fix: fix broadcasting volatile packets with binary attachments

The binary attachments of volatile packets were discarded (only the
header packet was sent) due to a bug introduced in [1].

Note: the `wsPreEncoded` option is removed by this commit, as I wasn't
able to find an elegant (read: non explosive) way to keep it.

[1]: 5579d40

Related: socketio/socket.io#3919

lib/index.ts

@@ -126,7 +126,7 @@ export class Adapter extends EventEmitter {
    */
   public broadcast(packet: any, opts: BroadcastOptions): void {
     const flags = opts.flags || {};
-    const basePacketOpts = {
+    const packetOpts = {
       preEncoded: true,
       volatile: flags.volatile,
       compress: flags.compress
@@ -135,21 +135,8 @@ export class Adapter extends EventEmitter {
     packet.nsp = this.nsp.name;
     const encodedPackets = this.encoder.encode(packet);
 
-    const packetOpts = encodedPackets.map(encodedPacket => {
-      if (typeof encodedPacket === "string") {
-        return {
-          ...basePacketOpts,
-          wsPreEncoded: "4" + encodedPacket // "4" being the "message" packet type in Engine.IO
-        };
-      } else {
-        return basePacketOpts;
-      }
-    });
-
     this.apply(opts, socket => {
-      for (let i = 0; i < encodedPackets.length; i++) {
-        socket.client.writeToEngine(encodedPackets[i], packetOpts[i]);
-      }
+      socket.client.writeToEngine(encodedPackets, packetOpts);
     });
   }
 

test/index.js

@@ -67,9 +67,8 @@ describe("socket.io-adapter", () => {
           id,
           client: {
             writeToEngine(payload, opts) {
-              expect(payload).to.eql("123");
+              expect(payload).to.eql(["123"]);
               expect(opts.preEncoded).to.eql(true);
-              expect(opts.wsPreEncoded).to.eql("4123");
               ids.push(id);
             }
           }
@@ -107,7 +106,8 @@ describe("socket.io-adapter", () => {
           id,
           client: {
             writeToEngine(payload, opts) {
-              expect(payload).to.be.a(Buffer);
+              expect(payload).to.be.a(Array);
+              expect(payload[0]).to.be.a(Buffer);
               expect(opts.preEncoded).to.eql(true);
               expect(opts.wsPreEncoded).to.be(undefined);
               ids.push(id);