curl_multi_socket(3) libcurl Manual 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,
int *running_handles);
CURLMcode curl_multi_socket_all(CURLM *multi_handle,
int *running_handles);
DESCRIPTION
These functions are deprecated. Do not use. See curl_multi_socket_ac-
tion(3) instead.
At return, the integer running_handles points to will contain the num-
ber 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_action(3) 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 CURL-
MOPT_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.
Usage of curl_multi_socket(3) is deprecated, whereas the function is
equivalent to curl_multi_socket_action(3) with ev_bitmask set to 0.
Force libcurl to (re-)check all its internal sockets and transfers in-
stead of just a single one by calling curl_multi_socket_all(3). Note
that there should not be any reason to use this function.
CALLBACK
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
sockets simultaneously.
The s argument is the actual socket value as you use it within your
system.
The action 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)
unregister
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(3) option.
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. Wait for activity on any of libcurl's sockets, use the timeout value
your callback has been told
7, 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
8. Go back to step 6.
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(multi_handle, fd, &running);
AVAILABILITY
This function was added in libcurl 7.15.4, and is deemed stable since
7.16.0.
curl_multi_socket(3) is deprecated, use curl_multi_socket_action(3) in-
stead!
RETURN VALUE
CURLMcode type, general libcurl multi interface error code.
The return code is for the whole multi stack. Problems still might have
occurred on individual transfers even when one of these functions re-
turn OK.
SEE ALSO
curl_multi_cleanup(3), curl_multi_init(3), curl_multi_fdset(3),
curl_multi_info_read(3), the hiperfifo.c example
libcurl 7.81.0 November 26, 2021 curl_multi_socket(3)
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