## NAME

CURLOPT_OPENSOCKETFUNCTION - set callback for opening sockets

## 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;
     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 CURLSOCKTYPE_ACCEPT is for sockets created after accept() - such as when doing active FTP. Future versions of libcurl may support more purposes.

The clientp pointer contains whatever user-defined value set using the CURLOPT_OPENSOCKETDATA 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 will signal an unrecoverable error to libcurl and it will return CURLE_COULDNT_CONNECT from the function that triggered this callback. This return code can be used for IP address blacklisting.

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 to signal that it already is connected.

## DEFAULT

The default behavior is the equivalent of this:

       return socket(addr->family, addr->socktype, addr->protocol);

## PROTOCOLS

All

## EXAMPLE

## AVAILABILITY

Added in 7.17.1.

## RETURN VALUE

Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.

## SEE ALSO

CURLOPT_OPENSOCKETDATA CURLOPT_SOCKOPTFUNCTION CURLOPT_CLOSESOCKETFUNCTION

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