curl_multi_socket_action(3)     libcurl Manual     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 _multi_socket_action&section=3">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 _multi_socket_action&section=3">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 _multi_info_read&section=3">curl_multi_info_read(3) to figure out which easy handle
       that completed.

       The _multi_socket_action&section=3">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
       _SOCKETFUNCTION&section=3">CURLMOPT_SOCKETFUNCTION(3) option to _multi_setopt&section=3">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 _TIMERFUNCTION&section=3">CURLMOPT_TIMERFUNCTION(3) option
       with _multi_setopt&section=3">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 _multi_socket_action&section=3">curl_multi_socket_action(3) function with
       the sockfd argument set to CURL_SOCKET_TIMEOUT. You can also use the
       _multi_timeout&section=3">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.

TYPICAL USAGE
       1. Create a multi handle

       2. Set the socket callback with _SOCKETFUNCTION&section=3">CURLMOPT_SOCKETFUNCTION(3)

       3. Set the timeout callback with _TIMERFUNCTION&section=3">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 _multi_socket_action&section=3">curl_multi_socket_action(3) with CURL_SOCKET_TIMEOUT.

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

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

libcurl 7.77.0                 November 5, 2020    curl_multi_socket_action(3)