fix(engineio/ws): extra byte in websocket binary frame on EIO v3 (#278)

In v3 of the engine.io protocol, the packet type byte is prepended to
the binary data that is sent out on a websocket binary frame.  This byte
needs to be stripped off the data before it's sent to the handler.

Closes #277.

Author: kelnos

engineioxide/src/transport/ws.rs

@@ -182,7 +182,11 @@ where
                 }
                 p => return Err(Error::BadPacket(p)),
             },
-            Message::Binary(data) => {
+            Message::Binary(mut data) => {
+                if socket.protocol == ProtocolVersion::V3 && !data.is_empty() {
+                    // The first byte is the message type, which we don't need.
+                    let _ = data.remove(0);
+                }
                 engine.handler.on_binary(data, socket.clone());
                 Ok(())
             }
@@ -212,7 +216,11 @@ where
         macro_rules! map_fn {
             ($item:ident) => {
                 let res = match $item {
-                    Packet::Binary(bin) | Packet::BinaryV3(bin) => {
+                    Packet::Binary(mut bin) | Packet::BinaryV3(mut bin) => {
+                        if socket.protocol == ProtocolVersion::V3 {
+                            // v3 protocol requires packet type as the first byte
+                            bin.insert(0, 0x04);
+                        }
                         tx.feed(Message::Binary(bin)).await
                     }
                     Packet::Close => {