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fix: detect a peer that vanishes without FIN or RST #6

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Merged
ralfbecher merged 1 commit into from
Sep 2, 2026
Merged

fix: detect a peer that vanishes without FIN or RST #6

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18 changes: 18 additions & 0 deletions src/TDSProxy/TDSConnection.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -482,6 +482,7 @@ public TDSConnection(TDSProxyService service,
// forward from inside to outside, because it seems ODBC and OLEDB clients assume their SSL layer will deliver them
// complete packets. Gross!
outsideClient.NoDelay = false;
EnableKeepAlive(outsideClient.Client);

_outsideEP = (IPEndPoint)outsideClient.Client.RemoteEndPoint;
_outsideClient = outsideClient;
Expand All @@ -492,13 +493,30 @@ public TDSConnection(TDSProxyService service,
_insideEP = insideEndPoint;
_insideClient = new TcpClient(_insideEP.AddressFamily) {NoDelay = false};
_insideClient.Connect(insideEndPoint);
EnableKeepAlive(_insideClient.Client);
_insideStream = _insideClient.GetStream();
_insideActiveStream = _insideStream; // Start with plain stream, may upgrade to SSL later
_serverTlsConfig = listener.ServerTlsConfig;

_processingTask = ProcessConnection();
}

/// <summary>
/// Turn on TCP keep-alive so a peer that disappears without FIN or RST is noticed.
/// A link that is cut rather than closed leaves a blocking read waiting forever:
/// nothing arrives, no error is raised, and the connection pair is stranded until the
/// process is restarted. With keep-alive the socket faults after roughly 90 seconds
/// (60s idle, then 3 probes 10s apart), the catch in ProcessConnection runs, and
/// Close() tears down BOTH legs — so the client is told as well.
/// </summary>
static void EnableKeepAlive(Socket socket)
{
socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.KeepAlive, true);
socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveTime, 60);
socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveInterval, 10);
socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveRetryCount, 3);
}

~TDSConnection()
{
if (_state != StateEnum.Closed)
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