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CURLOPT_PREREQFUNCTION(3)  Library Functions Manual  CURLOPT_PREREQFUNCTION(3)

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	proto-
       type shown above.

       This function gets called by libcurl after a connection has been	estab-
       lished 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	estab-
       lished  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)).

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

       This function is	passed the following arguments:

       conn_primary_ip
	      A	 null-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	null-terminated	pointer	to a C string containing the originat-
	      ing IP for this connection. IPv6 addresses are represented with-
	      out 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 con-
	      nection. This can	be a TCP or a UDP port number depending	on the
	      protocol.

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

       clientp
	      The pointer you set with CURLOPT_PREREQDATA(3).

DEFAULT
       NULL

PROTOCOLS
       This functionality affects all supported	protocols

EXAMPLE
       struct priv {
	 void *custom;
       };

       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:%d\n", conn_primary_ip, conn_primary_port);
	 return	CURL_PREREQFUNC_OK;
       }

       int main(void)
       {
	 struct	priv prereq_data;
	 CURL *curl = curl_easy_init();
	 if(curl) {
	   curl_easy_setopt(curl, CURLOPT_PREREQFUNCTION, prereq_callback);
	   curl_easy_setopt(curl, CURLOPT_PREREQDATA, &prereq_data);
	   curl_easy_perform(curl);
	 }
       }

AVAILABILITY
       Added in	curl 7.80.0

RETURN VALUE
       curl_easy_setopt(3) returns a CURLcode indicating success or error.

       CURLE_OK	(0) means everything was OK, non-zero means an error occurred,
       see libcurl-errors(3).

SEE ALSO
       CURLINFO_PRIMARY_IP(3), CURLINFO_PRIMARY_PORT(3), CURLOPT_PREREQDATA(3)

libcurl				  2025-06-03	     CURLOPT_PREREQFUNCTION(3)

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