In Win32, is there a way to test if a socket is non-blocking?

Question

In Win32, is there a way to test if a socket is non-blocking?

Under POSIX systems, I\'d do something like the following:

int is_non_blocking(int sock         


        

Answer 1

I agree with the accepted answer, there is no official way to determine the blocking state of a socket on Windows. In case you get a socket from a third party (let's say, you are a TLS library and you get the socket from upper layer) you cannot decide if it is in blocking state or not.

Despite this I have a working, unofficial and limited solution for the problem which works for me for a long time.

I attempt to read 0 bytes from the socket. In case it is a blocking socket it will return 0, in case it is a non-blocking it will return -1 and GetLastError equals WSAEWOULDBLOCK.

int IsBlocking(SOCKET s)
{
    int r = 0;
    unsigned char b[1];
    r = recv(s, b, 0, 0);
    if (r == 0)
        return 1;
    else if (r == -1 && GetLastError() == WSAEWOULDBLOCK)
        return 0;
    return -1; /* In  case it is a connection socket (TCP) and it is not in connected state you will get here 10060 */
}

Caveats:

• Works with UDP sockets
• Works with connected TCP sockets
• Doesn't work with unconnected TCP sockets