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How to reconnect to a socket gracefully

I have a following method that connects to an end point when my program starts
ChannelSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
var remoteIpAddress = IPAddress.Parse(ChannelIp);
ChannelEndPoint = new IPEndPoint(remoteIpAddress, ChannelPort);
ChannelSocket.Connect(ChannelEndPoint);
I also have a timer that is set to trigger every 60 seconds to call CheckConnectivity, that attempts to send an arbitrary byte array to the end point to make sure that the connection is still alive, and if the send fails, it will attempt to reconnect.
public bool CheckConnectivity(bool isReconnect)
{
if (ChannelSocket != null)
{
var blockingState = ChannelSocket.Blocking;
try
{
var tmp = new byte[] { 0 };
ChannelSocket.Blocking = false;
ChannelSocket.Send(tmp);
}
catch (SocketException e)
{
try
{
ReconnectChannel();
}
catch (Exception ex)
{
return false;
}
}
}
else
{
ConnectivityLog.Warn(string.Format("{0}:{1} is null!", ChannelIp, ChannelPort));
return false;
}
return true;
}
private void ReconnectChannel()
{
try
{
ChannelSocket.Shutdown(SocketShutdown.Both);
ChannelSocket.Disconnect(true);
ChannelSocket.Close();
}
catch (Exception ex)
{
ConnectivityLog.Error(ex);
}
ChannelSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
var remoteIpAddress = IPAddress.Parse(ChannelIp);
ChannelEndPoint = new IPEndPoint(remoteIpAddress, ChannelPort);
ChannelSocket.Connect(ChannelEndPoint);
Thread.Sleep(1000);
if (ChannelSocket.Connected)
{
ConnectivityLog.Info(string.Format("{0}:{1} is reconnected!", ChannelIp, ChannelPort));
}
else
{
ConnectivityLog.Warn(string.Format("{0}:{1} failed to reconnect!", ChannelIp, ChannelPort));
}
}
So how I'd test the above, is to physically unplug the LAN cable from my ethernet device, allowing my code to attempt to reconnect (which fails obviously) and reconnect back the LAN cable.
However, even after reconnecting the LAN cable (able to ping), ChannelSocket.Connect(ChannelEndPoint) in my Reconnect method always throws this error
No connection could be made because the target machine actively refused it 192.168.168.160:4001
If I were to restart my whole application, it connects successfully. How can I tweak my reconnect method such that I don't have to restart my application to reconnect back to my Ethernet device?

If an application closes a TCP/IP port, the protocol dictates that the port stays in TIME_WAIT state for a certain duration (default of 240 seconds on a windows machine).
See following for references -
http://en.wikipedia.org/wiki/Transmission_Control_Protocol
http://support.microsoft.com/kb/137984
http://www.pctools.com/guides/registry/detail/878/
What this means for your scenario - is that you cannot expect to close (willingly or unwillingly) and re-open a port within a short period of time (even several seconds). Despite some registry tweaks which you'd find on internet.. the port will be un-available for any app on windows, for a minimum of 30 seconds. (Again, default is 240 seconds)
Your options - here are limited...
From the documentation at http://msdn.microsoft.com/en-us/library/4xzx2d41(v=vs.110).aspx -
"If the socket has been previously disconnected, then you cannot use this (Connect) method to restore the connection. Use one of the asynchronous BeginConnect methods to reconnect. This is a limitation of the underlying provider."
The reason why documentation suggests that BeginConnect must be used is what I mentioned above.. It simply doesn't expect to be able to establish the connection right away.. and hence the only option is to make the call asynchronously, and while you wait for the connection to get established in several minutes, do expect and plan for it to fail. Essentially, likely not an ideal option.
If the long wait and uncertainty is not acceptable, then your other option is to somehow negotiate a different port between the client and server. (For example, in theory you could use UDP, which is connectionless, to negotiate the new TCP port you'd re-establish the connection on). Communication using UDP, in theory of course, itself is not guaranteed by design. But should work most of the times (Today, networking in typical org is not that flaky / unreliable). Subjective to scenario / opinion, perhaps better than option 1, but more work and smaller but finite chance of not working.
As suggested in one of the comments, this is where application layer protocols like http and http services have an advantage. Use them, instead of low level sockets, if you can.
If acceptable, this is the best option to go with.
(PS - FYI - For HTTP, there is a lot of special handling built into OS, including windows - For example, there is a dedicated driver Http.sys, specially for dealing with multiple apps trying to listen on same port 80 etc.. The details here are a topic for another time.. point is, there is lots of goodness and hard work done for you, when it comes to HTTP)

Maybe you should switch to a higher abstraction class, which better deals with all these nifty little details?
I'm going to use for these network connections the TcpListener and TcpClient classes. The usage of these classes is quite easy:
The client side:
public void GetInformationAsync(IPAddress ipAddress)
{
_Log.Info("Start retrieving informations from address " + ipAddress + ".");
var tcpClient = new TcpClient();
tcpClient.BeginConnect(ipAddress, _PortNumber, OnTcpClientConnected, tcpClient);
}
private void OnTcpClientConnected(IAsyncResult asyncResult)
{
try
{
using (var tcpClient = (TcpClient)asyncResult.AsyncState)
{
tcpClient.EndConnect(asyncResult);
var ipAddress = ((IPEndPoint)tcpClient.Client.RemoteEndPoint).Address;
var stream = tcpClient.GetStream();
stream.ReadTimeout = 5000;
_Log.Debug("Connection established to " + ipAddress + ".");
var formatter = new BinaryFormatter();
var information = (MyInformation)formatter.Deserialize(stream);
_Log.Info("Successfully retrieved information from address " + ipAddress + ".");
InformationAvailable.FireEvent(this, new InformationEventArgs(information));
}
}
catch (Exception ex)
{
_Log.Error("Error in retrieving informations.", ex);
return;
}
}
The server side:
public void Start()
{
ThrowIfDisposed();
if (_TcpServer != null;)
_TcpServer.Stop();
_TcpServer = new TcpListener(IPAddress.Any, _PortNumber);
_TcpServer.Start();
_TcpServer.BeginAcceptTcpClient(OnClientConnected, _TcpServer);
_Log.Info("Start listening for incoming connections on " + _TcpServer.LocalEndpoint + ".");
}
private void OnClientConnected(IAsyncResult asyncResult)
{
var tcpServer = (TcpListener)asyncResult.AsyncState;
IPAddress address = IPAddress.None;
try
{
if (tcpServer.Server != null
&& tcpServer.Server.IsBound)
tcpServer.BeginAcceptTcpClient(OnClientConnected, tcpServer);
using (var client = tcpServer.EndAcceptTcpClient(asyncResult))
{
address = ((IPEndPoint)client.Client.RemoteEndPoint).Address;
_Log.Debug("Client connected from address " + address + ".");
var formatter = new BinaryFormatter();
var informations = new MyInformation()
{
// Initialize properties with desired values.
};
var stream = client.GetStream();
formatter.Serialize(stream, description);
_Log.Debug("Sucessfully serialized information into network stream.");
}
}
catch (ObjectDisposedException)
{
// This normally happens, when the server will be stopped
// and their exists no other reliable way to check this state
// before calling EndAcceptTcpClient().
}
catch (Exception ex)
{
_Log.Error(String.Format("Cannot send instance information to {0}.", address), ex);
}
}
This code works and doesn't make any problems with a lost connection on the client side. If you have a lost connection on the server side you have to re-establish the listener, but that's another story.

In ReconnectChannel just dispose the ChannelSocket object.
try
{
`//ChannelSocket.Shutdown(SocketShutdown.Both);
//ChannelSocket.Disconnect(true);
//ChannelSocket.Close();
ChannelSocket.Dispose();`
}
This is working for me. Let me know if it doesn't work for you.

Ping to server for external connectivity

I have a c# application that has a module for checks the server connection. The relevant code is like the following:
private void PingCheck(string hostName)
{
using (var p = new Ping())
{
try
{
var pr = p.Send(hostName, 2000);
if (pr.Status != IPStatus.Success)
{
log.ErrorFormat("Ping error! Host = {0}, Ping status = {1}", hostName, pr.Status.ToString());
}
}
catch (Exception exc)
{
log.Error("Ping error!", exc);
}
}
}
We have deployed this application to our server that is inside the same network as the target machine. That's why this method checks internal connectivity. Is there any way to check server external connectivity? Because sometimes server connection is available in our network although connection from external network is down. How can I achieve this?

No, there is not, since you are on the server itself.
Either ping some resource outside to check connectivity, or use the NetworkInterface.GetIsNetworkAvailable() method to check whether there is an active connection.

Check if a port is open

I can't seem to find anything that tells me if a port in my router is open or not.
Is this even possible?
The code I have right now doesn't really seem to work...
private void ScanPort()
{
string hostname = "localhost";
int portno = 9081;
IPAddress ipa = (IPAddress) Dns.GetHostAddresses(hostname)[0];
try
{
System.Net.Sockets.Socket sock =
new System.Net.Sockets.Socket(System.Net.Sockets.AddressFamily.InterNetwork,
System.Net.Sockets.SocketType.Stream,
System.Net.Sockets.ProtocolType.Tcp);
sock.Connect(ipa, portno);
if (sock.Connected == true) // Port is in use and connection is successful
MessageBox.Show("Port is Closed");
sock.Close();
}
catch (System.Net.Sockets.SocketException ex)
{
if (ex.ErrorCode == 10061) // Port is unused and could not establish connection
MessageBox.Show("Port is Open!");
else
MessageBox.Show(ex.Message);
}
}

Try this:
using(TcpClient tcpClient = new TcpClient())
{
try {
tcpClient.Connect("127.0.0.1", 9081);
Console.WriteLine("Port open");
} catch (Exception) {
Console.WriteLine("Port closed");
}
}
You should probably change 127.0.0.1 to something like 192.168.0.1 or whatever your router's IP address is.

A better solution where you can even specify a timeout:
using System;
using System.Net.Sockets;
// ...
bool IsPortOpen(string host, int port, TimeSpan timeout)
{
try
{
using(var client = new TcpClient())
{
var result = client.BeginConnect(host, port, null, null);
var success = result.AsyncWaitHandle.WaitOne(timeout);
client.EndConnect(result);
return success;
}
}
catch
{
return false;
}
}
And, in F#:
open System
open System.Net.Sockets
let isPortOpen (host: string) (port: int) (timeout: TimeSpan): bool =
try
use client = new TcpClient()
let result = client.BeginConnect(host, port, null, null)
let success = result.AsyncWaitHandle.WaitOne timeout
client.EndConnect result
success
with
| _ -> false
let available = isPortOpen "stackoverflow.com" 80 (TimeSpan.FromSeconds 10.)
printf "Is stackoverflow available? %b" available

There is no way to know if the port is forwarded in your router, except if there is a program listening on that port.
As you may see in the Clinton answer, the .Net class being used is TcpClient and that is because you are using a TCP socket to connect to. That is the way operating systems make connections: using a socket. However, a router just forwards the packets (layer 3 of the OSI Model) in or out. In your case, what your router is doing is called: NAT. It is one public IP shared by a one or more private IPs. That´s why you are making a port forwarding.
There may be a lot of routers in the path of the packets, and you will never know what had happened.
Let´s imagine you are sending a letter in the traditional way. Perhaps you can write in the letter that the receiver must answer, in order to check he/she is there (you and the receiver are the sockets). If you receive an answer you will be sure he/she is there, but if you don´t receive anything you don´t know if the mailman (in your case the router) forgot to deliver the letter, or the receiver hadn´t answered. You would also never know if the mailman has asked a friend to deliver that letter. Moreover, the mailman won´t open the letter in order to know he/she may answer because you are waiting for a reply. All you may do is wait some time to receive the answer. If you don´t receive anything in that period you will assume that the receiver isn´t where you sent the letter. That is a "timeout".
I saw an answer mentioning the nmap software. It´s really a very good and complex soft, but I think it will work in the same way. If there is no app listening in that port, there is no way to know if it is open or not.
Please, let me know if I was clear.

If you're connecting to the loopback adapter — localhost or 127.0.0.1 (there's no place like 127.0.0.1!), you're unlikely to ever go out to the router. The OS is smart enough to recognize that it's a special address. Dunno if that holds true as well if you actually specify your machine's "real" IP address.
See also this question: What is the purpose of the Microsoft Loopback Adapter?
Also note that running traceroute localhost (tracert localhost in Windows) shows that the only network node involved is your own machine. The router is never involved.

Other than BeginConnect you can also use ConnectAsync (added in .NET Framework 4.5 I think?).
TcpClient client = null;
try {
client = new TcpClient();
var task = client.ConnectAsync(host, port);
if (task.Wait(timeout)) {//if fails within timeout, task.Wait still returns true.
if (client.Connected) {
// port reachable
}
else
// connection refused probably
}
else
// timed out
}
catch (Exception ex) {
// connection failed
}
finally {
client.Close();
}
Full project is here because paping refuses to run and I couldn't find another "ping host:port" tool to my likes.

A port forward on the router cannot be tested from inside the LAN, you need to connect from the WAN (internet) side to see if a port forward is working or not.
Several internet sites offer services to check if a port is open:
What's My IP Port Scanner
GRC | ShieldsUP!
If you want to check with your own code, then you need to make sure the TCP/IP connection is rerouted via an external proxy or setup a tunnel. This has nothing to do with your code, it's basic networking 101.

public static bool PortInUse(int port)
{
bool inUse = false;
IPGlobalProperties ipProperties = IPGlobalProperties.GetIPGlobalProperties();
IPEndPoint [] ipEndPoints = ipProperties.GetActiveTcpListeners();
foreach(IPEndPoint endPoint in ipEndPoints)
{
if(endPoint.Port == port)
{
inUse = true;
break;
}
}
return inUse;
}

For me, I needed something blocking until the connection to the port is available or after a certain amount of retries. So, I figured out this code:
public bool IsPortOpen(string host, int port, int timeout, int retry)
{
var retryCount = 0;
while (retryCount < retry)
{
if (retryCount > 0)
Thread.Sleep(timeout);
try
{
using (var client = new TcpClient())
{
var result = client.BeginConnect(host, port, null, null);
var success = result.AsyncWaitHandle.WaitOne(timeout);
if (success)
return true;
client.EndConnect(result);
}
}
catch
{
// ignored
}
finally { retryCount++; }
}
return false;
}
Hope this helps!

also you can use ConnectAsync like
public async Task<bool> IsIPAndPortOpen(string hostOrIPAddress, int port, TimeSpan timeOut)
{
try
{
using (var client = new TcpClient())
{
var ct = new CancellationTokenSource(timeOut).Token;
await client.ConnectAsync(hostOrIPAddress, port, ct);
return true;
}
}
catch
{
return false;
}
}

public string GetAvailablePort()
{int startingPort=1000;
string portnumberinformation = string.Empty;
IPEndPoint[] endPoints;
List<int> portArray = new List<int>();
IPGlobalPr`enter code here`operties properties = IPGlobalProperties.GetIPGlobalProperties();`enter code here`
//getting active tcp listners
endPoints = properties.GetActiveTcpListeners();
portArray.AddRange(from n in endPoints
where n.Port >= startingPort
select n.Port);
portArray.Sort();
for (int i = 0; i < portArray.Count; i++)
{
if (check condition)
{
do somting
}
}
return portnumberinformation;
}

If it is Router the simplest way to check it through online services like
Port Checker
Port Forwarding Test
You can also try using telenet to chek wether port is accessible or not
telenet [ip-address] [port]

Problem with configuring and starting WCF service

I have a problem with configuration and starting WCF service.
In my application there is a method that starts service. Something like this
void Start(string protocol, string address, string port)
{
host = new ServiceHost(_myService,
new Uri(String.Format("{0}://{1}{2}/Sample", protocol, address, port)));
//...Some configuration (bindings, behaviors, etc.)
host.Open();
}
Let my computer has an IP 192.168.0.1. When I pass 'address' parameter with a value '192.168.0.2' an error occurred
"A TCP error (10049: The requested address is not valid in its context.)
occurred while listening on IP Endpoint=192.168.0.2:1234"
That's right because it's not my IP. But after that if I pass correct value (my real IP) I get the same error about IP 192.168.0.2! So I can't reconfigure and restart server without restarting application.
Why does it happen? How can I avoid such behavior?

Looks like WCF caches a socket object in class ExclusiveTCPTransportManager.
It's seems to be good solution for me:
public static class WCFBugWorkaround
{
public static bool IsConnectionPossible(this ServiceHost host)
{
try
{
foreach (var baseAddress in host.BaseAddresses)
{
IPAddress[] ipAddresses = Dns.GetHostAddresses(baseAddress.DnsSafeHost);
IPAddress ipAddr = ipAddresses.Where(e => e.AddressFamily == AddressFamily.InterNetwork).FirstOrDefault();
if (ipAddr == null)
{
return false;
}
using (Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
{
System.Net.IPEndPoint localEP = new IPEndPoint(ipAddr, baseAddress.Port);
s.Bind(localEP);
}
}
}
catch (Exception ex)
{
return false;
}
return true;
}
}
ServiceHost host = ...;
...
if (host.IsConnectionPossible())
{
host.Open();
}
Thank's to Francheska for showing me the right direction :)

I can't see from your question how you are adding the correct endpoint, but I suspect you are attempting to modify the endpoint address. With WCF services, you cannot make changes to the endpoint address after calling
host.Open();
because at this point the service is (if you have no errors) up and accepting requests from clients at the specified address and port number.
You need to create a new ServiceHost object with the correct endpoint address (and dispose of the old one) if you wish to host the service at a new address.
EDIT:
After playing around with the example solution you have posted, I have found a solution to the issue. I think something is going wrong because you are using the same port number for both tries (in the example solution I downloaded you don't specify this, so the port defaulted to 808). The error you are experiencing vanishes if you change your code as follows to specify a different port number in the base address for the 2nd try:
try
{
var host2 = CreateServiceHost("localhost:5432", serviceImpl);
Console.WriteLine("#2, config: " + host2.BaseAddresses.First().ToString());
host2.Open();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
There seems to be something buggy underneath WCF itself, probably on a socket level, where the port is somehow still unavailable after the first error with the incorrect IP.
I did a quick google and found this article where someone experienced a delay in reusing a port after closing a socket. If you always need to use the same port number, perhaps you could wait a certain amount of time for the port to become free again before trying to create the service host again.

Unable to read data from the transport connection: the connection was closed

The exception is Remoting Exception - Authentication Failure. The detailed message says "Unable to read data from the transport connection: the connection was closed."
I'm having trouble with creating two simple servers that can comunicate as remote objects in C#. ServerInfo is just a class I created that holds the IP and Port and can give back the address. It works fine, as I used it before, and I've debugged it. Also the server is starting just fine, no exception is thrown, and the channel is registered without problems. I'm using Forms to do the interfaces, and call some of the methods on the server, but didn't find any problems in passing the parameters from the FormsApplication to the server when debugging. All seems fine in that chapter.
public ChordServerProgram()
{
RemotingServices.Marshal(this, "PADIBook");
nodeInt = 0;
}
public void startServer()
{
try
{
serverChannel = new TcpChannel(serverInfo.Port);
ChannelServices.RegisterChannel(serverChannel, true);
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
}
I run two instances of this program. Then startNode is called on one of the instances of the application. The port is fine, the address generated is fine as well. As you can see, I'm using the IP for localhost, since this server is just for testing purposes.
public void startNode(String portStr)
{
IPAddress address = IPAddress.Parse("127.0.0.1");
Int32 port = Int32.Parse(portStr);
serverInfo = new ServerInfo(address, port);
startServer();
//node = new ChordNode(serverInfo,this);
}
Then, in the other istance, through the interface again, I call another startNode method, giving it a seed server to get information from. This is where it goes wrong. When it calls the method on the seedServer proxy it just got, a RemotingException is thrown, due to an authentication failure. (The parameter I'll want to get is the node, I'm just using the int to make sure the ChordNode class has nothing to do with this error.)
public void startNode(String portStr, String seedStr)
{
IPAddress address = IPAddress.Parse("127.0.0.1");
Int32 port = Int32.Parse(portStr);
serverInfo = new ServerInfo(address, port);
IPAddress addressSeed = IPAddress.Parse("127.0.0.1");
Int32 portSeed = Int32.Parse(seedStr);
ServerInfo seedInfo = new ServerInfo(addressSeed, portSeed);
startServer();
ChordServerProgram seedServer = (ChordServerProgram)Activator.GetObject(typeof(ChordServerProgram), seedInfo.GetFullAddress());
// node = new ChordNode(serverInfo,this);
int seedNode = seedServer.nodeInt;
// node.chordJoin(seedNode.self);
}

Try setting the ensureSecurity to false, and it should start working.
ChannelServices.RegisterChannel(serverChannel, false);

You've specified that security is a must on your Remoting server in startServer() with:
ChannelServices.RegisterChannel(serverChannel, true);
Yet the 'client' end does not specify security, hence the authorisation error. You need to specify tcp channel security on both ends unless the server security setting is set to 'false'. In your second startNode method you need to do the following before using Activator.GetObject, note no port specified on the TcpChannel unlike the server end:
TcpChannel ClientChan = new TcpChannel();
ChannelServices.RegisterChannel(ClientChan, true);
Furthermore, unless you're doing it in some code you haven't given us, you also do not seem to have registered a well known service type server side, although you say it's been working in the debugger so maybe that's not necessary in the case. See MSDN on RegisterWellKnownServiceType.