Tribblix: manual page: CURLOPT

CURLOPT_PREREQFUNCTION(3) Introduction to Library Functions

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)).

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
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 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).