feat: add the "addTrailingSlash" option (#694)

The "addTrailingSlash" option allows to control whether a trailing
slash is added to the path of the HTTP requests created by the library:

- true (default): "/engine.io/"
- false: "/engine.io"

Related: socketio/socket.io-client#1550

Signed-off-by: iifawzi <iifawzie@gmail.com>

lib/socket.ts

@@ -206,6 +206,12 @@ export interface SocketOptions {
    */
   path: string;
 
+  /**
+   * Whether we should add a trailing slash to the request path.
+   * @default true
+   */
+  addTrailingSlash: boolean;
+
   /**
    * Either a single protocol string or an array of protocol strings. These strings are used to indicate sub-protocols,
    * so that a single server can implement multiple WebSocket sub-protocols (for example, you might want one server to
@@ -323,6 +329,7 @@ export class Socket extends Emitter<{}, {}, SocketReservedEvents> {
         upgrade: true,
         timestampParam: "t",
         rememberUpgrade: false,
+        addTrailingSlash: true,
         rejectUnauthorized: true,
         perMessageDeflate: {
           threshold: 1024
@@ -333,7 +340,9 @@ export class Socket extends Emitter<{}, {}, SocketReservedEvents> {
       opts
     );
 
-    this.opts.path = this.opts.path.replace(/\/$/, "") + "/";
+    this.opts.path =
+      this.opts.path.replace(/\/$/, "") +
+      (this.opts.addTrailingSlash ? "/" : "");
 
     if (typeof this.opts.query === "string") {
       this.opts.query = decode(this.opts.query);

test/engine.io-client.js

@@ -58,6 +58,12 @@ describe("engine.io-client", () => {
     expect(client.port).to.be("8080");
   });
 
+  it("should properly handle the addTrailingSlash option", () => {
+    const client = new Socket({ host: "localhost", addTrailingSlash: false });
+    expect(client.hostname).to.be("localhost");
+    expect(client.opts.path).to.be("/engine.io");
+  });
+
   it("should properly parse an IPv6 uri without port", () => {
     const client = new Socket("http://[::1]");
     expect(client.hostname).to.be("::1");