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157 lines
7.1 KiB
Groff
157 lines
7.1 KiB
Groff
.\" **************************************************************************
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.\" * _ _ ____ _
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.\" * Project ___| | | | _ \| |
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.\" * / __| | | | |_) | |
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.\" * | (__| |_| | _ <| |___
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.\" * \___|\___/|_| \_\_____|
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.\" *
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.\" * Copyright (C) 1998 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.
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.\" *
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.\" * This software is licensed as described in the file COPYING, which
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.\" * you should have received as part of this distribution. The terms
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.\" * are also available at https://curl.haxx.se/docs/copyright.html.
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.\" *
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.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
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.\" * copies of the Software, and permit persons to whom the Software is
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.\" * furnished to do so, under the terms of the COPYING file.
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.\" *
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.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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.\" * KIND, either express or implied.
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.\" *
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.\" **************************************************************************
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.TH curl_multi_socket_action 3 "9 Jul 2006" "libcurl 7.16.0" "libcurl Manual"
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.SH NAME
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curl_multi_socket_action \- reads/writes available data given an action
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.SH SYNOPSIS
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.nf
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#include <curl/curl.h>
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CURLMcode curl_multi_socket_action(CURLM * multi_handle,
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curl_socket_t sockfd,
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int ev_bitmask,
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int *running_handles);
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.fi
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.SH DESCRIPTION
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When the application has detected action on a socket handled by libcurl, it
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should call \fIcurl_multi_socket_action(3)\fP with the \fBsockfd\fP argument
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set to the socket with the action. When the events on a socket are known, they
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can be passed as an events bitmask \fBev_bitmask\fP by first setting
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\fBev_bitmask\fP to 0, and then adding using bitwise OR (|) any combination of
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events to be chosen from CURL_CSELECT_IN, CURL_CSELECT_OUT or
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CURL_CSELECT_ERR. When the events on a socket are unknown, pass 0 instead, and
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libcurl will test the descriptor internally. It is also permissible to pass
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CURL_SOCKET_TIMEOUT to the \fBsockfd\fP parameter in order to initiate the
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whole process or when a timeout occurs.
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At return, \fBrunning_handles\fP points to the number
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of running easy handles within the multi handle. When this number reaches
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zero, all transfers are complete/done. When you call
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\fIcurl_multi_socket_action(3)\fP on a specific socket and the counter
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decreases by one, it DOES NOT necessarily mean that this exact socket/transfer
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is the one that completed. Use \fIcurl_multi_info_read(3)\fP to figure out
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which easy handle that completed.
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The \fIcurl_multi_socket_action(3)\fP functions inform the application about
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updates in the socket (file descriptor) status by doing none, one, or multiple
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calls to the socket callback function set with the
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\fICURLMOPT_SOCKETFUNCTION(3)\fP option to \fIcurl_multi_setopt(3)\fP. They
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update the status with changes since the previous time the callback was
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called.
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Get the timeout time by setting the \fICURLMOPT_TIMERFUNCTION(3)\fP option
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with \fIcurl_multi_setopt(3)\fP. Your application will then get called with
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information on how long to wait for socket actions at most before doing the
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timeout action: call the \fIcurl_multi_socket_action(3)\fP function with the
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\fBsockfd\fP argument set to CURL_SOCKET_TIMEOUT. You can also use the
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\fIcurl_multi_timeout(3)\fP function to poll the value at any given time, but
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for an event-based system using the callback is far better than relying on
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polling the timeout value.
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.SH "CALLBACK DETAILS"
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The socket \fBcallback\fP function uses a prototype like this
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.nf
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int curl_socket_callback(CURL *easy, /* easy handle */
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curl_socket_t s, /* socket */
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int action, /* see values below */
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void *userp, /* private callback pointer */
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void *socketp); /* private socket pointer,
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\fBNULL\fP if not
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previously assigned with
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\fIcurl_multi_assign(3)\fP */
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.fi
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The callback MUST return 0.
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The \fIeasy\fP argument is a pointer to the easy handle that deals with this
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particular socket. Note that a single handle may work with several sockets
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simultaneously.
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The \fIs\fP argument is the actual socket value as you use it within your
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system.
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The \fIaction\fP argument to the callback has one of five values:
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.RS
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.IP "CURL_POLL_NONE (0)"
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register, not interested in readiness (yet)
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.IP "CURL_POLL_IN (1)"
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register, interested in read readiness
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.IP "CURL_POLL_OUT (2)"
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register, interested in write readiness
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.IP "CURL_POLL_INOUT (3)"
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register, interested in both read and write readiness
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.IP "CURL_POLL_REMOVE (4)"
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unregister
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.RE
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The \fIsocketp\fP argument is a private pointer you have previously set with
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\fIcurl_multi_assign(3)\fP to be associated with the \fIs\fP socket. If no
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pointer has been set, socketp will be NULL. This argument is of course a
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service to applications that want to keep certain data or structs that are
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strictly associated to the given socket.
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The \fIuserp\fP argument is a private pointer you have previously set with
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\fIcurl_multi_setopt(3)\fP and the CURLMOPT_SOCKETDATA option.
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.SH "RETURN VALUE"
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CURLMcode type, general libcurl multi interface error code.
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Before version 7.20.0: If you receive \fICURLM_CALL_MULTI_PERFORM\fP, this
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basically means that you should call \fIcurl_multi_socket_action(3)\fP again
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before you wait for more actions on libcurl's sockets. You don't have to do it
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immediately, but the return code means that libcurl may have more data
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available to return or that there may be more data to send off before it is
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"satisfied".
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The return code from this function is for the whole multi stack. Problems
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still might have occurred on individual transfers even when one of these
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functions return OK.
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.SH "TYPICAL USAGE"
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1. Create a multi handle
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2. Set the socket callback with CURLMOPT_SOCKETFUNCTION
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3. Set the timeout callback with CURLMOPT_TIMERFUNCTION, to get to know what
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timeout value to use when waiting for socket activities.
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4. Add easy handles with curl_multi_add_handle()
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5. Provide some means to manage the sockets libcurl is using, so you can check
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them for activity. This can be done through your application code, or by way
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of an external library such as libevent or glib.
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6. Call curl_multi_socket_action(..., CURL_SOCKET_TIMEOUT, 0, ...)
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to kickstart everything. To get one or more callbacks called.
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7. Wait for activity on any of libcurl's sockets, use the timeout value your
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callback has been told.
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8, When activity is detected, call curl_multi_socket_action() for the
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socket(s) that got action. If no activity is detected and the timeout expires,
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call \fIcurl_multi_socket_action(3)\fP with \fICURL_SOCKET_TIMEOUT\fP.
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.SH AVAILABILITY
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This function was added in libcurl 7.15.4, and is deemed stable since 7.16.0.
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.SH "SEE ALSO"
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.BR curl_multi_cleanup "(3), " curl_multi_init "(3), "
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.BR curl_multi_fdset "(3), " curl_multi_info_read "(3), "
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.BR "the hiperfifo.c example"
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