NAME

       CURLOPT_PREREQFUNCTION  -  user  callback  called  when  a  connection has been established, but before a
       request has been made.

SYNOPSIS

       #include <curl/curl.h>

       /* These are the return codes for the pre-request callback. */
       #define CURL_PREREQFUNC_OK 0
       #define CURL_PREREQFUNC_ABORT 1 /* fail the entire transfer */

       int prereq_callback(void *clientp,
                           char *conn_primary_ip,
                           char *conn_local_ip,
                           int conn_primary_port,
                           int conn_local_port);

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PREREQFUNCTION, prereq_callback);

DESCRIPTION

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

       This function gets called by libcurl after a connection has been established or  a  connection  has  been
       reused  (including  any  SSL handshaking), but before any request is actually made on the connection. For
       example, for HTTP, this callback is called once a connection has been  established  to  the  server,  but
       before a GET/HEAD/POST/etc request has been sent.

       This  function  may  be  called  multiple  times  if redirections are enabled and are being followed (see
       CURLOPT_FOLLOWLOCATION(3)).

       This function is passed the following information:

       conn_primary_ip
              A nul-terminated pointer to a C string containing the primary IP of the remote server  established
              with  this  connection.  For  FTP,  this  is the IP for the control connection. IPv6 addresses are
              represented without surrounding brackets.

       conn_local_ip
              A nul-terminated pointer to a C string containing the originating IP  for  this  connection.  IPv6
              addresses are represented without surrounding brackets.

       conn_primary_port
              The  primary  port number on the remote server established with this connection.  For FTP, this is
              the port for the control connection. This can be a TCP or a UDP port number  dependending  on  the
              protocol.

       conn_local_port
              The  originating  port  number  for  this  connection.  This  can  be  a  TCP or a UDP port number
              dependending on the protocol.

       clientp is the pointer you set with CURLOPT_PREREQDATA(3).

       The callback function must return CURL_PREREQFUNC_OK on success, or CURL_PREREQFUNC_ABORT  to  cause  the
       transfer to fail.

DEFAULT

       By default, this is NULL and unused.

PROTOCOLS

       ALL

EXAMPLE

       static int prereq_callback(void *clientp,
                                  char *conn_primary_ip,
                                  char *conn_local_ip,
                                  int conn_primary_port,
                                  int conn_local_port)
       {
         printf("Connection made to %s:%s\n", conn_primary_ip, conn_primary_port);
         return CURL_PREREQFUNC_OK;
       }

       {
         struct data prereq_data;
         curl_easy_setopt(CURL *handle, CURLOPT_PREREQFUNCTION, prereq_callback);
         curl_easy_setopt(CURL *handle, CURLOPT_PREREQDATA, &prereq_data);
       }

AVAILABILITY

       Added in 7.80.0

RETURN VALUE

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

SEE ALSO

       CURLOPT_PREREQDATA(3)

libcurl 7.81.0                                  November 04, 2021                      CURLOPT_PREREQFUNCTION(3)