curl-w32/docs/libcurl/opts/CURLOPT_OPENSOCKETFUNCTION.md

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---
c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_OPENSOCKETFUNCTION
Section: 3
Source: libcurl
See-also:
- CURLOPT_CLOSESOCKETFUNCTION (3)
- CURLOPT_OPENSOCKETFUNCTION (3)
- CURLOPT_SOCKOPTFUNCTION (3)
---
# NAME
CURLOPT_OPENSOCKETFUNCTION - callback for opening socket
# SYNOPSIS
~~~c
#include <curl/curl.h>
typedef enum {
CURLSOCKTYPE_IPCXN, /* socket created for a specific IP connection */
} curlsocktype;
struct curl_sockaddr {
int family;
int socktype;
int protocol;
unsigned int addrlen;
struct sockaddr addr;
};
curl_socket_t opensocket_callback(void *clientp,
curlsocktype purpose,
struct curl_sockaddr *address);
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_OPENSOCKETFUNCTION, opensocket_callback);
~~~
# DESCRIPTION
Pass a pointer to your callback function, which should match the prototype
shown above.
This callback function gets called by libcurl instead of the *socket(2)*
call. The callback's *purpose* argument identifies the exact purpose for
this particular socket. *CURLSOCKTYPE_IPCXN* is for IP based connections
and is the only purpose currently used in libcurl. Future versions of libcurl
may support more purposes.
The *clientp* pointer contains whatever user-defined value set using the
CURLOPT_OPENSOCKETDATA(3) function.
The callback gets the resolved peer address as the *address* argument and
is allowed to modify the address or refuse to connect completely. The callback
function should return the newly created socket or *CURL_SOCKET_BAD* in
case no connection could be established or another error was detected. Any
additional *setsockopt(2)* calls can of course be done on the socket at
the user's discretion. A *CURL_SOCKET_BAD* return value from the callback
function signals an unrecoverable error to libcurl and it returns
*CURLE_COULDNT_CONNECT* from the function that triggered this callback.
This return code can be used for IP address block listing.
If you want to pass in a socket with an already established connection, pass
the socket back with this callback and then use
CURLOPT_SOCKOPTFUNCTION(3) to signal that it already is connected.
# DEFAULT
The default behavior is the equivalent of this:
~~~c
return socket(addr->family, addr->socktype, addr->protocol);
~~~
# PROTOCOLS
All
# EXAMPLE
~~~c
/* make libcurl use the already established socket 'sockfd' */
static curl_socket_t opensocket(void *clientp,
curlsocktype purpose,
struct curl_sockaddr *address)
{
curl_socket_t sockfd;
sockfd = *(curl_socket_t *)clientp;
/* the actual externally set socket is passed in via the OPENSOCKETDATA
option */
return sockfd;
}
static int sockopt_callback(void *clientp, curl_socket_t curlfd,
curlsocktype purpose)
{
/* This return code was added in libcurl 7.21.5 */
return CURL_SOCKOPT_ALREADY_CONNECTED;
}
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode res;
extern int sockfd; /* the already connected one */
/* libcurl thinks that you connect to the host
* and port that you specify in the URL option. */
curl_easy_setopt(curl, CURLOPT_URL, "http://99.99.99.99:9999");
/* call this function to get a socket */
curl_easy_setopt(curl, CURLOPT_OPENSOCKETFUNCTION, opensocket);
curl_easy_setopt(curl, CURLOPT_OPENSOCKETDATA, &sockfd);
/* call this function to set options for the socket */
curl_easy_setopt(curl, CURLOPT_SOCKOPTFUNCTION, sockopt_callback);
res = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
}
~~~
# AVAILABILITY
Added in 7.17.1.
# RETURN VALUE
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.