How can i detected that the channel is closed with nio async?

using nio, I can wait accept, read data, write data asynchronously.
now i make a server program, and want to dected if a socket is closed by client, how can i do this?
thanks.

TO: ejp
In TCP the only way you can detect a dead connection is to attempt to write to it.
Eventually this will fail probably with a SocketException 'connection reset'.When should this happen? I don't seem to get any expection. The socket is registered for read only but it never gets read for reading again. The appropriate selection key indicates it is writable, but I don't have it registered for write operation.
Isn't there any other way to get around those dead sockets without trying to write at them? This would be quite an overhead, since server has to send some check_alive message periodically...

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How can I detect that there is an internet connection?

How can I detect that there is an internet connection?
Peter Goossens

How can I detect that there is an internet connection?
Peter Goossens
Peter,
You might want to experiment with this. It's not perfect, but...
Class
Imports System.IO
Imports System.Net
Namespace InternetConnection
Public Class SiteInfo
Private _displayName As String
Private _connectionString As String
Private Sub New(ByVal name As String, _
ByVal connectionString As String)
_displayName = name.Trim
_connectionString = connectionString.Trim
End Sub
''' <summary>
''' Gets the connection string of this instance.
''' </summary>
''' <value></value>
''' <returns></returns>
''' <remarks></remarks>
Public ReadOnly Property ConnectionString() As String
Get
Return _connectionString
End Get
End Property
''' <summary>
''' Gets the display name of this instance.
''' </summary>
''' <value></value>
''' <returns></returns>
''' <remarks></remarks>
Public ReadOnly Property DisplayName() As String
Get
Return _displayName
End Get
End Property
''' <summary>
''' A method which will add a new site to your collection of SiteInfo.
''' </summary>
''' <param name="siList">Your generic List(Of SiteInfo).</param>
''' <param name="displayName">The display name for this new instance
''' of SiteInfo.</param>
''' <param name="connectionString">The connection string for this
''' new instance of SiteInfo.</param>
''' <remarks></remarks>
Public Shared Sub AddNew(ByRef siList As List(Of SiteInfo), _
ByVal displayName As String, _
ByVal connectionString As String)
Try
If siList Is Nothing Then
Throw New NullReferenceException("The collection of SiteInfo cannot be null.")
ElseIf String.IsNullOrEmpty(displayName) OrElse displayName.Trim = "" Then
Throw New ArgumentException("The display name cannot be null or empty.")
ElseIf String.IsNullOrEmpty(connectionString) OrElse connectionString.Trim = "" Then
Throw New ArgumentException("The connection string cannot be null or empty.")
Else
If siList.Count > 0 Then
Dim findDuplicate As IEnumerable(Of SiteInfo) = _
From si As SiteInfo In siList _
Where si.DisplayName.ToLower.Replace(" "c, "") = _
displayName.ToLower.Replace(" "c, "") AndAlso _
si.ConnectionString.ToLower.Replace(" "c, "") = _
connectionString.ToLower.Replace(" "c, "")
If findDuplicate.Count <> 0 Then
Throw New ArgumentException("This is a duplicate entry.")
Else
siList.Add(New SiteInfo(displayName, connectionString))
End If
Else
siList.Add(New SiteInfo(displayName, connectionString))
End If
End If
Catch ex As Exception
Throw
End Try
End Sub
''' <summary>
''' A method which will return a boolean value to indicate internet
''' connection status.
''' </summary>
''' <param name="siList">Your generic List(Of SiteInfo).</param>
''' <param name="displayName">The display name for the instance
''' of SiteInfo to use.</param>
''' <returns></returns>
''' <remarks></remarks>
Public Shared Function InternetIsConnected(ByVal siList As List(Of SiteInfo), _
ByVal displayName As String) As Boolean
Dim retVal As Boolean = False
Try
If siList Is Nothing Then
Throw New NullReferenceException("The collection of SiteInfo cannot be null.")
ElseIf siList.Count = 0 Then
Throw New ArgumentOutOfRangeException("Count", "The collection of SiteInfo cannot be empty.")
ElseIf String.IsNullOrEmpty(displayName) OrElse displayName.Trim = "" Then
Throw New ArgumentException("The display name cannot be null or empty.")
Else
Dim findInstance As IEnumerable(Of SiteInfo) = _
From si As SiteInfo In siList _
Where si.DisplayName.ToLower.Replace(" "c, "") = _
displayName.ToLower.Replace(" "c, "")
If findInstance.Count <> 1 Then
Throw New ArgumentException("This instance is not in the collection of SiteInfo.")
Else
retVal = TestConnection(findInstance.First.ConnectionString)
End If
End If
Catch ex As Exception
Throw
End Try
Return retVal
End Function
Private Shared Function TestConnection(ByVal url As String) As Boolean
Dim retVal As Boolean = False
Try
Dim request As WebRequest = WebRequest.Create(url)
Using response As HttpWebResponse = DirectCast(request.GetResponse, HttpWebResponse)
Using dataStream As Stream = response.GetResponseStream
Using reader As New StreamReader(dataStream)
Dim responseFromServer As String = reader.ReadToEnd()
retVal = True
End Using
End Using
End Using
Catch ex As WebException
retVal = True
Catch ex As Exception
retVal = False
End Try
Return retVal
End Function
End Class
End Namespace
Example Usage
Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, _
ByVal e As System.EventArgs) _
Handles MyBase.Load
Dim siList As New List(Of InternetConnection.SiteInfo)
InternetConnection.SiteInfo.AddNew(siList, _
"Test1", _
"http://dev.virtualearth.net/REST/v1/Locations/37221?o=xml")
InternetConnection.SiteInfo.AddNew(siList, _
"Test2", _
"nothing here")
InternetConnection.SiteInfo.AddNew(siList, "Test3", _
"www.google.com")
InternetConnection.SiteInfo.AddNew(siList, "Test4", _
"http://fls-online.com")
' This will return true:
Dim bool1 As Boolean = _
InternetConnection.SiteInfo.InternetIsConnected(siList, _
"Test1")
' This will return false:
Dim bool2 As Boolean = _
InternetConnection.SiteInfo.InternetIsConnected(siList, _
"Test2")
' This will return false:
Dim bool3 As Boolean = _
InternetConnection.SiteInfo.InternetIsConnected(siList, _
"Test3")
' This will return true:
Dim bool4 As Boolean = _
InternetConnection.SiteInfo.InternetIsConnected(siList, _
"Test4")
Stop
End Sub
End Class
Let me know your results please?
Still lost in code, just at a little higher level.

Async tcp client and server. How can I determine that the client or the server is no longer available?

Hello. I would like to write async tcp client and server. I wrote this code but a have a problem, when I call the disconnect method on client or stop method on server. I can't identify that the client or the server is no longer connected.
I thought I will get an exception if the client or the server is not available but this is not happening.
private async void Process()
try
while (true)
var data = await this.Receive();
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How can I determine that the client or the server is no longer available?
Server
public class Server
private readonly Dictionary<IPEndPoint, TcpClient> clients = new Dictionary<IPEndPoint, TcpClient>();
private readonly List<CancellationTokenSource> cancellationTokens = new List<CancellationTokenSource>();
private TcpListener tcpListener;
private bool isStarted;
public event Action<string> NewMessage;
public async Task Start(int port)
this.tcpListener = TcpListener.Create(port);
this.tcpListener.Start();
this.isStarted = true;
while (this.isStarted)
var tcpClient = await this.tcpListener.AcceptTcpClientAsync();
var cts = new CancellationTokenSource();
this.cancellationTokens.Add(cts);
await Task.Factory.StartNew(() => this.Process(cts.Token, tcpClient), cts.Token, TaskCreationOptions.LongRunning, TaskScheduler.Default);
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this.isStarted = false;
foreach (var cancellationTokenSource in this.cancellationTokens)
cancellationTokenSource.Cancel();
foreach (var tcpClient in this.clients.Values)
tcpClient.GetStream().Close();
tcpClient.Close();
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try
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catch (Exception exception)
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try
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await stream.WriteAsync(buf, 0, buf.Length);
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var buf = new byte[length];
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public class Client
private TcpClient tcpClient;
private NetworkStream stream;
public event Action<string> NewMessage;
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try
this.tcpClient = new TcpClient();
await this.tcpClient.ConnectAsync(host, port);
this.stream = this.tcpClient.GetStream();
this.Process();
catch (Exception exception)
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this.tcpClient.Close();
catch (Exception exception)
public async void SendMessage(string message)
try
await this.Send(Encoding.ASCII.GetBytes(message));
catch (Exception exception)
private async void Process()
try
while (true)
var data = await this.Receive();
this.NewMessage.SafeInvoke(Encoding.ASCII.GetString(data));
catch (Exception exception)
private async Task Send(byte[] buf)
await this.stream.WriteAsync(BitConverter.GetBytes(buf.Length), 0, 4);
await this.stream.WriteAsync(buf, 0, buf.Length);
private async Task<byte[]> Receive()
var lengthBytes = new byte[4];
await this.stream.ReadAsync(lengthBytes, 0, 4);
var length = BitConverter.ToInt32(lengthBytes, 0);
var buf = new byte[length];
await this.stream.ReadAsync(buf, 0, buf.Length);
return buf;

Hi,
Have you debug these two applications? Does it go into the catch exception block when you close the client or the server?
According to my test, it will throw an exception when the client or the server is closed, just log the exception message in the catch block and then you'll get it:
private async void Process()
try
while (true)
var data = await this.Receive();
this.NewMessage.Invoke(Encoding.ASCII.GetString(data));
catch (Exception exception)
Console.WriteLine(exception.Message);
Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.
By the way, I don't know what the SafeInvoke method is, it may be an extension method, right? I used Invoke instead to test it.
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How can i detected that the channel is closed with nio async?

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