fix(connection): filter zombie connections part 2

readme.monitoring.md

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+# Production Connection Monitoring
+
+This document explains how to use the ProductionConnectionMonitor to diagnose connection accumulation issues in real-time.
+
+## Quick Start
+
+```typescript
+import ProductionConnectionMonitor from './.nogit/debug/production-connection-monitor.js';
+
+// After starting your proxy
+const monitor = new ProductionConnectionMonitor(proxy);
+monitor.start(5000); // Check every 5 seconds
+
+// The monitor will automatically capture diagnostics when:
+// - Connections exceed 50 (default threshold)
+// - Sudden spike of 20+ connections occurs
+// - You manually call monitor.forceCaptureNow()
+```
+
+## What Gets Captured
+
+When accumulation is detected, the monitor saves a JSON file with:
+
+### Connection Details
+- Socket states (destroyed, readable, writable, readyState)
+- Connection age and activity timestamps
+- Data transfer statistics (bytes sent/received)
+- Target host and port information
+- Keep-alive status
+- Event listener counts
+
+### System State
+- Memory usage
+- Event loop lag
+- Connection count trends
+- Termination statistics
+
+## Reading Diagnostic Files
+
+Files are saved to `.nogit/connection-diagnostics/` with names like:
+```
+accumulation_2025-06-07T20-20-43-733Z_force_capture.json
+```
+
+### Key Fields to Check
+
+1. **Socket States**
+   ```json
+   "incomingState": {
+     "destroyed": false,
+     "readable": true,
+     "writable": true,
+     "readyState": "open"
+   }
+   ```
+   - Both destroyed = zombie connection
+   - One destroyed = half-zombie
+   - Both alive but old = potential stuck connection
+
+2. **Data Transfer**
+   ```json
+   "bytesReceived": 36,
+   "bytesSent": 0,
+   "timeSinceLastActivity": 60000
+   ```
+   - No bytes sent back = stuck connection
+   - High bytes but old = slow backend
+   - No activity = idle connection
+
+3. **Connection Flags**
+   ```json
+   "hasReceivedInitialData": false,
+   "hasKeepAlive": true,
+   "connectionClosed": false
+   ```
+   - hasReceivedInitialData=false on non-TLS = immediate routing
+   - hasKeepAlive=true = extended timeout applies
+   - connectionClosed=false = still tracked
+
+## Common Patterns
+
+### 1. Hanging Backend Pattern
+```json
+{
+  "bytesReceived": 36,
+  "bytesSent": 0,
+  "age": 120000,
+  "targetHost": "backend.example.com",
+  "incomingState": { "destroyed": false },
+  "outgoingState": { "destroyed": false }
+}
+```
+**Fix**: The stuck connection detection (60s timeout) should clean these up.
+
+### 2. Zombie Connection Pattern
+```json
+{
+  "incomingState": { "destroyed": true },
+  "outgoingState": { "destroyed": true },
+  "connectionClosed": false
+}
+```
+**Fix**: The zombie detection should clean these up within 30s.
+
+### 3. Event Listener Leak Pattern
+```json
+{
+  "incomingListeners": {
+    "data": 15,
+    "error": 20,
+    "close": 18
+  }
+}
+```
+**Issue**: Event listeners accumulating, potential memory leak.
+
+### 4. No Outgoing Socket Pattern
+```json
+{
+  "outgoingState": { "exists": false },
+  "connectionClosed": false,
+  "age": 5000
+}
+```
+**Issue**: Connection setup failed but cleanup didn't trigger.
+
+## Forcing Diagnostic Capture
+
+To capture current state immediately:
+```typescript
+monitor.forceCaptureNow();
+```
+
+This is useful when you notice accumulation starting.
+
+## Automated Analysis
+
+The monitor automatically analyzes patterns and logs:
+- Zombie/half-zombie counts
+- Stuck connection counts
+- Old connection counts
+- Memory usage
+- Recommendations
+
+## Integration Example
+
+```typescript
+// In your proxy startup script
+import { SmartProxy } from '@push.rocks/smartproxy';
+import ProductionConnectionMonitor from './production-connection-monitor.js';
+
+async function startProxyWithMonitoring() {
+  const proxy = new SmartProxy({
+    // your config
+  });
+  
+  await proxy.start();
+  
+  // Start monitoring
+  const monitor = new ProductionConnectionMonitor(proxy);
+  monitor.start(5000);
+  
+  // Optional: Capture on specific events
+  process.on('SIGUSR1', () => {
+    console.log('Manual diagnostic capture triggered');
+    monitor.forceCaptureNow();
+  });
+  
+  // Graceful shutdown
+  process.on('SIGTERM', async () => {
+    monitor.stop();
+    await proxy.stop();
+    process.exit(0);
+  });
+}
+```
+
+## Troubleshooting
+
+### Monitor Not Detecting Accumulation
+- Check threshold settings (default: 50 connections)
+- Reduce check interval for faster detection
+- Use forceCaptureNow() to capture current state
+
+### Too Many False Positives
+- Increase accumulation threshold
+- Increase spike threshold
+- Adjust check interval
+
+### Missing Diagnostic Data
+- Ensure output directory exists and is writable
+- Check disk space
+- Verify process has write permissions
+
+## Next Steps
+
+1. Deploy the monitor to production
+2. Wait for accumulation to occur
+3. Share diagnostic files for analysis
+4. Apply targeted fixes based on patterns found
+
+The diagnostic data will reveal the exact state of connections when accumulation occurs, enabling precise fixes for your specific scenario.