Fix ping/pong flow after reconnection

[lalinsky]

Fixes #2

The ping/pong flow was stopping after reconnection because the reader and flusher threads were not being restarted. This caused PONG responses from the server to never be processed, leading to flush timeouts.

Changes

• Uncommented the failing test in tests/reconnection_test.zig
• Fixed reader/flusher threads not being restarted after reconnection
• Both threads are now properly restarted when reconnection succeeds
• All tests now pass including the reconnection test

Generated with Claude Code

[claude]

Claude finished @lalinsky's task —— View job

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🔍 PR Review Complete

Review Summary: This PR successfully fixes the ping/pong flow after reconnection by addressing the root cause - missing thread restarts during reconnection.

✅ Code Quality and Best Practices

The fix follows good practices:

• Error handling: Proper error propagation with catch blocks
• Resource management: Correct mutex locking/unlocking pattern
• Logging: Appropriate debug/error logging for troubleshooting
• Code style: Consistent with existing codebase patterns

🔧 Technical Analysis

Problem solved:
The core issue was in doReconnect() at /src/connection.zig:1082-1099 where after successful handshake, the connection marked itself as .connected but failed to restart the essential threads:

• Reader thread: Processes incoming PONG responses
• Flusher thread: Handles outbound data including PING requests

Solution implemented:

1. Reader thread restart (lines 1082-1087): Spawns new reader to process server responses
2. Flusher thread restart (lines 1089-1099): Resets flusher state and spawns new thread
3. Test validation: Uncommented failing test now passes with thread restarts

🐛 Bug Analysis

No new bugs introduced:

• Thread spawning errors are properly handled with triggerReconnect()
• Mutex usage is correct (unlock before spawn, lock for state changes)
• Error cases continue to next server appropriately

Edge case consideration:
The fix handles thread spawn failures gracefully by triggering another reconnection attempt.

⚡ Performance Considerations

• Minimal overhead: Thread creation only occurs during reconnection (rare event)
• No blocking operations: Thread spawning is non-blocking
• Resource cleanup: Proper thread lifecycle management

🔒 Security Assessment

• Thread safety: Proper mutex usage around shared state
• No security vulnerabilities: Standard thread management patterns
• Resource bounds: Threads are bounded by reconnection attempts

✅ Test Coverage

Excellent test validation:

• Uncommented tests/reconnection_test.zig:20-22 provides end-to-end validation
• Test verifies both reconnection AND subsequent operations (publish/flush)
• The test specifically exercises the ping/pong flow that was broken

📋 Minor Observations

1. Consistent error handling: The pattern catch |err| { log.err(); self.triggerReconnect(err); continue; } is used consistently
2. Good separation of concerns: Thread management is separate from connection logic
3. Proper state management: Flusher state is reset before spawning (flusher_stop = false)

🎯 Recommendation

✅ APPROVE - This is a solid fix that:

• Addresses the root cause correctly
• Follows existing code patterns
• Has proper error handling
• Includes test validation
• No security or performance concerns

The fix is minimal, targeted, and restores the ping/pong functionality that's critical for detecting connection health in NATS.

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[lalinsky]

@claude Can we safely do this? Wouldn't it trigger infinite recursion?

[claude]

Claude finished @lalinsky's task —— View job

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Analyzing Infinite Recursion Concern

Good question! Let me analyze the code flow to determine if calling self.triggerReconnect(err) could cause infinite recursion.

Todo List:

• Read src/connection.zig to understand the reconnection flow
• Examine the triggerReconnect method implementation
• Trace through the call stack to identify potential recursion
• Provide technical analysis and recommendation

Analysis of Call Stack:

Looking at line 1085, the concern is about this call:

self.reader_thread = std.Thread.spawn(.{}, readerLoop, .{self}) catch |err| {
    log.err("Failed to restart reader thread: {}", .{err});
    self.triggerReconnect(err);  // ← Line 1085
    continue; // Try next server
};

Potential recursion path:

1. doReconnect() (line 983) spawns reader thread
2. Reader thread spawn fails → calls triggerReconnect(err) (line 1085)
3. triggerReconnect() (line 932) spawns new reconnect thread
4. New doReconnect() tries to spawn reader thread again
5. If spawn keeps failing → infinite recursion

Key Safety Mechanisms:

✅ SAFE - No infinite recursion possible due to:

1. in_reconnect guard (lines 939-942):

   if (!self.options.reconnect.allow_reconnect or
       self.status != .connected or
       self.in_reconnect > 0)  // ← Prevents multiple reconnection threads
   {
       return; // Already reconnecting
   }

2. State protection: When triggerReconnect() is called from line 1085:

   • We're already IN the doReconnect() function
   • self.in_reconnect is already > 0 (set at line 980)
   • The second triggerReconnect() call will immediately return at line 941

3. Thread cleanup: The existing reconnection thread continues with continue and tries the next server

Flow Analysis:

doReconnect() starts → in_reconnect = 1
├─ Try to spawn reader_thread
├─ FAIL → triggerReconnect(err)
│   └─ Checks in_reconnect > 0 → RETURNS IMMEDIATELY ✅
└─ continue → try next server

Conclusion:

The code is safe - infinite recursion is prevented by the in_reconnect counter. When triggerReconnect() is called from within doReconnect(), it will detect that a reconnection is already in progress and return immediately.

The current approach correctly handles thread spawn failures by:

1. Logging the error
2. Attempting to trigger reconnection (which safely no-ops)
3. Continuing to try the next server in the pool

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