Cannot connect to Discord via websocket

[CompaqDisc]

Minecraft Version

1.19.x

Version

1.100.10

Details

Logs:
latest.log
debug.log

Root Cause

I've found out by fiddling with curl that this is caused by ComputerCraft/Netty adding an origin header to the request.

---

Action Performed:
I tried connecting to the Discord Gateway API using http.websocket(url, headers)

The Lua code for which was:

local api_base = "https://discord.com/api/v10"
local default_headers = {
    ["User-Agent"] = "DiscordBot (https://compaqdisc.com/, 1.0)"
}

-- Get gateway websocket uri
function get_gateway()
    resp = http.get(api_base .. "/gateway", default_headers)
    return textutils.unserializeJSON(resp.readAll())["url"]
end

function open_discord_ws(gateway_uri)
    return http.websocket(gateway_uri, default_headers)
end

gateway = get_gateway()
print("Discord gateway URI: " .. gateway)
ws, error = open_discord_ws(gateway ..  "/?v=10&encoding=json")
if ws == false then
    print(error)
    return
end
print(ws.receive())
ws.close()

Expected Result:
The connection would succeed and I would receive the expected WebSocket message, in the same manner as the tool wscat, invoked as per the following (and run from the same PC/IP address):

wscat -H "User-Agent: DiscordBot (https://compaqdisc.com/, 1.0)" --connect "wss://gateway.discord.gg/?v=10&encoding=json"

Actual Result:
My connection is disconnected with the error: Invalid handshake response getStatus: 403 Forbidden, which results from Cloudflare dropping the connection with a HTTP 403 / Cloudflare 1020.

Additionally:
The existing code works correctly if I instead try to connect to wss://api.kashall.dev/socket, which the author @kashalls has told me is written in NodeJS and is also behind Cloudflare. So my primary concern is if behind the scenes something odd is done that would result in such behaviour.

Requests (captured from Wireshark)
Successful (with wscat, it actually returns 301, because for testing I did this over http):

Transmission Control Protocol, Src Port: 33366, Dst Port: 80, Seq: 1, Ack: 1, Len: 302
Hypertext Transfer Protocol
    GET /?v=10&encoding=json HTTP/1.1\r\n
    Sec-WebSocket-Version: 13\r\n
    Sec-WebSocket-Key: 7QGr6iUbtzcY3l1PZ1Tk2w==\r\n
    Connection: Upgrade\r\n
    Upgrade: websocket\r\n
    User-Agent:  DiscordBot (https://compaqdisc.com/, 1.0)\r\n
    Sec-WebSocket-Extensions: permessage-deflate; client_max_window_bits\r\n
    Host: gateway.discord.gg\r\n
    \r\n
    [Full request URI: http://gateway.discord.gg/?v=10&encoding=json]
    [HTTP request 1/1]
    [Response in frame: 461]

Unsuccessful (ComputerCraft):

Transmission Control Protocol, Src Port: 57448, Dst Port: 80, Seq: 1, Ack: 1, Len: 399
Hypertext Transfer Protocol
    GET /?v=10&encoding=json HTTP/1.1\r\n
    User-Agent: DiscordBot (https://compaqdisc.com/, 1.0)\r\n
    host: gateway.discord.gg\r\n
    upgrade: websocket\r\n
    connection: upgrade\r\n
    sec-websocket-key: dnJmguIrvsyIKHB3ZSFxEA==\r\n
    origin: http://gateway.discord.gg\r\n
    sec-websocket-version: 13\r\n
    sec-websocket-extensions: permessage-deflate;client_no_context_takeover;client_max_window_bits,deflate-frame,x-webkit-deflate-frame\r\n
    \r\n
    [Full request URI: http://gateway.discord.gg/?v=10&encoding=json]
    [HTTP request 1/1]
    [Response in frame: 26]

[SquidDev]

Thank you for the detailed report, that's very useful! Maybe I need a separate issue label for websockets, the bugs are always so nasty >_>.

In this case, it looks to be an instance of netty/netty#9673. I think the easiest thing to do here is subclass WebSocketClientHandshaker13, override newHandshakeRequest and then remove the Origin header from the request if it's not present in the user-supplied custom headers.

Will have a look at that this evening. Should be easy, just unfortunate it needs to be done at all!

[CompaqDisc]

I'm happy that I was able to get things into the right hands!

Luckily this can be worked around in-game (at least in this particular situation) by defining the origin header content as an empty string like so:

local my_headers = {
    ["X-Foo"] = "bar",
    ["Origin"] = ""
}