Oliver Towers created TINKERPOP-2717:
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Summary: Gremlin.NET : WebSocketConnection does not check for
MessageType.Close, causing error InvalidOperationException: "Received data
deserialized into null object message. Cannot operate on it."
Key: TINKERPOP-2717
URL: https://issues.apache.org/jira/browse/TINKERPOP-2717
Project: TinkerPop
Issue Type: Bug
Components: dotnet
Affects Versions: 3.5.2, 3.4.13
Reporter: Oliver Towers
h2. Issue:
If the server sends a valid Close websocket message to the client, the client
will throw `InvalidOperationException` rather than acknowledge/cleanup the
connection gracefully.
See relevant point where exception is thrown.
[here|https://github.com/apache/tinkerpop/blob/7835e7a2c3b19a14f196525da844a2e35ba5a105/gremlin-dotnet/src/Gremlin.Net/Driver/Connection.cs#L123]
Close messages from the server can be expected when the server is doing a
graceful shutdown, and clients would be expected to reconnect.
h2. Details:
A Close websocket message being received by ClientWebSocket,
[WebSocketReceiveResult.MessageType|https://docs.microsoft.com/en-us/dotnet/api/system.net.websockets.websocketreceiveresult.messagetype?view=net-6.0]
will return `Close`. In this case, the message buffer will be zero-bytes, see
these
[remarks|https://docs.microsoft.com/en-us/dotnet/api/system.net.websockets.websocketreceiveresult.count?view=net-6.0#remarks].
Currently, Gremlin.NET does not check for this message type in
[WebSocketConnection.ReceiveMessageAsync|https://github.com/apache/tinkerpop/blob/7835e7a2c3b19a14f196525da844a2e35ba5a105/gremlin-dotnet/src/Gremlin.Net/Driver/WebSocketConnection.cs#L92]
and return a zero-length buffer. In
[Connection.HandleReceiveAsync|https://github.com/apache/tinkerpop/blob/7835e7a2c3b19a14f196525da844a2e35ba5a105/gremlin-dotnet/src/Gremlin.Net/Driver/Connection.cs#L118],
the attempt to deserialize the empty buffer returns `null` and the check fails.
h2. Potential Fix
# If `MessageType == Close` Throw a new connection closed exception from
`WebSocketConnection.ReceiveMessageAsync` which includes
`WebSocketReceiveResult.CloseStatus` and
WebSocketReceiveResult.CloseDescription` in the exception message and as
properties.
# This will be caught in `Connection.HandleRecieveAsync` and treated as fatal
and will call `CloseConnectionBecauseOfFailureAsync` and will handle completing
the close handshake with server per WebSocket protocol, and notifies pending
requests on the connection with the exception.
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