cups/api-httpipp.shtml - platform/external/libcups - Git at Google

 <!--
   "$Id: api-httpipp.shtml 6649 2007-07-11 21:46:42Z mike $"

   HTTP and IPP API introduction for the Common UNIX Printing System (CUPS).

   Copyright 2007-2008 by Apple Inc.
   Copyright 1997-2006 by Easy Software Products, all rights reserved.

   These coded instructions, statements, and computer programs are the
   property of Apple Inc. and are protected by Federal copyright
   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
   which should have been included with this file.  If this file is
   file is missing or damaged, see the license at "http://www.cups.org/".
 -->

 <h2 class='title'><a name='OVERVIEW'>Overview</a></h2>

 <p>The CUPS HTTP and IPP APIs provide low-level access to the HTTP and IPP
 protocols and CUPS scheduler. They are typically used by monitoring and
 administration programs to perform specific functions not supported by the
 high-level CUPS API functions.</p>

 <p>The HTTP APIs use an opaque structure called
 <a href='#http_t'><code>http_t</code></a> to manage connections to
 a particular HTTP or IPP server. The
 <a href='#httpConnectEncrypt'><code>httpConnectEncrypt</code></a> function is
 used to create an instance of this structure for a particular server.
 The constant <code>CUPS_HTTP_DEFAULT</code> can be used with all of the
 <code>cups</code> functions to refer to the default CUPS server - the functions
 create a per-thread <a href='#http_t'><code>http_t</code></a> as needed.</p>

 <p>The IPP APIs use two 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> structure 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>

 <p>The second 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 (<code>group_tag</code>), a
 value type tag (<code>value_tag</code>), the attribute name (<code>name</code>),
 and 1 or more values (<code>values[]</code>). Attributes are added to an
 <a href='#ipp_t'><code>ipp_t</code></a> structure using one of the
 <code>ippAdd</code> functions. For example, use
 <a href='#ippAddString'><code>ippAddString</code></a> to add a
 "requesting-user-name" string attribute to a request:</p>

 <pre class='example'>
 <a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(IPP_GET_JOBS);

 <a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "requesting-user-name",
              NULL, cupsUser());
 </pre>

 <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>

 <pre class='example'>
 #include &lt;cups/cups.h&gt;


 <a href='#ipp_t'>ipp_t</a> *<a name='get_jobs'>get_jobs</a>(void)
 {
   <a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(IPP_GET_JOBS);

   <a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "requesting-user-name",
                NULL, cupsUser());

   return (<a href='#cupsDoRequest'>cupsDoRequest</a>(CUPS_HTTP_DEFAULT, request, "/"));
 }
 </pre>

 <p>The <a href='#cupsDoRequest'><code>cupsDoRequest</code></a> function frees
 the request structure and returns an IPP response structure or NULL 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>

 <pre class='example'>
 <a href='#ipp_t'>ipp_t</a> *response;
 <a href='#ipp_attribute_t'>ipp_attribute_t</a> *attr;

 attr = <a href='#ippFindAttribute'>ippFindAttribute</a>(response, "printer-state", IPP_TAG_ENUM);
 </pre>

 <p>You can also walk the list of attributes with a simple <code>for</code> loop
 like this:</p>

 <pre class='example'>
 <a href='#ipp_t'>ipp_t</a> *response;
 <a href='#ipp_attribute_t'>ipp_attribute_t</a> *attr;

 for (attr = response->attrs; attr != NULL; attr = attr->next)
   if (attr->name == NULL)
     puts("--SEPARATOR--");
   else
     puts(attr->name);
 </pre>

 <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>

 <pre class='example'>
 <a href='#ipp_t'>ipp_t</a> *response = <a href='#get_jobs'>get_jobs</a>();

 if (response != NULL)
 {
   <a href='#ipp_attribute_t'>ipp_attribute_t</a> *attr;
   int job_id = 0;
   char *job_name = NULL;
   char *job_originating_user_name = NULL;

   puts("Job ID  Owner             Title");
   puts("------  ----------------  ---------------------------------");

   for (attr = response->attrs; attr != NULL; attr = attr->next)
   {
    /* Attributes without names are separators between jobs */
     if (attr->name == NULL)
     {
       if (job_id > 0 &amp;&amp; job_name != NULL &amp;&amp; job_originating_user_name != NULL)
         printf("%5d  %-16s  %s\n", job_id, job_originating_user_name, job_name);

       job_id = 0;
       job_name = NULL;
       job_originating_user_name = NULL;
       continue;
     }
     else if (!strcmp(attr->name, "job-id") &amp;&amp; attr->value_tag == IPP_TAG_INTEGER)
       job_id = attr->values[0].integer;
     else if (!strcmp(attr->name, "job-name") &amp;&amp; attr->value_tag == IPP_TAG_NAME)
       job_name = attr->values[0].string.text;
     else if (!strcmp(attr->name, "job-originating-user-name") &amp;&amp;
              attr->value_tag == IPP_TAG_NAME)
       job_originating_user_name = attr->values[0].string.text;
   }

   if (job_id > 0 &amp;&amp; job_name != NULL &amp;&amp; job_originating_user_name != NULL)
     printf("%5d  %-16s  %s\n", job_id, job_originating_user_name, job_name);
 }
 </pre>

 <h3><a name='CREATING_URI_STRINGS'>Creating URI Strings</a></h3>

 <p>To ensure proper encoding, the
 <a href='#httpAssembleURIf'><code>httpAssembleURIf</code></a> function must be
 used to format a "printer-uri" string for all printer-based requests:</p>

 <pre class='example'>
 const char *name = "Foo";
 char uri[1024];
 <a href='#ipp_t'>ipp_t</a> *request;

 <a href='#httpAssembleURIf'>httpAssembleURIf</a>(HTTP_URI_CODING_ALL, uri, sizeof(uri), "ipp", NULL, cupsServer(),
                  ippPort(), "/printers/%s", name);
 <a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_URI, "printer-uri", NULL, uri);
 </pre>

 <h3><a name='SENDING_REQUESTS_WITH_FILES'>Sending Requests with Files</a></h3>

 <p>The <a href='#cupsDoFileRequest'><code>cupsDoFileRequest</code></a> and
 <a href='#cupsDoIORequest'><code>cupsDoIORequest</code></a> functions are
 used for requests involving files. The
 <a href='#cupsDoFileRequest'><code>cupsDoFileRequest</code></a> function
 attaches the named file to a request and is typically used when sending a print
 file or changing a printer's PPD file:</p>

 <pre class='example'>
 const char *filename = "/usr/share/cups/data/testprint.ps";
 const char *name = "Foo";
 char uri[1024];
 char resource[1024];
 <a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(IPP_PRINT_JOB);
 <a href='#ipp_t'>ipp_t</a> *response;

 /* Use httpAssembleURIf for the printer-uri string */
 <a href='#httpAssembleURIf'>httpAssembleURIf</a>(HTTP_URI_CODING_ALL, uri, sizeof(uri), "ipp", NULL, cupsServer(),
                  ippPort(), "/printers/%s", name);
 <a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_URI, "printer-uri", NULL, uri);
 <a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "requesting-user-name",
              NULL, cupsUser());
 <a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "job-name",
              NULL, "testprint.ps");

 /* Use snprintf for the resource path */
 snprintf(resource, sizeof(resource), "/printers/%s", name);

 response = <a href='#cupsDoFileRequest'>cupsDoFileRequest</a>(CUPS_HTTP_DEFAULT, request, resource, filename);
 </pre>

 <p>The <a href='#cupsDoIORequest'><code>cupsDoIORequest</code></a> function
 optionally attaches a file to the request and optionally saves a file in the
 response from the server. It is used when using a pipe for the request
 attachment or when using a request that returns a file, currently only
 <code>CUPS_GET_DOCUMENT</code> and <code>CUPS_GET_PPD</code>. For example,
 the following code will download the PPD file for the sample HP LaserJet
 printer driver:</p>

 <pre class='example'>
 char tempfile[1024];
 int tempfd;
 <a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(CUPS_GET_PPD);
 <a href='#ipp_t'>ipp_t</a> *response;

 <a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "ppd-name",
              NULL, "laserjet.ppd");

 tempfd = cupsTempFd(tempfile, sizeof(tempfile));

 response = <a href='#cupsDoIORequest'>cupsDoIORequest</a>(CUPS_HTTP_DEFAULT, request, "/", -1, tempfd);
 </pre>

 <p>The example passes <code>-1</code> for the input file descriptor to specify
 that no file is to be attached to the request. The PPD file attached to the
 response is written to the temporary file descriptor we created using the
 <code>cupsTempFd</code> function.</p>

 <h3><a name='ASYNCHRONOUS_REQUEST_PROCESSING'>Asynchronous Request Processing</a></h3>

 <p>The <a href='#cupsSendRequest'><code>cupsSendRequest</code></a> and
 <a href='#cupsGetResponse'><code>cupsGetResponse</code></a> support
 asynchronous communications with the server. Unlike the other request
 functions, the IPP request is not automatically freed, so remember to
 free your request with the <a href='#ippDelete'><code>ippDelete</code></a>
 function.</p>

 <p>File data is attached to the request using the
 <a href='#cupsWriteRequestData'><code>cupsWriteRequestData</code></a>
 function, while file data returned from the server is read using the
 <a href='#cupsReadResponseData'><code>cupsReadResponseData</code></a>
 function. We can rewrite the previous <code>CUPS_GET_PPD</code> example
 to use the asynchronous functions quite easily:</p>

 <pre class='example'>
 char tempfile[1024];
 int tempfd;
 <a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(CUPS_GET_PPD);
 <a href='#ipp_t'>ipp_t</a> *response;

 <a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "ppd-name",
              NULL, "laserjet.ppd");

 tempfd = cupsTempFd(tempfile, sizeof(tempfile));

 if (<a href='#cupsSendRequest'>cupsSendRequest</a>(CUPS_HTTP_DEFAULT, request, "/") == HTTP_CONTINUE)
 {
   response = <a href='#cupsGetResponse'>cupsGetResponse</a>(CUPS_HTTP_DEFAULT, "/");

   if (response != NULL)
   {
     ssize_t bytes;
     char buffer[8192];

     while ((bytes = <a href='#cupsReadResponseData'>cupsReadResponseData</a>(CUPS_HTTP_DEFAULT, buffer, sizeof(buffer))) > 0)
       write(tempfd, buffer, bytes);
   }
 }

 /* Free the request! */
 <a href='#ippDelete'>ippDelete</a>(request);
 </pre>

 <p>The <a href='#cupsSendRequest'><code>cupsSendRequest</code></a> function
 returns the initial HTTP request status, typically either
 <code>HTTP_CONTINUE</code> or <code>HTTP_UNAUTHORIZED</code>. The latter status
 is returned when the request requires authentication of some sort. The
 <a href='#cupsDoAuthentication'><code>cupsDoAuthentication</code></a> function
 must be called when your see <code>HTTP_UNAUTHORIZED</code> and the request
 re-sent. We can add authentication support to our example code by using a
 <code>do ... while</code> loop:</p>

 <pre class='example'>
 char tempfile[1024];
 int tempfd;
 <a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(CUPS_GET_PPD);
 <a href='#ipp_t'>ipp_t</a> *response;
 http_status_t status;

 <a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "ppd-name",
              NULL, "laserjet.ppd");

 tempfd = cupsTempFd(tempfile, sizeof(tempfile));

 /* Loop for authentication */
 do
 {
   status = a href='#cupsSendRequest'>cupsSendRequest</a>(CUPS_HTTP_DEFAULT, request, "/");

   if (status == HTTP_UNAUTHORIZED)
   {
     /* Try to authenticate, break out of the loop if that fails */
     if (<a href='#cupsDoAuthentication'>cupsDoAuthentication</a>(CUPS_HTTP_DEFAULT, "POST", "/"))
       break;
   }
 }
 while (status != HTTP_CONTINUE &amp;&amp; status != HTTP_UNAUTHORIZED);

 if (status == HTTP_CONTINUE)
 {
   response = <a href='#cupsGetResponse'>cupsGetResponse</a>(CUPS_HTTP_DEFAULT, "/");

   if (response != NULL)
   {
     ssize_t bytes;
     char buffer[8192];

     while ((bytes = <a href='#cupsReadResponseData'>cupsReadResponseData</a>(CUPS_HTTP_DEFAULT, buffer, sizeof(buffer))) > 0)
       write(tempfd, buffer, bytes);
   }
 }

 /* Free the request! */
 <a href='#ippDelete'>ippDelete</a>(request);
 </pre>
	<!--
	"$Id: api-httpipp.shtml 6649 2007-07-11 21:46:42Z mike $"

	HTTP and IPP API introduction for the Common UNIX Printing System (CUPS).

	Copyright 2007-2008 by Apple Inc.
	Copyright 1997-2006 by Easy Software Products, all rights reserved.

	These coded instructions, statements, and computer programs are the
	property of Apple Inc. and are protected by Federal copyright
	law. Distribution and use rights are outlined in the file "LICENSE.txt"
	which should have been included with this file. If this file is
	file is missing or damaged, see the license at "http://www.cups.org/".
	-->

	<h2 class='title'><a name='OVERVIEW'>Overview</a></h2>

	<p>The CUPS HTTP and IPP APIs provide low-level access to the HTTP and IPP
	protocols and CUPS scheduler. They are typically used by monitoring and
	administration programs to perform specific functions not supported by the
	high-level CUPS API functions.</p>

	<p>The HTTP APIs use an opaque structure called
	<a href='#http_t'><code>http_t</code></a> to manage connections to
	a particular HTTP or IPP server. The
	<a href='#httpConnectEncrypt'><code>httpConnectEncrypt</code></a> function is
	used to create an instance of this structure for a particular server.
	The constant <code>CUPS_HTTP_DEFAULT</code> can be used with all of the
	<code>cups</code> functions to refer to the default CUPS server - the functions
	create a per-thread <a href='#http_t'><code>http_t</code></a> as needed.</p>

	<p>The IPP APIs use two 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> structure 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>

	<p>The second 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 (<code>group_tag</code>), a
	value type tag (<code>value_tag</code>), the attribute name (<code>name</code>),
	and 1 or more values (<code>values[]</code>). Attributes are added to an
	<a href='#ipp_t'><code>ipp_t</code></a> structure using one of the
	<code>ippAdd</code> functions. For example, use
	<a href='#ippAddString'><code>ippAddString</code></a> to add a
	"requesting-user-name" string attribute to a request:</p>

	<pre class='example'>
	<a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(IPP_GET_JOBS);

	<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "requesting-user-name",
	NULL, cupsUser());
	</pre>

	<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>

	<pre class='example'>
	#include <cups/cups.h>


	<a href='#ipp_t'>ipp_t</a> *<a name='get_jobs'>get_jobs</a>(void)
	{
	<a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(IPP_GET_JOBS);

	<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "requesting-user-name",
	NULL, cupsUser());

	return (<a href='#cupsDoRequest'>cupsDoRequest</a>(CUPS_HTTP_DEFAULT, request, "/"));
	}
	</pre>

	<p>The <a href='#cupsDoRequest'><code>cupsDoRequest</code></a> function frees
	the request structure and returns an IPP response structure or NULL 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>

	<pre class='example'>
	<a href='#ipp_t'>ipp_t</a> *response;
	<a href='#ipp_attribute_t'>ipp_attribute_t</a> *attr;

	attr = <a href='#ippFindAttribute'>ippFindAttribute</a>(response, "printer-state", IPP_TAG_ENUM);
	</pre>

	<p>You can also walk the list of attributes with a simple <code>for</code> loop
	like this:</p>

	<pre class='example'>
	<a href='#ipp_t'>ipp_t</a> *response;
	<a href='#ipp_attribute_t'>ipp_attribute_t</a> *attr;

	for (attr = response->attrs; attr != NULL; attr = attr->next)
	if (attr->name == NULL)
	puts("--SEPARATOR--");
	else
	puts(attr->name);
	</pre>

	<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>

	<pre class='example'>
	<a href='#ipp_t'>ipp_t</a> *response = <a href='#get_jobs'>get_jobs</a>();

	if (response != NULL)
	{
	<a href='#ipp_attribute_t'>ipp_attribute_t</a> *attr;
	int job_id = 0;
	char *job_name = NULL;
	char *job_originating_user_name = NULL;

	puts("Job ID Owner Title");
	puts("------ ---------------- ---------------------------------");

	for (attr = response->attrs; attr != NULL; attr = attr->next)
	{
	/* Attributes without names are separators between jobs */
	if (attr->name == NULL)
	{
	if (job_id > 0 && job_name != NULL && job_originating_user_name != NULL)
	printf("%5d %-16s %s\n", job_id, job_originating_user_name, job_name);

	job_id = 0;
	job_name = NULL;
	job_originating_user_name = NULL;
	continue;
	}
	else if (!strcmp(attr->name, "job-id") && attr->value_tag == IPP_TAG_INTEGER)
	job_id = attr->values[0].integer;
	else if (!strcmp(attr->name, "job-name") && attr->value_tag == IPP_TAG_NAME)
	job_name = attr->values[0].string.text;
	else if (!strcmp(attr->name, "job-originating-user-name") &&
	attr->value_tag == IPP_TAG_NAME)
	job_originating_user_name = attr->values[0].string.text;
	}

	if (job_id > 0 && job_name != NULL && job_originating_user_name != NULL)
	printf("%5d %-16s %s\n", job_id, job_originating_user_name, job_name);
	}
	</pre>

	<h3><a name='CREATING_URI_STRINGS'>Creating URI Strings</a></h3>

	<p>To ensure proper encoding, the
	<a href='#httpAssembleURIf'><code>httpAssembleURIf</code></a> function must be
	used to format a "printer-uri" string for all printer-based requests:</p>

	<pre class='example'>
	const char *name = "Foo";
	char uri[1024];
	<a href='#ipp_t'>ipp_t</a> *request;

	<a href='#httpAssembleURIf'>httpAssembleURIf</a>(HTTP_URI_CODING_ALL, uri, sizeof(uri), "ipp", NULL, cupsServer(),
	ippPort(), "/printers/%s", name);
	<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_URI, "printer-uri", NULL, uri);
	</pre>

	<h3><a name='SENDING_REQUESTS_WITH_FILES'>Sending Requests with Files</a></h3>

	<p>The <a href='#cupsDoFileRequest'><code>cupsDoFileRequest</code></a> and
	<a href='#cupsDoIORequest'><code>cupsDoIORequest</code></a> functions are
	used for requests involving files. The
	<a href='#cupsDoFileRequest'><code>cupsDoFileRequest</code></a> function
	attaches the named file to a request and is typically used when sending a print
	file or changing a printer's PPD file:</p>

	<pre class='example'>
	const char *filename = "/usr/share/cups/data/testprint.ps";
	const char *name = "Foo";
	char uri[1024];
	char resource[1024];
	<a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(IPP_PRINT_JOB);
	<a href='#ipp_t'>ipp_t</a> *response;

	/* Use httpAssembleURIf for the printer-uri string */
	<a href='#httpAssembleURIf'>httpAssembleURIf</a>(HTTP_URI_CODING_ALL, uri, sizeof(uri), "ipp", NULL, cupsServer(),
	ippPort(), "/printers/%s", name);
	<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_URI, "printer-uri", NULL, uri);
	<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "requesting-user-name",
	NULL, cupsUser());
	<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "job-name",
	NULL, "testprint.ps");

	/* Use snprintf for the resource path */
	snprintf(resource, sizeof(resource), "/printers/%s", name);

	response = <a href='#cupsDoFileRequest'>cupsDoFileRequest</a>(CUPS_HTTP_DEFAULT, request, resource, filename);
	</pre>

	<p>The <a href='#cupsDoIORequest'><code>cupsDoIORequest</code></a> function
	optionally attaches a file to the request and optionally saves a file in the
	response from the server. It is used when using a pipe for the request
	attachment or when using a request that returns a file, currently only
	<code>CUPS_GET_DOCUMENT</code> and <code>CUPS_GET_PPD</code>. For example,
	the following code will download the PPD file for the sample HP LaserJet
	printer driver:</p>

	<pre class='example'>
	char tempfile[1024];
	int tempfd;
	<a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(CUPS_GET_PPD);
	<a href='#ipp_t'>ipp_t</a> *response;

	<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "ppd-name",
	NULL, "laserjet.ppd");

	tempfd = cupsTempFd(tempfile, sizeof(tempfile));

	response = <a href='#cupsDoIORequest'>cupsDoIORequest</a>(CUPS_HTTP_DEFAULT, request, "/", -1, tempfd);
	</pre>

	<p>The example passes <code>-1</code> for the input file descriptor to specify
	that no file is to be attached to the request. The PPD file attached to the
	response is written to the temporary file descriptor we created using the
	<code>cupsTempFd</code> function.</p>

	<h3><a name='ASYNCHRONOUS_REQUEST_PROCESSING'>Asynchronous Request Processing</a></h3>

	<p>The <a href='#cupsSendRequest'><code>cupsSendRequest</code></a> and
	<a href='#cupsGetResponse'><code>cupsGetResponse</code></a> support
	asynchronous communications with the server. Unlike the other request
	functions, the IPP request is not automatically freed, so remember to
	free your request with the <a href='#ippDelete'><code>ippDelete</code></a>
	function.</p>

	<p>File data is attached to the request using the
	<a href='#cupsWriteRequestData'><code>cupsWriteRequestData</code></a>
	function, while file data returned from the server is read using the
	<a href='#cupsReadResponseData'><code>cupsReadResponseData</code></a>
	function. We can rewrite the previous <code>CUPS_GET_PPD</code> example
	to use the asynchronous functions quite easily:</p>

	<pre class='example'>
	char tempfile[1024];
	int tempfd;
	<a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(CUPS_GET_PPD);
	<a href='#ipp_t'>ipp_t</a> *response;

	<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "ppd-name",
	NULL, "laserjet.ppd");

	tempfd = cupsTempFd(tempfile, sizeof(tempfile));

	if (<a href='#cupsSendRequest'>cupsSendRequest</a>(CUPS_HTTP_DEFAULT, request, "/") == HTTP_CONTINUE)
	{
	response = <a href='#cupsGetResponse'>cupsGetResponse</a>(CUPS_HTTP_DEFAULT, "/");

	if (response != NULL)
	{
	ssize_t bytes;
	char buffer[8192];

	while ((bytes = <a href='#cupsReadResponseData'>cupsReadResponseData</a>(CUPS_HTTP_DEFAULT, buffer, sizeof(buffer))) > 0)
	write(tempfd, buffer, bytes);
	}
	}

	/* Free the request! */
	<a href='#ippDelete'>ippDelete</a>(request);
	</pre>

	<p>The <a href='#cupsSendRequest'><code>cupsSendRequest</code></a> function
	returns the initial HTTP request status, typically either
	<code>HTTP_CONTINUE</code> or <code>HTTP_UNAUTHORIZED</code>. The latter status
	is returned when the request requires authentication of some sort. The
	<a href='#cupsDoAuthentication'><code>cupsDoAuthentication</code></a> function
	must be called when your see <code>HTTP_UNAUTHORIZED</code> and the request
	re-sent. We can add authentication support to our example code by using a
	<code>do ... while</code> loop:</p>

	<pre class='example'>
	char tempfile[1024];
	int tempfd;
	<a href='#ipp_t'>ipp_t</a> *request = <a href='#ippNewRequest'>ippNewRequest</a>(CUPS_GET_PPD);
	<a href='#ipp_t'>ipp_t</a> *response;
	http_status_t status;

	<a href='#ippAddString'>ippAddString</a>(request, IPP_TAG_OPERATION, IPP_TAG_NAME, "ppd-name",
	NULL, "laserjet.ppd");

	tempfd = cupsTempFd(tempfile, sizeof(tempfile));

	/* Loop for authentication */
	do
	{
	status = a href='#cupsSendRequest'>cupsSendRequest</a>(CUPS_HTTP_DEFAULT, request, "/");

	if (status == HTTP_UNAUTHORIZED)
	{
	/* Try to authenticate, break out of the loop if that fails */
	if (<a href='#cupsDoAuthentication'>cupsDoAuthentication</a>(CUPS_HTTP_DEFAULT, "POST", "/"))
	break;
	}
	}
	while (status != HTTP_CONTINUE && status != HTTP_UNAUTHORIZED);

	if (status == HTTP_CONTINUE)
	{
	response = <a href='#cupsGetResponse'>cupsGetResponse</a>(CUPS_HTTP_DEFAULT, "/");

	if (response != NULL)
	{
	ssize_t bytes;
	char buffer[8192];

	while ((bytes = <a href='#cupsReadResponseData'>cupsReadResponseData</a>(CUPS_HTTP_DEFAULT, buffer, sizeof(buffer))) > 0)
	write(tempfd, buffer, bytes);
	}
	}

	/* Free the request! */
	<a href='#ippDelete'>ippDelete</a>(request);
	</pre>