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                     23: .TH CURLOPT_OPENSOCKETFUNCTION 3 "December 03, 2019" "libcurl 7.70.0" "curl_easy_setopt options"
                     24: 
                     25: .SH NAME
                     26: CURLOPT_OPENSOCKETFUNCTION \- set callback for opening sockets
                     27: .SH SYNOPSIS
                     28: .nf
                     29: #include <curl/curl.h>
                     30: 
                     31: typedef enum  {
                     32:   CURLSOCKTYPE_IPCXN,  /* socket created for a specific IP connection */
                     33: } curlsocktype;
                     34: 
                     35: struct curl_sockaddr {
                     36:   int family;
                     37:   int socktype;
                     38:   int protocol;
                     39:   unsigned int addrlen;
                     40:   struct sockaddr addr;
                     41: };
                     42: 
                     43: curl_socket_t opensocket_callback(void *clientp,
                     44:                                   curlsocktype purpose,
                     45:                                   struct curl_sockaddr *address);
                     46: 
                     47: CURLcode curl_easy_setopt(CURL *handle, CURLOPT_OPENSOCKETFUNCTION, opensocket_callback);
                     48: .SH DESCRIPTION
                     49: Pass a pointer to your callback function, which should match the prototype
                     50: shown above.
                     51: 
                     52: This callback function gets called by libcurl instead of the \fIsocket(2)\fP
                     53: call. The callback's \fIpurpose\fP argument identifies the exact purpose for
                     54: this particular socket. \fICURLSOCKTYPE_IPCXN\fP is for IP based connections
                     55: and is the only purpose currently used in libcurl. Future versions of libcurl
                     56: may support more purposes.
                     57: 
                     58: The \fIclientp\fP pointer contains whatever user-defined value set using the
                     59: \fICURLOPT_OPENSOCKETDATA(3)\fP function.
                     60: 
                     61: The callback gets the resolved peer address as the \fIaddress\fP argument and
                     62: is allowed to modify the address or refuse to connect completely. The callback
                     63: function should return the newly created socket or \fICURL_SOCKET_BAD\fP in
                     64: case no connection could be established or another error was detected. Any
                     65: additional \fIsetsockopt(2)\fP calls can of course be done on the socket at
                     66: the user's discretion.  A \fICURL_SOCKET_BAD\fP return value from the callback
                     67: function will signal an unrecoverable error to libcurl and it will return
                     68: \fICURLE_COULDNT_CONNECT\fP from the function that triggered this callback.
                     69: This return code can be used for IP address blacklisting.
                     70: 
                     71: If you want to pass in a socket with an already established connection, pass
                     72: the socket back with this callback and then use
                     73: \fICURLOPT_SOCKOPTFUNCTION(3)\fP to signal that it already is connected.
                     74: .SH DEFAULT
                     75: The default behavior is the equivalent of this:
                     76: .nf
                     77:    return socket(addr->family, addr->socktype, addr->protocol);
                     78: .fi
                     79: .SH PROTOCOLS
                     80: All
                     81: .SH EXAMPLE
                     82: .nf
                     83: /* make libcurl use the already established socket 'sockfd' */
                     84: 
                     85: static curl_socket_t opensocket(void *clientp,
                     86:                                 curlsocktype purpose,
                     87:                                 struct curl_sockaddr *address)
                     88: {
                     89:   curl_socket_t sockfd;
                     90:   sockfd = *(curl_socket_t *)clientp;
                     91:   /* the actual externally set socket is passed in via the OPENSOCKETDATA
                     92:      option */
                     93:   return sockfd;
                     94: }
                     95: 
                     96: static int sockopt_callback(void *clientp, curl_socket_t curlfd,
                     97:                             curlsocktype purpose)
                     98: {
                     99:   /* This return code was added in libcurl 7.21.5 */
                    100:   return CURL_SOCKOPT_ALREADY_CONNECTED;
                    101: }
                    102: 
                    103: curl = curl_easy_init();
                    104: if(curl) {
                    105:   /* libcurl will internally think that you connect to the host
                    106:    * and port that you specify in the URL option. */
                    107:   curl_easy_setopt(curl, CURLOPT_URL, "http://99.99.99.99:9999");
                    108:   /* call this function to get a socket */
                    109:   curl_easy_setopt(curl, CURLOPT_OPENSOCKETFUNCTION, opensocket);
                    110:   curl_easy_setopt(curl, CURLOPT_OPENSOCKETDATA, &sockfd);
                    111: 
                    112:   /* call this function to set options for the socket */
                    113:   curl_easy_setopt(curl, CURLOPT_SOCKOPTFUNCTION, sockopt_callback);
                    114: 
                    115:   res = curl_easy_perform(curl);
                    116: 
                    117:   curl_easy_cleanup(curl);
                    118: }
                    119: .fi
                    120: .SH AVAILABILITY
                    121: Added in 7.17.1.
                    122: .SH RETURN VALUE
                    123: Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
                    124: .SH "SEE ALSO"
                    125: .BR CURLOPT_OPENSOCKETDATA "(3), " CURLOPT_SOCKOPTFUNCTION "(3), "
                    126: .BR CURLOPT_CLOSESOCKETFUNCTION "(3), "