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Hello,

I have a tcplistener and a tcpclient. If the client computer went down for some reason, what would be the best way to handle disconnections.

Thanks in advance,

Minko

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Since marked this solved, here is a concise, practical checklist and a couple of small VB.NET snippets that show the reliable ways to detect and handle a client disconnect when using TcpListener/TcpClient.

Prefer detecting end-of-stream rather than checking Connected: a NetworkStream.Read that returns 0 bytes means the remote closed the connection gracefully (NetworkStream.Read docs). Non-blocking detection can use the socket Poll + Available check; Poll(..., SelectMode.SelectRead) with Available = 0 is a common indicator of a disconnect (Socket.Poll docs). Do not rely on Socket.Connected alone because it can be stale (Socket.Connected docs).

Minimal VB.NET examples:

' read-end detection
Dim bytes = stream.Read(buffer, 0, buffer.Length)
If bytes = 0 Then
    ' client closed connection
    client.Close()
End If
' poll + available (non-blocking)
If client.Client.Poll(1000, SelectMode.SelectRead) AndAlso client.Client.Available = 0 Then
    ' treat as disconnected
End If

Also:

  • Catch SocketException and IOException around reads/writes; treat these as disconnection or network error signals.
  • Use short read timeouts or an application-level heartbeat/ping (send a small message periodically and expect a response) for faster detection across NATs/firewalls.
  • If you want OS-level detection, enable TCP keep-alive via SetSocketOption, but prefer an app heartbeat for predictable timing (Socket.SetSocketOption docs).

Always close and dispose sockets and cancel any background loops when a disconnect is detected.

Member Avatar for Minko

I managed to sort this out so I will mark this as solved.

Minko

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