fix(webtransport): properly handle WebTransport-only connections

A WebTransport-only connection has no `request` attribute, so we need
to handle that case.

lib/socket.ts

@@ -292,16 +292,16 @@ export class Socket<
    */
   private buildHandshake(auth: object): Handshake {
     return {
-      headers: this.request.headers,
+      headers: this.request?.headers || {},
       time: new Date() + "",
       address: this.conn.remoteAddress,
-      xdomain: !!this.request.headers.origin,
+      xdomain: !!this.request?.headers.origin,
       // @ts-ignore
-      secure: !!this.request.connection.encrypted,
+      secure: !this.request || !!this.request.connection.encrypted,
       issued: +new Date(),
-      url: this.request.url!,
+      url: this.request?.url!,
       // @ts-ignore
-      query: this.request._query,
+      query: this.request?._query || {},
       auth,
     };
   }

test/socket.ts

@@ -684,6 +684,23 @@ describe("socket", () => {
     });
   });
 
+  it("should handshake a client without access to the Engine.IO request (WebTransport-only connection)", (done) => {
+    const io = new Server(0);
+    const clientSocket = createClient(io, "/");
+
+    io.engine.on("connection", (socket) => {
+      delete socket.request;
+    });
+
+    io.on("connection", (socket) => {
+      expect(socket.handshake.secure).to.be(true);
+      expect(socket.handshake.headers).to.eql({});
+      expect(socket.handshake.query).to.eql({});
+
+      success(done, io, clientSocket);
+    });
+  });
+
   it("should handle very large json", function (done) {
     this.timeout(30000);
     const io = new Server(0, { perMessageDeflate: false });