curl/docs/libcurl/curl_multi_socket.3

.\" $Id$
.\"
.TH curl_multi_socket 3 "9 Jul 2006" "libcurl 7.16.0" "libcurl Manual"
.SH NAME
curl_multi_socket \- reads/writes available data
.SH SYNOPSIS
.nf
#include <curl/curl.h>

CURLMcode curl_multi_socket_action(CURLM * multi_handle, 
                                   curl_socket_t sockfd, int ev_bitmask,
                                   int *running_handles);

CURLMcode curl_multi_socket(CURLM * multi_handle, curl_socket_t sockfd,
                            int *running_handles);

CURLMcode curl_multi_socket_all(CURLM *multi_handle,
                                int *running_handles);
.fi
.SH DESCRIPTION
Alternative versions of \fIcurl_multi_perform(3)\fP that allows the
application to pass in the file descriptor/socket that has been detected to
have \&"action" on it 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_socket_action(3)\fP with the \fBsockfd\fP argument set to the
socket with the action. When the events on a socket are known, they can be
passed as an events bitmask \fBev_bitmask\fP by first setting \fBev_bitmask\fP
to 0, and then adding using bitwise OR (|) any combination of events to be
chosen from CURL_CSELECT_IN, CURL_CSELECT_OUT or CURL_CSELECT_ERR. When the
events on a socket are unknown, pass 0 instead, and libcurl will test the
descriptor internally.

At return, the int \fBrunning_handles\fP points to will contain the number of
still running easy handles within the multi handle. When this number reaches
zero, all transfers are complete/done. Note that when you call
\fIcurl_multi_socket_action(3)\fP on a specific socket and the counter
decreases by one, it DOES NOT necessarily mean that this exact socket/transfer
is the one that completed. Use \fIcurl_multi_info_read(3)\fP to figure out
which easy handle that completed.

The curl_multi_socket functions inform the application about updates in the
socket (file descriptor) status by doing none, one or multiple calls to the
socket callback function set 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.

Force libcurl to (re-)check all its internal sockets and transfers instead of
just a single one by calling \fBcurl_multi_socket_all(3)\fP. Note that there
should rarely be reasons to use this function!

Get the timeout time - how long to 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, by setting the
\fICURLMOPT_TIMERFUNCTION\fP option with \fIcurl_multi_setopt(3)\fP. You can
also use the \fIcurl_multi_timeout(3)\fP function to poll the value at any
given time, but for an event-based system using the callback is far better
than relying on polling the timeout value.

Usage of \fIcurl_multi_socket(3)\fP is deprecated, whereas the function is
equivalent to \fIcurl_multi_socket_action(3)\fP, when \fBev_bitmask\fP is set 
to 0.

.SH "CALLBACK DETAILS"

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 callback pointer */
                           void *socketp); /* private socket pointer */

.fi
The callback MUST return 0.

The \fIeasy\fP argument is a pointer to the easy handle that deals with this
particular socket. Note that a single handle may work with several sockets
simultaneously.

The \fIs\fP argument is the actual socket value as you use it within your
system.

The \fIaction\fP 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)"
unregister
.RE

The \fIsocketp\fP argument is a private pointer you have previously set with
\fIcurl_multi_assign(3)\fP to be associated with the \fIs\fP socket. If no
pointer has been set, socketp will be NULL. This argument is of course a
service to applications that want to keep certain data or structs that are
strictly associated to the given socket.

The \fIuserp\fP argument is a private pointer you have previously set with
\fIcurl_multi_setopt(3)\fP and the CURLMOPT_SOCKETDATA option.
.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_socket(3)\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. Set the timeout callback with CURLMOPT_TIMERFUNCTION, to get to know what
timeout value to use when waiting for socket activities.

4. Add easy handles with curl_multi_add_handle()

5. Provide some means to manage the sockets libcurl is using, so you can check
them for activity. This can be done through your application code, or by way
of an external library such as libevent or glib.

6. Wait for activity on any of libcurl's sockets, use the timeout value your
callback has been told

7, When activity is detected, call curl_multi_socket_action() for the
socket(s) that got action. If no activity is detected and the timeout expires,
call \fIcurl_multi_socket_action(3)\fP with \fICURL_SOCKET_TIMEOUT\fP

8. Go back to step 6.
.SH AVAILABILITY
This function was added in libcurl 7.15.4, although deemed stable since
7.16.0.

\fIcurl_multi_socket(3)\fP is deprecated, use
\fIcurl_multi_socket_action(3)\fP instead!
.SH "SEE ALSO"
.BR curl_multi_cleanup "(3), " curl_multi_init "(3), "
.BR curl_multi_fdset "(3), " curl_multi_info_read "(3), "
.BR "the hiperfifo.c example"