1===================== 2Nanopb: API reference 3===================== 4 5.. include :: menu.rst 6 7.. contents :: 8 9 10 11 12Compilation options 13=================== 14The following options can be specified in one of two ways: 15 161. Using the -D switch on the C compiler command line. 172. By #defining them at the top of pb.h. 18 19You must have the same settings for the nanopb library and all code that 20includes pb.h. 21 22============================ ================================================ 23PB_NO_PACKED_STRUCTS Disable packed structs. Increases RAM usage but 24 is necessary on some platforms that do not 25 support unaligned memory access. 26PB_ENABLE_MALLOC Set this to enable dynamic allocation support 27 in the decoder. 28PB_MAX_REQUIRED_FIELDS Maximum number of required fields to check for 29 presence. Default value is 64. Increases stack 30 usage 1 byte per every 8 fields. Compiler 31 warning will tell if you need this. 32PB_FIELD_16BIT Add support for tag numbers > 255 and fields 33 larger than 255 bytes or 255 array entries. 34 Increases code size 3 bytes per each field. 35 Compiler error will tell if you need this. 36PB_FIELD_32BIT Add support for tag numbers > 65535 and fields 37 larger than 65535 bytes or 65535 array entries. 38 Increases code size 9 bytes per each field. 39 Compiler error will tell if you need this. 40PB_NO_ERRMSG Disables the support for error messages; only 41 error information is the true/false return 42 value. Decreases the code size by a few hundred 43 bytes. 44PB_BUFFER_ONLY Disables the support for custom streams. Only 45 supports encoding and decoding with memory 46 buffers. Speeds up execution and decreases code 47 size slightly. 48PB_OLD_CALLBACK_STYLE Use the old function signature (void\* instead 49 of void\*\*) for callback fields. This was the 50 default until nanopb-0.2.1. 51PB_SYSTEM_HEADER Replace the standard header files with a single 52 header file. It should define all the required 53 functions and typedefs listed on the 54 `overview page`_. Value must include quotes, 55 for example *#define PB_SYSTEM_HEADER "foo.h"*. 56PB_WITHOUT_64BIT Disable 64-bit support, for old compilers or 57 for a slight speedup on 8-bit platforms. 58============================ ================================================ 59 60The PB_MAX_REQUIRED_FIELDS, PB_FIELD_16BIT and PB_FIELD_32BIT settings allow 61raising some datatype limits to suit larger messages. Their need is recognized 62automatically by C-preprocessor #if-directives in the generated .pb.h files. 63The default setting is to use the smallest datatypes (least resources used). 64 65.. _`overview page`: index.html#compiler-requirements 66 67 68Proto file options 69================== 70The generator behaviour can be adjusted using these options, defined in the 71'nanopb.proto' file in the generator folder: 72 73============================ ================================================ 74max_size Allocated size for *bytes* and *string* fields. 75max_count Allocated number of entries in arrays 76 (*repeated* fields). 77int_size Override the integer type of a field. 78 (To use e.g. uint8_t to save RAM.) 79type Type of the generated field. Default value 80 is *FT_DEFAULT*, which selects automatically. 81 You can use *FT_CALLBACK*, *FT_POINTER*, 82 *FT_STATIC* or *FT_IGNORE* to 83 force a callback field, a dynamically 84 allocated field, a static field or to 85 completely ignore the field. 86long_names Prefix the enum name to the enum value in 87 definitions, i.e. *EnumName_EnumValue*. Enabled 88 by default. 89packed_struct Make the generated structures packed. 90 NOTE: This cannot be used on CPUs that break 91 on unaligned accesses to variables. 92skip_message Skip the whole message from generation. 93no_unions Generate 'oneof' fields as optional fields 94 instead of C unions. 95msgid Specifies a unique id for this message type. 96 Can be used by user code as an identifier. 97anonymous_oneof Generate 'oneof' fields as anonymous unions. 98fixed_length Generate 'bytes' fields with constant length 99 (max_size must also be defined). 100fixed_count Generate arrays with constant length 101 (max_count must also be defined). 102============================ ================================================ 103 104These options can be defined for the .proto files before they are converted 105using the nanopb-generatory.py. There are three ways to define the options: 106 1071. Using a separate .options file. 108 This is the preferred way as of nanopb-0.2.1, because it has the best 109 compatibility with other protobuf libraries. 1102. Defining the options on the command line of nanopb_generator.py. 111 This only makes sense for settings that apply to a whole file. 1123. Defining the options in the .proto file using the nanopb extensions. 113 This is the way used in nanopb-0.1, and will remain supported in the 114 future. It however sometimes causes trouble when using the .proto file 115 with other protobuf libraries. 116 117The effect of the options is the same no matter how they are given. The most 118common purpose is to define maximum size for string fields in order to 119statically allocate them. 120 121Defining the options in a .options file 122--------------------------------------- 123The preferred way to define options is to have a separate file 124'myproto.options' in the same directory as the 'myproto.proto'. :: 125 126 # myproto.proto 127 message MyMessage { 128 required string name = 1; 129 repeated int32 ids = 4; 130 } 131 132:: 133 134 # myproto.options 135 MyMessage.name max_size:40 136 MyMessage.ids max_count:5 137 138The generator will automatically search for this file and read the 139options from it. The file format is as follows: 140 141* Lines starting with '#' or '//' are regarded as comments. 142* Blank lines are ignored. 143* All other lines should start with a field name pattern, followed by one or 144 more options. For example: *"MyMessage.myfield max_size:5 max_count:10"*. 145* The field name pattern is matched against a string of form *'Message.field'*. 146 For nested messages, the string is *'Message.SubMessage.field'*. 147* The field name pattern may use the notation recognized by Python fnmatch(): 148 149 - *\** matches any part of string, like 'Message.\*' for all fields 150 - *\?* matches any single character 151 - *[seq]* matches any of characters 's', 'e' and 'q' 152 - *[!seq]* matches any other character 153 154* The options are written as *'option_name:option_value'* and several options 155 can be defined on same line, separated by whitespace. 156* Options defined later in the file override the ones specified earlier, so 157 it makes sense to define wildcard options first in the file and more specific 158 ones later. 159 160To debug problems in applying the options, you can use the *-v* option for the 161plugin. Plugin options are specified in front of the output path: 162 163 protoc ... --nanopb_out=-v:. message.proto 164 165Protoc doesn't currently pass include path into plugins. Therefore if your 166*.proto* is in a subdirectory, nanopb may have trouble finding the associated 167*.options* file. A workaround is to specify include path separately to the 168nanopb plugin, like: 169 170 protoc -Isubdir --nanopb_out=-Isubdir:. message.proto 171 172If preferred, the name of the options file can be set using plugin argument 173*-f*. 174 175Defining the options on command line 176------------------------------------ 177The nanopb_generator.py has a simple command line option *-s OPTION:VALUE*. 178The setting applies to the whole file that is being processed. 179 180Defining the options in the .proto file 181--------------------------------------- 182The .proto file format allows defining custom options for the fields. 183The nanopb library comes with *nanopb.proto* which does exactly that, allowing 184you do define the options directly in the .proto file:: 185 186 import "nanopb.proto"; 187 188 message MyMessage { 189 required string name = 1 [(nanopb).max_size = 40]; 190 repeated int32 ids = 4 [(nanopb).max_count = 5]; 191 } 192 193A small complication is that you have to set the include path of protoc so that 194nanopb.proto can be found. This file, in turn, requires the file 195*google/protobuf/descriptor.proto*. This is usually installed under 196*/usr/include*. Therefore, to compile a .proto file which uses options, use a 197protoc command similar to:: 198 199 protoc -I/usr/include -Inanopb/generator -I. --nanopb_out=. message.proto 200 201The options can be defined in file, message and field scopes:: 202 203 option (nanopb_fileopt).max_size = 20; // File scope 204 message Message 205 { 206 option (nanopb_msgopt).max_size = 30; // Message scope 207 required string fieldsize = 1 [(nanopb).max_size = 40]; // Field scope 208 } 209 210 211pb.h 212==== 213 214pb_byte_t 215--------- 216Type used for storing byte-sized data, such as raw binary input and bytes-type fields. :: 217 218 typedef uint_least8_t pb_byte_t; 219 220For most platforms this is equivalent to `uint8_t`. Some platforms however do not support 2218-bit variables, and on those platforms 16 or 32 bits need to be used for each byte. 222 223pb_type_t 224--------- 225Type used to store the type of each field, to control the encoder/decoder behaviour. :: 226 227 typedef uint_least8_t pb_type_t; 228 229The low-order nibble of the enumeration values defines the function that can be used for encoding and decoding the field data: 230 231=========================== ===== ================================================ 232LTYPE identifier Value Storage format 233=========================== ===== ================================================ 234PB_LTYPE_VARINT 0x00 Integer. 235PB_LTYPE_UVARINT 0x01 Unsigned integer. 236PB_LTYPE_SVARINT 0x02 Integer, zigzag encoded. 237PB_LTYPE_FIXED32 0x03 32-bit integer or floating point. 238PB_LTYPE_FIXED64 0x04 64-bit integer or floating point. 239PB_LTYPE_BYTES 0x05 Structure with *size_t* field and byte array. 240PB_LTYPE_STRING 0x06 Null-terminated string. 241PB_LTYPE_SUBMESSAGE 0x07 Submessage structure. 242PB_LTYPE_EXTENSION 0x08 Point to *pb_extension_t*. 243PB_LTYPE_FIXED_LENGTH_BYTES 0x09 Inline *pb_byte_t* array of fixed size. 244=========================== ===== ================================================ 245 246The bits 4-5 define whether the field is required, optional or repeated: 247 248==================== ===== ================================================ 249HTYPE identifier Value Field handling 250==================== ===== ================================================ 251PB_HTYPE_REQUIRED 0x00 Verify that field exists in decoded message. 252PB_HTYPE_OPTIONAL 0x10 Use separate *has_<field>* boolean to specify 253 whether the field is present. 254 (Unless it is a callback) 255PB_HTYPE_REPEATED 0x20 A repeated field with preallocated array. 256 Separate *<field>_count* for number of items. 257 (Unless it is a callback) 258==================== ===== ================================================ 259 260The bits 6-7 define the how the storage for the field is allocated: 261 262==================== ===== ================================================ 263ATYPE identifier Value Allocation method 264==================== ===== ================================================ 265PB_ATYPE_STATIC 0x00 Statically allocated storage in the structure. 266PB_ATYPE_CALLBACK 0x40 A field with dynamic storage size. Struct field 267 actually contains a pointer to a callback 268 function. 269==================== ===== ================================================ 270 271 272pb_field_t 273---------- 274Describes a single structure field with memory position in relation to others. The descriptions are usually autogenerated. :: 275 276 typedef struct pb_field_s pb_field_t; 277 struct pb_field_s { 278 pb_size_t tag; 279 pb_type_t type; 280 pb_size_t data_offset; 281 pb_ssize_t size_offset; 282 pb_size_t data_size; 283 pb_size_t array_size; 284 const void *ptr; 285 } pb_packed; 286 287:tag: Tag number of the field or 0 to terminate a list of fields. 288:type: LTYPE, HTYPE and ATYPE of the field. 289:data_offset: Offset of field data, relative to the end of the previous field. 290:size_offset: Offset of *bool* flag for optional fields or *size_t* count for arrays, relative to field data. 291:data_size: Size of a single data entry, in bytes. For PB_LTYPE_BYTES, the size of the byte array inside the containing structure. For PB_HTYPE_CALLBACK, size of the C data type if known. 292:array_size: Maximum number of entries in an array, if it is an array type. 293:ptr: Pointer to default value for optional fields, or to submessage description for PB_LTYPE_SUBMESSAGE. 294 295The *uint8_t* datatypes limit the maximum size of a single item to 255 bytes and arrays to 255 items. Compiler will give error if the values are too large. The types can be changed to larger ones by defining *PB_FIELD_16BIT*. 296 297pb_bytes_array_t 298---------------- 299An byte array with a field for storing the length:: 300 301 typedef struct { 302 pb_size_t size; 303 pb_byte_t bytes[1]; 304 } pb_bytes_array_t; 305 306In an actual array, the length of *bytes* may be different. 307 308pb_callback_t 309------------- 310Part of a message structure, for fields with type PB_HTYPE_CALLBACK:: 311 312 typedef struct _pb_callback_t pb_callback_t; 313 struct _pb_callback_t { 314 union { 315 bool (*decode)(pb_istream_t *stream, const pb_field_t *field, void **arg); 316 bool (*encode)(pb_ostream_t *stream, const pb_field_t *field, void * const *arg); 317 } funcs; 318 319 void *arg; 320 }; 321 322A pointer to the *arg* is passed to the callback when calling. It can be used to store any information that the callback might need. 323 324Previously the function received just the value of *arg* instead of a pointer to it. This old behaviour can be enabled by defining *PB_OLD_CALLBACK_STYLE*. 325 326When calling `pb_encode`_, *funcs.encode* is used, and similarly when calling `pb_decode`_, *funcs.decode* is used. The function pointers are stored in the same memory location but are of incompatible types. You can set the function pointer to NULL to skip the field. 327 328pb_wire_type_t 329-------------- 330Protocol Buffers wire types. These are used with `pb_encode_tag`_. :: 331 332 typedef enum { 333 PB_WT_VARINT = 0, 334 PB_WT_64BIT = 1, 335 PB_WT_STRING = 2, 336 PB_WT_32BIT = 5 337 } pb_wire_type_t; 338 339pb_extension_type_t 340------------------- 341Defines the handler functions and auxiliary data for a field that extends 342another message. Usually autogenerated by *nanopb_generator.py*:: 343 344 typedef struct { 345 bool (*decode)(pb_istream_t *stream, pb_extension_t *extension, 346 uint32_t tag, pb_wire_type_t wire_type); 347 bool (*encode)(pb_ostream_t *stream, const pb_extension_t *extension); 348 const void *arg; 349 } pb_extension_type_t; 350 351In the normal case, the function pointers are *NULL* and the decoder and 352encoder use their internal implementations. The internal implementations 353assume that *arg* points to a *pb_field_t* that describes the field in question. 354 355To implement custom processing of unknown fields, you can provide pointers 356to your own functions. Their functionality is mostly the same as for normal 357callback fields, except that they get called for any unknown field when decoding. 358 359pb_extension_t 360-------------- 361Ties together the extension field type and the storage for the field value:: 362 363 typedef struct { 364 const pb_extension_type_t *type; 365 void *dest; 366 pb_extension_t *next; 367 bool found; 368 } pb_extension_t; 369 370:type: Pointer to the structure that defines the callback functions. 371:dest: Pointer to the variable that stores the field value 372 (as used by the default extension callback functions.) 373:next: Pointer to the next extension handler, or *NULL*. 374:found: Decoder sets this to true if the extension was found. 375 376PB_GET_ERROR 377------------ 378Get the current error message from a stream, or a placeholder string if 379there is no error message:: 380 381 #define PB_GET_ERROR(stream) (string expression) 382 383This should be used for printing errors, for example:: 384 385 if (!pb_decode(...)) 386 { 387 printf("Decode failed: %s\n", PB_GET_ERROR(stream)); 388 } 389 390The macro only returns pointers to constant strings (in code memory), 391so that there is no need to release the returned pointer. 392 393PB_RETURN_ERROR 394--------------- 395Set the error message and return false:: 396 397 #define PB_RETURN_ERROR(stream,msg) (sets error and returns false) 398 399This should be used to handle error conditions inside nanopb functions 400and user callback functions:: 401 402 if (error_condition) 403 { 404 PB_RETURN_ERROR(stream, "something went wrong"); 405 } 406 407The *msg* parameter must be a constant string. 408 409 410 411pb_encode.h 412=========== 413 414pb_ostream_from_buffer 415---------------------- 416Constructs an output stream for writing into a memory buffer. This is just a helper function, it doesn't do anything you couldn't do yourself in a callback function. It uses an internal callback that stores the pointer in stream *state* field. :: 417 418 pb_ostream_t pb_ostream_from_buffer(pb_byte_t *buf, size_t bufsize); 419 420:buf: Memory buffer to write into. 421:bufsize: Maximum number of bytes to write. 422:returns: An output stream. 423 424After writing, you can check *stream.bytes_written* to find out how much valid data there is in the buffer. 425 426pb_write 427-------- 428Writes data to an output stream. Always use this function, instead of trying to call stream callback manually. :: 429 430 bool pb_write(pb_ostream_t *stream, const pb_byte_t *buf, size_t count); 431 432:stream: Output stream to write to. 433:buf: Pointer to buffer with the data to be written. 434:count: Number of bytes to write. 435:returns: True on success, false if maximum length is exceeded or an IO error happens. 436 437If an error happens, *bytes_written* is not incremented. Depending on the callback used, calling pb_write again after it has failed once may be dangerous. Nanopb itself never does this, instead it returns the error to user application. The builtin pb_ostream_from_buffer is safe to call again after failed write. 438 439pb_encode 440--------- 441Encodes the contents of a structure as a protocol buffers message and writes it to output stream. :: 442 443 bool pb_encode(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct); 444 445:stream: Output stream to write to. 446:fields: A field description array, usually autogenerated. 447:src_struct: Pointer to the data that will be serialized. 448:returns: True on success, false on IO error, on detectable errors in field description, or if a field encoder returns false. 449 450Normally pb_encode simply walks through the fields description array and serializes each field in turn. However, submessages must be serialized twice: first to calculate their size and then to actually write them to output. This causes some constraints for callback fields, which must return the same data on every call. 451 452pb_encode_delimited 453------------------- 454Calculates the length of the message, encodes it as varint and then encodes the message. :: 455 456 bool pb_encode_delimited(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct); 457 458(parameters are the same as for `pb_encode`_.) 459 460A common way to indicate the message length in Protocol Buffers is to prefix it with a varint. 461This function does this, and it is compatible with *parseDelimitedFrom* in Google's protobuf library. 462 463.. sidebar:: Encoding fields manually 464 465 The functions with names *pb_encode_\** are used when dealing with callback fields. The typical reason for using callbacks is to have an array of unlimited size. In that case, `pb_encode`_ will call your callback function, which in turn will call *pb_encode_\** functions repeatedly to write out values. 466 467 The tag of a field must be encoded separately with `pb_encode_tag_for_field`_. After that, you can call exactly one of the content-writing functions to encode the payload of the field. For repeated fields, you can repeat this process multiple times. 468 469 Writing packed arrays is a little bit more involved: you need to use `pb_encode_tag` and specify `PB_WT_STRING` as the wire type. Then you need to know exactly how much data you are going to write, and use `pb_encode_varint`_ to write out the number of bytes before writing the actual data. Substreams can be used to determine the number of bytes beforehand; see `pb_encode_submessage`_ source code for an example. 470 471pb_get_encoded_size 472------------------- 473Calculates the length of the encoded message. :: 474 475 bool pb_get_encoded_size(size_t *size, const pb_field_t fields[], const void *src_struct); 476 477:size: Calculated size of the encoded message. 478:fields: A field description array, usually autogenerated. 479:src_struct: Pointer to the data that will be serialized. 480:returns: True on success, false on detectable errors in field description or if a field encoder returns false. 481 482pb_encode_tag 483------------- 484Starts a field in the Protocol Buffers binary format: encodes the field number and the wire type of the data. :: 485 486 bool pb_encode_tag(pb_ostream_t *stream, pb_wire_type_t wiretype, uint32_t field_number); 487 488:stream: Output stream to write to. 1-5 bytes will be written. 489:wiretype: PB_WT_VARINT, PB_WT_64BIT, PB_WT_STRING or PB_WT_32BIT 490:field_number: Identifier for the field, defined in the .proto file. You can get it from field->tag. 491:returns: True on success, false on IO error. 492 493pb_encode_tag_for_field 494----------------------- 495Same as `pb_encode_tag`_, except takes the parameters from a *pb_field_t* structure. :: 496 497 bool pb_encode_tag_for_field(pb_ostream_t *stream, const pb_field_t *field); 498 499:stream: Output stream to write to. 1-5 bytes will be written. 500:field: Field description structure. Usually autogenerated. 501:returns: True on success, false on IO error or unknown field type. 502 503This function only considers the LTYPE of the field. You can use it from your field callbacks, because the source generator writes correct LTYPE also for callback type fields. 504 505Wire type mapping is as follows: 506 507============================================= ============ 508LTYPEs Wire type 509============================================= ============ 510VARINT, UVARINT, SVARINT PB_WT_VARINT 511FIXED64 PB_WT_64BIT 512STRING, BYTES, SUBMESSAGE, FIXED_LENGTH_BYTES PB_WT_STRING 513FIXED32 PB_WT_32BIT 514============================================= ============ 515 516pb_encode_varint 517---------------- 518Encodes a signed or unsigned integer in the varint_ format. Works for fields of type `bool`, `enum`, `int32`, `int64`, `uint32` and `uint64`:: 519 520 bool pb_encode_varint(pb_ostream_t *stream, uint64_t value); 521 522:stream: Output stream to write to. 1-10 bytes will be written. 523:value: Value to encode. Just cast e.g. int32_t directly to uint64_t. 524:returns: True on success, false on IO error. 525 526.. _varint: http://code.google.com/apis/protocolbuffers/docs/encoding.html#varints 527 528pb_encode_svarint 529----------------- 530Encodes a signed integer in the 'zig-zagged' format. Works for fields of type `sint32` and `sint64`:: 531 532 bool pb_encode_svarint(pb_ostream_t *stream, int64_t value); 533 534(parameters are the same as for `pb_encode_varint`_ 535 536pb_encode_string 537---------------- 538Writes the length of a string as varint and then contents of the string. Works for fields of type `bytes` and `string`:: 539 540 bool pb_encode_string(pb_ostream_t *stream, const pb_byte_t *buffer, size_t size); 541 542:stream: Output stream to write to. 543:buffer: Pointer to string data. 544:size: Number of bytes in the string. Pass `strlen(s)` for strings. 545:returns: True on success, false on IO error. 546 547pb_encode_fixed32 548----------------- 549Writes 4 bytes to stream and swaps bytes on big-endian architectures. Works for fields of type `fixed32`, `sfixed32` and `float`:: 550 551 bool pb_encode_fixed32(pb_ostream_t *stream, const void *value); 552 553:stream: Output stream to write to. 554:value: Pointer to a 4-bytes large C variable, for example `uint32_t foo;`. 555:returns: True on success, false on IO error. 556 557pb_encode_fixed64 558----------------- 559Writes 8 bytes to stream and swaps bytes on big-endian architecture. Works for fields of type `fixed64`, `sfixed64` and `double`:: 560 561 bool pb_encode_fixed64(pb_ostream_t *stream, const void *value); 562 563:stream: Output stream to write to. 564:value: Pointer to a 8-bytes large C variable, for example `uint64_t foo;`. 565:returns: True on success, false on IO error. 566 567pb_encode_submessage 568-------------------- 569Encodes a submessage field, including the size header for it. Works for fields of any message type:: 570 571 bool pb_encode_submessage(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct); 572 573:stream: Output stream to write to. 574:fields: Pointer to the autogenerated field description array for the submessage type, e.g. `MyMessage_fields`. 575:src: Pointer to the structure where submessage data is. 576:returns: True on success, false on IO errors, pb_encode errors or if submessage size changes between calls. 577 578In Protocol Buffers format, the submessage size must be written before the submessage contents. Therefore, this function has to encode the submessage twice in order to know the size beforehand. 579 580If the submessage contains callback fields, the callback function might misbehave and write out a different amount of data on the second call. This situation is recognized and *false* is returned, but garbage will be written to the output before the problem is detected. 581 582 583 584 585 586 587 588 589 590 591 592 593pb_decode.h 594=========== 595 596pb_istream_from_buffer 597---------------------- 598Helper function for creating an input stream that reads data from a memory buffer. :: 599 600 pb_istream_t pb_istream_from_buffer(const pb_byte_t *buf, size_t bufsize); 601 602:buf: Pointer to byte array to read from. 603:bufsize: Size of the byte array. 604:returns: An input stream ready to use. 605 606pb_read 607------- 608Read data from input stream. Always use this function, don't try to call the stream callback directly. :: 609 610 bool pb_read(pb_istream_t *stream, pb_byte_t *buf, size_t count); 611 612:stream: Input stream to read from. 613:buf: Buffer to store the data to, or NULL to just read data without storing it anywhere. 614:count: Number of bytes to read. 615:returns: True on success, false if *stream->bytes_left* is less than *count* or if an IO error occurs. 616 617End of file is signalled by *stream->bytes_left* being zero after pb_read returns false. 618 619pb_decode 620--------- 621Read and decode all fields of a structure. Reads until EOF on input stream. :: 622 623 bool pb_decode(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct); 624 625:stream: Input stream to read from. 626:fields: A field description array. Usually autogenerated. 627:dest_struct: Pointer to structure where data will be stored. 628:returns: True on success, false on IO error, on detectable errors in field description, if a field encoder returns false or if a required field is missing. 629 630In Protocol Buffers binary format, EOF is only allowed between fields. If it happens anywhere else, pb_decode will return *false*. If pb_decode returns false, you cannot trust any of the data in the structure. 631 632In addition to EOF, the pb_decode implementation supports terminating a message with a 0 byte. This is compatible with the official Protocol Buffers because 0 is never a valid field tag. 633 634For optional fields, this function applies the default value and sets *has_<field>* to false if the field is not present. 635 636If *PB_ENABLE_MALLOC* is defined, this function may allocate storage for any pointer type fields. 637In this case, you have to call `pb_release`_ to release the memory after you are done with the message. 638On error return `pb_decode` will release the memory itself. 639 640pb_decode_noinit 641---------------- 642Same as `pb_decode`_, except does not apply the default values to fields. :: 643 644 bool pb_decode_noinit(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct); 645 646(parameters are the same as for `pb_decode`_.) 647 648The destination structure should be filled with zeros before calling this function. Doing a *memset* manually can be slightly faster than using `pb_decode`_ if you don't need any default values. 649 650In addition to decoding a single message, this function can be used to merge two messages, so that 651values from previous message will remain if the new message does not contain a field. 652 653This function *will not* release the message even on error return. If you use *PB_ENABLE_MALLOC*, 654you will need to call `pb_release`_ yourself. 655 656pb_decode_delimited 657------------------- 658Same as `pb_decode`_, except that it first reads a varint with the length of the message. :: 659 660 bool pb_decode_delimited(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct); 661 662(parameters are the same as for `pb_decode`_.) 663 664A common method to indicate message size in Protocol Buffers is to prefix it with a varint. 665This function is compatible with *writeDelimitedTo* in the Google's Protocol Buffers library. 666 667pb_release 668---------- 669Releases any dynamically allocated fields:: 670 671 void pb_release(const pb_field_t fields[], void *dest_struct); 672 673:fields: A field description array. Usually autogenerated. 674:dest_struct: Pointer to structure where data is stored. If NULL, function does nothing. 675 676This function is only available if *PB_ENABLE_MALLOC* is defined. It will release any 677pointer type fields in the structure and set the pointers to NULL. 678 679pb_decode_tag 680------------- 681Decode the tag that comes before field in the protobuf encoding:: 682 683 bool pb_decode_tag(pb_istream_t *stream, pb_wire_type_t *wire_type, uint32_t *tag, bool *eof); 684 685:stream: Input stream to read from. 686:wire_type: Pointer to variable where to store the wire type of the field. 687:tag: Pointer to variable where to store the tag of the field. 688:eof: Pointer to variable where to store end-of-file status. 689:returns: True on success, false on error or EOF. 690 691When the message (stream) ends, this function will return false and set *eof* to true. On other 692errors, *eof* will be set to false. 693 694pb_skip_field 695------------- 696Remove the data for a field from the stream, without actually decoding it:: 697 698 bool pb_skip_field(pb_istream_t *stream, pb_wire_type_t wire_type); 699 700:stream: Input stream to read from. 701:wire_type: Type of field to skip. 702:returns: True on success, false on IO error. 703 704.. sidebar:: Decoding fields manually 705 706 The functions with names beginning with *pb_decode_* are used when dealing with callback fields. The typical reason for using callbacks is to have an array of unlimited size. In that case, `pb_decode`_ will call your callback function repeatedly, which can then store the values into e.g. filesystem in the order received in. 707 708 For decoding numeric (including enumerated and boolean) values, use `pb_decode_varint`_, `pb_decode_svarint`_, `pb_decode_fixed32`_ and `pb_decode_fixed64`_. They take a pointer to a 32- or 64-bit C variable, which you may then cast to smaller datatype for storage. 709 710 For decoding strings and bytes fields, the length has already been decoded. You can therefore check the total length in *stream->bytes_left* and read the data using `pb_read`_. 711 712 Finally, for decoding submessages in a callback, simply use `pb_decode`_ and pass it the *SubMessage_fields* descriptor array. 713 714pb_decode_varint 715---------------- 716Read and decode a varint_ encoded integer. :: 717 718 bool pb_decode_varint(pb_istream_t *stream, uint64_t *dest); 719 720:stream: Input stream to read from. 1-10 bytes will be read. 721:dest: Storage for the decoded integer. Value is undefined on error. 722:returns: True on success, false if value exceeds uint64_t range or an IO error happens. 723 724pb_decode_svarint 725----------------- 726Similar to `pb_decode_varint`_, except that it performs zigzag-decoding on the value. This corresponds to the Protocol Buffers *sint32* and *sint64* datatypes. :: 727 728 bool pb_decode_svarint(pb_istream_t *stream, int64_t *dest); 729 730(parameters are the same as `pb_decode_varint`_) 731 732pb_decode_fixed32 733----------------- 734Decode a *fixed32*, *sfixed32* or *float* value. :: 735 736 bool pb_decode_fixed32(pb_istream_t *stream, void *dest); 737 738:stream: Input stream to read from. 4 bytes will be read. 739:dest: Pointer to destination *int32_t*, *uint32_t* or *float*. 740:returns: True on success, false on IO errors. 741 742This function reads 4 bytes from the input stream. 743On big endian architectures, it then reverses the order of the bytes. 744Finally, it writes the bytes to *dest*. 745 746pb_decode_fixed64 747----------------- 748Decode a *fixed64*, *sfixed64* or *double* value. :: 749 750 bool pb_decode_fixed64(pb_istream_t *stream, void *dest); 751 752:stream: Input stream to read from. 8 bytes will be read. 753:dest: Pointer to destination *int64_t*, *uint64_t* or *double*. 754:returns: True on success, false on IO errors. 755 756Same as `pb_decode_fixed32`_, except this reads 8 bytes. 757 758pb_make_string_substream 759------------------------ 760Decode the length for a field with wire type *PB_WT_STRING* and create a substream for reading the data. :: 761 762 bool pb_make_string_substream(pb_istream_t *stream, pb_istream_t *substream); 763 764:stream: Original input stream to read the length and data from. 765:substream: New substream that has limited length. Filled in by the function. 766:returns: True on success, false if reading the length fails. 767 768This function uses `pb_decode_varint`_ to read an integer from the stream. This is interpreted as a number of bytes, and the substream is set up so that its `bytes_left` is initially the same as the length, and its callback function and state the same as the parent stream. 769 770pb_close_string_substream 771------------------------- 772Close the substream created with `pb_make_string_substream`_. :: 773 774 void pb_close_string_substream(pb_istream_t *stream, pb_istream_t *substream); 775 776:stream: Original input stream to read the length and data from. 777:substream: Substream to close 778 779This function copies back the state from the substream to the parent stream. 780It must be called after done with the substream. 781