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deps/curl/docs/libcurl/curl_multi_socket_action.md

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+---
+c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
+SPDX-License-Identifier: curl
+Title: curl_multi_socket_action
+Section: 3
+Source: libcurl
+See-also:
+  - curl_multi_cleanup (3)
+  - curl_multi_fdset (3)
+  - curl_multi_info_read (3)
+  - curl_multi_init (3)
+  - the hiperfifo.c example
+---
+
+# NAME
+
+curl_multi_socket_action - reads/writes available data given an action
+
+# SYNOPSIS
+
+~~~c
+#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 tests 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 then gets 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
+
+~~~c
+int main(void)
+{
+  /* 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;
+  CURLM *multi; /* the stack we work with */
+  int fd; /* the descriptor that had action */
+  int bitmask; /* what activity that happened */
+  CURLMcode mc = curl_multi_socket_action(multi, fd, bitmask, &running);
+  if(mc)
+    printf("error: %s\n", curl_multi_strerror(mc));
+}
+~~~
+
+# 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)