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---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_PREREQFUNCTION
Section: 3
Source: libcurl
See-also:
- CURLINFO_PRIMARY_IP (3)
- CURLINFO_PRIMARY_PORT (3)
- CURLOPT_PREREQDATA (3)
Protocol:
- All
Added-in: 7.80.0
---
# NAME
CURLOPT_PREREQFUNCTION - user callback called when a connection has been
established, but before a request has been made.
# SYNOPSIS
~~~c
#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 pointer to a null-terminated 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 pointer to a null-terminated 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%
# EXAMPLE
~~~c
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%
# 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).
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