curl_multi_socket - reads/writes available data
CURLMcode curl_multi_socket_action(CURLM * multi_handle,
curl_socket_t sockfd, int ev_bitmask,
CURLMcode curl_multi_socket(CURLM * multi_handle, curl_socket_t sockfd,
CURLMcode curl_multi_socket_all(CURLM *multi_handle,
Alternative versions of curl_multi_perform(3) that allows the applica-
tion 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 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 com-
bination of events to be choosen 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 running_handles 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
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 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_SOCKETFUNC-
TION option to curl_multi_setopt(3). They update the status with
changes since the previous time this function was called.
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). This
is typically done as the first function call before the application has
any knowledge about what sockets libcurl uses.
Applications should call curl_multi_timeout(3) to figure out how long
to wait for socket actions - at most - before doing the timeout action:
call the curl_multi_socket(3) function with the sockfd argument set to
Usage of curl_multi_socket(3) is depricated, whereas the function is
equivalent to curl_multi_socket_action(3), when ev_bitmask is set to 0.
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 callback pointer */
void *socketp); /* private socket pointer */
The callback MUST return 0.
The easy argument is a pointer to the easy handle that deals with this
particular socket. Note that a single handle may work with several
The s argument is the actual socket value as you use it within your
The action argument to the callback has one of five values:
register, not interested in readiness (yet)
register, interested in read readiness
register, interested in write readiness
register, interested in both read and write readiness
The socketp argument is a private pointer you have previously set with
curl_multi_assign(3) to be associated with the s socket. If no pointer
has been set, socketp will be NULL. This argument is of course a ser-
vice to applications that want to keep certain data or structs that are
strictly associated to the given socket.
The userp argument is a private pointer you have previously set with
curl_multi_setopt(3) and the CURLMOPT_SOCKETDATA option.
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 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.
1. Create a multi handle
2. Set the socket callback with CURLMOPT_SOCKETFUNCTION
3. Add easy handles
4. Call curl_multi_socket_all() first once
5. Setup a "collection" of sockets to supervise when your socket call-
back is called.
6. Use curl_multi_timeout() to figure out how long to wait for action
7. Wait for action on any of libcurl's sockets
8, When action happens, call curl_multi_socket_action() for the
socket(s) that got action.
9. Go back to step 6.
This function was added in libcurl 7.15.4, although deemed stablesince
curl_multi_socket(3) is deprecated, use curl_multi_socket_action(3)
curl_multi_cleanup(3), curl_multi_init(3), curl_multi_fdset(3),
libcurl 7.16.0 9 Jul 2006 curl_multi_socket(3)
Man(1) output converted with