[Feature suggestion & draft] Redesigned browser dialer

[PoneyClairDeLune]

A continuation of #3832. Aimed at maximizing throughput and minimizing resource consumption on the browser side, and also potentially allowing arbitrary headers with the browser dialer.

Prerequisites

This draft is designed with the following assumptions.

• The web server implementation in Go supports routable HTTP servers with streaming and WebSocket support.
• The implementation of maps in Go is 💫 blazingly fast 💫.
• The user has a recent installation of a modern browser (Chromium, Firefox or Safari).

Design

Still not fleshed out. Critiques are welcomed!

Web routes

WS /control

The control plane. This is the only place where any form of processing can happen with all possible latest web features. Xray can command the browser dialer on what and how to connect through it. If request bodies from Meek-like transports are not streamed, this should also carry the body of the request.

Message structure

Byte length	Required?	Use
4 (uint32)	Y	Length of payload. MSB to eliminate uncertainty of endianness with a somewhat fast implementation, or LSB to maximize speed. Should always be 0 for WebSocket connections and streamed web requests.
variable	Y	JSON-encoded command.
variable	N	Raw payload. Currently only used by non-streamed requests to post to remote.

Commands

{
	"m": "WS", // Method, can be "WS", "GET" or "POST"
	"p": "", // A string or an array of strings for expected **WebSocket** protocols
	"r": "", // Remote URL
	"i": 65535, // A numerical (positive integer) or a web-safe random string ID to distinguish connections
	"h": {} // A map of non-restricted custom headers to send to the server, cannot be used for WebSocket
}

WS /data?id=<socketId>

For Chrome 124 and later. Where contents of WebSocket connections are passed through without any processing.

WebSocketStream - MDN

GET/POST /data?id=<socketId>

For Chrome 105 and later. Where contents of all web-compliant connections are passed through without any processing. Has the exact same use as above, only that for each duplex connection, a get-post pair is created due to browsers refusing to support HTTP/2 cleartext.

Send ReadableStream in request body - caniuse.com

Browser-side behaviour

Criteria	WebSocket behaviour
WebSocketStream	WebSocketStream pass-through 1
Anything else	Iterated WebSocket

Criteria	Meek-like behaviour
Chrome 105+	Request stream pass-through
Anything else	Iterated bodies (memory leak)

• 1: Using streamed requests instead of streamed WebSocket on the local machine may yield better performance, as instead of native piping, server to client messages could all be in pass-through.

[RPRX]

https://github.com/XTLS/Xray-core/pull/3832

And somehow the browser dialer of SplitHTTP is implemented via WebSocket instead of fetch request in either direction.

关于这个我想起来了，因为初版 browser dialer 写于 2021 年，而 chromium 在 2022 年才支持 streaming requests with fetch

并且 websocket 没有任何同源限制，不过问题不大，https://github.com/XTLS/Xray-core/pull/3830 加了跨域 header 就没问题了，~~话说加跨域 header 前竟然也能用~~

[RPRX]

~~刚又仔细看了一眼发现自己已读乱回了~~

[PoneyClairDeLune]

https://github.com/XTLS/Xray-core/blob/main/transport/internet/browser_dialer/dialer.go#L35

Went through the Go code for the browser dialer today. Not sure what purpose does the CSRF token serve, but if they're utilized to reject local scanning initiated from websites, an origin filter should suffice. Suppose a random website initiates a WebSocket connection to the browser dialer, but no matter how they try, the Origin header will always be set, thus the same effect could be achieved by simply rejecting WebSocket connections with a mismatched Origin header.

---

Another thought: Maybe the browser dialer page could benefit from some visual overhaul...

[PoneyClairDeLune]

Have been discussing with Fangliding regarding the redesigned dialer. Would it be acceptable for the browser dialer to only support Chromium browsers, or some kind of fallback mechanism is needed?

Furthermore, it's later discovered that major browser vendors limit persistent connections to destinations. 256 (full-duplex) in total for WebSockets, 6 (half-duplex) for normal web requests. This effectively made reliance on WebSocket for data pass-through a requirement, as well as mandating some kind of multiplexing for the browser so that it never passes the limit. May not be urgent on the Xray side at the moment, but it might be better kept in mind for future renovations.

[PoneyClairDeLune]

I'll just do a Chromium-only dialer first then until feedbacks come in.