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https://issues.apache.org/jira/browse/TINKERPOP-2717?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17504518#comment-17504518
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Oliver Towers commented on TINKERPOP-2717:
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[~Florian Hockmann] - published the pull request. I did end up adding a new
interface so that ClientWebSocket was mockable, so feel free to comment if a
different approach is preferred.
> 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: 3.4.13, 3.5.2
> Reporter: Oliver Towers
> Priority: Minor
>
> 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 {{MessageType.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, and notifies pending requests on the
> connection with the closed connection exception.
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