From 4b48bdd3e537d5f8aa4f3007cbd265c35ebd8a6e Mon Sep 17 00:00:00 2001
From: Erik Little <nuclear.ace@gmail.com>
Date: Tue, 6 Jun 2017 07:52:35 -0400
Subject: [PATCH] guard creating prefixless data

---
 Source/SocketIO/Engine/SocketEngine.swift | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/Source/SocketIO/Engine/SocketEngine.swift b/Source/SocketIO/Engine/SocketEngine.swift
index 969011b..d6994a2 100644
--- a/Source/SocketIO/Engine/SocketEngine.swift
+++ b/Source/SocketIO/Engine/SocketEngine.swift
@@ -223,7 +223,11 @@ public final class SocketEngine : NSObject, URLSessionDelegate, SocketEnginePoll
 
     private func handleBase64(message: String) {
         // binary in base64 string
-        let noPrefix = String(message[message.index(message.startIndex, offsetBy: 2)..<message.endIndex])!
+        guard let noPrefix = String(message[message.index(message.startIndex, offsetBy: 2)..<message.endIndex]) else {
+            client?.parseEngineBinaryData(Data())
+
+            return
+        }
 
         if let data = Data(base64Encoded: noPrefix, options: .ignoreUnknownCharacters) {
             client?.parseEngineBinaryData(data)