windows - Finding TCP ports used by application

Question

All right, so I'm extending my company's flexlm vendor daemon to be a little bit more revealing to client applications.

I need to be able to find out what port lmgrd is listening on before clients connect. The API documentation seems to be rather barren, and I believe they keep most of their code in a compiled form so I can't just look at their source.

Is it possible to call upon the awesome power of the Windows API to find out what ports a particular process is using? If Process Explorer from Sysinternals can do it, I should be able to, right? What would be some sample code for this?

It needs to support Windows XP and higher since many of our clients have yet to upgrade.

I should note that it turns out FLEX has support for pulling the port from the license file. I don't have the code in front of me, but know that this isn't the best way to find out what ports your vendor daemon/lmgrd is running.

Answer 1

GetTcpTable2 -- see below

GetTcpTable2 function

The GetTcpTable function retrieves the IPv4 TCP connection table.

This will fill in a MIB_TCPTABLE structure.

typedef struct _MIB_TCPTABLE {
  DWORD      dwNumEntries;
  MIB_TCPROW table[ANY_SIZE];
} MIB_TCPTABLE, *PMIB_TCPTABLE;

And now the MIB_TCPROW

typedef struct _MIB_TCPROW {
  DWORD dwState;
  DWORD dwLocalAddr;
  DWORD dwLocalPort;
  DWORD dwRemoteAddr;
  DWORD dwRemotePort;
} MIB_TCPROW, *PMIB_TCPROW;

IMPORTANT:

You need to use GetTcpTable2 in order to get the corresponding PID associated as well.

typedef struct _MIB_TCPROW2 {
  DWORD                        dwState;
  DWORD                        dwLocalAddr;
  DWORD                        dwLocalPort;
  DWORD                        dwRemoteAddr;
  DWORD                        dwRemotePort;
  DWORD                        dwOwningPid;
  TCP_CONNECTION_OFFLOAD_STATE dwOffloadState;
} MIB_TCPROW2, *PMIB_TCPROW2;

dwOwningPid