curl_multi_socket(3)

NAME
curl_multi_socket - reads/writes available data

SYNOPSIS
#include <curl/curl.h> CURLMcode curl_multi_socket(CURLM * multi_handle,
                        curl_socket_t sockfd,
                        curl_socket_callback callback,
                        void *userp); CURLMcode curl_multi_socket_all(CURLM *multi_handle,
                        curl_socket_callback callback,
                        void *userp);

DESCRIPTION
Alternative versions of curl_multi_perform() 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 on a socket handled by libcurl, call curl_multi_perform() with the sockfd 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 in the callback argument. They update the status with changes since the previous time this function was used. If callback is NULL, no callback will be called. A status change may also be a new timeout only, having the same IN/OUT status as before. If you want to force libcurl to (re-)check all its internal sockets and transfers instead of just a single one, you call curl_multi_socket_all(3) instead. An application should call curl_multi_timeout(3) to figure out how long it should wait for socket actions - at most - before doing the timeout action: call the curl_multi_socket(3) function with the sockfd argument set to CURL_SOCKET_TIMEOUT. curl_multi_perform(3) is the exact equivalent of calling curl_multi_socket_all(handle, NULL, NULL); The socket callback function uses a prototype like this
     int curl_socket_callback(CURL *easy,      /* easy handle */
                              curl_socket_t s, /* socket */
                              int action,      /* see values below */
                              void *userp);    /* "private" pointer */
The callback MUST return 0. The action (third) argument to the callback has one of five values:

    CURL_POLL_NONE (0)
        register, not interested in readiness (yet)

    CURL_POLL_IN (1)
        register, interested in read readiness

    CURL_POLL_OUT (2)
        register, interested in write readiness

    CURL_POLL_INOUT (3)
        register, interested in both read and write readiness

    CURL_POLL_REMOVE (4)
        deregister

RETURN VALUE
CURLMcode type, general libcurl multi interface error code. If you receive CURLM_CALL_MULTI_PERFORM, this basically means that you should call curl_multi_perform again, before you select() on more actions. 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.

TYPICAL USAGE
Call curl_multi_socket_all() first. Setup a "collection" of sockets to supervise, then when action happens call curl_multi_socket() for the easy handle that got the action.

AVAILABILITY
This function was added in libcurl 7.16.0

SEE ALSO
curl_multi_cleanup(3), curl_multi_init(3), curl_multi_fdset(3), curl_multi_info_read(3)