Getting PID of peer socket on Windows

Question

I am writing a web proxy and when a request comes in (typically from the browser on the machine), I\'d like to also get the pid and any other requesting application. Is ther

Answer 1

What you are asking for is only possible if the client and server are running on the same machine.

When a client is connected to the proxy, the proxy can use getpeername() to query the socket for the remote client IP/Port (or use the IP/Port reported by accept()) and getsockname() to get its local server IP/Port. Then the proxy can use GetTcpTable2() (IPv4) or GetTcp6Table2() (IPv6) to retrieve a list of active TCP connections and loop through it looking for a connection that matches the IP/Port pairs. If found, the list entry will tell you the process ID that owns that connection.

For example:

DWORD GetClientPid(SOCKET client)
{
    DWORD pid = 0;

    sockaddr_in ServerAddr = {0};
    int ServerAddrSize = sizeof(ServerAddr);

    sockaddr_in ClientAddr = {0};
    int ClientAddrSize = sizeof(ClientAddr);

    if ((getsockname(client, (sockaddr*)&ServerAddr, &ServerAddrSize) == 0) &&
        (getpeername(client, (sockaddr*)&ClientAddr, &ClientAddrSize) == 0))
    {
        PMIB_TCPTABLE2 TcpTable = NULL;
        ULONG TcpTableSize = 0;
        ULONG result;

        do
        {
            result = GetTcpTable2(TcpTable, &TcpTableSize, TRUE);
            if (result != ERROR_INSUFFICIENT_BUFFER)
                break;

            LocalFree(TcpTable);
            TcpTable = (PMIB_TCPTABLE2) LocalAlloc(LMEM_FIXED, TcpTableSize);
        }
        while (TcpTable != NULL);

        if (result == NO_ERROR)
        {
            for (DWORD dw = 0; dw < TcpTable->dwNumEntries; ++dw)
            {
                PMIB_TCPROW2 row = &(TcpTable->table[dw]);

                if ((row->dwState == MIB_TCP_STATE_ESTAB) &&
                    (row->dwLocalAddr == ClientAddr.sin_addr.s_addr) &&
                    ((row->dwLocalPort & 0xFFFF) == ClientAddr.sin_port) &&
                    (row->dwRemoteAddr == ServerAddr.sin_addr.s_addr) &&
                    ((row->dwRemotePort & 0xFFFF) == ServerAddr.sin_port))
                {
                    pid = row->dwOwningPid;
                    break;
                }
            }
        }

        LocalFree(TcpTable);
    }

    return pid;
}

SOCKET client = accept(server, NULL, NULL);
if (client != INVALID_SOCKET)
{
    DWORD ClientPid = GetClientPid(client);
    ...
}