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                     23: .TH CURLOPT_SOCKOPTFUNCTION 3 "May 15, 2017" "libcurl 7.70.0" "curl_easy_setopt options"
                     24: 
                     25: .SH NAME
                     26: CURLOPT_SOCKOPTFUNCTION \- set callback for setting socket options
                     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_ACCEPT, /* socket created by accept() call */
                     34:   CURLSOCKTYPE_LAST    /* never use */
                     35: } curlsocktype;
                     36: 
                     37: #define CURL_SOCKOPT_OK 0
                     38: #define CURL_SOCKOPT_ERROR 1 /* causes libcurl to abort and return
                     39:                                 CURLE_ABORTED_BY_CALLBACK */
                     40: #define CURL_SOCKOPT_ALREADY_CONNECTED 2
                     41: 
                     42: int sockopt_callback(void *clientp,
                     43:                      curl_socket_t curlfd,
                     44:                      curlsocktype purpose);
                     45: 
                     46: CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SOCKOPTFUNCTION, sockopt_callback);
                     47: .SH DESCRIPTION
                     48: Pass a pointer to your callback function, which should match the prototype
                     49: shown above.
                     50: 
                     51: When set, this callback function gets called by libcurl when the socket has
                     52: been created, but before the connect call to allow applications to change
                     53: specific socket options. The callback's \fIpurpose\fP argument identifies the
                     54: exact purpose for this particular socket:
                     55: 
                     56: \fICURLSOCKTYPE_IPCXN\fP for actively created connections or since 7.28.0
                     57: \fICURLSOCKTYPE_ACCEPT\fP for FTP when the connection was setup with PORT/EPSV
                     58: (in earlier versions these sockets weren't passed to this callback).
                     59: 
                     60: Future versions of libcurl may support more purposes. libcurl passes the newly
                     61: created socket descriptor to the callback in the \fIcurlfd\fP parameter so
                     62: additional setsockopt() calls can be done at the user's discretion.
                     63: 
                     64: The \fIclientp\fP pointer contains whatever user-defined value set using the
                     65: \fICURLOPT_SOCKOPTDATA(3)\fP function.
                     66: 
                     67: Return \fICURL_SOCKOPT_OK\fP from the callback on success. Return
                     68: \fICURL_SOCKOPT_ERROR\fP from the callback function to signal an unrecoverable
                     69: error to the library and it will close the socket and return
                     70: \fICURLE_COULDNT_CONNECT\fP.
                     71: Alternatively, the callback function can return
                     72: \fICURL_SOCKOPT_ALREADY_CONNECTED\fP, to tell libcurl that the socket is
                     73: already connected and then libcurl will not attempt to connect it. This allows
                     74: an application to pass in an already connected socket with
                     75: \fICURLOPT_OPENSOCKETFUNCTION(3)\fP and then have this function make libcurl
                     76: not attempt to connect (again).
                     77: .SH DEFAULT
                     78: By default, this callback is NULL and unused.
                     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: .fi
                    119: .SH AVAILABILITY
                    120: Added in 7.16.0. The \fICURL_SOCKOPT_ALREADY_CONNECTED\fP return code was
                    121: added in 7.21.5.
                    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_SOCKOPTDATA "(3), " CURLOPT_OPENSOCKETFUNCTION "(3), "