1<!-- 2 HTTP and IPP API introduction for CUPS. 3 4 Copyright 2007-2012 by Apple Inc. 5 Copyright 1997-2006 by Easy Software Products, all rights reserved. 6 7 These coded instructions, statements, and computer programs are the 8 property of Apple Inc. and are protected by Federal copyright 9 law. Distribution and use rights are outlined in the file "LICENSE.txt" 10 which should have been included with this file. If this file is 11 file is missing or damaged, see the license at "http://www.cups.org/". 12--> 13 14<h2 class='title'><a name='OVERVIEW'>Overview</a></h2> 15 16<p>The CUPS HTTP and IPP APIs provide low-level access to the HTTP and IPP 17protocols and CUPS scheduler. They are typically used by monitoring and 18administration programs to perform specific functions not supported by the 19high-level CUPS API functions.</p> 20 21<p>The HTTP APIs use an opaque structure called 22<a href='#http_t'><code>http_t</code></a> to manage connections to 23a particular HTTP or IPP server. The 24<a href='#httpConnectEncrypt'><code>httpConnectEncrypt</code></a> function is 25used to create an instance of this structure for a particular server. 26The constant <code>CUPS_HTTP_DEFAULT</code> can be used with all of the 27<code>cups</code> functions to refer to the default CUPS server - the functions 28create a per-thread <a href='#http_t'><code>http_t</code></a> as needed.</p> 29 30<p>The IPP APIs use two opaque structures for requests (messages sent to the CUPS scheduler) and responses (messages sent back to your application from the scheduler). The <a href='#ipp_t'><code>ipp_t</code></a> type holds a complete request or response and is allocated using the <a href='#ippNew'><code>ippNew</code></a> or <a href='#ippNewRequest'><code>ippNewRequest</code></a> functions and freed using the <a href='#ippDelete'><code>ippDelete</code></a> function.</p> 31 32<p>The second opaque structure is called <a href='#ipp_attribute_t'><code>ipp_attribute_t</code></a> and holds a single IPP attribute which consists of a group tag (<a href='#ippGetGroupTag'><code>ippGetGroupTag</code></a>), a value type tag (<a href='#ippGetValueTag'><code>ippGetValueTag</code></a>), the attribute name (<a href='#ippGetName'><code>ippGetName</code></a>), and 1 or more values (<a href='#ippGetCount'><code>ippGetCount</code></a>, <a href='#ippGetBoolean'><code>ippGetBoolean</code></a>, <a href='#ippGetCollection'><code>ippGetCollection</code></a>, <a href='#ippGetDate'><code>ippGetDate</code></a>, <a href='#ippGetInteger'><code>ippGetInteger</code></a>, <a href='#ippGetRange'><code>ippGetRange</code></a>, <a href='#ippGetResolution'><code>ippGetResolution</code></a>, and <a href='#ippGetString'><code>ippGetString</code></a>). Attributes are added to an <a href='#ipp_t'><code>ipp_t</code></a> pointer using one of the <code>ippAdd</code> functions. For example, use <a href='#ippAddString'><code>ippAddString</code></a> to add the "printer-uri" and "requesting-user-name" string attributes to a request:</p> 33 34<pre class='example'> 35<a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(IPP_GET_JOBS); 36 37<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_URI, "printer-uri", 38 NULL, "ipp://localhost/printers/"); 39<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "requesting-user-name", 40 NULL, cupsUser()); 41</pre> 42 43<p>Once you have created an IPP request, use the <code>cups</code> functions to send the request to and read the response from the server. For example, the <a href='#cupsDoRequest'><code>cupsDoRequest</code></a> function can be used for simple query operations that do not involve files:</p> 44 45<pre class='example'> 46#include <cups/cups.h> 47 48 49<a href='#ipp_t'>ipp_t</a> *<a name='get_jobs'>get_jobs</a>(void) 50{ 51 <a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(IPP_GET_JOBS); 52 53 <a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_URI, "printer-uri", 54 NULL, "ipp://localhost/printers/"); 55 <a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "requesting-user-name", 56 NULL, cupsUser()); 57 58 return (<a href='#cupsDoRequest'>cupsDoRequest</a>(CUPS_HTTP_DEFAULT, request, "/")); 59} 60</pre> 61 62<p>The <a href='#cupsDoRequest'><code>cupsDoRequest</code></a> function frees the request and returns an IPP response or <code>NULL</code> pointer if the request could not be sent to the server. Once you have a response from the server, you can either use the <a href='#ippFindAttribute'><code>ippFindAttribute</code></a> and <a href='#ippFindNextAttribute'><code>ippFindNextAttribute</code></a> functions to find specific attributes, for example:</p> 63 64<pre class='example'> 65<a href='#ipp_t'>ipp_t</a> *response; 66<a href='#ipp_attribute_t'>ipp_attribute_t</a> *attr; 67 68attr = <a href='#ippFindAttribute'>ippFindAttribute</a>(response, "printer-state", IPP_TAG_ENUM); 69</pre> 70 71<p>You can also walk the list of attributes with a simple <code>for</code> loop like this:</p> 72 73<pre class='example'> 74<a href='#ipp_t'>ipp_t</a> *response; 75<a href='#ipp_attribute_t'>ipp_attribute_t</a> *attr; 76 77for (attr = <a href='#ippFirstAttribute'>ippFirstAttribute</a>(response); attr != NULL; attr = <a href='#ippNextAttribute'>ippNextAttribute</a>(response)) 78 if (ippGetName(attr) == NULL) 79 puts("--SEPARATOR--"); 80 else 81 puts(ippGetName(attr)); 82</pre> 83 84<p>The <code>for</code> loop approach is normally used when collecting attributes for multiple objects (jobs, printers, etc.) in a response. Attributes with <code>NULL</code> names indicate a separator between the attributes of each object. For example, the following code will list the jobs returned from our previous <a href='#get_jobs'><code>get_jobs</code></a> example code:</p> 85 86<pre class='example'> 87<a href='#ipp_t'>ipp_t</a> *response = <a href='#get_jobs'>get_jobs</a>(); 88 89if (response != NULL) 90{ 91 <a href='#ipp_attribute_t'>ipp_attribute_t</a> *attr; 92 const char *attrname; 93 int job_id = 0; 94 const char *job_name = NULL; 95 const char *job_originating_user_name = NULL; 96 97 puts("Job ID Owner Title"); 98 puts("------ ---------------- ---------------------------------"); 99 100 for (attr = <a href='#ippFirstAttribute'>ippFirstAttribute</a>(response); attr != NULL; attr = <a href='#ippNextAttribute'>ippNextAttribute</a>(response)) 101 { 102 /* Attributes without names are separators between jobs */ 103 attrname = ippGetName(attr); 104 if (attrname == NULL) 105 { 106 if (job_id > 0) 107 { 108 if (job_name == NULL) 109 job_name = "(withheld)"; 110 111 if (job_originating_user_name == NULL) 112 job_originating_user_name = "(withheld)"; 113 114 printf("%5d %-16s %s\n", job_id, job_originating_user_name, job_name); 115 } 116 117 job_id = 0; 118 job_name = NULL; 119 job_originating_user_name = NULL; 120 continue; 121 } 122 else if (!strcmp(attrname, "job-id") && ippGetValueTag(attr) == IPP_TAG_INTEGER) 123 job_id = ippGetInteger(attr, 0); 124 else if (!strcmp(attrname, "job-name") && ippGetValueTag(attr) == IPP_TAG_NAME) 125 job_name = ippGetString(attr, 0, NULL); 126 else if (!strcmp(attrname, "job-originating-user-name") && 127 ippGetValueTag(attr) == IPP_TAG_NAME) 128 job_originating_user_name = ippGetString(attr, 0, NULL); 129 } 130 131 if (job_id > 0) 132 { 133 if (job_name == NULL) 134 job_name = "(withheld)"; 135 136 if (job_originating_user_name == NULL) 137 job_originating_user_name = "(withheld)"; 138 139 printf("%5d %-16s %s\n", job_id, job_originating_user_name, job_name); 140 } 141} 142</pre> 143 144<h3><a name='CREATING_URI_STRINGS'>Creating URI Strings</a></h3> 145 146<p>To ensure proper encoding, the 147<a href='#httpAssembleURIf'><code>httpAssembleURIf</code></a> function must be 148used to format a "printer-uri" string for all printer-based requests:</p> 149 150<pre class='example'> 151const char *name = "Foo"; 152char uri[1024]; 153<a href='#ipp_t'>ipp_t</a> *request; 154 155<a href='#httpAssembleURIf'>httpAssembleURIf</a>(HTTP_URI_CODING_ALL, uri, sizeof(uri), "ipp", NULL, cupsServer(), 156 ippPort(), "/printers/%s", name); 157<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_URI, "printer-uri", NULL, uri); 158</pre> 159 160<h3><a name='SENDING_REQUESTS_WITH_FILES'>Sending Requests with Files</a></h3> 161 162<p>The <a href='#cupsDoFileRequest'><code>cupsDoFileRequest</code></a> and 163<a href='#cupsDoIORequest'><code>cupsDoIORequest</code></a> functions are 164used for requests involving files. The 165<a href='#cupsDoFileRequest'><code>cupsDoFileRequest</code></a> function 166attaches the named file to a request and is typically used when sending a print 167file or changing a printer's PPD file:</p> 168 169<pre class='example'> 170const char *filename = "/usr/share/cups/data/testprint.ps"; 171const char *name = "Foo"; 172char uri[1024]; 173char resource[1024]; 174<a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(IPP_PRINT_JOB); 175<a href='#ipp_t'>ipp_t</a> *response; 176 177/* Use httpAssembleURIf for the printer-uri string */ 178<a href='#httpAssembleURIf'>httpAssembleURIf</a>(HTTP_URI_CODING_ALL, uri, sizeof(uri), "ipp", NULL, cupsServer(), 179 ippPort(), "/printers/%s", name); 180<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_URI, "printer-uri", NULL, uri); 181<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "requesting-user-name", 182 NULL, cupsUser()); 183<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "job-name", 184 NULL, "testprint.ps"); 185 186/* Use snprintf for the resource path */ 187snprintf(resource, sizeof(resource), "/printers/%s", name); 188 189response = <a href='#cupsDoFileRequest'>cupsDoFileRequest</a>(CUPS_HTTP_DEFAULT, request, resource, filename); 190</pre> 191 192<p>The <a href='#cupsDoIORequest'><code>cupsDoIORequest</code></a> function 193optionally attaches a file to the request and optionally saves a file in the 194response from the server. It is used when using a pipe for the request 195attachment or when using a request that returns a file, currently only 196<code>CUPS_GET_DOCUMENT</code> and <code>CUPS_GET_PPD</code>. For example, 197the following code will download the PPD file for the sample HP LaserJet 198printer driver:</p> 199 200<pre class='example'> 201char tempfile[1024]; 202int tempfd; 203<a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(CUPS_GET_PPD); 204<a href='#ipp_t'>ipp_t</a> *response; 205 206<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "ppd-name", 207 NULL, "laserjet.ppd"); 208 209tempfd = cupsTempFd(tempfile, sizeof(tempfile)); 210 211response = <a href='#cupsDoIORequest'>cupsDoIORequest</a>(CUPS_HTTP_DEFAULT, request, "/", -1, tempfd); 212</pre> 213 214<p>The example passes <code>-1</code> for the input file descriptor to specify 215that no file is to be attached to the request. The PPD file attached to the 216response is written to the temporary file descriptor we created using the 217<code>cupsTempFd</code> function.</p> 218 219<h3><a name='ASYNCHRONOUS_REQUEST_PROCESSING'>Asynchronous Request Processing</a></h3> 220 221<p>The <a href='#cupsSendRequest'><code>cupsSendRequest</code></a> and 222<a href='#cupsGetResponse'><code>cupsGetResponse</code></a> support 223asynchronous communications with the server. Unlike the other request 224functions, the IPP request is not automatically freed, so remember to 225free your request with the <a href='#ippDelete'><code>ippDelete</code></a> 226function.</p> 227 228<p>File data is attached to the request using the 229<a href='#cupsWriteRequestData'><code>cupsWriteRequestData</code></a> 230function, while file data returned from the server is read using the 231<a href='#cupsReadResponseData'><code>cupsReadResponseData</code></a> 232function. We can rewrite the previous <code>CUPS_GET_PPD</code> example 233to use the asynchronous functions quite easily:</p> 234 235<pre class='example'> 236char tempfile[1024]; 237int tempfd; 238<a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(CUPS_GET_PPD); 239<a href='#ipp_t'>ipp_t</a> *response; 240 241<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "ppd-name", 242 NULL, "laserjet.ppd"); 243 244tempfd = cupsTempFd(tempfile, sizeof(tempfile)); 245 246if (<a href='#cupsSendRequest'>cupsSendRequest</a>(CUPS_HTTP_DEFAULT, request, "/") == HTTP_CONTINUE) 247{ 248 response = <a href='#cupsGetResponse'>cupsGetResponse</a>(CUPS_HTTP_DEFAULT, "/"); 249 250 if (response != NULL) 251 { 252 ssize_t bytes; 253 char buffer[8192]; 254 255 while ((bytes = <a href='#cupsReadResponseData'>cupsReadResponseData</a>(CUPS_HTTP_DEFAULT, buffer, sizeof(buffer))) > 0) 256 write(tempfd, buffer, bytes); 257 } 258} 259 260/* Free the request! */ 261<a href='#ippDelete'>ippDelete</a>(request); 262</pre> 263 264<p>The <a href='#cupsSendRequest'><code>cupsSendRequest</code></a> function 265returns the initial HTTP request status, typically either 266<code>HTTP_CONTINUE</code> or <code>HTTP_UNAUTHORIZED</code>. The latter status 267is returned when the request requires authentication of some sort. The 268<a href='#cupsDoAuthentication'><code>cupsDoAuthentication</code></a> function 269must be called when your see <code>HTTP_UNAUTHORIZED</code> and the request 270re-sent. We can add authentication support to our example code by using a 271<code>do ... while</code> loop:</p> 272 273<pre class='example'> 274char tempfile[1024]; 275int tempfd; 276<a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(CUPS_GET_PPD); 277<a href='#ipp_t'>ipp_t</a> *response; 278http_status_t status; 279 280<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "ppd-name", 281 NULL, "laserjet.ppd"); 282 283tempfd = cupsTempFd(tempfile, sizeof(tempfile)); 284 285/* Loop for authentication */ 286do 287{ 288 status = <a href='#cupsSendRequest'>cupsSendRequest</a>(CUPS_HTTP_DEFAULT, request, "/"); 289 290 if (status == HTTP_UNAUTHORIZED) 291 { 292 /* Try to authenticate, break out of the loop if that fails */ 293 if (<a href='#cupsDoAuthentication'>cupsDoAuthentication</a>(CUPS_HTTP_DEFAULT, "POST", "/")) 294 break; 295 } 296} 297while (status != HTTP_CONTINUE && status != HTTP_UNAUTHORIZED); 298 299if (status == HTTP_CONTINUE) 300{ 301 response = <a href='#cupsGetResponse'>cupsGetResponse</a>(CUPS_HTTP_DEFAULT, "/"); 302 303 if (response != NULL) 304 { 305 ssize_t bytes; 306 char buffer[8192]; 307 308 while ((bytes = <a href='#cupsReadResponseData'>cupsReadResponseData</a>(CUPS_HTTP_DEFAULT, buffer, sizeof(buffer))) > 0) 309 write(tempfd, buffer, bytes); 310 } 311} 312 313/* Free the request! */ 314<a href='#ippDelete'>ippDelete</a>(request); 315</pre> 316