Re: socket bind always returns 0, why?

Geoff <geoff@invalid.invalid>
Tue, 27 May 2014 17:45:32 -0700
On Tue, 27 May 2014 10:27:58 -0700 (PDT), wrote:

The following code returns 0 from the bind, even when netstat clearly shows that the port is taken by another process, ie the following function will always return true. Why?

bool isPortAvailable( int port )
           SOCKET candidateSocket;

           if(( candidateSocket = socket( AF_INET, SOCK_STREAM, 0 )) == -1 )
               return false;

           struct sockaddr_in serverAddress;
           memset (&serverAddress, 0, sizeof (serverAddress));

           serverAddress.sin_family = AF_INET;
           serverAddress.sin_addr.s_addr = htonl( INADDR_ANY );
           serverAddress.sin_port = htons( port );

           if( ::bind( candidateSocket, (struct sockaddr*)&serverAddress, sizeof( serverAddress )) != 0 )
               closesocket( candidateSocket );
               return false;

           closesocket( candidateSocket );
           return true;

My first guess would be that the other process has the port on a
distinct IP address, your bind is to INADDR_ANY. This would let your
process have a port listening on which, IIRC, is distinct
from another process listening on for example. To prove
this guess correct, use the same IP address to which the other process
is bound and see if this function fails.

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