CODEWITHSUNDEEP
c#.netnetwork-programmingsocketstcp
Nate
Nate

Reputation: 30636

Determine if a server is listening on a given port

I need to poll a server, which is running some propriatary software, to determine if this service is running. Using wireshark, I've been able to narrow down the TCP port its using, but it appears that the traffic is encrypted.

In my case, its a safe bet that if the server is accepting connections (i.e. telnet serverName 1234) the service is up and all is OK. In other words, I don't need do any actual data exchange, just open a connection and then safely close it.

I'm wondering how I can emulate this with C# and Sockets. My network programming basically ends with WebClient, so any help here is really appreciated.

Upvotes: 7

Views: 22274

Answers (4)

ZaChickster
ZaChickster

Reputation: 429

I've used the following code. There is one caveat ... in a high transaction environment, the client's available ports may run out as the sockets are not released by the OS at the same rate they are released by the .NET code.

If anyone's got a better idea, please post. I've seen snowball issues arise where the server can no longer make outgoing connections. I'm working on a better solution ...

public static bool IsServerUp(string server, int port, int timeout)
    {
        bool isUp;

        try
        {
            using (TcpClient tcp = new TcpClient())
            {
                IAsyncResult ar = tcp.BeginConnect(server, port, null, null);
                WaitHandle wh = ar.AsyncWaitHandle;

                try
                {
                    if (!wh.WaitOne(TimeSpan.FromMilliseconds(timeout), false))
                    {
                        tcp.EndConnect(ar);
                        tcp.Close();
                        throw new SocketException();
                    }

                    isUp = true;
                    tcp.EndConnect(ar);
                }
                finally
                {
                    wh.Close();
                }
            } 
        }
        catch (SocketException e)
        {
            LOGGER.Warn(string.Format("TCP connection to server {0} failed.", server), e);
            isUp = false;
        }

        return isUp;

Upvotes: 2

ChaosPandion
ChaosPandion

Reputation: 78242

The process is actually very simple.

using (var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
{
    try
    {
        socket.Connect(host, port);
    }
    catch (SocketException ex)
    {
        if (ex.SocketErrorCode == SocketError.ConnectionRefused) 
        {
            // ...
        }
    }
}

Upvotes: 10

Phil Lamb
Phil Lamb

Reputation: 1437

Just use TcpClient try to connect to the server, TcpClient.Connect will throw an exception if the connection fails.

bool IsListening(string server, int port)
{
    using(TcpClient client = new TcpClient())
    {
        try
        {
            client.Connect(server, port);
        }
        catch(SocketException)
        {
            return false;
        }
        client.Close();
        return true;
    }
}

Upvotes: 4

compie
compie

Reputation: 10526

Use the TcpClient class to connect the server.

Upvotes: 0

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