fix: handle aborted requests

Previously, an aborted request (for example, when the user closes its
tab) would not close the session right away and would simply time out
upon the next failed heartbeat.

Author: darrachequesne

lib/transports/polling.ts

@@ -38,7 +38,7 @@ export class Polling extends Transport {
    * @private
    */
   private onPollRequest(
-    _req: Request,
+    req: Request,
     responseHeaders: Headers,
   ): Promise<Response> {
     if (this.pollingPromise) {
@@ -51,6 +51,10 @@ export class Polling extends Transport {
 
     debug("new polling request");
 
+    req.signal.addEventListener("abort", () => {
+      this.onError("polling request aborted");
+    });
+
     return new Promise<Response>((resolve, reject) => {
       this.pollingPromise = { resolve, reject, responseHeaders };
 
@@ -72,6 +76,10 @@ export class Polling extends Transport {
   ): Promise<Response> {
     debug("new data request");
 
+    req.signal.addEventListener("abort", () => {
+      this.onError("data request aborted");
+    });
+
     const data = await req.text();
 
     if (data.length > this.opts.maxHttpBufferSize) {

test/engine.test.ts

@@ -14,6 +14,7 @@ async function initLongPollingSession() {
   return JSON.parse(content.substring(1)).sid;
 }
 
+// imported from https://github.com/socketio/socket.io/blob/main/docs/engine.io-protocol/v4-test-suite
 describe("Engine.IO protocol", () => {
   beforeAll(() => {
     const engine = new Server({
@@ -313,6 +314,25 @@ describe("Engine.IO protocol", () => {
 
         expect(pollResponse.status).toEqual(400);
       });
+
+      it("closes the session upon cancelled polling request", async () => {
+        const sid = await initLongPollingSession();
+        const controller = new AbortController();
+
+        fetch(`${URL}/engine.io/?EIO=4&transport=polling&sid=${sid}`, {
+          signal: controller.signal,
+        }).catch(() => {});
+
+        await sleep(5);
+
+        controller.abort();
+
+        const pollResponse = await fetch(
+          `${URL}/engine.io/?EIO=4&transport=polling&sid=${sid}`,
+        );
+
+        expect(pollResponse.status).toEqual(400);
+      });
     });
 
     describe("WebSocket", () => {

test/socket.test.ts

@@ -25,6 +25,7 @@ async function initSocketIOConnection() {
   return socket;
 }
 
+// imported from https://github.com/socketio/socket.io/tree/main/docs/socket.io-protocol/v5-test-suite
 describe("Socket.IO protocol", () => {
   beforeAll(() => {
     const io = new Server();