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.TH CURLOPT_OPENSOCKETFUNCTION 3 "16 Jun 2014" "libcurl 7.37.0" "curl_easy_setopt options"
.SH NAME
CURLOPT_OPENSOCKETFUNCTION \- set callback for opening sockets
.SH SYNOPSIS
.nf
#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);
.SH 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 \fIsocket(2)\fP
call. The callback's \fIpurpose\fP argument identifies the exact purpose for
this particular socket: \fICURLSOCKTYPE_IPCXN\fP is for IP based connections
and \fICURLSOCKTYPE_ACCEPT\fP is for sockets created after accept() - such as
when doing active FTP. Future versions of libcurl may support more
purposes.

The \fIclientp\fP pointer contains whatever user-defined value set using the
\fICURLOPT_OPENSOCKETDATA(3)\fP function.

The callback gets the resolved peer address as the \fIaddress\fP argument and
is allowed to modify the address or refuse to connect completely. The callback
function should return the newly created socket or \fICURL_SOCKET_BAD\fP in
case no connection could be established or another error was detected. Any
additional \fIsetsockopt(2)\fP calls can of course be done on the socket at
the user's discretion.  A \fICURL_SOCKET_BAD\fP return value from the callback
function will signal an unrecoverable error to libcurl and it will return
\fICURLE_COULDNT_CONNECT\fP 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
\fICURLOPT_SOCKOPTFUNCTION(3)\fP to signal that it already is connected.
.SH DEFAULT
The default behavior is the equivalent of this:
.nf
   return socket(addr->family, addr->socktype, addr->protocol);
.fi
.SH PROTOCOLS
All
.SH EXAMPLE
.SH AVAILABILITY
Added in 7.17.1.
.SH RETURN VALUE
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
.SH "SEE ALSO"
.BR CURLOPT_OPENSOCKETDATA "(3), " CURLOPT_SOCKOPTFUNCTION "(3), "
.BR CURLOPT_CLOSESOCKETFUNCTION "(3), "