.\" $Id$
.\"
.TH curl_multi_socket 3 "21 Dec 2005" "libcurl 7.16.0" "libcurl Manual"
.SH NAME
curl_multi_socket \- reads/writes available data
.SH SYNOPSIS
#include <curl/curl.h>

CURLMcode curl_multi_socket(CURLM * multi_handle, curl_socket_t sockfd);

CURLMcode curl_multi_socket_all(CURLM *multi_handle);
.SH DESCRIPTION
Alternative versions of \fIcurl_multi_perform()\fP that allows the application
to pass in one of the file descriptors/sockets that have been detected to have
\&"action" on them and let libcurl perform. This allows libcurl to not have to
scan through all possible file descriptors to check for action. When the
application has detected action on a socket handled by libcurl, it should call
\fIcurl_multi_perform()\fP with the \fBsockfd\fP argument set to the socket
with the action.

These functions inform the application about updates in the socket (file
descriptor) status by doing none, one or multiple calls to the
curl_socket_callback given with the CURLMOPT_SOCKETFUNCTION option to
\fIcurl_multi_setopt(3)\fP. They update the status with changes since the
previous time this function was called.

If you want to force libcurl to (re-)check all its internal sockets and
transfers instead of just a single one, you call
\fBcurl_multi_socket_all(3)\fP instead.

An application should call \fBcurl_multi_timeout(3)\fP to figure out how long
it should wait for socket actions \- at most \- before doing the timeout
action: call the \fBcurl_multi_socket(3)\fP function with the \fBsockfd\fP
argument set to CURL_SOCKET_TIMEOUT.

The socket \fBcallback\fP function uses a prototype like this
.nf

     int curl_socket_callback(CURL *easy,      /* easy handle */
                              curl_socket_t s, /* socket */
                              int action,      /* see values below */
                              void *userp);    /* "private" pointer */

.fi
The callback MUST return 0.

The \fIaction\fP (third) argument to the callback has one of five values:
.RS
.IP "CURL_POLL_NONE (0)"
register, not interested in readiness (yet)
.IP "CURL_POLL_IN (1)"
register, interested in read readiness
.IP "CURL_POLL_OUT (2)"
register, interested in write readiness
.IP "CURL_POLL_INOUT (3)"
register, interested in both read and write readiness
.IP "CURL_POLL_REMOVE (4)"
deregister
.RE
.SH "RETURN VALUE"
CURLMcode type, general libcurl multi interface error code.

If you receive \fICURLM_CALL_MULTI_PERFORM\fP, this basically means that you
should call \fIcurl_multi_perform\fP again, before you wait for more actions
on libcurl's sockets. You don't have to do it immediately, but the return code
means that libcurl may have more data available to return or that there may be
more data to send off before it is "satisfied".

NOTE that this only returns errors etc regarding the whole multi stack. There
might still have occurred problems on individual transfers even when this
function returns OK.
.SH "TYPICAL USAGE"
1. Create a multi handle

2. Set the socket callback with CURLMOPT_SOCKETFUNCTION

3. Add easy handles

4. Call curl_multi_socket_all() first once

5. Setup a "collection" of sockets to supervise when your socket
callback is called.

6. Use curl_multi_timeout() to figure out how long to wait for action

7. Wait for action on any of libcurl's sockets

8, When action happens, call curl_multi_socket() for the socket(s) that got
action.

9. Go back to step 6.
.SH AVAILABILITY
This function was added in libcurl 7.16.0
.SH "SEE ALSO"
.BR curl_multi_cleanup "(3), " curl_multi_init "(3), "
.BR curl_multi_fdset "(3), " curl_multi_info_read "(3)"