fix(ws): Handle socket emitted errors

src/__tests__/use.ts

@@ -404,6 +404,59 @@ for (const { tServer, itForWS, startTServer } of tServers) {
       });
     });
 
+    // uWebSocket.js cannot have errors emitted on the socket
+    // TODO-db-211027 fastify-websocket
+    itForWS(
+      'should report socket emitted errors to clients by closing the connection',
+      async () => {
+        const { url, waitForClient } = await startTServer();
+
+        const client = await createTClient(url);
+
+        const emittedError = new Error("I'm a teapot");
+
+        await waitForClient((client) => {
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+          client.socket!.emit('error', emittedError);
+        });
+
+        await client.waitForClose((event) => {
+          expect(event.code).toBe(CloseCode.InternalServerError); // CloseCode.InternalServerError: Internal server error
+          expect(event.reason).toBe(emittedError.message);
+          expect(event.wasClean).toBeTruthy(); // because the server reported the error
+        });
+      },
+    );
+
+    // uWebSocket.js cannot have errors emitted on the socket
+    // TODO-db-211027 fastify-websocket
+    itForWS('should limit the socket emitted error message size', async () => {
+      const { url, waitForClient } = await startTServer();
+
+      const client = await createTClient(url);
+      client.ws.send(
+        stringifyMessage<MessageType.ConnectionInit>({
+          type: MessageType.ConnectionInit,
+        }),
+      );
+
+      await waitForClient((client) => {
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        client.socket!.emit(
+          'error',
+          new Error(
+            'i am exactly 124 characters long i am exactly 124 characters long i am exactly 124 characters long i am exactly 124 characte',
+          ),
+        );
+      });
+
+      await client.waitForClose((event) => {
+        expect(event.code).toBe(CloseCode.InternalServerError);
+        expect(event.reason).toBe('Internal server error');
+        expect(event.wasClean).toBeTruthy(); // because the server reported the error
+      });
+    });
+
     it('should limit the internal server error message size', async () => {
       const { url } = await startTServer({
         onConnect: () => {

src/__tests__/utils/tservers.ts

@@ -31,6 +31,7 @@ afterEach(async () => {
 });
 
 export interface TServerClient {
+  socket: ws | null; // null when uWS
   send(data: string): void;
   onMessage(cb: (message: string) => void): () => void;
   close(code?: number, data?: string): void;
@@ -216,6 +217,7 @@ export async function startWSTServer(
 
   function toClient(socket: ws): TServerClient {
     return {
+      socket,
       send: (data) => socket.send(data),
       onMessage: (cb) => {
         const listener = (data: unknown) => cb(String(data));
@@ -479,6 +481,7 @@ export async function startFastifyWSTServer(
 
   function toClient(socket: ws): TServerClient {
     return {
+      socket,
       send: (data) => socket.send(data),
       onMessage: (cb) => {
         const listener = (data: unknown) => cb(String(data));

src/use/ws.ts

@@ -80,6 +80,21 @@ export function useServer<
   });
 
   ws.on('connection', (socket, request) => {
+    socket.on('error', (err) => {
+      console.error(
+        'Internal error emitted on a WebSocket socket. ' +
+          'Please check your implementation.',
+        err,
+      );
+      socket.close(
+        CloseCode.InternalServerError,
+        // close reason should fit in one frame https://datatracker.ietf.org/doc/html/rfc6455#section-5.2
+        isProd || err.message.length > 123
+          ? 'Internal server error'
+          : err.message,
+      );
+    });
+
     // keep alive through ping-pong messages
     let pongWait: NodeJS.Timeout | null = null;
     const pingInterval =