fix: ignore packets when the transport is silently closed

darrachequesne · darrachequesne · commit 46e6de08e378 · 2021-04-01T00:05:23.000+02:00
In some cases, a "Transport not open" error could be thrown when the transport was silently closed in the onbeforeunload event (added in [1]). To reproduce: ```js window.addEventListener("unload", () => { socket.write("..."); }); ``` [1]: ed48b5d Backported from master: d291a4c
diff --git a/lib/transport.js b/lib/transport.js
@@ -1,5 +1,6 @@
 const parser = require("engine.io-parser");
 const Emitter = require("component-emitter");
+const debug = require("debug")("engine.io-client:transport");
 
 class Transport extends Emitter {
   /**
@@ -70,7 +71,8 @@ class Transport extends Emitter {
     if ("open" === this.readyState) {
       this.write(packets);
     } else {
-      throw new Error("Transport not open");
+      // this might happen if the transport was silently closed in the beforeunload event handler
+      debug("transport is not open, discarding packets");
     }
   }
 
diff --git a/test/connection.js b/test/connection.js
@@ -188,4 +188,34 @@ describe("connection", function() {
       });
     });
   }
+
+  if (env.browser && typeof addEventListener === "function") {
+    it("should close the socket when receiving a beforeunload event", done => {
+      const socket = new Socket();
+
+      const createEvent = name => {
+        if (typeof Event === "function") {
+          return new Event(name);
+        } else {
+          // polyfill for IE
+          const event = document.createEvent("Event");
+          event.initEvent(name, true, true);
+          return event;
+        }
+      };
+
+      socket.on("open", () => {
+        const handler = () => {
+          expect(socket.transport.readyState).to.eql("closed");
+          expect(() => socket.write("ignored")).to.not.throwException();
+
+          removeEventListener("beforeunload", handler, false);
+          done();
+        };
+
+        addEventListener("beforeunload", handler, false);
+        dispatchEvent(createEvent("beforeunload"));
+      });
+    });
+  }
 });

Original file line number	Diff line number	Diff line change
`@@ -1,5 +1,6 @@`
`1`	`1`	`const parser = require("engine.io-parser");`
`2`	`2`	`const Emitter = require("component-emitter");`
	`3`	`+const debug = require("debug")("engine.io-client:transport");`
`3`	`4`
`4`	`5`	`class Transport extends Emitter {`
`5`	`6`	`/**`
`@@ -70,7 +71,8 @@ class Transport extends Emitter {`
`70`	`71`	`if ("open" === this.readyState) {`
`71`	`72`	`this.write(packets);`
`72`	`73`	`} else {`
`73`		`- throw new Error("Transport not open");`
	`74`	`+ // this might happen if the transport was silently closed in the beforeunload event handler`
	`75`	`+ debug("transport is not open, discarding packets");`
`74`	`76`	`}`
`75`	`77`	`}`
`76`	`78`