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curl_multi_socket_action(3)         libcurl        curl_multi_socket_action(3)

NAME
       curl_multi_socket_action - reads/writes available data given an action

SYNOPSIS
       #include <curl/curl.h>

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

DESCRIPTION
       When the application has detected action on a socket handled by
       libcurl, it should call curl_multi_socket_action(3) with the sockfd
       argument set to the socket with the action. When the events on a socket
       are known, they can be passed as an events bitmask ev_bitmask by first
       setting ev_bitmask 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. It is also permissible to pass CURL_SOCKET_TIMEOUT to the
       sockfd parameter in order to initiate the whole process or when a
       timeout occurs.

       At return, running_handles points to the number of running easy handles
       within the multi handle. When this number reaches zero, all transfers
       are complete/done. When you call curl_multi_socket_action(3) 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 curl_multi_info_read(3) to figure out which easy handle
       that completed.

       The curl_multi_socket_action(3) function informs 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(3) option to curl_multi_setopt(3). They update
       the status with changes since the previous time the callback was
       called.

       Get the timeout time by setting the CURLMOPT_TIMERFUNCTION(3) option
       with curl_multi_setopt(3). Your application will then get called with
       information on how long to wait for socket actions at most before doing
       the timeout action: call the curl_multi_socket_action(3) function with
       the sockfd argument set to CURL_SOCKET_TIMEOUT. You can also use the
       curl_multi_timeout(3) 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.

       When this function returns error, the state of all transfers are
       uncertain and they cannot be continued. curl_multi_socket_action(3)
       should not be called again on the same multi handle after an error has
       been returned, unless first removing all the handles and adding new
       ones.

TYPICAL USAGE
       1. Create a multi handle

       2. Set the socket callback with CURLMOPT_SOCKETFUNCTION(3)

       3. Set the timeout callback with CURLMOPT_TIMERFUNCTION(3), 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. Call curl_multi_socket_action(..., CURL_SOCKET_TIMEOUT, 0, ...) to
       kickstart everything. To get one or more callbacks called.

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

       8, 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 curl_multi_socket_action(3) with CURL_SOCKET_TIMEOUT.

EXAMPLE
       /* the event-library gets told when there activity on the socket 'fd',
          which we translate to a call to curl_multi_socket_action() */
       int running;
       rc = curl_multi_socket_action(multi_handle, fd, EVENT,
                                     &running);

AVAILABILITY
       This function was added in libcurl 7.15.4, and is deemed stable since
       7.16.0.

RETURN VALUE
       CURLMcode type, general libcurl multi interface error code. See
       libcurl-errors(3)

SEE ALSO
       curl_multi_cleanup(3), curl_multi_init(3),  curl_multi_fdset(3),
       curl_multi_info_read(3),  the hiperfifo.c example

libcurl 8.1.2                   April 26, 2023     curl_multi_socket_action(3)