Tribblix: manual page: CURLOPT

CURLOPT_SOCKOPTFUNCTION(3) Introduction to Library Functions

NAME

CURLOPT_SOCKOPTFUNCTION - callback for setting socket options

SYNOPSIS

#include <curl/curl.h>

typedef enum {
CURLSOCKTYPE_IPCXN, /* socket created for a specific IP connection */
CURLSOCKTYPE_ACCEPT, /* socket created by accept() call */
CURLSOCKTYPE_LAST /* never use */
} curlsocktype;

#define CURL_SOCKOPT_OK 0
#define CURL_SOCKOPT_ERROR 1 /* causes libcurl to abort and return
CURLE_ABORTED_BY_CALLBACK */
#define CURL_SOCKOPT_ALREADY_CONNECTED 2

int sockopt_callback(void *clientp,
curl_socket_t curlfd,
curlsocktype purpose);

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SOCKOPTFUNCTION, sockopt_callback);

DESCRIPTION

Pass a pointer to your callback function, which should match the
prototype shown above.

When set, this callback function gets called by libcurl when the
socket has been created, but before the connect call to allow
applications to change specific socket options. The callback's
purpose argument identifies the exact purpose for this particular
socket:

CURLSOCKTYPE_IPCXN for actively created connections or since 7.28.0
CURLSOCKTYPE_ACCEPT for FTP when the connection was setup with
PORT/EPSV (in earlier versions these sockets were not passed to this
callback).

Future versions of libcurl may support more purposes. libcurl passes
the newly created socket descriptor to the callback in the curlfd
parameter so additional setsockopt() calls can be done at the user's
discretion.

The clientp pointer contains whatever user-defined value set using
the CURLOPT_SOCKOPTDATA(3) function.

Return CURL_SOCKOPT_OK from the callback on success. Return
CURL_SOCKOPT_ERROR from the callback function to signal an
unrecoverable error to the library and it closes the socket and
returns CURLE_COULDNT_CONNECT for CURLSOCKTYPE_IPCXN and
CURLE_ABORTED_BY_CALLBACK for CURLSOCKTYPE_ACCEPT.

The callback function may return CURL_SOCKOPT_ALREADY_CONNECTED for
CURLSOCKTYPE_IPCXN, to tell libcurl that the socket is already
connected and then libcurl does no attempt to connect. This allows an
application to pass in an already connected socket with
CURLOPT_OPENSOCKETFUNCTION(3) and then have this function make
libcurl not attempt to connect (again).

DEFAULT

NULL

PROTOCOLS

This functionality affects all supported protocols

EXAMPLE

/* 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)
{
return CURL_SOCKOPT_ALREADY_CONNECTED;
}

int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode result;
int sockfd; /* our custom file descriptor */
/* 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);

result = curl_easy_perform(curl);

curl_easy_cleanup(curl);
}
}

AVAILABILITY

Added in curl 7.16.0

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).