fix(websocket): fix timer blocking writes (#670)

hyperlink · darrachequesne · commit f30a10b7f455 · 2021-06-22T23:58:27.000+02:00
An immediate setTimeout was used to unblock the WebSocket write. Unfortunately, this setTimeout can be throttled by browsers when the tab is backgrounded. This can lead to missed pong responses to server pings, which eventually leads to disconnection. Related: #649
diff --git a/lib/transports/websocket-constructor.browser.js b/lib/transports/websocket-constructor.browser.js
@@ -1,7 +1,17 @@
 const globalThis = require("../globalThis");
+const nextTick = (() => {
+  const isPromiseAvailable =
+    typeof Promise === "function" && typeof Promise.resolve === "function";
+  if (isPromiseAvailable) {
+    return cb => Promise.resolve().then(cb);
+  } else {
+    return cb => setTimeout(cb, 0);
+  }
+})();
 
 module.exports = {
   WebSocket: globalThis.WebSocket || globalThis.MozWebSocket,
   usingBrowserWebSocket: true,
-  defaultBinaryType: "arraybuffer"
+  defaultBinaryType: "arraybuffer",
+  nextTick
 };
diff --git a/lib/transports/websocket-constructor.js b/lib/transports/websocket-constructor.js
@@ -1,5 +1,6 @@
 module.exports = {
   WebSocket: require("ws"),
   usingBrowserWebSocket: false,
-  defaultBinaryType: "nodebuffer"
+  defaultBinaryType: "nodebuffer",
+  nextTick: process.nextTick
 };
diff --git a/lib/transports/websocket.js b/lib/transports/websocket.js
@@ -6,7 +6,8 @@ const { pick } = require("../util");
 const {
   WebSocket,
   usingBrowserWebSocket,
-  defaultBinaryType
+  defaultBinaryType,
+  nextTick
 } = require("./websocket-constructor");
 
 const debug = require("debug")("engine.io-client:websocket");
@@ -161,10 +162,10 @@ class WS extends Transport {
         if (lastPacket) {
           // fake drain
           // defer to next tick to allow Socket to clear writeBuffer
-          setTimeout(() => {
+          nextTick(() => {
             this.writable = true;
             this.emit("drain");
-          }, 0);
+          });
         }
       });
     }
