perf(websocket): use bound callbacks

Instead of allocating one temporary function for each WebSocket
`send()` call.

Regarding the test removal, the permessage-deflate threshold was
implemented in the "ws" package in [1], so it's not needed anymore.

[1]: websockets/ws@6b3904b

lib/transports/websocket.ts

@@ -1,5 +1,6 @@
 import { Transport } from "../transport";
 import debugModule from "debug";
+import type { Packet, RawData } from "engine.io-parser";
 
 const debug = debugModule("engine:ws");
 
@@ -45,52 +46,27 @@ export class WebSocket extends Transport {
     return true;
   }
 
-  /**
-   * Writes a packet payload.
-   *
-   * @param {Array} packets
-   * @api private
-   */
-  send(packets) {
+  send(packets: Packet[]) {
     this.writable = false;
 
     for (let i = 0; i < packets.length; i++) {
       const packet = packets[i];
       const isLast = i + 1 === packets.length;
 
-      // always creates a new object since ws modifies it
-      const opts: { compress?: boolean } = {};
-      if (packet.options) {
-        opts.compress = packet.options.compress;
-      }
-
-      const onSent = (err) => {
-        if (err) {
-          return this.onError("write error", err.stack);
-        } else if (isLast) {
-          this.writable = true;
-          this.emit("drain");
-        }
-      };
-
-      const send = (data) => {
-        if (this.perMessageDeflate) {
-          const len =
-            "string" === typeof data ? Buffer.byteLength(data) : data.length;
-          if (len < this.perMessageDeflate.threshold) {
-            opts.compress = false;
-          }
-        }
-        debug('writing "%s"', data);
-        this.socket.send(data, opts, onSent);
-      };
-
       if (this._canSendPreEncodedFrame(packet)) {
         // the WebSocket frame was computed with WebSocket.Sender.frame()
         // see https://github.com/websockets/ws/issues/617#issuecomment-283002469
-        this.socket._sender.sendFrame(packet.options.wsPreEncodedFrame, onSent);
+        this.socket._sender.sendFrame(
+          // @ts-ignore
+          packet.options.wsPreEncodedFrame,
+          isLast ? this._onSentLast : this._onSent
+        );
       } else {
-        this.parser.encodePacket(packet, this.supportsBinary, send);
+        this.parser.encodePacket(
+          packet,
+          this.supportsBinary,
+          isLast ? this._doSendLast : this._doSend
+        );
       }
     }
   }
@@ -100,20 +76,39 @@ export class WebSocket extends Transport {
    * @param packet
    * @private
    */
-  private _canSendPreEncodedFrame(packet) {
+  private _canSendPreEncodedFrame(packet: Packet) {
     return (
       !this.perMessageDeflate &&
       typeof this.socket?._sender?.sendFrame === "function" &&
+      // @ts-ignore
       packet.options?.wsPreEncodedFrame !== undefined
     );
   }
 
-  /**
-   * Closes the transport.
-   *
-   * @api private
-   */
-  doClose(fn) {
+  private _doSend = (data: RawData) => {
+    this.socket.send(data, this._onSent);
+  };
+
+  private _doSendLast = (data: RawData) => {
+    this.socket.send(data, this._onSentLast);
+  };
+
+  private _onSent = (err?: Error) => {
+    if (err) {
+      this.onError("write error", err.stack);
+    }
+  };
+
+  private _onSentLast = (err?: Error) => {
+    if (err) {
+      this.onError("write error", err.stack);
+    } else {
+      this.writable = true;
+      this.emit("drain");
+    }
+  };
+
+  doClose(fn?: () => void) {
     debug("closing");
     this.socket.close();
     fn && fn();

test/server.js

@@ -3337,68 +3337,6 @@ describe("server", () => {
     });
   });
 
-  describe("permessage-deflate", () => {
-    it("should set threshold", function (done) {
-      if (process.env.EIO_WS_ENGINE === "uws") {
-        return this.skip();
-      }
-      const engine = listen(
-        { transports: ["websocket"], perMessageDeflate: { threshold: 0 } },
-        (port) => {
-          engine.on("connection", (conn) => {
-            const socket = conn.transport.socket;
-            const send = socket.send;
-            socket.send = (data, opts, callback) => {
-              socket.send = send;
-              socket.send(data, opts, callback);
-
-              expect(opts.compress).to.be(true);
-              conn.close();
-              done();
-            };
-
-            const buf = Buffer.allocUnsafe(100);
-            for (let i = 0; i < buf.length; i++) buf[i] = i % 0xff;
-            conn.send(buf, { compress: true });
-          });
-          new ClientSocket(`http://localhost:${port}`, {
-            transports: ["websocket"],
-          });
-        }
-      );
-    });
-
-    it("should not compress when the byte size is below threshold", function (done) {
-      if (process.env.EIO_WS_ENGINE === "uws") {
-        return this.skip();
-      }
-      const engine = listen(
-        { transports: ["websocket"], perMessageDeflate: true },
-        (port) => {
-          engine.on("connection", (conn) => {
-            const socket = conn.transport.socket;
-            const send = socket.send;
-            socket.send = (data, opts, callback) => {
-              socket.send = send;
-              socket.send(data, opts, callback);
-
-              expect(opts.compress).to.be(false);
-              conn.close();
-              done();
-            };
-
-            const buf = Buffer.allocUnsafe(100);
-            for (let i = 0; i < buf.length; i++) buf[i] = i % 0xff;
-            conn.send(buf, { compress: true });
-          });
-          new ClientSocket(`http://localhost:${port}`, {
-            transports: ["websocket"],
-          });
-        }
-      );
-    });
-  });
-
   describe("extraHeaders", function () {
     this.timeout(5000);