Implement proxy chain connection accumulation fix and add comprehensive tests

- Updated socket handling to prevent connection accumulation in chained proxies.
- Introduced centralized bidirectional forwarding for consistent socket management.
- Enhanced cleanup logic to ensure immediate closure of sockets when one closes.
- Added tests to verify connection behavior under various scenarios, including backend failures and rapid reconnections.

ts/core/utils/socket-utils.ts

@@ -109,7 +109,8 @@ export function createSocketCleanupHandler(
 export function createIndependentSocketHandlers(
   clientSocket: plugins.net.Socket | plugins.tls.TLSSocket,
   serverSocket: plugins.net.Socket | plugins.tls.TLSSocket,
-  onBothClosed: (reason: string) => void
+  onBothClosed: (reason: string) => void,
+  options: { enableHalfOpen?: boolean } = {}
 ): { cleanupClient: (reason: string) => Promise<void>, cleanupServer: (reason: string) => Promise<void> } {
   let clientClosed = false;
   let serverClosed = false;
@@ -127,8 +128,13 @@ export function createIndependentSocketHandlers(
     clientClosed = true;
     clientReason = reason;
     
-    // Allow server to continue if still active
-    if (!serverClosed && serverSocket.writable) {
+    // Default behavior: close both sockets when one closes (required for proxy chains)
+    if (!serverClosed && !options.enableHalfOpen) {
+      serverSocket.destroy();
+    }
+    
+    // Half-open support (opt-in only)
+    if (!serverClosed && serverSocket.writable && options.enableHalfOpen) {
       // Half-close: stop reading from client, let server finish
       clientSocket.pause();
       clientSocket.unpipe(serverSocket);
@@ -145,8 +151,13 @@ export function createIndependentSocketHandlers(
     serverClosed = true;
     serverReason = reason;
     
-    // Allow client to continue if still active
-    if (!clientClosed && clientSocket.writable) {
+    // Default behavior: close both sockets when one closes (required for proxy chains)
+    if (!clientClosed && !options.enableHalfOpen) {
+      clientSocket.destroy();
+    }
+    
+    // Half-open support (opt-in only)
+    if (!clientClosed && clientSocket.writable && options.enableHalfOpen) {
       // Half-close: stop reading from server, let client finish
       serverSocket.pause();
       serverSocket.unpipe(clientSocket);
@@ -194,6 +205,79 @@ export function setupSocketHandlers(
   });
 }
 
+/**
+ * Setup bidirectional data forwarding between two sockets with proper cleanup
+ * @param clientSocket The client/incoming socket
+ * @param serverSocket The server/outgoing socket
+ * @param handlers Object containing optional handlers for data and cleanup
+ * @returns Cleanup functions for both sockets
+ */
+export function setupBidirectionalForwarding(
+  clientSocket: plugins.net.Socket | plugins.tls.TLSSocket,
+  serverSocket: plugins.net.Socket | plugins.tls.TLSSocket,
+  handlers: {
+    onClientData?: (chunk: Buffer) => void;
+    onServerData?: (chunk: Buffer) => void;
+    onCleanup: (reason: string) => void;
+    enableHalfOpen?: boolean;
+  }
+): { cleanupClient: (reason: string) => Promise<void>, cleanupServer: (reason: string) => Promise<void> } {
+  // Set up cleanup handlers
+  const { cleanupClient, cleanupServer } = createIndependentSocketHandlers(
+    clientSocket,
+    serverSocket,
+    handlers.onCleanup,
+    { enableHalfOpen: handlers.enableHalfOpen }
+  );
+  
+  // Set up error and close handlers
+  setupSocketHandlers(clientSocket, cleanupClient, undefined, 'client');
+  setupSocketHandlers(serverSocket, cleanupServer, undefined, 'server');
+  
+  // Set up data forwarding with backpressure handling
+  clientSocket.on('data', (chunk: Buffer) => {
+    if (handlers.onClientData) {
+      handlers.onClientData(chunk);
+    }
+    
+    if (serverSocket.writable) {
+      const flushed = serverSocket.write(chunk);
+      
+      // Handle backpressure
+      if (!flushed) {
+        clientSocket.pause();
+        serverSocket.once('drain', () => {
+          if (!clientSocket.destroyed) {
+            clientSocket.resume();
+          }
+        });
+      }
+    }
+  });
+  
+  serverSocket.on('data', (chunk: Buffer) => {
+    if (handlers.onServerData) {
+      handlers.onServerData(chunk);
+    }
+    
+    if (clientSocket.writable) {
+      const flushed = clientSocket.write(chunk);
+      
+      // Handle backpressure
+      if (!flushed) {
+        serverSocket.pause();
+        clientSocket.once('drain', () => {
+          if (!serverSocket.destroyed) {
+            serverSocket.resume();
+          }
+        });
+      }
+    }
+  });
+  
+  return { cleanupClient, cleanupServer };
+}
+
 /**
  * Pipe two sockets together with proper cleanup on either end
  * @param socket1 First socket