488 <entry>32-bit unsigned integer in the message's byte order.</entry> 489 <entry>4</entry> 490 </row><row> 491 <entry><literal>INT64</literal></entry> 492 <entry>64-bit signed integer in the message's byte order.</entry> 493 <entry>8</entry> 494 </row><row> 495 <entry><literal>UINT64</literal></entry> 496 <entry>64-bit unsigned integer in the message's byte order.</entry> 497 <entry>8</entry> 498 </row><row> 499 <entry><literal>DOUBLE</literal></entry> 500 <entry>64-bit IEEE 754 double in the message's byte order.</entry> 501 <entry>8</entry> 502 </row><row> 503 <entry><literal>STRING</literal></entry> 504 <entry>A <literal>UINT32</literal> indicating the string's 505 length in bytes excluding its terminating nul, followed by 506 string data of the given length, followed by a terminating nul 507 byte. 508 </entry> 509 <entry> 510 4 (for the length) 511 </entry> 512 </row><row> 513 <entry><literal>OBJECT_PATH</literal></entry> 514 <entry>Exactly the same as <literal>STRING</literal> except the 515 content must be a valid object path (see below). 516 </entry> 517 <entry> 518 4 (for the length) 519 </entry> 520 </row><row> 521 <entry><literal>SIGNATURE</literal></entry> 522 <entry>The same as <literal>STRING</literal> except the length is a single 523 byte (thus signatures have a maximum length of 255) 524 and the content must be a valid signature (see below). 525 </entry> 526 <entry> 527 1 528 </entry> 529 </row><row> 530 <entry><literal>ARRAY</literal></entry> 531 <entry> 532 A <literal>UINT32</literal> giving the length of the array data in bytes, followed by 533 alignment padding to the alignment boundary of the array element type, 534 followed by each array element. The array length is from the 535 end of the alignment padding to the end of the last element, 536 i.e. it does not include the padding after the length, 537 or any padding after the last element. 538 Arrays have a maximum length defined to be 2 to the 26th power or 539 67108864. Implementations must not send or accept arrays exceeding this 540 length. 541 </entry> 542 <entry> 543 4 (for the length) 544 </entry> 545 </row><row> 546 <entry><literal>STRUCT</literal></entry> 547 <entry> 548 A struct must start on an 8-byte boundary regardless of the 549 type of the struct fields. The struct value consists of each 550 field marshaled in sequence starting from that 8-byte 551 alignment boundary. 552 </entry> 553 <entry> 554 8 555 </entry> 556 </row><row> 557 <entry><literal>VARIANT</literal></entry> 558 <entry> 559 A variant type has a marshaled <literal>SIGNATURE</literal> 560 followed by a marshaled value with the type 561 given in the signature. 562 Unlike a message signature, the variant signature 563 can contain only a single complete type. 564 So "i" is OK, "ii" is not. 565 </entry> 566 <entry> 567 1 (alignment of the signature) 568 </entry> 569 </row><row> 570 <entry><literal>DICT_ENTRY</literal></entry> 571 <entry> 572 Identical to STRUCT. 573 </entry> 574 <entry> 575 8 576 </entry> 577 </row> 578 </tbody> 579 </tgroup> 580 </informaltable> 581 </para> 582 583 <sect3 id="message-protocol-marshaling-object-path"> 584 <title>Valid Object Paths</title> 585 586 <para> 587 An object path is a name used to refer to an object instance. 588 Conceptually, each participant in a D-Bus message exchange may have 589 any number of object instances (think of C++ or Java objects) and each 590 such instance will have a path. Like a filesystem, the object 591 instances in an application form a hierarchical tree. 592 </para> 593 594 <para> 595 The following rules define a valid object path. Implementations must 596 not send or accept messages with invalid object paths. 597 <itemizedlist> 598 <listitem> 599 <para> 600 The path may be of any length. 601 </para> 602 </listitem> 603 <listitem> 604 <para> 605 The path must begin with an ASCII '/' (integer 47) character, 606 and must consist of elements separated by slash characters. 607 </para> 608 </listitem> 609 <listitem> 610 <para> 611 Each element must only contain the ASCII characters 612 "[A-Z][a-z][0-9]_" 613 </para> 614 </listitem> 615 <listitem> 616 <para> 617 No element may be the empty string. 618 </para> 619 </listitem> 620 <listitem> 621 <para> 622 Multiple '/' characters cannot occur in sequence. 623 </para> 624 </listitem> 625 <listitem> 626 <para> 627 A trailing '/' character is not allowed unless the 628 path is the root path (a single '/' character). 629 </para> 630 </listitem> 631 </itemizedlist> 632 </para> 633 634 </sect3> 635 636 637 <sect3 id="message-protocol-marshaling-signature"> 638 <title>Valid Signatures</title> 639 <para> 640 An implementation must not send or accept invalid signatures. 641 Valid signatures will conform to the following rules: 642 <itemizedlist> 643 <listitem> 644 <para> 645 The signature ends with a nul byte. 646 </para> 647 </listitem> 648 <listitem> 649 <para> 650 The signature is a list of single complete types. 651 Arrays must have element types, and structs must 652 have both open and close parentheses. 653 </para> 654 </listitem> 655 <listitem> 656 <para> 657 Only type codes and open and close parentheses are 658 allowed in the signature. The <literal>STRUCT</literal> type code 659 is not allowed in signatures, because parentheses 660 are used instead. 661 </para> 662 </listitem> 663 <listitem> 664 <para> 665 The maximum depth of container type nesting is 32 array type 666 codes and 32 open parentheses. This implies that the maximum 667 total depth of recursion is 64, for an "array of array of array 668 of ... struct of struct of struct of ..." where there are 32 669 array and 32 struct. 670 </para> 671 </listitem> 672 <listitem> 673 <para> 674 The maximum length of a signature is 255. 675 </para> 676 </listitem> 677 <listitem> 678 <para> 679 Signatures must be nul-terminated. 680 </para> 681 </listitem> 682 </itemizedlist> 683 </para> 684 </sect3> 685 686 </sect2> 687 688 <sect2 id="message-protocol-messages"> 689 <title>Message Format</title> 690 691 <para> 692 A message consists of a header and a body. The header is a block of 693 values with a fixed signature and meaning. The body is a separate block 694 of values, with a signature specified in the header. 695 </para> 696 697 <para> 698 The length of the header must be a multiple of 8, allowing the body to 699 begin on an 8-byte boundary when storing the entire message in a single 700 buffer. If the header does not naturally end on an 8-byte boundary 701 up to 7 bytes of nul-initialized alignment padding must be added. 702 </para> 703 704 <para> 705 The message body need not end on an 8-byte boundary. 706 </para> 707 708 <para> 709 The maximum length of a message, including header, header alignment padding, 710 and body is 2 to the 27th power or 134217728. Implementations must not 711 send or accept messages exceeding this size. 712 </para> 713 714 <para> 715 The signature of the header is: 716 <programlisting> 717 "yyyyuua(yv)" 718 </programlisting> 719 Written out more readably, this is: 720 <programlisting> 721 BYTE, BYTE, BYTE, BYTE, UINT32, UINT32, ARRAY of STRUCT of (BYTE,VARIANT) 722 </programlisting> 723 </para> 724 725 <para> 726 These values have the following meanings: 727 <informaltable> 728 <tgroup cols="2"> 729 <thead> 730 <row> 731 <entry>Value</entry> 732 <entry>Description</entry> 733 </row> 734 </thead> 735 <tbody> 736 <row> 737 <entry>1st <literal>BYTE</literal></entry> 738 <entry>Endianness flag; ASCII 'l' for little-endian 739 or ASCII 'B' for big-endian. Both header and body are 740 in this endianness.</entry> 741 </row> 742 <row> 743 <entry>2nd <literal>BYTE</literal></entry> 744 <entry><firstterm>Message type</firstterm>. Unknown types must be ignored. 745 Currently-defined types are described below. 746 </entry> 747 </row> 748 <row> 749 <entry>3rd <literal>BYTE</literal></entry> 750 <entry>Bitwise OR of flags. Unknown flags 751 must be ignored. Currently-defined flags are described below. 752 </entry> 753 </row> 754 <row> 755 <entry>4th <literal>BYTE</literal></entry> 756 <entry>Major protocol version of the sending application. If 757 the major protocol version of the receiving application does not 758 match, the applications will not be able to communicate and the 759 D-Bus connection must be disconnected. The major protocol 760 version for this version of the specification is 0. 761 FIXME this field is stupid and pointless to put in 762 every message. 763 </entry> 764 </row> 765 <row> 766 <entry>1st <literal>UINT32</literal></entry> 767 <entry>Length in bytes of the message body, starting 768 from the end of the header. The header ends after 769 its alignment padding to an 8-boundary. 770 </entry> 771 </row> 772 <row> 773 <entry>2nd <literal>UINT32</literal></entry> 774 <entry>The serial of this message, used as a cookie 775 by the sender to identify the reply corresponding 776 to this request. 777 </entry> 778 </row> 779 <row> 780 <entry><literal>ARRAY</literal> of <literal>STRUCT</literal> of (<literal>BYTE</literal>,<literal>VARIANT</literal>)</entry> 781 <entry>An array of zero or more <firstterm>header 782 fields</firstterm> where the byte is the field code, and the 783 variant is the field value. The message type determines 784 which fields are required. 785 </entry> 786 </row> 787 </tbody> 788 </tgroup> 789 </informaltable> 790 </para> 791 <para> 792 <firstterm>Message types</firstterm> that can appear in the second byte 793 of the header are: 794 <informaltable> 795 <tgroup cols="3"> 796 <thead> 797 <row> 798 <entry>Conventional name</entry> 799 <entry>Decimal value</entry> 800 <entry>Description</entry> 801 </row> 802 </thead> 803 <tbody> 804 <row> 805 <entry><literal>INVALID</literal></entry> 806 <entry>0</entry> 807 <entry>This is an invalid type.</entry> 808 </row> 809 <row> 810 <entry><literal>METHOD_CALL</literal></entry> 811 <entry>1</entry> 812 <entry>Method call.</entry> 813 </row> 814 <row> 815 <entry><literal>METHOD_RETURN</literal></entry> 816 <entry>2</entry> 817 <entry>Method reply with returned data.</entry> 818 </row> 819 <row> 820 <entry><literal>ERROR</literal></entry> 821 <entry>3</entry> 822 <entry>Error reply. If the first argument exists and is a 823 string, it is an error message.</entry> 824 </row> 825 <row> 826 <entry><literal>SIGNAL</literal></entry> 827 <entry>4</entry> 828 <entry>Signal emission.</entry> 829 </row> 830 </tbody> 831 </tgroup> 832 </informaltable> 833 </para> 834 <para> 835 Flags that can appear in the third byte of the header: 836 <informaltable> 837 <tgroup cols="3"> 838 <thead> 839 <row> 840 <entry>Conventional name</entry> 841 <entry>Hex value</entry> 842 <entry>Description</entry> 843 </row> 844 </thead> 845 <tbody> 846 <row> 847 <entry><literal>NO_REPLY_EXPECTED</literal></entry> 848 <entry>0x1</entry> 849 <entry>This message does not expect method return replies or 850 error replies; the reply can be omitted as an 851 optimization. However, it is compliant with this specification 852 to return the reply despite this flag and the only harm 853 from doing so is extra network traffic. 854 </entry> 855 </row> 856 <row> 857 <entry><literal>NO_AUTO_START</literal></entry> 858 <entry>0x2</entry> 859 <entry>The bus must not launch an owner 860 for the destination name in response to this message. 861 </entry> 862 </row> 863 </tbody> 864 </tgroup> 865 </informaltable> 866 </para> 867 868 <sect3 id="message-protocol-header-fields"> 869 <title>Header Fields</title> 870 871 <para> 872 The array at the end of the header contains <firstterm>header 873 fields</firstterm>, where each field is a 1-byte field code followed 874 by a field value. A header must contain the required header fields for 875 its message type, and zero or more of any optional header 876 fields. Future versions of this protocol specification may add new 877 fields. Implementations must ignore fields they do not 878 understand. Implementations must not invent their own header fields; 879 only changes to this specification may introduce new header fields. 880 </para> 881 882 <para> 883 Again, if an implementation sees a header field code that it does not 884 expect, it must ignore that field, as it will be part of a new 885 (but compatible) version of this specification. This also applies 886 to known header fields appearing in unexpected messages, for 887 example: if a signal has a reply serial it must be ignored 888 even though it has no meaning as of this version of the spec. 889 </para> 890 891 <para> 892 However, implementations must not send or accept known header fields 893 with the wrong type stored in the field value. So for example a 894 message with an <literal>INTERFACE</literal> field of type 895 <literal>UINT32</literal> would be considered corrupt. 896 </para> 897 898 <para> 899 Here are the currently-defined header fields: 900 <informaltable> 901 <tgroup cols="5"> 902 <thead> 903 <row> 904 <entry>Conventional Name</entry> 905 <entry>Decimal Code</entry> 906 <entry>Type</entry> 907 <entry>Required In</entry> 908 <entry>Description</entry> 909 </row> 910 </thead> 911 <tbody> 912 <row> 913 <entry><literal>INVALID</literal></entry> 914 <entry>0</entry> 915 <entry>N/A</entry> 916 <entry>not allowed</entry> 917 <entry>Not a valid field name (error if it appears in a message)</entry> 918 </row> 919 <row> 920 <entry><literal>PATH</literal></entry> 921 <entry>1</entry> 922 <entry><literal>OBJECT_PATH</literal></entry> 923 <entry><literal>METHOD_CALL</literal>, <literal>SIGNAL</literal></entry> 924 <entry>The object to send a call to, 925 or the object a signal is emitted from. 926 </entry> 927 </row> 928 <row> 929 <entry><literal>INTERFACE</literal></entry> 930 <entry>2</entry> 931 <entry><literal>STRING</literal></entry> 932 <entry><literal>SIGNAL</literal></entry> 933 <entry> 934 The interface to invoke a method call on, or 935 that a signal is emitted from. Optional for 936 method calls, required for signals. 937 </entry> 938 </row> 939 <row> 940 <entry><literal>MEMBER</literal></entry> 941 <entry>3</entry> 942 <entry><literal>STRING</literal></entry> 943 <entry><literal>METHOD_CALL</literal>, <literal>SIGNAL</literal></entry> 944 <entry>The member, either the method name or signal name.</entry> 945 </row> 946 <row> 947 <entry><literal>ERROR_NAME</literal></entry> 948 <entry>4</entry> 949 <entry><literal>STRING</literal></entry> 950 <entry><literal>ERROR</literal></entry> 951 <entry>The name of the error that occurred, for errors</entry> 952 </row> 953 <row> 954 <entry><literal>REPLY_SERIAL</literal></entry> 955 <entry>5</entry> 956 <entry><literal>UINT32</literal></entry> 957 <entry><literal>ERROR</literal>, <literal>METHOD_RETURN</literal></entry> 958 <entry>The serial number of the message this message is a reply 959 to. (The serial number is the second <literal>UINT32</literal> in the header.)</entry> 960 </row> 961 <row> 962 <entry><literal>DESTINATION</literal></entry> 963 <entry>6</entry> 964 <entry><literal>STRING</literal></entry> 965 <entry>optional</entry> 966 <entry>The name of the connection this message is intended for. 967 Only used in combination with the message bus, see 968 <xref linkend="message-bus"/>.</entry> 969 </row> 970 <row> 971 <entry><literal>SENDER</literal></entry> 972 <entry>7</entry> 973 <entry><literal>STRING</literal></entry> 974 <entry>optional</entry> 975 <entry>Unique name of the sending connection. 976 The message bus fills in this field so it is reliable; the field is 977 only meaningful in combination with the message bus.</entry> 978 </row> 979 <row> 980 <entry><literal>SIGNATURE</literal></entry> 981 <entry>8</entry> 982 <entry><literal>SIGNATURE</literal></entry> 983 <entry>optional</entry> 984 <entry>The signature of the message body. 985 If omitted, it is assumed to be the 986 empty signature "" (i.e. the body must be 0-length).</entry> 987 </row> 988 </tbody> 989 </tgroup> 990 </informaltable> 991 </para> 992 </sect3> 993 </sect2> 994 995 <sect2 id="message-protocol-names"> 996 <title>Valid Names</title> 997 <para> 998 The various names in D-Bus messages have some restrictions. 999 </para> 1000 <para> 1001 There is a <firstterm>maximum name length</firstterm> 1002 of 255 which applies to bus names, interfaces, and members. 1003 </para> 1004 <sect3 id="message-protocol-names-interface"> 1005 <title>Interface names</title> 1006 <para> 1007 Interfaces have names with type <literal>STRING</literal>, meaning that 1008 they must be valid UTF-8. However, there are also some 1009 additional restrictions that apply to interface names 1010 specifically: 1011 <itemizedlist> 1012 <listitem><para>Interface names are composed of 1 or more elements separated by 1013 a period ('.') character. All elements must contain at least 1014 one character. 1015 </para> 1016 </listitem> 1017 <listitem><para>Each element must only contain the ASCII characters 1018 "[A-Z][a-z][0-9]_" and must not begin with a digit. 1019 </para> 1020 </listitem> 1021 1022 <listitem><para>Interface names must contain at least one '.' (period) 1023 character (and thus at least two elements). 1024 </para></listitem> 1025 1026 <listitem><para>Interface names must not begin with a '.' (period) character.</para></listitem> 1027 <listitem><para>Interface names must not exceed the maximum name length.</para></listitem> 1028 </itemizedlist> 1029 </para> 1030 </sect3> 1031 <sect3 id="message-protocol-names-bus"> 1032 <title>Bus names</title> 1033 <para> 1034 Connections have one or more bus names associated with them. 1035 A connection has exactly one bus name that is a unique connection 1036 name. The unique connection name remains with the connection for 1037 its entire lifetime. 1038 A bus name is of type <literal>STRING</literal>, 1039 meaning that it must be valid UTF-8. However, there are also 1040 some additional restrictions that apply to bus names 1041 specifically: 1042 <itemizedlist> 1043 <listitem><para>Bus names that start with a colon (':') 1044 character are unique connection names. 1045 </para> 1046 </listitem> 1047 <listitem><para>Bus names are composed of 1 or more elements separated by 1048 a period ('.') character. All elements must contain at least 1049 one character. 1050 </para> 1051 </listitem> 1052 <listitem><para>Each element must only contain the ASCII characters 1053 "[A-Z][a-z][0-9]_-". Only elements that are part of a unique 1054 connection name may begin with a digit, elements in 1055 other bus names must not begin with a digit. 1056 </para> 1057 </listitem> 1058 1059 <listitem><para>Bus names must contain at least one '.' (period) 1060 character (and thus at least two elements). 1061 </para></listitem> 1062 1063 <listitem><para>Bus names must not begin with a '.' (period) character.</para></listitem> 1064 <listitem><para>Bus names must not exceed the maximum name length.</para></listitem> 1065 </itemizedlist> 1066 </para> 1067 <para> 1068 Note that the hyphen ('-') character is allowed in bus names but 1069 not in interface names. 1070 </para> 1071 </sect3> 1072 <sect3 id="message-protocol-names-member"> 1073 <title>Member names</title> 1074 <para> 1075 Member (i.e. method or signal) names: 1076 <itemizedlist> 1077 <listitem><para>Must only contain the ASCII characters 1078 "[A-Z][a-z][0-9]_" and may not begin with a 1079 digit.</para></listitem> 1080 <listitem><para>Must not contain the '.' (period) character.</para></listitem> 1081 <listitem><para>Must not exceed the maximum name length.</para></listitem> 1082 <listitem><para>Must be at least 1 byte in length.</para></listitem> 1083 </itemizedlist> 1084 </para> 1085 </sect3> 1086 <sect3 id="message-protocol-names-error"> 1087 <title>Error names</title> 1088 <para> 1089 Error names have the same restrictions as interface names. 1090 </para> 1091 </sect3> 1092 </sect2> 1093 1094 <sect2 id="message-protocol-types"> 1095 <title>Message Types</title> 1096 <para> 1097 Each of the message types (<literal>METHOD_CALL</literal>, <literal>METHOD_RETURN</literal>, <literal>ERROR</literal>, and 1098 <literal>SIGNAL</literal>) has its own expected usage conventions and header fields. 1099 This section describes these conventions. 1100 </para> 1101 <sect3 id="message-protocol-types-method"> 1102 <title>Method Calls</title> 1103 <para> 1104 Some messages invoke an operation on a remote object. These are 1105 called method call messages and have the type tag <literal>METHOD_CALL</literal>. Such 1106 messages map naturally to methods on objects in a typical program. 1107 </para> 1108 <para> 1109 A method call message is required to have a <literal>MEMBER</literal> header field 1110 indicating the name of the method. Optionally, the message has an 1111 <literal>INTERFACE</literal> field giving the interface the method is a part of. In the 1112 absence of an <literal>INTERFACE</literal> field, if two interfaces on the same object have 1113 a method with the same name, it is undefined which of the two methods 1114 will be invoked. Implementations may also choose to return an error in 1115 this ambiguous case. However, if a method name is unique 1116 implementations must not require an interface field. 1117 </para> 1118 <para> 1119 Method call messages also include a <literal>PATH</literal> field 1120 indicating the object to invoke the method on. If the call is passing 1121 through a message bus, the message will also have a 1122 <literal>DESTINATION</literal> field giving the name of the connection 1123 to receive the message. 1124 </para> 1125 <para> 1126 When an application handles a method call message, it is required to 1127 return a reply. The reply is identified by a <literal>REPLY_SERIAL</literal> header field 1128 indicating the serial number of the <literal>METHOD_CALL</literal> being replied to. The 1129 reply can have one of two types; either <literal>METHOD_RETURN</literal> or <literal>ERROR</literal>. 1130 </para> 1131 <para> 1132 If the reply has type <literal>METHOD_RETURN</literal>, the arguments to the reply message 1133 are the return value(s) or "out parameters" of the method call. 1134 If the reply has type <literal>ERROR</literal>, then an "exception" has been thrown, 1135 and the call fails; no return value will be provided. It makes 1136 no sense to send multiple replies to the same method call. 1137 </para> 1138 <para> 1139 Even if a method call has no return values, a <literal>METHOD_RETURN</literal> 1140 reply is required, so the caller will know the method 1141 was successfully processed. 1142 </para> 1143 <para> 1144 The <literal>METHOD_RETURN</literal> or <literal>ERROR</literal> reply message must have the <literal>REPLY_SERIAL</literal> 1145 header field. 1146 </para> 1147 <para> 1148 If a <literal>METHOD_CALL</literal> message has the flag <literal>NO_REPLY_EXPECTED</literal>, 1149 then as an optimization the application receiving the method 1150 call may choose to omit the reply message (regardless of 1151 whether the reply would have been <literal>METHOD_RETURN</literal> or <literal>ERROR</literal>). 1152 However, it is also acceptable to ignore the <literal>NO_REPLY_EXPECTED</literal> 1153 flag and reply anyway. 1154 </para> 1155 <para> 1156 Unless a message has the flag <literal>NO_AUTO_START</literal>, if the 1157 destination name does not exist then a program to own the destination 1158 name will be started before the message is delivered. The message 1159 will be held until the new program is successfully started or has 1160 failed to start; in case of failure, an error will be returned. This 1161 flag is only relevant in the context of a message bus, it is ignored 1162 during one-to-one communication with no intermediate bus. 1163 </para> 1164 <sect4 id="message-protocol-types-method-apis"> 1165 <title>Mapping method calls to native APIs</title> 1166 <para> 1167 APIs for D-Bus may map method calls to a method call in a specific 1168 programming language, such as C++, or may map a method call written 1169 in an IDL to a D-Bus message. 1170 </para> 1171 <para> 1172 In APIs of this nature, arguments to a method are often termed "in" 1173 (which implies sent in the <literal>METHOD_CALL</literal>), or "out" (which implies 1174 returned in the <literal>METHOD_RETURN</literal>). Some APIs such as CORBA also have 1175 "inout" arguments, which are both sent and received, i.e. the caller 1176 passes in a value which is modified. Mapped to D-Bus, an "inout" 1177 argument is equivalent to an "in" argument, followed by an "out" 1178 argument. You can't pass things "by reference" over the wire, so 1179 "inout" is purely an illusion of the in-process API. 1180 </para> 1181 <para> 1182 Given a method with zero or one return values, followed by zero or more 1183 arguments, where each argument may be "in", "out", or "inout", the 1184 caller constructs a message by appending each "in" or "inout" argument, 1185 in order. "out" arguments are not represented in the caller's message. 1186 </para> 1187 <para> 1188 The recipient constructs a reply by appending first the return value 1189 if any, then each "out" or "inout" argument, in order. 1190 "in" arguments are not represented in the reply message. 1191 </para> 1192 <para> 1193 Error replies are normally mapped to exceptions in languages that have 1194 exceptions. 1195 </para> 1196 <para> 1197 In converting from native APIs to D-Bus, it is perhaps nice to 1198 map D-Bus naming conventions ("FooBar") to native conventions 1199 such as "fooBar" or "foo_bar" automatically. This is OK 1200 as long as you can say that the native API is one that 1201 was specifically written for D-Bus. It makes the most sense 1202 when writing object implementations that will be exported 1203 over the bus. Object proxies used to invoke remote D-Bus 1204 objects probably need the ability to call any D-Bus method, 1205 and thus a magic name mapping like this could be a problem. 1206 </para> 1207 <para> 1208 This specification doesn't require anything of native API bindings; 1209 the preceding is only a suggested convention for consistency 1210 among bindings. 1211 </para> 1212 </sect4> 1213 </sect3> 1214 1215 <sect3 id="message-protocol-types-signal"> 1216 <title>Signal Emission</title> 1217 <para> 1218 Unlike method calls, signal emissions have no replies. 1219 A signal emission is simply a single message of type <literal>SIGNAL</literal>. 1220 It must have three header fields: <literal>PATH</literal> giving the object 1221 the signal was emitted from, plus <literal>INTERFACE</literal> and <literal>MEMBER</literal> giving 1222 the fully-qualified name of the signal. The <literal>INTERFACE</literal> header is required 1223 for signals, though it is optional for method calls. 1224 </para> 1225 </sect3> 1226 1227 <sect3 id="message-protocol-types-errors"> 1228 <title>Errors</title> 1229 <para> 1230 Messages of type <literal>ERROR</literal> are most commonly replies 1231 to a <literal>METHOD_CALL</literal>, but may be returned in reply 1232 to any kind of message. The message bus for example 1233 will return an <literal>ERROR</literal> in reply to a signal emission if 1234 the bus does not have enough memory to send the signal. 1235 </para> 1236 <para> 1237 An <literal>ERROR</literal> may have any arguments, but if the first 1238 argument is a <literal>STRING</literal>, it must be an error message. 1239 The error message may be logged or shown to the user 1240 in some way. 1241 </para> 1242 </sect3> 1243 1244 <sect3 id="message-protocol-types-notation"> 1245 <title>Notation in this document</title> 1246 <para> 1247 This document uses a simple pseudo-IDL to describe particular method 1248 calls and signals. Here is an example of a method call: 1249 <programlisting> 1250 org.freedesktop.DBus.StartServiceByName (in STRING name, in UINT32 flags, 1251 out UINT32 resultcode) 1252 </programlisting> 1253 This means <literal>INTERFACE</literal> = org.freedesktop.DBus, <literal>MEMBER</literal> = StartServiceByName, 1254 <literal>METHOD_CALL</literal> arguments are <literal>STRING</literal> and <literal>UINT32</literal>, <literal>METHOD_RETURN</literal> argument 1255 is <literal>UINT32</literal>. Remember that the <literal>MEMBER</literal> field can't contain any '.' (period) 1256 characters so it's known that the last part of the name in 1257 the "IDL" is the member name. 1258 </para> 1259 <para> 1260 In C++ that might end up looking like this: 1261 <programlisting> 1262 unsigned int org::freedesktop::DBus::StartServiceByName (const char *name, 1263 unsigned int flags); 1264 </programlisting> 1265 or equally valid, the return value could be done as an argument: 1266 <programlisting> 1267 void org::freedesktop::DBus::StartServiceByName (const char *name, 1268 unsigned int flags, 1269 unsigned int *resultcode); 1270 </programlisting> 1271 It's really up to the API designer how they want to make 1272 this look. You could design an API where the namespace wasn't used 1273 in C++, using STL or Qt, using varargs, or whatever you wanted. 1274 </para> 1275 <para> 1276 Signals are written as follows: 1277 <programlisting> 1278 org.freedesktop.DBus.NameLost (STRING name) 1279 </programlisting> 1280 Signals don't specify "in" vs. "out" because only 1281 a single direction is possible. 1282 </para> 1283 <para> 1284 It isn't especially encouraged to use this lame pseudo-IDL in actual 1285 API implementations; you might use the native notation for the 1286 language you're using, or you might use COM or CORBA IDL, for example. 1287 </para> 1288 </sect3> 1289 </sect2> 1290 1291 <sect2 id="message-protocol-handling-invalid"> 1292 <title>Invalid Protocol and Spec Extensions</title> 1293 1294 <para> 1295 For security reasons, the D-Bus protocol should be strictly parsed and 1296 validated, with the exception of defined extension points. Any invalid 1297 protocol or spec violations should result in immediately dropping the 1298 connection without notice to the other end. Exceptions should be 1299 carefully considered, e.g. an exception may be warranted for a 1300 well-understood idiosyncrasy of a widely-deployed implementation. In 1301 cases where the other end of a connection is 100% trusted and known to 1302 be friendly, skipping validation for performance reasons could also make 1303 sense in certain cases. 1304 </para> 1305 1306 <para> 1307 Generally speaking violations of the "must" requirements in this spec 1308 should be considered possible attempts to exploit security, and violations 1309 of the "should" suggestions should be considered legitimate (though perhaps 1310 they should generate an error in some cases). 1311 </para> 1312 1313 <para> 1314 The following extension points are built in to D-Bus on purpose and must 1315 not be treated as invalid protocol. The extension points are intended 1316 for use by future versions of this spec, they are not intended for third 1317 parties. At the moment, the only way a third party could extend D-Bus 1318 without breaking interoperability would be to introduce a way to negotiate new 1319 feature support as part of the auth protocol, using EXTENSION_-prefixed 1320 commands. There is not yet a standard way to negotiate features. 1321 <itemizedlist> 1322 <listitem> 1323 <para> 1324 In the authentication protocol (see <xref linkend="auth-protocol"/>) unknown 1325 commands result in an ERROR rather than a disconnect. This enables 1326 future extensions to the protocol. Commands starting with EXTENSION_ are 1327 reserved for third parties. 1328 </para> 1329 </listitem> 1330 <listitem> 1331 <para> 1332 The authentication protocol supports pluggable auth mechanisms. 1333 </para> 1334 </listitem> 1335 <listitem> 1336 <para> 1337 The address format (see <xref linkend="addresses"/>) supports new 1338 kinds of transport. 1339 </para> 1340 </listitem> 1341 <listitem> 1342 <para> 1343 Messages with an unknown type (something other than 1344 <literal>METHOD_CALL</literal>, <literal>METHOD_RETURN</literal>, 1345 <literal>ERROR</literal>, <literal>SIGNAL</literal>) are ignored. 1346 Unknown-type messages must still be well-formed in the same way 1347 as the known messages, however. They still have the normal 1348 header and body. 1349 </para> 1350 </listitem> 1351 <listitem> 1352 <para> 1353 Header fields with an unknown or unexpected field code must be ignored, 1354 though again they must still be well-formed. 1355 </para> 1356 </listitem> 1357 <listitem> 1358 <para> 1359 New standard interfaces (with new methods and signals) can of course be added. 1360 </para> 1361 </listitem> 1362 </itemizedlist> 1363 </para> 1364 1365 </sect2> 1366 1367 </sect1> 1368 1369 <sect1 id="auth-protocol"> 1370 <title>Authentication Protocol</title> 1371 <para> 1372 Before the flow of messages begins, two applications must 1373 authenticate. A simple plain-text protocol is used for 1374 authentication; this protocol is a SASL profile, and maps fairly 1375 directly from the SASL specification. The message encoding is 1376 NOT used here, only plain text messages. 1377 </para> 1378 <para> 1379 In examples, "C:" and "S:" indicate lines sent by the client and 1380 server respectively. 1381 </para> 1382 <sect2 id="auth-protocol-overview"> 1383 <title>Protocol Overview</title> 1384 <para> 1385 The protocol is a line-based protocol, where each line ends with 1386 \r\n. Each line begins with an all-caps ASCII command name containing 1387 only the character range [A-Z_], a space, then any arguments for the 1388 command, then the \r\n ending the line. The protocol is 1389 case-sensitive. All bytes must be in the ASCII character set. 1390 1391 Commands from the client to the server are as follows: 1392 1393 <itemizedlist> 1394 <listitem><para>AUTH [mechanism] [initial-response]</para></listitem> 1395 <listitem><para>CANCEL</para></listitem> 1396 <listitem><para>BEGIN</para></listitem> 1397 <listitem><para>DATA <data in hex encoding></para></listitem> 1398 <listitem><para>ERROR [human-readable error explanation]</para></listitem> 1399 </itemizedlist> 1400 1401 From server to client are as follows: 1402 1403 <itemizedlist> 1404 <listitem><para>REJECTED <space-separated list of mechanism names></para></listitem> 1405 <listitem><para>OK <GUID in hex></para></listitem> 1406 <listitem><para>DATA <data in hex encoding></para></listitem> 1407 <listitem><para>ERROR</para></listitem> 1408 </itemizedlist> 1409 </para> 1410 <para> 1411 Unofficial extensions to the command set must begin with the letters 1412 "EXTENSION_", to avoid conflicts with future official commands. 1413 For example, "EXTENSION_COM_MYDOMAIN_DO_STUFF". 1414 </para> 1415 </sect2> 1416 <sect2 id="auth-nul-byte"> 1417 <title>Special credentials-passing nul byte</title> 1418 <para> 1419 Immediately after connecting to the server, the client must send a 1420 single nul byte. This byte may be accompanied by credentials 1421 information on some operating systems that use sendmsg() with 1422 SCM_CREDS or SCM_CREDENTIALS to pass credentials over UNIX domain 1423 sockets. However, the nul byte must be sent even on other kinds of 1424 socket, and even on operating systems that do not require a byte to be 1425 sent in order to transmit credentials. The text protocol described in 1426 this document begins after the single nul byte. If the first byte 1427 received from the client is not a nul byte, the server may disconnect 1428 that client. 1429 </para> 1430 <para> 1431 A nul byte in any context other than the initial byte is an error; 1432 the protocol is ASCII-only. 1433 </para> 1434 <para> 1435 The credentials sent along with the nul byte may be used with the 1436 SASL mechanism EXTERNAL. 1437 </para> 1438 </sect2> 1439 <sect2 id="auth-command-auth"> 1440 <title>AUTH command</title> 1441 <para> 1442 If an AUTH command has no arguments, it is a request to list 1443 available mechanisms. The server must respond with a REJECTED 1444 command listing the mechanisms it understands, or with an error. 1445 </para> 1446 <para> 1447 If an AUTH command specifies a mechanism, and the server supports 1448 said mechanism, the server should begin exchanging SASL 1449 challenge-response data with the client using DATA commands. 1450 </para> 1451 <para> 1452 If the server does not support the mechanism given in the AUTH 1453 command, it must send either a REJECTED command listing the mechanisms 1454 it does support, or an error. 1455 </para> 1456 <para> 1457 If the [initial-response] argument is provided, it is intended for use 1458 with mechanisms that have no initial challenge (or an empty initial 1459 challenge), as if it were the argument to an initial DATA command. If 1460 the selected mechanism has an initial challenge and [initial-response] 1461 was provided, the server should reject authentication by sending 1462 REJECTED. 1463 </para> 1464 <para> 1465 If authentication succeeds after exchanging DATA commands, 1466 an OK command must be sent to the client. 1467 </para> 1468 <para> 1469 The first octet received by the client after the \r\n of the OK 1470 command must be the first octet of the authenticated/encrypted 1471 stream of D-Bus messages. 1472 </para> 1473 <para> 1474 The first octet received by the server after the \r\n of the BEGIN 1475 command from the client must be the first octet of the 1476 authenticated/encrypted stream of D-Bus messages. 1477 </para> 1478 </sect2> 1479 <sect2 id="auth-command-cancel"> 1480 <title>CANCEL Command</title> 1481 <para> 1482 At any time up to sending the BEGIN command, the client may send a 1483 CANCEL command. On receiving the CANCEL command, the server must 1484 send a REJECTED command and abort the current authentication 1485 exchange. 1486 </para> 1487 </sect2> 1488 <sect2 id="auth-command-data"> 1489 <title>DATA Command</title> 1490 <para> 1491 The DATA command may come from either client or server, and simply 1492 contains a hex-encoded block of data to be interpreted 1493 according to the SASL mechanism in use. 1494 </para> 1495 <para> 1496 Some SASL mechanisms support sending an "empty string"; 1497 FIXME we need some way to do this. 1498 </para> 1499 </sect2> 1500 <sect2 id="auth-command-begin"> 1501 <title>BEGIN Command</title> 1502 <para> 1503 The BEGIN command acknowledges that the client has received an 1504 OK command from the server, and that the stream of messages 1505 is about to begin. 1506 </para> 1507 <para> 1508 The first octet received by the server after the \r\n of the BEGIN 1509 command from the client must be the first octet of the 1510 authenticated/encrypted stream of D-Bus messages. 1511 </para> 1512 </sect2> 1513 <sect2 id="auth-command-rejected"> 1514 <title>REJECTED Command</title> 1515 <para> 1516 The REJECTED command indicates that the current authentication 1517 exchange has failed, and further exchange of DATA is inappropriate. 1518 The client would normally try another mechanism, or try providing 1519 different responses to challenges. 1520 </para><para> 1521 Optionally, the REJECTED command has a space-separated list of 1522 available auth mechanisms as arguments. If a server ever provides 1523 a list of supported mechanisms, it must provide the same list 1524 each time it sends a REJECTED message. Clients are free to 1525 ignore all lists received after the first. 1526 </para> 1527 </sect2> 1528 <sect2 id="auth-command-ok"> 1529 <title>OK Command</title> 1530 <para> 1531 The OK command indicates that the client has been authenticated, 1532 and that further communication will be a stream of D-Bus messages 1533 (optionally encrypted, as negotiated) rather than this protocol. 1534 </para> 1535 <para> 1536 The first octet received by the client after the \r\n of the OK 1537 command must be the first octet of the authenticated/encrypted 1538 stream of D-Bus messages. 1539 </para> 1540 <para> 1541 The client must respond to the OK command by sending a BEGIN 1542 command, followed by its stream of messages, or by disconnecting. 1543 The server must not accept additional commands using this protocol 1544 after the OK command has been sent. 1545 </para> 1546 <para> 1547 The OK command has one argument, which is the GUID of the server. 1548 See <xref linkend="addresses"/> for more on server GUIDs. 1549 </para> 1550 </sect2> 1551 <sect2 id="auth-command-error"> 1552 <title>ERROR Command</title> 1553 <para> 1554 The ERROR command indicates that either server or client did not 1555 know a command, does not accept the given command in the current 1556 context, or did not understand the arguments to the command. This 1557 allows the protocol to be extended; a client or server can send a 1558 command present or permitted only in new protocol versions, and if 1559 an ERROR is received instead of an appropriate response, fall back 1560 to using some other technique. 1561 </para> 1562 <para> 1563 If an ERROR is sent, the server or client that sent the 1564 error must continue as if the command causing the ERROR had never been 1565 received. However, the the server or client receiving the error 1566 should try something other than whatever caused the error; 1567 if only canceling/rejecting the authentication. 1568 </para> 1569 <para> 1570 If the D-Bus protocol changes incompatibly at some future time, 1571 applications implementing the new protocol would probably be able to 1572 check for support of the new protocol by sending a new command and 1573 receiving an ERROR from applications that don't understand it. Thus the 1574 ERROR feature of the auth protocol is an escape hatch that lets us 1575 negotiate extensions or changes to the D-Bus protocol in the future. 1576 </para> 1577 </sect2> 1578 <sect2 id="auth-examples"> 1579 <title>Authentication examples</title> 1580 1581 <para> 1582 <figure> 1583 <title>Example of successful magic cookie authentication</title> 1584 <programlisting> 1585 (MAGIC_COOKIE is a made up mechanism) 1586 1587 C: AUTH MAGIC_COOKIE 3138363935333137393635383634 1588 S: OK 1234deadbeef 1589 C: BEGIN 1590 </programlisting> 1591 </figure> 1592 <figure> 1593 <title>Example of finding out mechanisms then picking one</title> 1594 <programlisting> 1595 C: AUTH 1596 S: REJECTED KERBEROS_V4 SKEY 1597 C: AUTH SKEY 7ab83f32ee 1598 S: DATA 8799cabb2ea93e 1599 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f 1600 S: OK 1234deadbeef 1601 C: BEGIN 1602 </programlisting> 1603 </figure> 1604 <figure> 1605 <title>Example of client sends unknown command then falls back to regular auth</title> 1606 <programlisting> 1607 C: FOOBAR 1608 S: ERROR 1609 C: AUTH MAGIC_COOKIE 3736343435313230333039 1610 S: OK 1234deadbeef 1611 C: BEGIN 1612 </programlisting> 1613 </figure> 1614 <figure> 1615 <title>Example of server doesn't support initial auth mechanism</title> 1616 <programlisting> 1617 C: AUTH MAGIC_COOKIE 3736343435313230333039 1618 S: REJECTED KERBEROS_V4 SKEY 1619 C: AUTH SKEY 7ab83f32ee 1620 S: DATA 8799cabb2ea93e 1621 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f 1622 S: OK 1234deadbeef 1623 C: BEGIN 1624 </programlisting> 1625 </figure> 1626 <figure> 1627 <title>Example of wrong password or the like followed by successful retry</title> 1628 <programlisting> 1629 C: AUTH MAGIC_COOKIE 3736343435313230333039 1630 S: REJECTED KERBEROS_V4 SKEY 1631 C: AUTH SKEY 7ab83f32ee 1632 S: DATA 8799cabb2ea93e 1633 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f 1634 S: REJECTED 1635 C: AUTH SKEY 7ab83f32ee 1636 S: DATA 8799cabb2ea93e 1637 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f 1638 S: OK 1234deadbeef 1639 C: BEGIN 1640 </programlisting> 1641 </figure> 1642 <figure> 1643 <title>Example of skey cancelled and restarted</title> 1644 <programlisting> 1645 C: AUTH MAGIC_COOKIE 3736343435313230333039 1646 S: REJECTED KERBEROS_V4 SKEY 1647 C: AUTH SKEY 7ab83f32ee 1648 S: DATA 8799cabb2ea93e 1649 C: CANCEL 1650 S: REJECTED 1651 C: AUTH SKEY 7ab83f32ee 1652 S: DATA 8799cabb2ea93e 1653 C: DATA 8ac876e8f68ee9809bfa876e6f9876g8fa8e76e98f 1654 S: OK 1234deadbeef 1655 C: BEGIN 1656 </programlisting> 1657 </figure> 1658 </para> 1659 </sect2> 1660 <sect2 id="auth-states"> 1661 <title>Authentication state diagrams</title> 1662 1663 <para> 1664 This section documents the auth protocol in terms of 1665 a state machine for the client and the server. This is 1666 probably the most robust way to implement the protocol. 1667 </para> 1668 1669 <sect3 id="auth-states-client"> 1670 <title>Client states</title> 1671 1672 <para> 1673 To more precisely describe the interaction between the 1674 protocol state machine and the authentication mechanisms the 1675 following notation is used: MECH(CHALL) means that the 1676 server challenge CHALL was fed to the mechanism MECH, which 1677 returns one of 1678 1679 <itemizedlist> 1680 <listitem> 1681 <para> 1682 CONTINUE(RESP) means continue the auth conversation 1683 and send RESP as the response to the server; 1684 </para> 1685 </listitem> 1686 1687 <listitem> 1688 <para> 1689 OK(RESP) means that after sending RESP to the server 1690 the client side of the auth conversation is finished 1691 and the server should return "OK"; 1692 </para> 1693 </listitem> 1694 1695 <listitem> 1696 <para> 1697 ERROR means that CHALL was invalid and could not be 1698 processed. 1699 </para> 1700 </listitem> 1701 </itemizedlist> 1702 1703 Both RESP and CHALL may be empty. 1704 </para> 1705 1706 <para> 1707 The Client starts by getting an initial response from the 1708 default mechanism and sends AUTH MECH RESP, or AUTH MECH if 1709 the mechanism did not provide an initial response. If the 1710 mechanism returns CONTINUE, the client starts in state 1711 <emphasis>WaitingForData</emphasis>, if the mechanism 1712 returns OK the client starts in state 1713 <emphasis>WaitingForOK</emphasis>. 1714 </para> 1715 1716 <para> 1717 The client should keep track of available mechanisms and 1718 which it mechanisms it has already attempted. This list is 1719 used to decide which AUTH command to send. When the list is 1720 exhausted, the client should give up and close the 1721 connection. 1722 </para> 1723 1724 <formalpara> 1725 <title><emphasis>WaitingForData</emphasis></title> 1726 <para> 1727 <itemizedlist> 1728 <listitem> 1729 <para> 1730 Receive DATA CHALL 1731 <simplelist> 1732 <member> 1733 MECH(CHALL) returns CONTINUE(RESP) → send 1734 DATA RESP, goto 1735 <emphasis>WaitingForData</emphasis> 1736 </member> 1737 1738 <member> 1739 MECH(CHALL) returns OK(RESP) → send DATA 1740 RESP, goto <emphasis>WaitingForOK</emphasis> 1741 </member> 1742 1743 <member> 1744 MECH(CHALL) returns ERROR → send ERROR 1745 [msg], goto <emphasis>WaitingForData</emphasis> 1746 </member> 1747 </simplelist> 1748 </para> 1749 </listitem> 1750 1751 <listitem> 1752 <para> 1753 Receive REJECTED [mechs] → 1754 send AUTH [next mech], goto 1755 WaitingForData or <emphasis>WaitingForOK</emphasis> 1756 </para> 1757 </listitem> 1758 <listitem> 1759 <para> 1760 Receive ERROR → send 1761 CANCEL, goto 1762 <emphasis>WaitingForReject</emphasis> 1763 </para> 1764 </listitem> 1765 <listitem> 1766 <para> 1767 Receive OK → send 1768 BEGIN, terminate auth 1769 conversation, authenticated 1770 </para> 1771 </listitem> 1772 <listitem> 1773 <para> 1774 Receive anything else → send 1775 ERROR, goto 1776 <emphasis>WaitingForData</emphasis> 1777 </para> 1778 </listitem> 1779 </itemizedlist> 1780 </para> 1781 </formalpara> 1782 1783 <formalpara> 1784 <title><emphasis>WaitingForOK</emphasis></title> 1785 <para> 1786 <itemizedlist> 1787 <listitem> 1788 <para> 1789 Receive OK → send BEGIN, terminate auth 1790 conversation, <emphasis>authenticated</emphasis> 1791 </para> 1792 </listitem> 1793 <listitem> 1794 <para> 1795 Receive REJECT [mechs] → send AUTH [next mech], 1796 goto <emphasis>WaitingForData</emphasis> or 1797 <emphasis>WaitingForOK</emphasis> 1798 </para> 1799 </listitem> 1800 1801 <listitem> 1802 <para> 1803 Receive DATA → send CANCEL, goto 1804 <emphasis>WaitingForReject</emphasis> 1805 </para> 1806 </listitem> 1807 1808 <listitem> 1809 <para> 1810 Receive ERROR → send CANCEL, goto 1811 <emphasis>WaitingForReject</emphasis> 1812 </para> 1813 </listitem> 1814 1815 <listitem> 1816 <para> 1817 Receive anything else → send ERROR, goto 1818 <emphasis>WaitingForOK</emphasis> 1819 </para> 1820 </listitem> 1821 </itemizedlist> 1822 </para> 1823 </formalpara> 1824 1825 <formalpara> 1826 <title><emphasis>WaitingForReject</emphasis></title> 1827 <para> 1828 <itemizedlist> 1829 <listitem> 1830 <para> 1831 Receive REJECT [mechs] → send AUTH [next mech], 1832 goto <emphasis>WaitingForData</emphasis> or 1833 <emphasis>WaitingForOK</emphasis> 1834 </para> 1835 </listitem> 1836 1837 <listitem> 1838 <para> 1839 Receive anything else → terminate auth 1840 conversation, disconnect 1841 </para> 1842 </listitem> 1843 </itemizedlist> 1844 </para> 1845 </formalpara> 1846 1847 </sect3> 1848 1849 <sect3 id="auth-states-server"> 1850 <title>Server states</title> 1851 1852 <para> 1853 For the server MECH(RESP) means that the client response 1854 RESP was fed to the the mechanism MECH, which returns one of 1855 1856 <itemizedlist> 1857 <listitem> 1858 <para> 1859 CONTINUE(CHALL) means continue the auth conversation and 1860 send CHALL as the challenge to the client; 1861 </para> 1862 </listitem> 1863 1864 <listitem> 1865 <para> 1866 OK means that the client has been successfully 1867 authenticated; 1868 </para> 1869 </listitem> 1870 1871 <listitem> 1872 <para> 1873 REJECT means that the client failed to authenticate or 1874 there was an error in RESP. 1875 </para> 1876 </listitem> 1877 </itemizedlist> 1878 1879 The server starts out in state 1880 <emphasis>WaitingForAuth</emphasis>. If the client is 1881 rejected too many times the server must disconnect the 1882 client. 1883 </para> 1884 1885 <formalpara> 1886 <title><emphasis>WaitingForAuth</emphasis></title> 1887 <para> 1888 <itemizedlist> 1889 1890 <listitem> 1891 <para> 1892 Receive AUTH → send REJECTED [mechs], goto 1893 <emphasis>WaitingForAuth</emphasis> 1894 </para> 1895 </listitem> 1896 1897 <listitem> 1898 <para> 1899 Receive AUTH MECH RESP 1900 1901 <simplelist> 1902 <member> 1903 MECH not valid mechanism → send REJECTED 1904 [mechs], goto 1905 <emphasis>WaitingForAuth</emphasis> 1906 </member> 1907 1908 <member> 1909 MECH(RESP) returns CONTINUE(CHALL) → send 1910 DATA CHALL, goto 1911 <emphasis>WaitingForData</emphasis> 1912 </member> 1913 1914 <member> 1915 MECH(RESP) returns OK → send OK, goto 1916 <emphasis>WaitingForBegin</emphasis> 1917 </member> 1918 1919 <member> 1920 MECH(RESP) returns REJECT → send REJECTED 1921 [mechs], goto 1922 <emphasis>WaitingForAuth</emphasis> 1923 </member> 1924 </simplelist> 1925 </para> 1926 </listitem> 1927 1928 <listitem> 1929 <para> 1930 Receive BEGIN → terminate 1931 auth conversation, disconnect 1932 </para> 1933 </listitem> 1934 1935 <listitem> 1936 <para> 1937 Receive ERROR → send REJECTED [mechs], goto 1938 <emphasis>WaitingForAuth</emphasis> 1939 </para> 1940 </listitem> 1941 1942 <listitem> 1943 <para> 1944 Receive anything else → send 1945 ERROR, goto 1946 <emphasis>WaitingForAuth</emphasis> 1947 </para> 1948 </listitem> 1949 </itemizedlist> 1950 </para> 1951 </formalpara> 1952 1953 1954 <formalpara> 1955 <title><emphasis>WaitingForData</emphasis></title> 1956 <para> 1957 <itemizedlist> 1958 <listitem> 1959 <para> 1960 Receive DATA RESP 1961 <simplelist> 1962 <member> 1963 MECH(RESP) returns CONTINUE(CHALL) → send 1964 DATA CHALL, goto 1965 <emphasis>WaitingForData</emphasis> 1966 </member> 1967 1968 <member> 1969 MECH(RESP) returns OK → send OK, goto 1970 <emphasis>WaitingForBegin</emphasis> 1971 </member> 1972 1973 <member> 1974 MECH(RESP) returns REJECT → send REJECTED 1975 [mechs], goto 1976 <emphasis>WaitingForAuth</emphasis> 1977 </member> 1978 </simplelist> 1979 </para> 1980 </listitem> 1981 1982 <listitem> 1983 <para> 1984 Receive BEGIN → terminate auth conversation, 1985 disconnect 1986 </para> 1987 </listitem> 1988 1989 <listitem> 1990 <para> 1991 Receive CANCEL → send REJECTED [mechs], goto 1992 <emphasis>WaitingForAuth</emphasis> 1993 </para> 1994 </listitem> 1995 1996 <listitem> 1997 <para> 1998 Receive ERROR → send REJECTED [mechs], goto 1999 <emphasis>WaitingForAuth</emphasis> 2000 </para> 2001 </listitem> 2002 2003 <listitem> 2004 <para> 2005 Receive anything else → send ERROR, goto 2006 <emphasis>WaitingForData</emphasis> 2007 </para> 2008 </listitem> 2009 </itemizedlist> 2010 </para> 2011 </formalpara> 2012 2013 <formalpara> 2014 <title><emphasis>WaitingForBegin</emphasis></title> 2015 <para> 2016 <itemizedlist> 2017 <listitem> 2018 <para> 2019 Receive BEGIN → terminate auth conversation, 2020 client authenticated 2021 </para> 2022 </listitem> 2023 2024 <listitem> 2025 <para> 2026 Receive CANCEL → send REJECTED [mechs], goto 2027 <emphasis>WaitingForAuth</emphasis> 2028 </para> 2029 </listitem> 2030 2031 <listitem> 2032 <para> 2033 Receive ERROR → send REJECTED [mechs], goto 2034 <emphasis>WaitingForAuth</emphasis> 2035 </para> 2036 </listitem> 2037 2038 <listitem> 2039 <para> 2040 Receive anything else → send ERROR, goto 2041 <emphasis>WaitingForBegin</emphasis> 2042 </para> 2043 </listitem> 2044 </itemizedlist> 2045 </para> 2046 </formalpara> 2047 2048 </sect3> 2049 2050 </sect2> 2051 <sect2 id="auth-mechanisms"> 2052 <title>Authentication mechanisms</title> 2053 <para> 2054 This section describes some new authentication mechanisms. 2055 D-Bus also allows any standard SASL mechanism of course. 2056 </para> 2057 <sect3 id="auth-mechanisms-sha"> 2058 <title>DBUS_COOKIE_SHA1</title> 2059 <para> 2060 The DBUS_COOKIE_SHA1 mechanism is designed to establish that a client 2061 has the ability to read a private file owned by the user being 2062 authenticated. If the client can prove that it has access to a secret 2063 cookie stored in this file, then the client is authenticated. 2064 Thus the security of DBUS_COOKIE_SHA1 depends on a secure home 2065 directory. 2066 </para> 2067 <para> 2068 Authentication proceeds as follows: 2069 <itemizedlist> 2070 <listitem> 2071 <para> 2072 The client sends the username it would like to authenticate 2073 as. 2074 </para> 2075 </listitem> 2076 <listitem> 2077 <para> 2078 The server sends the name of its "cookie context" (see below); a 2079 space character; the integer ID of the secret cookie the client 2080 must demonstrate knowledge of; a space character; then a 2081 hex-encoded randomly-generated challenge string. 2082 </para> 2083 </listitem> 2084 <listitem> 2085 <para> 2086 The client locates the cookie, and generates its own hex-encoded 2087 randomly-generated challenge string. The client then 2088 concatenates the server's hex-encoded challenge, a ":" 2089 character, its own hex-encoded challenge, another ":" character, 2090 and the hex-encoded cookie. It computes the SHA-1 hash of this 2091 composite string. It sends back to the server the client's 2092 hex-encoded challenge string, a space character, and the SHA-1 2093 hash. 2094 </para> 2095 </listitem> 2096 <listitem> 2097 <para> 2098 The server generates the same concatenated string used by the 2099 client and computes its SHA-1 hash. It compares the hash with 2100 the hash received from the client; if the two hashes match, the 2101 client is authenticated. 2102 </para> 2103 </listitem> 2104 </itemizedlist> 2105 </para> 2106 <para> 2107 Each server has a "cookie context," which is a name that identifies a 2108 set of cookies that apply to that server. A sample context might be 2109 "org_freedesktop_session_bus". Context names must be valid ASCII, 2110 nonzero length, and may not contain the characters slash ("/"), 2111 backslash ("\"), space (" "), newline ("\n"), carriage return ("\r"), 2112 tab ("\t"), or period ("."). There is a default context, 2113 "org_freedesktop_general" that's used by servers that do not specify 2114 otherwise. 2115 </para> 2116 <para> 2117 Cookies are stored in a user's home directory, in the directory 2118 <filename>~/.dbus-keyrings/</filename>. This directory must 2119 not be readable or writable by other users. If it is, 2120 clients and servers must ignore it. The directory 2121 contains cookie files named after the cookie context. 2122 </para> 2123 <para> 2124 A cookie file contains one cookie per line. Each line 2125 has three space-separated fields: 2126 <itemizedlist> 2127 <listitem> 2128 <para> 2129 The cookie ID number, which must be a non-negative integer and 2130 may not be used twice in the same file. 2131 </para> 2132 </listitem> 2133 <listitem> 2134 <para> 2135 The cookie's creation time, in UNIX seconds-since-the-epoch 2136 format. 2137 </para> 2138 </listitem> 2139 <listitem> 2140 <para> 2141 The cookie itself, a hex-encoded random block of bytes. The cookie 2142 may be of any length, though obviously security increases 2143 as the length increases. 2144 </para> 2145 </listitem> 2146 </itemizedlist> 2147 </para> 2148 <para> 2149 Only server processes modify the cookie file. 2150 They must do so with this procedure: 2151 <itemizedlist> 2152 <listitem> 2153 <para> 2154 Create a lockfile name by appending ".lock" to the name of the 2155 cookie file. The server should attempt to create this file 2156 using <literal>O_CREAT | O_EXCL</literal>. If file creation 2157 fails, the lock fails. Servers should retry for a reasonable 2158 period of time, then they may choose to delete an existing lock 2159 to keep users from having to manually delete a stale 2160 lock. <footnote><para>Lockfiles are used instead of real file 2161 locking <literal>fcntl()</literal> because real locking 2162 implementations are still flaky on network 2163 filesystems.</para></footnote> 2164 </para> 2165 </listitem> 2166 <listitem> 2167 <para> 2168 Once the lockfile has been created, the server loads the cookie 2169 file. It should then delete any cookies that are old (the 2170 timeout can be fairly short), or more than a reasonable 2171 time in the future (so that cookies never accidentally 2172 become permanent, if the clock was set far into the future 2173 at some point). If no recent keys remain, the 2174 server may generate a new key. 2175 </para> 2176 </listitem> 2177 <listitem> 2178 <para> 2179 The pruned and possibly added-to cookie file 2180 must be resaved atomically (using a temporary 2181 file which is rename()'d). 2182 </para> 2183 </listitem> 2184 <listitem> 2185 <para> 2186 The lock must be dropped by deleting the lockfile. 2187 </para> 2188 </listitem> 2189 </itemizedlist> 2190 </para> 2191 <para> 2192 Clients need not lock the file in order to load it, 2193 because servers are required to save the file atomically. 2194 </para> 2195 </sect3> 2196 </sect2> 2197 </sect1> 2198 <sect1 id="addresses"> 2199 <title>Server Addresses</title> 2200 <para> 2201 Server addresses consist of a transport name followed by a colon, and 2202 then an optional, comma-separated list of keys and values in the form key=value. 2203 Each value is escaped. 2204 </para> 2205 <para> 2206 For example: 2207 <programlisting>unix:path=/tmp/dbus-test</programlisting> 2208 Which is the address to a unix socket with the path /tmp/dbus-test. 2209 </para> 2210 <para> 2211 Value escaping is similar to URI escaping but simpler. 2212 <itemizedlist> 2213 <listitem> 2214 <para> 2215 The set of optionally-escaped bytes is: 2216 <literal>[0-9A-Za-z_-/.\]</literal>. To escape, each 2217 <emphasis>byte</emphasis> (note, not character) which is not in the 2218 set of optionally-escaped bytes must be replaced with an ASCII 2219 percent (<literal>%</literal>) and the value of the byte in hex. 2220 The hex value must always be two digits, even if the first digit is 2221 zero. The optionally-escaped bytes may be escaped if desired. 2222 </para> 2223 </listitem> 2224 <listitem> 2225 <para> 2226 To unescape, append each byte in the value; if a byte is an ASCII 2227 percent (<literal>%</literal>) character then append the following 2228 hex value instead. It is an error if a <literal>%</literal> byte 2229 does not have two hex digits following. It is an error if a 2230 non-optionally-escaped byte is seen unescaped. 2231 </para> 2232 </listitem> 2233 </itemizedlist> 2234 The set of optionally-escaped bytes is intended to preserve address 2235 readability and convenience. 2236 </para> 2237 2238 <para> 2239 A server may specify a key-value pair with the key <literal>guid</literal> 2240 and the value a hex-encoded 16-byte sequence. <xref linkend="uuids"/> 2241 describes the format of the <literal>guid</literal> field. If present, 2242 this UUID may be used to distinguish one server address from another. A 2243 server should use a different UUID for each address it listens on. For 2244 example, if a message bus daemon offers both UNIX domain socket and TCP 2245 connections, but treats clients the same regardless of how they connect, 2246 those two connections are equivalent post-connection but should have 2247 distinct UUIDs to distinguish the kinds of connection. 2248 </para> 2249 2250 <para> 2251 The intent of the address UUID feature is to allow a client to avoid 2252 opening multiple identical connections to the same server, by allowing the 2253 client to check whether an address corresponds to an already-existing 2254 connection. Comparing two addresses is insufficient, because addresses 2255 can be recycled by distinct servers, and equivalent addresses may look 2256 different if simply compared as strings (for example, the host in a TCP 2257 address can be given as an IP address or as a hostname). 2258 </para> 2259 2260 <para> 2261 Note that the address key is <literal>guid</literal> even though the 2262 rest of the API and documentation says "UUID," for historical reasons. 2263 </para> 2264 2265 <para> 2266 [FIXME clarify if attempting to connect to each is a requirement 2267 or just a suggestion] 2268 When connecting to a server, multiple server addresses can be 2269 separated by a semi-colon. The library will then try to connect 2270 to the first address and if that fails, it'll try to connect to 2271 the next one specified, and so forth. For example 2272 <programlisting>unix:path=/tmp/dbus-test;unix:path=/tmp/dbus-test2</programlisting> 2273 </para> 2274 2275 </sect1> 2276 2277 <sect1 id="transports"> 2278 <title>Transports</title> 2279 <para> 2280 [FIXME we need to specify in detail each transport and its possible arguments] 2281 2282 Current transports include: unix domain sockets (including 2283 abstract namespace on linux), TCP/IP, and a debug/testing transport using 2284 in-process pipes. Future possible transports include one that 2285 tunnels over X11 protocol. 2286 </para> 2287 2288 <sect2 id="transports-unix-domain-sockets"> 2289 <title>Unix Domain Sockets</title> 2290 <para> 2291 Unix domain sockets can be either paths in the file system or on Linux 2292 kernels, they can be abstract which are similar to paths but 2293 do not show up in the file system. 2294 </para> 2295 2296 <para> 2297 When a socket is opened by the D-Bus library it truncates the path 2298 name right before the first trailing Nul byte. This is true for both 2299 normal paths and abstract paths. Note that this is a departure from 2300 previous versions of D-Bus that would create sockets with a fixed 2301 length path name. Names which were shorter than the fixed length 2302 would be padded by Nul bytes. 2303 </para> 2304 </sect2> 2305 </sect1> 2306 2307 <sect1 id="naming-conventions"> 2308 <title>Naming Conventions</title> 2309 2310 <para> 2311 D-Bus namespaces are all lowercase and correspond to reversed domain 2312 names, as with Java. e.g. "org.freedesktop" 2313 </para> 2314 <para> 2315 Interface, signal, method, and property names are "WindowsStyleCaps", note 2316 that the first letter is capitalized, unlike Java. 2317 </para> 2318 <para> 2319 Object paths are normally all lowercase with underscores used rather than 2320 hyphens. 2321 </para> 2322 </sect1> 2323 2324 <sect1 id="uuids"> 2325 <title>UUIDs</title> 2326 <para> 2327 A working D-Bus implementation uses universally-unique IDs in two places. 2328 First, each server address has a UUID identifying the address, 2329 as described in <xref linkend="addresses"/>. Second, each operating 2330 system kernel instance running a D-Bus client or server has a UUID 2331 identifying that kernel, retrieved by invoking the method 2332 org.freedesktop.DBus.Peer.GetMachineId() (see <xref 2333 linkend="standard-interfaces-peer"/>). 2334 </para> 2335 <para> 2336 The term "UUID" in this document is intended literally, i.e. an 2337 identifier that is universally unique. It is not intended to refer to 2338 RFC4122, and in fact the D-Bus UUID is not compatible with that RFC. 2339 </para> 2340 <para> 2341 The UUID must contain 128 bits of data and be hex-encoded. The 2342 hex-encoded string may not contain hyphens or other non-hex-digit 2343 characters, and it must be exactly 32 characters long. To generate a 2344 UUID, the current reference implementation concatenates 96 bits of random 2345 data followed by the 32-bit time in seconds since the UNIX epoch (in big 2346 endian byte order). 2347 </para> 2348 <para> 2349 It would also be acceptable and probably better to simply generate 128 2350 bits of random data, as long as the random number generator is of high 2351 quality. The timestamp could conceivably help if the random bits are not 2352 very random. With a quality random number generator, collisions are 2353 extremely unlikely even with only 96 bits, so it's somewhat academic. 2354 </para> 2355 <para> 2356 Implementations should, however, stick to random data for the first 96 bits 2357 of the UUID. 2358 </para> 2359 </sect1> 2360 2361 <sect1 id="standard-interfaces"> 2362 <title>Standard Interfaces</title> 2363 <para> 2364 See <xref linkend="message-protocol-types-notation"/> for details on 2365 the notation used in this section. There are some standard interfaces 2366 that may be useful across various D-Bus applications. 2367 </para> 2368 <sect2 id="standard-interfaces-peer"> 2369 <title><literal>org.freedesktop.DBus.Peer</literal></title> 2370 <para> 2371 The <literal>org.freedesktop.DBus.Peer</literal> interface 2372 has two methods: 2373 <programlisting> 2374 org.freedesktop.DBus.Peer.Ping () 2375 org.freedesktop.DBus.Peer.GetMachineId (out STRING machine_uuid) 2376 </programlisting> 2377 </para> 2378 <para> 2379 On receipt of the <literal>METHOD_CALL</literal> message 2380 <literal>org.freedesktop.DBus.Peer.Ping</literal>, an application should do 2381 nothing other than reply with a <literal>METHOD_RETURN</literal> as 2382 usual. It does not matter which object path a ping is sent to. The 2383 reference implementation handles this method automatically. 2384 </para> 2385 <para> 2386 On receipt of the <literal>METHOD_CALL</literal> message 2387 <literal>org.freedesktop.DBus.Peer.GetMachineId</literal>, an application should 2388 reply with a <literal>METHOD_RETURN</literal> containing a hex-encoded 2389 UUID representing the identity of the machine the process is running on. 2390 This UUID must be the same for all processes on a single system at least 2391 until that system next reboots. It should be the same across reboots 2392 if possible, but this is not always possible to implement and is not 2393 guaranteed. 2394 It does not matter which object path a GetMachineId is sent to. The 2395 reference implementation handles this method automatically. 2396 </para> 2397 <para> 2398 The UUID is intended to be per-instance-of-the-operating-system, so may represent 2399 a virtual machine running on a hypervisor, rather than a physical machine. 2400 Basically if two processes see the same UUID, they should also see the same 2401 shared memory, UNIX domain sockets, process IDs, and other features that require 2402 a running OS kernel in common between the processes. 2403 </para> 2404 <para> 2405 The UUID is often used where other programs might use a hostname. Hostnames 2406 can change without rebooting, however, or just be "localhost" - so the UUID 2407 is more robust. 2408 </para> 2409 <para> 2410 <xref linkend="uuids"/> explains the format of the UUID. 2411 </para> 2412 </sect2> 2413 2414 <sect2 id="standard-interfaces-introspectable"> 2415 <title><literal>org.freedesktop.DBus.Introspectable</literal></title> 2416 <para> 2417 This interface has one method: 2418 <programlisting> 2419 org.freedesktop.DBus.Introspectable.Introspect (out STRING xml_data) 2420 </programlisting> 2421 </para> 2422 <para> 2423 Objects instances may implement 2424 <literal>Introspect</literal> which returns an XML description of 2425 the object, including its interfaces (with signals and methods), objects 2426 below it in the object path tree, and its properties. 2427 </para> 2428 <para> 2429 <xref linkend="introspection-format"/> describes the format of this XML string. 2430 </para> 2431 </sect2> 2432 <sect2 id="standard-interfaces-properties"> 2433 <title><literal>org.freedesktop.DBus.Properties</literal></title> 2434 <para> 2435 Many native APIs will have a concept of object <firstterm>properties</firstterm> 2436 or <firstterm>attributes</firstterm>. These can be exposed via the 2437 <literal>org.freedesktop.DBus.Properties</literal> interface. 2438 </para> 2439 <para> 2440 <programlisting> 2441 org.freedesktop.DBus.Properties.Get (in STRING interface_name, 2442 in STRING property_name, 2443 out VARIANT value); 2444 org.freedesktop.DBus.Properties.Set (in STRING interface_name, 2445 in STRING property_name, 2446 in VARIANT value); 2447 </programlisting> 2448 </para> 2449 <para> 2450 The available properties and whether they are writable can be determined 2451 by calling <literal>org.freedesktop.DBus.Introspectable.Introspect</literal>, 2452 see <xref linkend="standard-interfaces-introspectable"/>. 2453 </para> 2454 <para> 2455 An empty string may be provided for the interface name; in this case, 2456 if there are multiple properties on an object with the same name, 2457 the results are undefined (picking one by according to an arbitrary 2458 deterministic rule, or returning an error, are the reasonable 2459 possibilities). 2460 </para> 2461 </sect2> 2462 </sect1> 2463 2464 <sect1 id="introspection-format"> 2465 <title>Introspection Data Format</title> 2466 <para> 2467 As described in <xref linkend="standard-interfaces-introspectable"/>, 2468 objects may be introspected at runtime, returning an XML string 2469 that describes the object. The same XML format may be used in 2470 other contexts as well, for example as an "IDL" for generating 2471 static language bindings. 2472 </para> 2473 <para> 2474 Here is an example of introspection data: 2475 <programlisting> 2476 <!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN" 2477 "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd"> 2478 <node name="/org/freedesktop/sample_object"> 2479 <interface name="org.freedesktop.SampleInterface"> 2480 <method name="Frobate"> 2481 <arg name="foo" type="i" direction="in"/> 2482 <arg name="bar" type="s" direction="out"/> 2483 <arg name="baz" type="a{us}" direction="out"/> 2484 <annotation name="org.freedesktop.DBus.Deprecated" value="true"/> 2485 </method> 2486 <method name="Bazify"> 2487 <arg name="bar" type="(iiu)" direction="in"/> 2488 <arg name="bar" type="v" direction="out"/> 2489 </method> 2490 <method name="Mogrify"> 2491 <arg name="bar" type="(iiav)" direction="in"/> 2492 </method> 2493 <signal name="Changed"> 2494 <arg name="new_value" type="b"/> 2495 </signal> 2496 <property name="Bar" type="y" access="readwrite"/> 2497 </interface> 2498 <node name="child_of_sample_object"/> 2499 <node name="another_child_of_sample_object"/> 2500 </node> 2501 </programlisting> 2502 </para> 2503 <para> 2504 A more formal DTD and spec needs writing, but here are some quick notes. 2505 <itemizedlist> 2506 <listitem> 2507 <para> 2508 Only the root <node> element can omit the node name, as it's 2509 known to be the object that was introspected. If the root 2510 <node> does have a name attribute, it must be an absolute 2511 object path. If child <node> have object paths, they must be 2512 relative. 2513 </para> 2514 </listitem> 2515 <listitem> 2516 <para> 2517 If a child <node> has any sub-elements, then they 2518 must represent a complete introspection of the child. 2519 If a child <node> is empty, then it may or may 2520 not have sub-elements; the child must be introspected 2521 in order to find out. The intent is that if an object 2522 knows that its children are "fast" to introspect 2523 it can go ahead and return their information, but 2524 otherwise it can omit it. 2525 </para> 2526 </listitem> 2527 <listitem> 2528 <para> 2529 The direction element on <arg> may be omitted, 2530 in which case it defaults to "in" for method calls 2531 and "out" for signals. Signals only allow "out" 2532 so while direction may be specified, it's pointless. 2533 </para> 2534 </listitem> 2535 <listitem> 2536 <para> 2537 The possible directions are "in" and "out", 2538 unlike CORBA there is no "inout" 2539 </para> 2540 </listitem> 2541 <listitem> 2542 <para> 2543 The possible property access flags are 2544 "readwrite", "read", and "write" 2545 </para> 2546 </listitem> 2547 <listitem> 2548 <para> 2549 Multiple interfaces can of course be listed for 2550 one <node>. 2551 </para> 2552 </listitem> 2553 <listitem> 2554 <para> 2555 The "name" attribute on arguments is optional. 2556 </para> 2557 </listitem> 2558 </itemizedlist> 2559 </para> 2560 <para> 2561 Method, interface, property, and signal elements may have 2562 "annotations", which are generic key/value pairs of metadata. 2563 They are similar conceptually to Java's annotations and C# attributes. 2564 Well-known annotations: 2565 </para> 2566 <informaltable> 2567 <tgroup cols="3"> 2568 <thead> 2569 <row> 2570 <entry>Name</entry> 2571 <entry>Values (separated by ,)</entry> 2572 <entry>Description</entry> 2573 </row> 2574 </thead> 2575 <tbody> 2576 <row> 2577 <entry>org.freedesktop.DBus.Deprecated</entry> 2578 <entry>true,false</entry> 2579 <entry>Whether or not the entity is deprecated; defaults to false</entry> 2580 </row> 2581 <row> 2582 <entry>org.freedesktop.DBus.GLib.CSymbol</entry> 2583 <entry>(string)</entry> 2584 <entry>The C symbol; may be used for methods and interfaces</entry> 2585 </row> 2586 <row> 2587 <entry>org.freedesktop.DBus.Method.NoReply</entry> 2588 <entry>true,false</entry> 2589 <entry>If set, don't expect a reply to the method call; defaults to false.</entry> 2590 </row> 2591 </tbody> 2592 </tgroup> 2593 </informaltable> 2594 </sect1> 2595 <sect1 id="message-bus"> 2596 <title>Message Bus Specification</title> 2597 <sect2 id="message-bus-overview"> 2598 <title>Message Bus Overview</title> 2599 <para> 2600 The message bus accepts connections from one or more applications. 2601 Once connected, applications can exchange messages with other 2602 applications that are also connected to the bus. 2603 </para> 2604 <para> 2605 In order to route messages among connections, the message bus keeps a 2606 mapping from names to connections. Each connection has one 2607 unique-for-the-lifetime-of-the-bus name automatically assigned. 2608 Applications may request additional names for a connection. Additional 2609 names are usually "well-known names" such as 2610 "org.freedesktop.TextEditor". When a name is bound to a connection, 2611 that connection is said to <firstterm>own</firstterm> the name. 2612 </para> 2613 <para> 2614 The bus itself owns a special name, <literal>org.freedesktop.DBus</literal>. 2615 This name routes messages to the bus, allowing applications to make 2616 administrative requests. For example, applications can ask the bus 2617 to assign a name to a connection. 2618 </para> 2619 <para> 2620 Each name may have <firstterm>queued owners</firstterm>. When an 2621 application requests a name for a connection and the name is already in 2622 use, the bus will optionally add the connection to a queue waiting for 2623 the name. If the current owner of the name disconnects or releases 2624 the name, the next connection in the queue will become the new owner. 2625 </para> 2626 2627 <para> 2628 This feature causes the right thing to happen if you start two text 2629 editors for example; the first one may request "org.freedesktop.TextEditor", 2630 and the second will be queued as a possible owner of that name. When 2631 the first exits, the second will take over. 2632 </para> 2633 2634 <para> 2635 Messages may have a <literal>DESTINATION</literal> field (see <xref 2636 linkend="message-protocol-header-fields"/>). If the 2637 <literal>DESTINATION</literal> field is present, it specifies a message 2638 recipient by name. Method calls and replies normally specify this field. 2639 </para> 2640 2641 <para> 2642 Signals normally do not specify a destination; they are sent to all 2643 applications with <firstterm>message matching rules</firstterm> that 2644 match the message. 2645 </para> 2646 2647 <para> 2648 When the message bus receives a method call, if the 2649 <literal>DESTINATION</literal> field is absent, the call is taken to be 2650 a standard one-to-one message and interpreted by the message bus 2651 itself. For example, sending an 2652 <literal>org.freedesktop.DBus.Peer.Ping</literal> message with no 2653 <literal>DESTINATION</literal> will cause the message bus itself to 2654 reply to the ping immediately; the message bus will not make this 2655 message visible to other applications. 2656 </para> 2657 2658 <para> 2659 Continuing the <literal>org.freedesktop.DBus.Peer.Ping</literal> example, if 2660 the ping message were sent with a <literal>DESTINATION</literal> name of 2661 <literal>com.yoyodyne.Screensaver</literal>, then the ping would be 2662 forwarded, and the Yoyodyne Corporation screensaver application would be 2663 expected to reply to the ping. 2664 </para> 2665 </sect2> 2666 2667 <sect2 id="message-bus-names"> 2668 <title>Message Bus Names</title> 2669 <para> 2670 Each connection has at least one name, assigned at connection time and 2671 returned in response to the 2672 <literal>org.freedesktop.DBus.Hello</literal> method call. This 2673 automatically-assigned name is called the connection's <firstterm>unique 2674 name</firstterm>. Unique names are never reused for two different 2675 connections to the same bus. 2676 </para> 2677 <para> 2678 Ownership of a unique name is a prerequisite for interaction with 2679 the message bus. It logically follows that the unique name is always 2680 the first name that an application comes to own, and the last 2681 one that it loses ownership of. 2682 </para> 2683 <para> 2684 Unique connection names must begin with the character ':' (ASCII colon 2685 character); bus names that are not unique names must not begin 2686 with this character. (The bus must reject any attempt by an application 2687 to manually request a name beginning with ':'.) This restriction 2688 categorically prevents "spoofing"; messages sent to a unique name 2689 will always go to the expected connection. 2690 </para> 2691 <para> 2692 When a connection is closed, all the names that it owns are deleted (or 2693 transferred to the next connection in the queue if any). 2694 </para> 2695 <para> 2696 A connection can request additional names to be associated with it using 2697 the <literal>org.freedesktop.DBus.RequestName</literal> message. <xref 2698 linkend="message-protocol-names-bus"/> describes the format of a valid 2699 name. These names can be released again using the 2700 <literal>org.freedesktop.DBus.ReleaseName</literal> message. 2701 </para> 2702 2703 <sect3 id="bus-messages-request-name"> 2704 <title><literal>org.freedesktop.DBus.RequestName</literal></title> 2705 <para> 2706 As a method: 2707 <programlisting> 2708 UINT32 RequestName (in STRING name, in UINT32 flags) 2709 </programlisting> 2710 Message arguments: 2711 <informaltable> 2712 <tgroup cols="3"> 2713 <thead> 2714 <row> 2715 <entry>Argument</entry> 2716 <entry>Type</entry> 2717 <entry>Description</entry> 2718 </row> 2719 </thead> 2720 <tbody> 2721 <row> 2722 <entry>0</entry> 2723 <entry>STRING</entry> 2724 <entry>Name to request</entry> 2725 </row> 2726 <row> 2727 <entry>1</entry> 2728 <entry>UINT32</entry> 2729 <entry>Flags</entry> 2730 </row> 2731 </tbody> 2732 </tgroup> 2733 </informaltable> 2734 Reply arguments: 2735 <informaltable> 2736 <tgroup cols="3"> 2737 <thead> 2738 <row> 2739 <entry>Argument</entry> 2740 <entry>Type</entry> 2741 <entry>Description</entry> 2742 </row> 2743 </thead> 2744 <tbody> 2745 <row> 2746 <entry>0</entry> 2747 <entry>UINT32</entry> 2748 <entry>Return value</entry> 2749 </row> 2750 </tbody> 2751 </tgroup> 2752 </informaltable> 2753 </para> 2754 <para> 2755 This method call should be sent to 2756 <literal>org.freedesktop.DBus</literal> and asks the message bus to 2757 assign the given name to the method caller. Each name maintains a 2758 queue of possible owners, where the head of the queue is the primary 2759 or current owner of the name. Each potential owner in the queue 2760 maintains the DBUS_NAME_FLAG_ALLOW_REPLACEMENT and 2761 DBUS_NAME_FLAG_DO_NOT_QUEUE settings from its latest RequestName 2762 call. When RequestName is invoked the following occurs: 2763 <itemizedlist> 2764 <listitem> 2765 <para> 2766 If the method caller is currently the primary owner of the name, 2767 the DBUS_NAME_FLAG_ALLOW_REPLACEMENT and DBUS_NAME_FLAG_DO_NOT_QUEUE 2768 values are updated with the values from the new RequestName call, 2769 and nothing further happens. 2770 </para> 2771 </listitem> 2772 2773 <listitem> 2774 <para> 2775 If the current primary owner (head of the queue) has 2776 DBUS_NAME_FLAG_ALLOW_REPLACEMENT set, and the RequestName 2777 invocation has the DBUS_NAME_FLAG_REPLACE_EXISTING flag, then 2778 the caller of RequestName replaces the current primary owner at 2779 the head of the queue and the current primary owner moves to the 2780 second position in the queue. If the caller of RequestName was 2781 in the queue previously its flags are updated with the values from 2782 the new RequestName in addition to moving it to the head of the queue. 2783 </para> 2784 </listitem> 2785 2786 <listitem> 2787 <para> 2788 If replacement is not possible, and the method caller is 2789 currently in the queue but not the primary owner, its flags are 2790 updated with the values from the new RequestName call. 2791 </para> 2792 </listitem> 2793 2794 <listitem> 2795 <para> 2796 If replacement is not possible, and the method caller is 2797 currently not in the queue, the method caller is appended to the 2798 queue. 2799 </para> 2800 </listitem> 2801 2802 <listitem> 2803 <para> 2804 If any connection in the queue has DBUS_NAME_FLAG_DO_NOT_QUEUE 2805 set and is not the primary owner, it is removed from the 2806 queue. This can apply to the previous primary owner (if it 2807 was replaced) or the method caller (if it updated the 2808 DBUS_NAME_FLAG_DO_NOT_QUEUE flag while still stuck in the 2809 queue, or if it was just added to the queue with that flag set). 2810 </para> 2811 </listitem> 2812 </itemizedlist> 2813 </para> 2814 <para> 2815 Note that DBUS_NAME_FLAG_REPLACE_EXISTING results in "jumping the 2816 queue," even if another application already in the queue had specified 2817 DBUS_NAME_FLAG_REPLACE_EXISTING. This comes up if a primary owner 2818 that does not allow replacement goes away, and the next primary owner 2819 does allow replacement. In this case, queued items that specified 2820 DBUS_NAME_FLAG_REPLACE_EXISTING <emphasis>do not</emphasis> 2821 automatically replace the new primary owner. In other words, 2822 DBUS_NAME_FLAG_REPLACE_EXISTING is not saved, it is only used at the 2823 time RequestName is called. This is deliberate to avoid an infinite loop 2824 anytime two applications are both DBUS_NAME_FLAG_ALLOW_REPLACEMENT 2825 and DBUS_NAME_FLAG_REPLACE_EXISTING. 2826 </para> 2827 <para> 2828 The flags argument contains any of the following values logically ORed 2829 together: 2830 2831 <informaltable> 2832 <tgroup cols="3"> 2833 <thead> 2834 <row> 2835 <entry>Conventional Name</entry> 2836 <entry>Value</entry> 2837 <entry>Description</entry> 2838 </row> 2839 </thead> 2840 <tbody> 2841 <row> 2842 <entry>DBUS_NAME_FLAG_ALLOW_REPLACEMENT</entry> 2843 <entry>0x1</entry> 2844 <entry> 2845 2846 If an application A specifies this flag and succeeds in 2847 becoming the owner of the name, and another application B 2848 later calls RequestName with the 2849 DBUS_NAME_FLAG_REPLACE_EXISTING flag, then application A 2850 will lose ownership and receive a 2851 <literal>org.freedesktop.DBus.NameLost</literal> signal, and 2852 application B will become the new owner. If DBUS_NAME_FLAG_ALLOW_REPLACEMENT 2853 is not specified by application A, or DBUS_NAME_FLAG_REPLACE_EXISTING 2854 is not specified by application B, then application B will not replace 2855 application A as the owner. 2856 2857 </entry> 2858 </row> 2859 <row> 2860 <entry>DBUS_NAME_FLAG_REPLACE_EXISTING</entry> 2861 <entry>0x2</entry> 2862 <entry> 2863 2864 Try to replace the current owner if there is one. If this 2865 flag is not set the application will only become the owner of 2866 the name if there is no current owner. If this flag is set, 2867 the application will replace the current owner if 2868 the current owner specified DBUS_NAME_FLAG_ALLOW_REPLACEMENT. 2869 2870 </entry> 2871 </row> 2872 <row> 2873 <entry>DBUS_NAME_FLAG_DO_NOT_QUEUE</entry> 2874 <entry>0x4</entry> 2875 <entry> 2876 2877 Without this flag, if an application requests a name that is 2878 already owned, the application will be placed in a queue to 2879 own the name when the current owner gives it up. If this 2880 flag is given, the application will not be placed in the 2881 queue, the request for the name will simply fail. This flag 2882 also affects behavior when an application is replaced as 2883 name owner; by default the application moves back into the 2884 waiting queue, unless this flag was provided when the application 2885 became the name owner. 2886 2887 </entry> 2888 </row> 2889 </tbody> 2890 </tgroup> 2891 </informaltable> 2892 2893 The return code can be one of the following values: 2894 2895 <informaltable> 2896 <tgroup cols="3"> 2897 <thead> 2898 <row> 2899 <entry>Conventional Name</entry> 2900 <entry>Value</entry> 2901 <entry>Description</entry> 2902 </row> 2903 </thead> 2904 <tbody> 2905 <row> 2906 <entry>DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER</entry> 2907 <entry>1</entry> <entry>The caller is now the primary owner of 2908 the name, replacing any previous owner. Either the name had no 2909 owner before, or the caller specified 2910 DBUS_NAME_FLAG_REPLACE_EXISTING and the current owner specified 2911 DBUS_NAME_FLAG_ALLOW_REPLACEMENT.</entry> 2912 </row> 2913 <row> 2914 <entry>DBUS_REQUEST_NAME_REPLY_IN_QUEUE</entry> 2915 <entry>2</entry> 2916 2917 <entry>The name already had an owner, 2918 DBUS_NAME_FLAG_DO_NOT_QUEUE was not specified, and either 2919 the current owner did not specify 2920 DBUS_NAME_FLAG_ALLOW_REPLACEMENT or the requesting 2921 application did not specify DBUS_NAME_FLAG_REPLACE_EXISTING. 2922 </entry> 2923 </row> 2924 <row> 2925 <entry>DBUS_REQUEST_NAME_REPLY_EXISTS</entry> <entry>3</entry> 2926 <entry>The name already has an owner, 2927 DBUS_NAME_FLAG_DO_NOT_QUEUE was specified, and either 2928 DBUS_NAME_FLAG_ALLOW_REPLACEMENT was not specified by the 2929 current owner, or DBUS_NAME_FLAG_REPLACE_EXISTING was not 2930 specified by the requesting application.</entry> 2931 </row> 2932 <row> 2933 <entry>DBUS_REQUEST_NAME_REPLY_ALREADY_OWNER</entry> 2934 <entry>4</entry> 2935 <entry>The application trying to request ownership of a name is already the owner of it.</entry> 2936 </row> 2937 </tbody> 2938 </tgroup> 2939 </informaltable> 2940 </para> 2941 </sect3> 2942 2943 <sect3 id="bus-messages-release-name"> 2944 <title><literal>org.freedesktop.DBus.ReleaseName</literal></title> 2945 <para> 2946 As a method: 2947 <programlisting> 2948 UINT32 ReleaseName (in STRING name) 2949 </programlisting> 2950 Message arguments: 2951 <informaltable> 2952 <tgroup cols="3"> 2953 <thead> 2954 <row> 2955 <entry>Argument</entry> 2956 <entry>Type</entry> 2957 <entry>Description</entry> 2958 </row> 2959 </thead> 2960 <tbody> 2961 <row> 2962 <entry>0</entry> 2963 <entry>STRING</entry> 2964 <entry>Name to release</entry> 2965 </row> 2966 </tbody> 2967 </tgroup> 2968 </informaltable> 2969 Reply arguments: 2970 <informaltable> 2971 <tgroup cols="3"> 2972 <thead> 2973 <row> 2974 <entry>Argument</entry> 2975 <entry>Type</entry> 2976 <entry>Description</entry> 2977 </row> 2978 </thead> 2979 <tbody> 2980 <row> 2981 <entry>0</entry> 2982 <entry>UINT32</entry> 2983 <entry>Return value</entry> 2984 </row> 2985 </tbody> 2986 </tgroup> 2987 </informaltable> 2988 </para> 2989 <para> 2990 This method call should be sent to 2991 <literal>org.freedesktop.DBus</literal> and asks the message bus to 2992 release the method caller's claim to the given name. If the caller is 2993 the primary owner, a new primary owner will be selected from the 2994 queue if any other owners are waiting. If the caller is waiting in 2995 the queue for the name, the caller will removed from the queue and 2996 will not be made an owner of the name if it later becomes available. 2997 If there are no other owners in the queue for the name, it will be 2998 removed from the bus entirely. 2999 3000 The return code can be one of the following values: 3001 3002 <informaltable> 3003 <tgroup cols="3"> 3004 <thead> 3005 <row> 3006 <entry>Conventional Name</entry> 3007 <entry>Value</entry> 3008 <entry>Description</entry> 3009 </row> 3010 </thead> 3011 <tbody> 3012 <row> 3013 <entry>DBUS_RELEASE_NAME_REPLY_RELEASED</entry> 3014 <entry>1</entry> <entry>The caller has released his claim on 3015 the given name. Either the caller was the primary owner of 3016 the name, and the name is now unused or taken by somebody 3017 waiting in the queue for the name, or the caller was waiting 3018 in the queue for the name and has now been removed from the 3019 queue.</entry> 3020 </row> 3021 <row> 3022 <entry>DBUS_RELEASE_NAME_REPLY_NON_EXISTENT</entry> 3023 <entry>2</entry> 3024 <entry>The given name does not exist on this bus.</entry> 3025 </row> 3026 <row> 3027 <entry>DBUS_RELEASE_NAME_REPLY_NOT_OWNER</entry> 3028 <entry>3</entry> 3029 <entry>The caller was not the primary owner of this name, 3030 and was also not waiting in the queue to own this name.</entry> 3031 </row> 3032 </tbody> 3033 </tgroup> 3034 </informaltable> 3035 </para> 3036 </sect3> 3037 </sect2> 3038 3039 <sect2 id="message-bus-routing"> 3040 <title>Message Bus Message Routing</title> 3041 <para> 3042 FIXME 3043 </para> 3044 <sect3 id="message-bus-routing-match-rules"> 3045 <title>Match Rules</title> 3046 <para> 3047 An important part of the message bus routing protocol is match 3048 rules. Match rules describe what messages can be sent to a client 3049 based on the contents of the message. When a message is routed 3050 through the bus it is compared to clients' match rules. If any 3051 of the rules match, the message is dispatched to the client. 3052 If none of the rules match the message never leaves the bus. This 3053 is an effective way to control traffic over the bus and to make sure 3054 only relevant message need to be processed by the client. 3055 </para> 3056 <para> 3057 Match rules are added using the AddMatch bus method 3058 (see xref linkend="bus-messages-add-match"/>). Rules are 3059 specified as a string of comma separated key/value pairs. 3060 Excluding a key from the rule indicates a wildcard match. 3061 For instance excluding the the member from a match rule but 3062 adding a sender would let all messages from that sender through. 3063 An example of a complete rule would be 3064 "type='signal',sender='org.freedesktop.DBus',interface='org.freedesktop.DBus',member='Foo',path='/bar/foo',destination=':452345.34',arg2='bar'" 3065 </para> 3066 <para> 3067 The following table describes the keys that can be used to create 3068 a match rule: 3069 The following table summarizes the D-Bus types. 3070 <informaltable> 3071 <tgroup cols="3"> 3072 <thead> 3073 <row> 3074 <entry>Key</entry> 3075 <entry>Possible Values</entry> 3076 <entry>Description</entry> 3077 </row> 3078 </thead> 3079 <tbody> 3080 <row> 3081 <entry><literal>type</literal></entry> 3082 <entry>'signal', 'method_call', 'method_return', 'error'</entry> 3083 <entry>Match on the message type. An example of a type match is type='signal'</entry> 3084 </row> 3085 <row> 3086 <entry><literal>sender</literal></entry> 3087 <entry>A bus or unique name (see <xref linkend="term-bus-name"/> 3088 and <xref linkend="term-unique-name"/> respectively) 3089 </entry> 3090 <entry>Match messages sent by a particular sender. An example of a sender match 3091 is sender='org.freedesktop.Hal'</entry> 3092 </row> 3093 <row> 3094 <entry><literal>interface</literal></entry> 3095 <entry>An interface name (see <xref linkend="message-protocol-names-interface"/>)</entry> 3096 <entry>Match messages sent over or to a particular interface. An example of an 3097 interface match is interface='org.freedesktop.Hal.Manager'. 3098 If a message omits the interface header, it must not match any rule 3099 that specifies this key.</entry> 3100 </row> 3101 <row> 3102 <entry><literal>member</literal></entry> 3103 <entry>Any valid method or signal name</entry> 3104 <entry>Matches messages which have the give method or signal name. An example of 3105 a member match is member='NameOwnerChanged'</entry> 3106 </row> 3107 <row> 3108 <entry><literal>path</literal></entry> 3109 <entry>An object path (see <xref linkend="message-protocol-marshaling-object-path"/>)</entry> 3110 <entry>Matches messages which are sent from or to the given object. An example of a 3111 path match is path='/org/freedesktop/Hal/Manager'</entry> 3112 </row> 3113 <row> 3114 <entry><literal>destination</literal></entry> 3115 <entry>A unique name (see <xref linkend="term-unique-name"/>)</entry> 3116 <entry>Matches messages which are being sent to the given unique name. An 3117 example of a destination match is destination=':1.0'</entry> 3118 </row> 3119 <row> 3120 <entry><literal>arg[0, 1, 2, 3, ...]</literal></entry> 3121 <entry>Any string</entry> 3122 <entry>Arg matches are special and are used for further restricting the 3123 match based on the arguments in the body of a message. As of this time 3124 only string arguments can be matched. An example of an argument match 3125 would be arg3='Foo'. Only argument indexes from 0 to 63 should be 3126 accepted.</entry> 3127 </row> 3128 </tbody> 3129 </tgroup> 3130 </informaltable> 3131 </para> 3132 </sect3> 3133 </sect2> 3134 <sect2 id="message-bus-starting-services"> 3135 <title>Message Bus Starting Services</title> 3136 <para> 3137 The message bus can start applications on behalf of other applications. 3138 In CORBA terms, this would be called <firstterm>activation</firstterm>. 3139 An application that can be started in this way is called a 3140 <firstterm>service</firstterm>. 3141 </para> 3142 <para> 3143 With D-Bus, starting a service is normally done by name. That is, 3144 applications ask the message bus to start some program that will own a 3145 well-known name, such as <literal>org.freedesktop.TextEditor</literal>. 3146 This implies a contract documented along with the name 3147 <literal>org.freedesktop.TextEditor</literal> for which objects 3148 the owner of that name will provide, and what interfaces those 3149 objects will have. 3150 </para> 3151 <para> 3152 To find an executable corresponding to a particular name, the bus daemon 3153 looks for <firstterm>service description files</firstterm>. Service 3154 description files define a mapping from names to executables. Different 3155 kinds of message bus will look for these files in different places, see 3156 <xref linkend="message-bus-types"/>. 3157 </para> 3158 <para> 3159 [FIXME the file format should be much better specified than "similar to 3160 .desktop entries" esp. since desktop entries are already 3161 badly-specified. ;-)] Service description files have the ".service" file 3162 extension. The message bus will only load service description files 3163 ending with .service; all other files will be ignored. The file format 3164 is similar to that of <ulink 3165 url="http://www.freedesktop.org/standards/desktop-entry-spec/desktop-entry-spec.html">desktop 3166 entries</ulink>. All service description files must be in UTF-8 3167 encoding. To ensure that there will be no name collisions, service files 3168 must be namespaced using the same mechanism as messages and service 3169 names. 3170 3171 <figure> 3172 <title>Example service description file</title> 3173 <programlisting> 3174 # Sample service description file 3175 [D-BUS Service] 3176 Names=org.freedesktop.ConfigurationDatabase;org.gnome.GConf; 3177 Exec=/usr/libexec/gconfd-2 3178 </programlisting> 3179 </figure> 3180 </para> 3181 <para> 3182 When an application asks to start a service by name, the bus daemon tries to 3183 find a service that will own that name. It then tries to spawn the 3184 executable associated with it. If this fails, it will report an 3185 error. [FIXME what happens if two .service files offer the same service; 3186 what kind of error is reported, should we have a way for the client to 3187 choose one?] 3188 </para> 3189 <para> 3190 The executable launched will have the environment variable 3191 <literal>DBUS_STARTER_ADDRESS</literal> set to the address of the 3192 message bus so it can connect and request the appropriate names. 3193 </para> 3194 <para> 3195 The executable being launched may want to know whether the message bus 3196 starting it is one of the well-known message buses (see <xref 3197 linkend="message-bus-types"/>). To facilitate this, the bus must also set 3198 the <literal>DBUS_STARTER_BUS_TYPE</literal> environment variable if it is one 3199 of the well-known buses. The currently-defined values for this variable 3200 are <literal>system</literal> for the systemwide message bus, 3201 and <literal>session</literal> for the per-login-session message 3202 bus. The new executable must still connect to the address given 3203 in <literal>DBUS_STARTER_ADDRESS</literal>, but may assume that the 3204 resulting connection is to the well-known bus. 3205 </para> 3206 <para> 3207 [FIXME there should be a timeout somewhere, either specified 3208 in the .service file, by the client, or just a global value 3209 and if the client being activated fails to connect within that 3210 timeout, an error should be sent back.] 3211 </para> 3212 3213 <sect3 id="message-bus-starting-services-scope"> 3214 <title>Message Bus Service Scope</title> 3215 <para> 3216 The "scope" of a service is its "per-", such as per-session, 3217 per-machine, per-home-directory, or per-display. The reference 3218 implementation doesn't yet support starting services in a different 3219 scope from the message bus itself. So e.g. if you start a service 3220 on the session bus its scope is per-session. 3221 </para> 3222 <para> 3223 We could add an optional scope to a bus name. For example, for 3224 per-(display,session pair), we could have a unique ID for each display 3225 generated automatically at login and set on screen 0 by executing a 3226 special "set display ID" binary. The ID would be stored in a 3227 <literal>_DBUS_DISPLAY_ID</literal> property and would be a string of 3228 random bytes. This ID would then be used to scope names. 3229 Starting/locating a service could be done by ID-name pair rather than 3230 only by name. 3231 </para> 3232 <para> 3233 Contrast this with a per-display scope. To achieve that, we would 3234 want a single bus spanning all sessions using a given display. 3235 So we might set a <literal>_DBUS_DISPLAY_BUS_ADDRESS</literal> 3236 property on screen 0 of the display, pointing to this bus. 3237 </para> 3238 </sect3> 3239 </sect2> 3240 3241 <sect2 id="message-bus-types"> 3242 <title>Well-known Message Bus Instances</title> 3243 <para> 3244 Two standard message bus instances are defined here, along with how 3245 to locate them and where their service files live. 3246 </para> 3247 <sect3 id="message-bus-types-login"> 3248 <title>Login session message bus</title> 3249 <para> 3250 Each time a user logs in, a <firstterm>login session message 3251 bus</firstterm> may be started. All applications in the user's login 3252 session may interact with one another using this message bus. 3253 </para> 3254 <para> 3255 The address of the login session message bus is given 3256 in the <literal>DBUS_SESSION_BUS_ADDRESS</literal> environment 3257 variable. If that variable is not set, applications may 3258 also try to read the address from the X Window System root 3259 window property <literal>_DBUS_SESSION_BUS_ADDRESS</literal>. 3260 The root window property must have type <literal>STRING</literal>. 3261 The environment variable should have precedence over the 3262 root window property. 3263 </para> 3264 <para> 3265 [FIXME specify location of .service files, probably using 3266 DESKTOP_DIRS etc. from basedir specification, though login session 3267 bus is not really desktop-specific] 3268 </para> 3269 </sect3> 3270 <sect3 id="message-bus-types-system"> 3271 <title>System message bus</title> 3272 <para> 3273 A computer may have a <firstterm>system message bus</firstterm>, 3274 accessible to all applications on the system. This message bus may be 3275 used to broadcast system events, such as adding new hardware devices, 3276 changes in the printer queue, and so forth. 3277 </para> 3278 <para> 3279 The address of the system message bus is given 3280 in the <literal>DBUS_SYSTEM_BUS_ADDRESS</literal> environment 3281 variable. If that variable is not set, applications should try 3282 to connect to the well-known address 3283 <literal>unix:path=/var/run/dbus/system_bus_socket</literal>. 3284 <footnote> 3285 <para> 3286 The D-Bus reference implementation actually honors the 3287 <literal>$(localstatedir)</literal> configure option 3288 for this address, on both client and server side. 3289 </para> 3290 </footnote> 3291 </para> 3292 <para> 3293 [FIXME specify location of system bus .service files] 3294 </para> 3295 </sect3> 3296 </sect2> 3297 3298 <sect2 id="message-bus-messages"> 3299 <title>Message Bus Messages</title> 3300 <para> 3301 The special message bus name <literal>org.freedesktop.DBus</literal> 3302 responds to a number of additional messages. 3303 </para> 3304 3305 <sect3 id="bus-messages-hello"> 3306 <title><literal>org.freedesktop.DBus.Hello</literal></title> 3307 <para> 3308 As a method: 3309 <programlisting> 3310 STRING Hello () 3311 </programlisting> 3312 Reply arguments: 3313 <informaltable> 3314 <tgroup cols="3"> 3315 <thead> 3316 <row> 3317 <entry>Argument</entry> 3318 <entry>Type</entry> 3319 <entry>Description</entry> 3320 </row> 3321 </thead> 3322 <tbody> 3323 <row> 3324 <entry>0</entry> 3325 <entry>STRING</entry> 3326 <entry>Unique name assigned to the connection</entry> 3327 </row> 3328 </tbody> 3329 </tgroup> 3330 </informaltable> 3331 </para> 3332 <para> 3333 Before an application is able to send messages to other applications 3334 it must send the <literal>org.freedesktop.DBus.Hello</literal> message 3335 to the message bus to obtain a unique name. If an application without 3336 a unique name tries to send a message to another application, or a 3337 message to the message bus itself that isn't the 3338 <literal>org.freedesktop.DBus.Hello</literal> message, it will be 3339 disconnected from the bus. 3340 </para> 3341 <para> 3342 There is no corresponding "disconnect" request; if a client wishes to 3343 disconnect from the bus, it simply closes the socket (or other 3344 communication channel). 3345 </para> 3346 </sect3> 3347 <sect3 id="bus-messages-list-names"> 3348 <title><literal>org.freedesktop.DBus.ListNames</literal></title> 3349 <para> 3350 As a method: 3351 <programlisting> 3352 ARRAY of STRING ListNames () 3353 </programlisting> 3354 Reply arguments: 3355 <informaltable> 3356 <tgroup cols="3"> 3357 <thead> 3358 <row> 3359 <entry>Argument</entry> 3360 <entry>Type</entry> 3361 <entry>Description</entry> 3362 </row> 3363 </thead> 3364 <tbody> 3365 <row> 3366 <entry>0</entry> 3367 <entry>ARRAY of STRING</entry> 3368 <entry>Array of strings where each string is a bus name</entry> 3369 </row> 3370 </tbody> 3371 </tgroup> 3372 </informaltable> 3373 </para> 3374 <para> 3375 Returns a list of all currently-owned names on the bus. 3376 </para> 3377 </sect3> 3378 <sect3 id="bus-messages-list-activatable-names"> 3379 <title><literal>org.freedesktop.DBus.ListActivatableNames</literal></title> 3380 <para> 3381 As a method: 3382 <programlisting> 3383 ARRAY of STRING ListActivatableNames () 3384 </programlisting> 3385 Reply arguments: 3386 <informaltable> 3387 <tgroup cols="3"> 3388 <thead> 3389 <row> 3390 <entry>Argument</entry> 3391 <entry>Type</entry> 3392 <entry>Description</entry> 3393 </row> 3394 </thead> 3395 <tbody> 3396 <row> 3397 <entry>0</entry> 3398 <entry>ARRAY of STRING</entry> 3399 <entry>Array of strings where each string is a bus name</entry> 3400 </row> 3401 </tbody> 3402 </tgroup> 3403 </informaltable> 3404 </para> 3405 <para> 3406 Returns a list of all names that can be activated on the bus. 3407 </para> 3408 </sect3> 3409 <sect3 id="bus-messages-name-exists"> 3410 <title><literal>org.freedesktop.DBus.NameHasOwner</literal></title> 3411 <para> 3412 As a method: 3413 <programlisting> 3414 BOOLEAN NameHasOwner (in STRING name) 3415 </programlisting> 3416 Message arguments: 3417 <informaltable> 3418 <tgroup cols="3"> 3419 <thead> 3420 <row> 3421 <entry>Argument</entry> 3422 <entry>Type</entry> 3423 <entry>Description</entry> 3424 </row> 3425 </thead> 3426 <tbody> 3427 <row> 3428 <entry>0</entry> 3429 <entry>STRING</entry> 3430 <entry>Name to check</entry> 3431 </row> 3432 </tbody> 3433 </tgroup> 3434 </informaltable> 3435 Reply arguments: 3436 <informaltable> 3437 <tgroup cols="3"> 3438 <thead> 3439 <row> 3440 <entry>Argument</entry> 3441 <entry>Type</entry> 3442 <entry>Description</entry> 3443 </row> 3444 </thead> 3445 <tbody> 3446 <row> 3447 <entry>0</entry> 3448 <entry>BOOLEAN</entry> 3449 <entry>Return value, true if the name exists</entry> 3450 </row> 3451 </tbody> 3452 </tgroup> 3453 </informaltable> 3454 </para> 3455 <para> 3456 Checks if the specified name exists (currently has an owner). 3457 </para> 3458 </sect3> 3459 3460 <sect3 id="bus-messages-name-owner-changed"> 3461 <title><literal>org.freedesktop.DBus.NameOwnerChanged</literal></title> 3462 <para> 3463 This is a signal: 3464 <programlisting> 3465 NameOwnerChanged (STRING name, STRING old_owner, STRING new_owner) 3466 </programlisting> 3467 Message arguments: 3468 <informaltable> 3469 <tgroup cols="3"> 3470 <thead> 3471 <row> 3472 <entry>Argument</entry> 3473 <entry>Type</entry> 3474 <entry>Description</entry> 3475 </row> 3476 </thead> 3477 <tbody> 3478 <row> 3479 <entry>0</entry> 3480 <entry>STRING</entry> 3481 <entry>Name with a new owner</entry> 3482 </row> 3483 <row> 3484 <entry>1</entry> 3485 <entry>STRING</entry> 3486 <entry>Old owner or empty string if none</entry> 3487 </row> 3488 <row> 3489 <entry>2</entry> 3490 <entry>STRING</entry> 3491 <entry>New owner or empty string if none</entry> 3492 </row> 3493 </tbody> 3494 </tgroup> 3495 </informaltable> 3496 </para> 3497 <para> 3498 This signal indicates that the owner of a name has changed. 3499 It's also the signal to use to detect the appearance of 3500 new names on the bus. 3501 </para> 3502 </sect3> 3503 <sect3 id="bus-messages-name-lost"> 3504 <title><literal>org.freedesktop.DBus.NameLost</literal></title> 3505 <para> 3506 This is a signal: 3507 <programlisting> 3508 NameLost (STRING name) 3509 </programlisting> 3510 Message arguments: 3511 <informaltable> 3512 <tgroup cols="3"> 3513 <thead> 3514 <row> 3515 <entry>Argument</entry> 3516 <entry>Type</entry> 3517 <entry>Description</entry> 3518 </row> 3519 </thead> 3520 <tbody> 3521 <row> 3522 <entry>0</entry> 3523 <entry>STRING</entry> 3524 <entry>Name which was lost</entry> 3525 </row> 3526 </tbody> 3527 </tgroup> 3528 </informaltable> 3529 </para> 3530 <para> 3531 This signal is sent to a specific application when it loses 3532 ownership of a name. 3533 </para> 3534 </sect3> 3535 3536 <sect3 id="bus-messages-name-acquired"> 3537 <title><literal>org.freedesktop.DBus.NameAcquired</literal></title> 3538 <para> 3539 This is a signal: 3540 <programlisting> 3541 NameAcquired (STRING name) 3542 </programlisting> 3543 Message arguments: 3544 <informaltable> 3545 <tgroup cols="3"> 3546 <thead> 3547 <row> 3548 <entry>Argument</entry> 3549 <entry>Type</entry> 3550 <entry>Description</entry> 3551 </row> 3552 </thead> 3553 <tbody> 3554 <row> 3555 <entry>0</entry> 3556 <entry>STRING</entry> 3557 <entry>Name which was acquired</entry> 3558 </row> 3559 </tbody> 3560 </tgroup> 3561 </informaltable> 3562 </para> 3563 <para> 3564 This signal is sent to a specific application when it gains 3565 ownership of a name. 3566 </para> 3567 </sect3> 3568 3569 <sect3 id="bus-messages-start-service-by-name"> 3570 <title><literal>org.freedesktop.DBus.StartServiceByName</literal></title> 3571 <para> 3572 As a method: 3573 <programlisting> 3574 UINT32 StartServiceByName (in STRING name, in UINT32 flags) 3575 </programlisting> 3576 Message arguments: 3577 <informaltable> 3578 <tgroup cols="3"> 3579 <thead> 3580 <row> 3581 <entry>Argument</entry> 3582 <entry>Type</entry> 3583 <entry>Description</entry> 3584 </row> 3585 </thead> 3586 <tbody> 3587 <row> 3588 <entry>0</entry> 3589 <entry>STRING</entry> 3590 <entry>Name of the service to start</entry> 3591 </row> 3592 <row> 3593 <entry>1</entry> 3594 <entry>UINT32</entry> 3595 <entry>Flags (currently not used)</entry> 3596 </row> 3597 </tbody> 3598 </tgroup> 3599 </informaltable> 3600 Reply arguments: 3601 <informaltable> 3602 <tgroup cols="3"> 3603 <thead> 3604 <row> 3605 <entry>Argument</entry> 3606 <entry>Type</entry> 3607 <entry>Description</entry> 3608 </row> 3609 </thead> 3610 <tbody> 3611 <row> 3612 <entry>0</entry> 3613 <entry>UINT32</entry> 3614 <entry>Return value</entry> 3615 </row> 3616 </tbody> 3617 </tgroup> 3618 </informaltable> 3619 Tries to launch the executable associated with a name. For more information, see <xref linkend="message-bus-starting-services"/>. 3620 3621 </para> 3622 <para> 3623 The return value can be one of the following values: 3624 <informaltable> 3625 <tgroup cols="3"> 3626 <thead> 3627 <row> 3628 <entry>Identifier</entry> 3629 <entry>Value</entry> 3630 <entry>Description</entry> 3631 </row> 3632 </thead> 3633 <tbody> 3634 <row> 3635 <entry>DBUS_START_REPLY_SUCCESS</entry> 3636 <entry>1</entry> 3637 <entry>The service was successfully started.</entry> 3638 </row> 3639 <row> 3640 <entry>DBUS_START_REPLY_ALREADY_RUNNING</entry> 3641 <entry>2</entry> 3642 <entry>A connection already owns the given name.</entry> 3643 </row> 3644 </tbody> 3645 </tgroup> 3646 </informaltable> 3647 </para> 3648 3649 </sect3> 3650 3651 <sect3 id="bus-messages-get-name-owner"> 3652 <title><literal>org.freedesktop.DBus.GetNameOwner</literal></title> 3653 <para> 3654 As a method: 3655 <programlisting> 3656 STRING GetNameOwner (in STRING name) 3657 </programlisting> 3658 Message arguments: 3659 <informaltable> 3660 <tgroup cols="3"> 3661 <thead> 3662 <row> 3663 <entry>Argument</entry> 3664 <entry>Type</entry> 3665 <entry>Description</entry> 3666 </row> 3667 </thead> 3668 <tbody> 3669 <row> 3670 <entry>0</entry> 3671 <entry>STRING</entry> 3672 <entry>Name to get the owner of</entry> 3673 </row> 3674 </tbody> 3675 </tgroup> 3676 </informaltable> 3677 Reply arguments: 3678 <informaltable> 3679 <tgroup cols="3"> 3680 <thead> 3681 <row> 3682 <entry>Argument</entry> 3683 <entry>Type</entry> 3684 <entry>Description</entry> 3685 </row> 3686 </thead> 3687 <tbody> 3688 <row> 3689 <entry>0</entry> 3690 <entry>STRING</entry> 3691 <entry>Return value, a unique connection name</entry> 3692 </row> 3693 </tbody> 3694 </tgroup> 3695 </informaltable> 3696 Returns the unique connection name of the primary owner of the name 3697 given. If the requested name doesn't have an owner, returns a 3698 <literal>org.freedesktop.DBus.Error.NameHasNoOwner</literal> error. 3699 </para> 3700 </sect3> 3701 3702 <sect3 id="bus-messages-get-connection-unix-user"> 3703 <title><literal>org.freedesktop.DBus.GetConnectionUnixUser</literal></title> 3704 <para> 3705 As a method: 3706 <programlisting> 3707 UINT32 GetConnectionUnixUser (in STRING connection_name) 3708 </programlisting> 3709 Message arguments: 3710 <informaltable> 3711 <tgroup cols="3"> 3712 <thead> 3713 <row> 3714 <entry>Argument</entry> 3715 <entry>Type</entry> 3716 <entry>Description</entry> 3717 </row> 3718 </thead> 3719 <tbody> 3720 <row> 3721 <entry>0</entry> 3722 <entry>STRING</entry> 3723 <entry>Name of the connection to query</entry> 3724 </row> 3725 </tbody> 3726 </tgroup> 3727 </informaltable> 3728 Reply arguments: 3729 <informaltable> 3730 <tgroup cols="3"> 3731 <thead> 3732 <row> 3733 <entry>Argument</entry> 3734 <entry>Type</entry> 3735 <entry>Description</entry> 3736 </row> 3737 </thead> 3738 <tbody> 3739 <row> 3740 <entry>0</entry> 3741 <entry>UINT32</entry> 3742 <entry>unix user id</entry> 3743 </row> 3744 </tbody> 3745 </tgroup> 3746 </informaltable> 3747 Returns the unix uid of the process connected to the server. If unable to 3748 determine it, a <literal>org.freedesktop.DBus.Error.Failed</literal> 3749 error is returned. 3750 </para> 3751 </sect3> 3752 3753 <sect3 id="bus-messages-add-match"> 3754 <title><literal>org.freedesktop.DBus.AddMatch</literal></title> 3755 <para> 3756 As a method: 3757 <programlisting> 3758 AddMatch (in STRING rule) 3759 </programlisting> 3760 Message arguments: 3761 <informaltable> 3762 <tgroup cols="3"> 3763 <thead> 3764 <row> 3765 <entry>Argument</entry> 3766 <entry>Type</entry> 3767 <entry>Description</entry> 3768 </row> 3769 </thead> 3770 <tbody> 3771 <row> 3772 <entry>0</entry> 3773 <entry>STRING</entry> 3774 <entry>Match rule to add to the connection</entry> 3775 </row> 3776 </tbody> 3777 </tgroup> 3778 </informaltable> 3779 Adds a match rule to match messages going through the message bus (see <xref linkend='message-bus-routing-match-rules'/>). 3780 If the bus does not have enough resources the <literal>org.freedesktop.DBus.Error.OOM</literal> 3781 error is returned. 3782 </para> 3783 </sect3> 3784 <sect3 id="bus-messages-remove-match"> 3785 <title><literal>org.freedesktop.DBus.RemoveMatch</literal></title> 3786 <para> 3787 As a method: 3788 <programlisting> 3789 RemoveMatch (in STRING rule) 3790 </programlisting> 3791 Message arguments: 3792 <informaltable> 3793 <tgroup cols="3"> 3794 <thead> 3795 <row> 3796 <entry>Argument</entry> 3797 <entry>Type</entry> 3798 <entry>Description</entry> 3799 </row> 3800 </thead> 3801 <tbody> 3802 <row> 3803 <entry>0</entry> 3804 <entry>STRING</entry> 3805 <entry>Match rule to remove from the connection</entry> 3806 </row> 3807 </tbody> 3808 </tgroup> 3809 </informaltable> 3810 Removes the first rule that matches (see <xref linkend='message-bus-routing-match-rules'/>). 3811 If the rule is not found the <literal>org.freedesktop.DBus.Error.MatchRuleNotFound</literal> 3812 error is returned. 3813 </para> 3814 </sect3> 3815 3816 </sect2> 3817 3818 </sect1> 3819<!-- 3820 <appendix id="implementation-notes"> 3821 <title>Implementation notes</title> 3822 <sect1 id="implementation-notes-subsection"> 3823 <title></title> 3824 <para> 3825 </para> 3826 </sect1> 3827 </appendix> 3828--> 3829 3830 <glossary><title>Glossary</title> 3831 <para> 3832 This glossary defines some of the terms used in this specification. 3833 </para> 3834 3835 <glossentry id="term-bus-name"><glossterm>Bus Name</glossterm> 3836 <glossdef> 3837 <para> 3838 The message bus maintains an association between names and 3839 connections. (Normally, there's one connection per application.) A 3840 bus name is simply an identifier used to locate connections. For 3841 example, the hypothetical <literal>com.yoyodyne.Screensaver</literal> 3842 name might be used to send a message to a screensaver from Yoyodyne 3843 Corporation. An application is said to <firstterm>own</firstterm> a 3844 name if the message bus has associated the application's connection 3845 with the name. Names may also have <firstterm>queued 3846 owners</firstterm> (see <xref linkend="term-queued-owner"/>). 3847 The bus assigns a unique name to each connection, 3848 see <xref linkend="term-unique-name"/>. Other names 3849 can be thought of as "well-known names" and are 3850 used to find applications that offer specific functionality. 3851 </para> 3852 </glossdef> 3853 </glossentry> 3854 3855 <glossentry id="term-message"><glossterm>Message</glossterm> 3856 <glossdef> 3857 <para> 3858 A message is the atomic unit of communication via the D-Bus 3859 protocol. It consists of a <firstterm>header</firstterm> and a 3860 <firstterm>body</firstterm>; the body is made up of 3861 <firstterm>arguments</firstterm>. 3862 </para> 3863 </glossdef> 3864 </glossentry> 3865 3866 <glossentry id="term-message-bus"><glossterm>Message Bus</glossterm> 3867 <glossdef> 3868 <para> 3869 The message bus is a special application that forwards 3870 or routes messages between a group of applications 3871 connected to the message bus. It also manages 3872 <firstterm>names</firstterm> used for routing 3873 messages. 3874 </para> 3875 </glossdef> 3876 </glossentry> 3877 3878 <glossentry id="term-name"><glossterm>Name</glossterm> 3879 <glossdef> 3880 <para> 3881 See <xref linkend="term-bus-name"/>. "Name" may 3882 also be used to refer to some of the other names 3883 in D-Bus, such as interface names. 3884 </para> 3885 </glossdef> 3886 </glossentry> 3887 3888 <glossentry id="namespace"><glossterm>Namespace</glossterm> 3889 <glossdef> 3890 <para> 3891 Used to prevent collisions when defining new interfaces or bus 3892 names. The convention used is the same one Java uses for defining 3893 classes: a reversed domain name. 3894 </para> 3895 </glossdef> 3896 </glossentry> 3897 3898 <glossentry id="term-object"><glossterm>Object</glossterm> 3899 <glossdef> 3900 <para> 3901 Each application contains <firstterm>objects</firstterm>, which have 3902 <firstterm>interfaces</firstterm> and 3903 <firstterm>methods</firstterm>. Objects are referred to by a name, 3904 called a <firstterm>path</firstterm>. 3905 </para> 3906 </glossdef> 3907 </glossentry> 3908 3909 <glossentry id="one-to-one"><glossterm>One-to-One</glossterm> 3910 <glossdef> 3911 <para> 3912 An application talking directly to another application, without going 3913 through a message bus. One-to-one connections may be "peer to peer" or 3914 "client to server." The D-Bus protocol has no concept of client 3915 vs. server after a connection has authenticated; the flow of messages 3916 is symmetrical (full duplex). 3917 </para> 3918 </glossdef> 3919 </glossentry> 3920 3921 <glossentry id="term-path"><glossterm>Path</glossterm> 3922 <glossdef> 3923 <para> 3924 Object references (object names) in D-Bus are organized into a 3925 filesystem-style hierarchy, so each object is named by a path. As in 3926 LDAP, there's no difference between "files" and "directories"; a path 3927 can refer to an object, while still having child objects below it. 3928 </para> 3929 </glossdef> 3930 </glossentry> 3931 3932 <glossentry id="term-queued-owner"><glossterm>Queued Name Owner</glossterm> 3933 <glossdef> 3934 <para> 3935 Each bus name has a primary owner; messages sent to the name go to the 3936 primary owner. However, certain names also maintain a queue of 3937 secondary owners "waiting in the wings." If the primary owner releases 3938 the name, then the first secondary owner in the queue automatically 3939 becomes the new owner of the name. 3940 </para> 3941 </glossdef> 3942 </glossentry> 3943 3944 <glossentry id="term-service"><glossterm>Service</glossterm> 3945 <glossdef> 3946 <para> 3947 A service is an executable that can be launched by the bus daemon. 3948 Services normally guarantee some particular features, for example they 3949 may guarantee that they will request a specific name such as 3950 "org.freedesktop.Screensaver", have a singleton object 3951 "/org/freedesktop/Application", and that object will implement the 3952 interface "org.freedesktop.ScreensaverControl". 3953 </para> 3954 </glossdef> 3955 </glossentry> 3956 3957 <glossentry id="term-service-description-files"><glossterm>Service Description Files</glossterm> 3958 <glossdef> 3959 <para> 3960 ".service files" tell the bus about service applications that can be 3961 launched (see <xref linkend="term-service"/>). Most importantly they 3962 provide a mapping from bus names to services that will request those 3963 names when they start up. 3964 </para> 3965 </glossdef> 3966 </glossentry> 3967 3968 <glossentry id="term-unique-name"><glossterm>Unique Connection Name</glossterm> 3969 <glossdef> 3970 <para> 3971 The special name automatically assigned to each connection by the 3972 message bus. This name will never change owner, and will be unique 3973 (never reused during the lifetime of the message bus). 3974 It will begin with a ':' character. 3975 </para> 3976 </glossdef> 3977 </glossentry> 3978 3979 </glossary> 3980</article> 3981 3982