manually send the initial SSE headers before the main server connection starts and add a background process to send keep-alive pings

server-http.js

@@ -23,6 +23,7 @@ const RATE_LIMIT_MAX_REQUESTS = 50; // 50 requests per minute per IP
 const MEMORY_THRESHOLD_MB = 450;
 const CIRCUIT_BREAKER_THRESHOLD = 5;
 const CIRCUIT_BREAKER_TIMEOUT_MS = 60000;
+const SSE_HEARTBEAT_INTERVAL_MS = 20000; // 20 seconds to prevent proxy timeout
 
 // Initialize data loader
 console.error('Loading HPR knowledge base data...');
@@ -662,7 +663,6 @@ ${match.context}
 const app = express();
 
 // Trust proxy headers (required for Render, Heroku, etc.)
-// This allows rate limiting to work correctly behind reverse proxies
 app.set('trust proxy', true);
 
 // Enable CORS
@@ -700,6 +700,8 @@ app.get('/health', (req, res) => {
 
 // SSE endpoint for MCP
 app.get('/sse', async (req, res) => {
+  let pingInterval = null; // Declare pingInterval to be accessible in req.on('close')
+
   try {
     // Check system health
     checkMemory();
@@ -708,6 +710,31 @@ app.get('/sse', async (req, res) => {
     activeRequests++;
     console.error(`New SSE connection. Active requests: ${activeRequests}`);
 
+    // === START SSE FIXES FOR RENDER/PROXY TIMEOUTS ===
+    
+    // 1. Send no-buffering headers and flush immediately
+    res.writeHead(200, {
+      'Content-Type': 'text/event-stream',
+      'Cache-Control': 'no-cache',
+      'Connection': 'keep-alive',
+      // CRITICAL: Tells proxies (like NGINX) not to buffer the response
+      'X-Accel-Buffering': 'no', 
+    });
+
+    // Send an initial comment (ping) to complete the HTTP handshake and flush headers
+    res.write(':\n'); 
+    res.flushHeaders(); 
+    
+    // 2. Start the heartbeat/ping interval
+    pingInterval = setInterval(() => {
+        // Send a comment line (which is ignored by clients) every 20s
+        res.write(':\n');
+        // NOTE: In a real-world scenario, you might also need to call res.flush()
+        // or ensure your underlying HTTP library flushes the write.
+    }, SSE_HEARTBEAT_INTERVAL_MS); 
+
+    // === END SSE FIXES ===
+
     // Create a new MCP server instance for this connection
     const server = createMCPServer();
 
@@ -723,19 +750,28 @@ app.get('/sse', async (req, res) => {
     // Handle connection close
     req.on('close', () => {
       activeRequests--;
+      if (pingInterval) {
+          clearInterval(pingInterval); // STOP THE PING ON CLOSE
+      }
       console.error(`SSE connection closed. Active requests: ${activeRequests}`);
     });
 
   } catch (error) {
     activeRequests--;
+    if (pingInterval) {
+        clearInterval(pingInterval); // Stop ping on connection failure
+    }
     console.error('SSE connection error:', error.message);
 
     if (!res.headersSent) {
+      // Send a 503 error if headers haven't been sent yet
       res.status(503).json({
         error: error.message,
         circuitBreaker: circuitBreaker.state,
       });
     }
+    // If headers were sent (i.e., stream started but failed mid-way), 
+    // simply let the connection close, which the client will see as an error.
   }
 });
 
@@ -769,6 +805,7 @@ app.listen(PORT, () => {
   console.error(`  - Request timeout: ${REQUEST_TIMEOUT_MS}ms`);
   console.error(`  - Rate limit: ${RATE_LIMIT_MAX_REQUESTS} requests per ${RATE_LIMIT_WINDOW_MS / 1000}s`);
   console.error(`  - Memory threshold: ${MEMORY_THRESHOLD_MB}MB`);
+  console.error(`  - SSE Heartbeat: ${SSE_HEARTBEAT_INTERVAL_MS / 1000}s`);
 });
 
 // Graceful shutdown
@@ -780,4 +817,4 @@ process.on('SIGTERM', () => {
 process.on('SIGINT', () => {
   console.error('SIGINT received, shutting down gracefully...');
   process.exit(0);
-});
+});