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22 .TH curl_multi_socket_action 3 "9 Jul 2006" "libcurl 7.16.0" "libcurl Manual"
24 curl_multi_socket_action \- reads/writes available data given an action
27 #include <curl/curl.h>
29 CURLMcode curl_multi_socket_action(CURLM * multi_handle,
30 curl_socket_t sockfd, int ev_bitmask,
31 int *running_handles);
34 When the application has detected action on a socket handled by libcurl, it
35 should call \fIcurl_multi_socket_action(3)\fP with the \fBsockfd\fP argument
36 set to the socket with the action. When the events on a socket are known, they
37 can be passed as an events bitmask \fBev_bitmask\fP by first setting
38 \fBev_bitmask\fP to 0, and then adding using bitwise OR (|) any combination of
39 events to be chosen from CURL_CSELECT_IN, CURL_CSELECT_OUT or
40 CURL_CSELECT_ERR. When the events on a socket are unknown, pass 0 instead, and
41 libcurl will test the descriptor internally. It is also permissible to pass
42 CURL_SOCKET_TIMEOUT to the \fBsockfd\fP parameter in order to initiate the
43 whole process or when a timeout occurs.
45 At return, the integer \fBrunning_handles\fP points to will contain the number
46 of running easy handles within the multi handle. When this number reaches
47 zero, all transfers are complete/done. When you call
48 \fIcurl_multi_socket_action(3)\fP on a specific socket and the counter
49 decreases by one, it DOES NOT necessarily mean that this exact socket/transfer
50 is the one that completed. Use \fIcurl_multi_info_read(3)\fP to figure out
51 which easy handle that completed.
53 The \fBcurl_multi_socket_action(3)\fP functions inform the application about
54 updates in the socket (file descriptor) status by doing none, one, or multiple
55 calls to the socket callback function set with the CURLMOPT_SOCKETFUNCTION
56 option to \fIcurl_multi_setopt(3)\fP. They update the status with changes
57 since the previous time the callback was called.
59 Get the timeout time by setting the \fICURLMOPT_TIMERFUNCTION\fP option with
60 \fIcurl_multi_setopt(3)\fP. Your application will then get called with
61 information on how long to wait for socket actions at most before doing the
62 timeout action: call the \fBcurl_multi_socket_action(3)\fP function with the
63 \fBsockfd\fP argument set to CURL_SOCKET_TIMEOUT. You can also use the
64 \fIcurl_multi_timeout(3)\fP function to poll the value at any given time, but
65 for an event-based system using the callback is far better than relying on
66 polling the timeout value.
67 .SH "CALLBACK DETAILS"
69 The socket \fBcallback\fP function uses a prototype like this
72 int curl_socket_callback(CURL *easy, /* easy handle */
73 curl_socket_t s, /* socket */
74 int action, /* see values below */
75 void *userp, /* private callback pointer */
76 void *socketp); /* private socket pointer,
78 previously assigned with
79 \fBcurl_multi_assign(3)\fP */
82 The callback MUST return 0.
84 The \fIeasy\fP argument is a pointer to the easy handle that deals with this
85 particular socket. Note that a single handle may work with several sockets
88 The \fIs\fP argument is the actual socket value as you use it within your
91 The \fIaction\fP argument to the callback has one of five values:
93 .IP "CURL_POLL_NONE (0)"
94 register, not interested in readiness (yet)
95 .IP "CURL_POLL_IN (1)"
96 register, interested in read readiness
97 .IP "CURL_POLL_OUT (2)"
98 register, interested in write readiness
99 .IP "CURL_POLL_INOUT (3)"
100 register, interested in both read and write readiness
101 .IP "CURL_POLL_REMOVE (4)"
105 The \fIsocketp\fP argument is a private pointer you have previously set with
106 \fIcurl_multi_assign(3)\fP to be associated with the \fIs\fP socket. If no
107 pointer has been set, socketp will be NULL. This argument is of course a
108 service to applications that want to keep certain data or structs that are
109 strictly associated to the given socket.
111 The \fIuserp\fP argument is a private pointer you have previously set with
112 \fIcurl_multi_setopt(3)\fP and the CURLMOPT_SOCKETDATA option.
114 CURLMcode type, general libcurl multi interface error code.
116 Before version 7.20.0: If you receive \fICURLM_CALL_MULTI_PERFORM\fP, this
117 basically means that you should call \fIcurl_multi_socket_action(3)\fP again
118 before you wait for more actions on libcurl's sockets. You don't have to do it
119 immediately, but the return code means that libcurl may have more data
120 available to return or that there may be more data to send off before it is
123 The return code from this function is for the whole multi stack. Problems
124 still might have occurred on individual transfers even when one of these
127 1. Create a multi handle
129 2. Set the socket callback with CURLMOPT_SOCKETFUNCTION
131 3. Set the timeout callback with CURLMOPT_TIMERFUNCTION, to get to know what
132 timeout value to use when waiting for socket activities.
134 4. Add easy handles with curl_multi_add_handle()
136 5. Provide some means to manage the sockets libcurl is using, so you can check
137 them for activity. This can be done through your application code, or by way
138 of an external library such as libevent or glib.
140 6. Call curl_multi_socket_action(..., CURL_SOCKET_TIMEOUT, 0, ...)
141 to kickstart everything. To get one or more callbacks called.
143 7. Wait for activity on any of libcurl's sockets, use the timeout value your
144 callback has been told.
146 8, When activity is detected, call curl_multi_socket_action() for the
147 socket(s) that got action. If no activity is detected and the timeout expires,
148 call \fIcurl_multi_socket_action(3)\fP with \fICURL_SOCKET_TIMEOUT\fP.
150 This function was added in libcurl 7.15.4, and is deemed stable since 7.16.0.
152 .BR curl_multi_cleanup "(3), " curl_multi_init "(3), "
153 .BR curl_multi_fdset "(3), " curl_multi_info_read "(3), "
154 .BR "the hiperfifo.c example"