fix: properly detect plain objects

The typeof check was not sufficient, as it also matches arrays and
nulls.

Author: darrachequesne

lib/index.ts

@@ -131,6 +131,11 @@ export class Encoder {
   }
 }
 
+// see https://stackoverflow.com/questions/8511281/check-if-a-value-is-an-object-in-javascript
+function isObject(value: any): boolean {
+  return Object.prototype.toString.call(value) === "[object Object]";
+}
+
 interface DecoderReservedEvents {
   decoded: (packet: Packet) => void;
 }
@@ -280,11 +285,11 @@ export class Decoder extends Emitter<{}, {}, DecoderReservedEvents> {
   private static isPayloadValid(type: PacketType, payload: any): boolean {
     switch (type) {
       case PacketType.CONNECT:
-        return typeof payload === "object";
+        return isObject(payload);
       case PacketType.DISCONNECT:
         return payload === undefined;
       case PacketType.CONNECT_ERROR:
-        return typeof payload === "string" || typeof payload === "object";
+        return typeof payload === "string" || isObject(payload);
       case PacketType.EVENT:
       case PacketType.BINARY_EVENT:
         return (

test/parser.js

@@ -115,6 +115,7 @@ describe("socket.io-parser", () => {
 
     isInvalidPayload('442["some","data"');
     isInvalidPayload('0/admin,"invalid"');
+    isInvalidPayload("0[]");
     isInvalidPayload("1/admin,{}");
     isInvalidPayload('2/admin,"invalid');
     isInvalidPayload("2/admin,{}");