curl/docs/libcurl/opts/CURLOPT_PREREQFUNCTION.md
Daniel Stenberg eefcc1bda4
docs: introduce "curldown" for libcurl man page format
curldown is this new file format for libcurl man pages. It is markdown
inspired with differences:

- Each file has a set of leading headers with meta-data
- Supports a small subset of markdown
- Uses .md file extensions for editors/IDE/GitHub to treat them nicely
- Generates man pages very similar to the previous ones
- Generates man pages that still convert nicely to HTML on the website
- Detects and highlights mentions of curl symbols automatically (when
  their man page section is specified)

tools:

- cd2nroff: converts from curldown to nroff man page
- nroff2cd: convert an (old) nroff man page to curldown
- cdall: convert many nroff pages to curldown versions
- cd2cd: verifies and updates a curldown to latest curldown

This setup generates .3 versions of all the curldown versions at build time.

CI:

Since the documentation is now technically markdown in the eyes of many
things, the CI runs many more tests and checks on this documentation,
including proselint, link checkers and tests that make sure we capitalize the
first letter after a period...

Closes #12730
2024-01-23 00:29:02 +01:00

125 lines
3.3 KiB
Markdown

---
c: Copyright (C) Daniel Stenberg, <daniel.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)
---
# 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.
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
By default, this is NULL and unused.
# PROTOCOLS
ALL
# 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
Added in 7.80.0
# RETURN VALUE
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.