CURLMOPT_SOCKETFUNCTION(3)

1CURLMOPT_SOCKETFUNCTION(3)          libcurl         CURLMOPT_SOCKETFUNCTION(3)
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NAME

6       CURLMOPT_SOCKETFUNCTION - callback informed about what to wait for
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SYNOPSIS

9       #include <curl/curl.h>
10
11       int socket_callback(CURL *easy,      /* easy handle */
12                           curl_socket_t s, /* socket */
13                           int what,        /* describes the socket */
14                           void *clientp,   /* private callback pointer */
15                           void *socketp);  /* private socket pointer */
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17       CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_SOCKETFUNCTION, socket_callback);
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DESCRIPTION

20       Pass a pointer to your callback function, which should match the proto‐
21       type shown above.
22
23       When the curl_multi_socket_action(3) function is called, it  uses  this
24       callback  to  inform  the application about updates in the socket (file
25       descriptor) status by  doing  none,  one,  or  multiple  calls  to  the
26       socket_callback. The callback function gets status updates with changes
27       since the previous time the callback was called. If the given  callback
28       pointer is set to NULL, no callback will be called.
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30       libcurl  then  expects  the  application to monitor the sockets for the
31       specific activities and tell libcurl again when  something  happens  on
32       one of them. Tell libcurl by calling curl_multi_socket_action(3).
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CALLBACK ARGUMENTS

35       easy identifies the specific transfer for which this update is related.
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37       s is the specific socket this function invocation concerns. If the what
38       argument is not CURL_POLL_REMOVE then it holds information  about  what
39       activity  on this socket the application is supposed to monitor. Subse‐
40       quent calls to this callback might update the what bits  for  a  socket
41       that is already monitored.
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43       The  socket  callback  should  return 0 on success, and -1 on error. If
44       this callback returns error, all transfers  currently  in  progress  in
45       this multi handle will be aborted and fail.
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47       clientp is set with CURLMOPT_SOCKETDATA(3).
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49       socketp is set with curl_multi_assign(3) or will be NULL.
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51       The  what  parameter  informs  the  callback on the status of the given
52       socket. It can hold one of these values:
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54       CURL_POLL_IN
55              Wait for incoming data. For the socket to become readable.
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57       CURL_POLL_OUT
58              Wait for outgoing data. For the socket to become writable.
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60       CURL_POLL_INOUT
61              Wait for incoming and outgoing data. For the  socket  to  become
62              readable or writable.
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64       CURL_POLL_REMOVE
65              The  specified  socket/file  descriptor  is  no  longer  used by
66              libcurl for any active transfer. It might soon be added again.
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DEFAULT

69       NULL (no callback)
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PROTOCOLS

72       All
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EXAMPLE

75       static int sock_cb(CURL *e, curl_socket_t s, int what, void *cbp, void *sockp)
76       {
77         GlobalInfo *g = cbp;
78         SockInfo *fdp = sockp;
79
80         if(what == CURL_POLL_REMOVE) {
81           remsock(fdp);
82         }
83         else {
84           if(!fdp) {
85             addsock(s, e, what, g);
86           }
87           else {
88             setsock(fdp, s, e, what, g);
89           }
90         }
91         return 0;
92       }
93
94       main()
95       {
96         GlobalInfo setup;
97         /* ... use socket callback and custom pointer */
98         curl_multi_setopt(multi, CURLMOPT_SOCKETFUNCTION, sock_cb);
99         curl_multi_setopt(multi, CURLMOPT_SOCKETDATA, &setup);
100       }
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AVAILABILITY

103       Added in 7.15.4
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RETURN VALUE

106       Returns CURLM_OK.
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