Improvements in Close()

[josesimoes]

Description

• The reply to a peer-started close now carries only the peer's status code.
• Protocol errors are now closed with a proper status code and reason.
• Calling Close() when the connection isn't Open does nothing, including while answering the peer close.
• Invalid close frames from the peer are now answered with 1002.
• Close codes in the 3000 - 4999 range are now echoed back to the peer.
• Update Intellisesne commetns and README.

Motivation and Context

• Further improvements started with Fix potential deadlock in WebSocket timeout checker #249 and Improve handling of connections closed by the peer #248

How Has This Been Tested?

Screenshots

Types of changes

• Improvement (non-breaking change that improves a feature, code or algorithm)
• Bug fix (non-breaking change which fixes an issue with code or algorithm)
• New feature (non-breaking change which adds functionality to code)
• Breaking change (fix or feature that would cause existing functionality to change)
• Config and build (change in the configuration and build system, has no impact on code or features)
• Dependencies (update dependencies and changes associated, has no impact on code or features)
• Unit Tests (add new Unit Test(s) or improved existing one(s), has no impact on code or features)
• Documentation (changes or updates in the documentation, has no impact on code or features)

Checklist:

• My code follows the code style of this project (only if there are changes in source code).
• My changes require an update to the documentation (there are changes that require the docs website to be updated).
• I have updated the documentation accordingly (the changes require an update on the docs in this repo).
• I have read the CONTRIBUTING document.
• I have tested everything locally and all new and existing tests passed (only if there are changes in source code).
• I have added new tests to cover my changes.

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📝 Summary

Summary by CodeRabbit

• Bug Fixes

  • Improved WebSocket close-handshake behavior, including handling and echoing the peer’s close status.
  • Prevented message sending from continuing after a close message is sent, including during fragmented messages.
  • Error frames now retain their close status.

• Documentation

  • Clarified that Close is non-blocking, how queued messages and timeouts affect shutdown, and when closure is synchronous.
  • Updated the documented close event name to ConnectionClosed.

Walkthrough

The close handshake now records the peer’s close status, limits which connection states can start or answer a close, and changes sender behavior during shutdown. The README describes the close behavior and names the ConnectionClosed event.

Changes

Close handshake

Layer / File(s)	Summary
Close state and peer status WebSockets/WebSocket.cs, WebSockets/ReceiveAndControllThread.cs, WebSockets/WebSocketReceiver.cs, README.md	The close path passes and records the peer’s status. Application-level closes require an open connection, while peer-close responses can begin from CloseReceived. Error frames now store the supplied close status. The README documents close behavior and uses ConnectionClosed as the event name.
Sender shutdown and fragmented messages WebSockets/WebSocketSender.cs	The sender tracks intentional stop requests, waits for one before exiting its close-frame wait, and stops sending fragmented messages after a close is queued.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Peer
  participant ReceiveAndControllThread
  participant WebSocket
  participant WebSocketSender
  Peer->>ReceiveAndControllThread: Send close frame with status
  ReceiveAndControllThread->>WebSocket: Record peer status
  ReceiveAndControllThread->>WebSocket: Request close response
  WebSocket->>WebSocketSender: Queue close frame
  WebSocketSender->>Peer: Send close frame

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Merge Risk: 🟡 Moderate · up to f2f06

Peer close handshakes can return the wrong status code, and the documented delivery guarantee can mislead callers when sending times out. Correct the validation and documentation before merging.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title is concise, descriptive, directly related to the WebSocket close-handling changes, under 50 characters, and does not end with a full stop.
Description check	✅ Passed	The description clearly explains the close-handling changes, protocol-error behavior, documentation updates, motivation, and change type.

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[josesimoes]

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Actionable comments posted: 2

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
In `@WebSockets/ReceiveAndControllThread.cs`:
- Line 109: Update close-frame validation in the receive loop around statusCode
so only permitted peer close codes are accepted, including the 3000–4999
private-use range, while reserved codes such as 1004 are rejected. Keep
WebSocketCloseStatus.Empty only for an empty close payload; treat a one-byte
payload or any prohibited code as invalid and close with ProtocolError instead
of allowing it to fall through to TryMarkCloseReceived.

In `@WebSockets/WebSocket.cs`:
- Line 232: Update the `RawClose()` XML documentation and the corresponding
`EndpointUnavailable` documentation to state that closing waits only up to
`ServerTimeout` for the close message, and that if the timeout expires first,
the connection closes without the message necessarily being sent. Preserve the
note that queued messages may not be sent.

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Run ID: 97742223-0bc9-469a-a13c-e9b6d5472730

📥 Commits

Reviewing files that changed from the base of the PR and between 96ee407 and f2f06b9.

📒 Files selected for processing (5)

• README.md
• WebSockets/ReceiveAndControllThread.cs
• WebSockets/WebSocket.cs
• WebSockets/WebSocketReceiver.cs
• WebSockets/WebSocketSender.cs

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