fix: restore close code 4200 for graceful shutdown

[lilfaf]

PR #139 incorrectly changed the WebSocket close code for graceful server shutdown from 4200 to 4009, breaking pusher-js auto-reconnect behavior.

According to Pusher protocol:

• 4000-4099: Client SHOULD NOT reconnect (auth failures, unauthorized)
• 4200-4299: Client SHOULD reconnect immediately (server going away)

Code 4009 means "Connection is unauthorized" which tells clients not to reconnect. The fix restores 4200 for server shutdown, matching Soketi's behavior.

Note: terminate_user_connections keeps 4009 as this is for API-initiated user termination where the app deliberately kicks users - this matches Soketi and is correct behavior.

Description

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Performance improvement
• Code refactoring

Testing

• Unit tests pass
• Integration tests pass
• Manual testing completed

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Build Artifacts

Additional Notes

[gemini-code-assist]

Summary of Changes

Hello @lilfaf, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical bug that caused client applications to incorrectly handle server shutdowns. By reverting the WebSocket close code for graceful server termination from '4009' back to '4200', the change ensures that clients, particularly those relying on 'pusher-js', will now correctly attempt to re-establish connections when the server goes offline temporarily, thereby preventing unintended service interruptions from the client's perspective.

Highlights

• WebSocket Close Code Correction: Restored the WebSocket close code for graceful server shutdown from '4009' to '4200'. This change ensures that clients, especially those using 'pusher-js', correctly interpret server disconnections as temporary and attempt to auto-reconnect.
• Client Reconnection Behavior: The previous '4009' close code incorrectly signaled clients not to reconnect, as it falls within the range for unauthorized or unrecoverable errors. The '4200' code, however, correctly indicates a server-initiated shutdown where immediate reconnection is desired, aligning with the Pusher protocol.

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[gemini-code-assist]

Code Review

This pull request correctly restores the WebSocket close code to 4200 for graceful server shutdowns, which is essential for allowing clients like pusher-js to auto-reconnect as expected. The change aligns with the Pusher protocol specification. My review includes a suggestion to improve code maintainability by defining the new close code and reason as named constants.