fix(realtime): ensure WebSocket connections are properly closed in teardown

[tanmaysharma2001]

🔍 Description

Fixed a critical memory leak in RealtimeClient._teardownConnection() where WebSocket connections were not properly closed before being nullified, causing connections to remain open in memory indefinitely.

What changed?

Enhanced the _teardownConnection() method in packages/core/realtime-js/src/RealtimeClient.ts to:

• Check WebSocket connection state before cleanup
• Explicitly call conn.close() for OPEN or CONNECTING connections
• Add error handling with try-catch to gracefully handle close failures
• Log any errors during connection closure for debugging

Before:

private _teardownConnection(): void {
  if (this.conn) {
    this.conn.onopen = null
    this.conn.onerror = null
    this.conn.onmessage = null
    this.conn.onclose = null
    this.conn = null  // reference nullified without ensuring closure
  }
}

After:

private _teardownConnection(): void {
  if (this.conn) {
    // Ensure connection is properly closed first
    if (
      this.conn.readyState === SOCKET_STATES.open ||
      this.conn.readyState === SOCKET_STATES.connecting
    ) {
      try {
        this.conn.close()
      } catch (e) {
        this.log('error', 'Error closing connection', e)
      }
    }

    this.conn.onopen = null
    this.conn.onerror = null
    this.conn.onmessage = null
    this.conn.onclose = null
    this.conn = null
  }
  this._clearAllTimers()
  this.channels.forEach((channel) => channel.teardown())
}

Why was this change needed?

The original implementation would set WebSocket event handlers to null and nullify the connection reference without first ensuring the WebSocket was properly closed. This caused:

• Memory Leaks: WebSocket connections remain open in memory in long-running applications
• Resource Exhaustion: Accumulation of unclosed connections over time
• Connection Limits: Could hit browser/system connection limits in high-traffic scenarios

Closes #1840

🔄 Breaking changes

• [☑️] This PR contains no breaking changes

📋 Checklist

• [☑️] I have read the Contributing Guidelines
• [☑️] My PR title follows the conventional commit format: <type>(<scope>): <description>
• [☑️] I have run npx nx format to ensure consistent code formatting
• [☑️] I have added tests for new functionality (if applicable)
• [☑️] I have updated documentation (if applicable)

📝 Additional notes

Technical details:

• Uses existing SOCKET_STATES enum constants for readyState checks
• Leverages existing this.log() method for error reporting
• Maintains all existing cleanup logic (_clearAllTimers(), channel teardown)
• No changes to public API or behavior

Testing:

• Existing unit tests continue to pass
• Integration tests validate proper connection lifecycle
• Recommended manual testing: Long-running applications with frequent connection cycles
• Affected packages:
  • @supabase/realtime-js (primary fix)
  • @supabase/supabase-js (indirect benefit)

[coveralls]

coverage: 95.276% (+13.5%) from 81.737%
when pulling d4cb87e on tanmaysharma2001:feat/ws-mem-leak-fix
into d1ba7d9 on supabase:master.