Provided by: libcurl4-doc_7.88.1-8ubuntu1_all bug


       CURLOPT_SOCKOPTFUNCTION - callback for setting socket options


       #include <curl/curl.h>

       typedef enum  {
         CURLSOCKTYPE_IPCXN,  /* socket created for a specific IP connection */
         CURLSOCKTYPE_ACCEPT, /* socket created by accept() call */
         CURLSOCKTYPE_LAST    /* never use */
       } curlsocktype;

       #define CURL_SOCKOPT_OK 0
       #define CURL_SOCKOPT_ERROR 1 /* causes libcurl to abort and return
                                       CURLE_ABORTED_BY_CALLBACK */

       int sockopt_callback(void *clientp,
                            curl_socket_t curlfd,
                            curlsocktype purpose);

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SOCKOPTFUNCTION, sockopt_callback);


       Pass a pointer to your callback function, which should match the prototype shown above.

       When  set, this callback function gets called by libcurl when the socket has been created,
       but before the connect call to allow applications to change specific socket  options.  The
       callback's purpose argument identifies the exact purpose for this particular socket:

       CURLSOCKTYPE_IPCXN  for  actively  created connections or since 7.28.0 CURLSOCKTYPE_ACCEPT
       for FTP when the connection was setup with PORT/EPSV (in earlier  versions  these  sockets
       were not passed to this callback).

       Future  versions  of  libcurl  may support more purposes. libcurl passes the newly created
       socket descriptor to the callback in the curlfd parameter so additional setsockopt() calls
       can be done at the user's discretion.

       The    clientp    pointer   contains   whatever   user-defined   value   set   using   the
       CURLOPT_SOCKOPTDATA(3) function.

       Return CURL_SOCKOPT_OK from the callback on success. Return  CURL_SOCKOPT_ERROR  from  the
       callback  function  to  signal an unrecoverable error to the library and it will close the
       socket and return CURLE_COULDNT_CONNECT.  Alternatively, the callback function can  return
       CURL_SOCKOPT_ALREADY_CONNECTED,  to  tell libcurl that the socket is already connected and
       then libcurl will not attempt to connect it. This allows an  application  to  pass  in  an
       already  connected  socket  with CURLOPT_OPENSOCKETFUNCTION(3) and then have this function
       make libcurl not attempt to connect (again).


       By default, this callback is NULL and unused.




       /* make libcurl use the already established socket 'sockfd' */

       static curl_socket_t opensocket(void *clientp,
                                       curlsocktype purpose,
                                       struct curl_sockaddr *address)
         curl_socket_t sockfd;
         sockfd = *(curl_socket_t *)clientp;
         /* the actual externally set socket is passed in via the OPENSOCKETDATA
            option */
         return sockfd;

       static int sockopt_callback(void *clientp, curl_socket_t curlfd,
                                   curlsocktype purpose)
         /* This return code was added in libcurl 7.21.5 */

       curl = curl_easy_init();
       if(curl) {
         /* libcurl will internally think that you connect to the host
          * and port that you specify in the URL option. */
         curl_easy_setopt(curl, CURLOPT_URL, "");
         /* call this function to get a socket */
         curl_easy_setopt(curl, CURLOPT_OPENSOCKETFUNCTION, opensocket);
         curl_easy_setopt(curl, CURLOPT_OPENSOCKETDATA, &sockfd);

         /* call this function to set options for the socket */
         curl_easy_setopt(curl, CURLOPT_SOCKOPTFUNCTION, sockopt_callback);

         res = curl_easy_perform(curl);



       Added in 7.16.0. The CURL_SOCKOPT_ALREADY_CONNECTED return code was added in 7.21.5.


       Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.