Cannot connect to Discord via websocket

[CompaqDisc]

Minecraft Version

1.19.x

Version

1.101.2

Details

Logs: https://mclo.gs/gFl7WdD

Root Cause

I've found out by fiddling with curl that this is caused by ComputerCraft 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]

[CompaqDisc]

Closing as this affects, and has been reported to, upstream. cc-tweaked/CC-Tweaked#1197