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)