✨ feat: Host a relay on Hetzner (#114)

We are hosting a [MoQ](https://quic.video) relay on a remote (bare
metal) server on Hetzner

With a lot of help from @victorpahuus

packages/moq/transport/setup.ts

@@ -0,0 +1,163 @@
+import { Reader, Writer } from "./stream"
+
+export type Message = Client | Server
+export type Role = "publisher" | "subscriber" | "both"
+
+export enum Version {
+	DRAFT_00 = 0xff000000,
+	DRAFT_01 = 0xff000001,
+	DRAFT_02 = 0xff000002,
+	DRAFT_03 = 0xff000003,
+	DRAFT_04 = 0xff000004,
+	KIXEL_00 = 0xbad00,
+	KIXEL_01 = 0xbad01,
+}
+
+// NOTE: These are forked from moq-transport-00.
+//   1. messages lack a sized length
+//   2. parameters are not optional and written in order (role + path)
+//   3. role indicates local support only, not remote support
+
+export interface Client {
+	versions: Version[]
+	role: Role
+	params?: Parameters
+}
+
+export interface Server {
+	version: Version
+	params?: Parameters
+}
+
+export class Stream {
+	recv: Decoder
+	send: Encoder
+
+	constructor(r: Reader, w: Writer) {
+		this.recv = new Decoder(r)
+		this.send = new Encoder(w)
+	}
+}
+
+export type Parameters = Map<bigint, Uint8Array>
+
+export class Decoder {
+	r: Reader
+
+	constructor(r: Reader) {
+		this.r = r
+	}
+
+	async client(): Promise<Client> {
+		const type = await this.r.u53()
+		if (type !== 0x40) throw new Error(`client SETUP type must be 0x40, got ${type}`)
+
+		const count = await this.r.u53()
+
+		const versions = []
+		for (let i = 0; i < count; i++) {
+			const version = await this.r.u53()
+			versions.push(version)
+		}
+
+		const params = await this.parameters()
+		const role = this.role(params?.get(0n))
+
+		return {
+			versions,
+			role,
+			params,
+		}
+	}
+
+	async server(): Promise<Server> {
+		const type = await this.r.u53()
+		if (type !== 0x41) throw new Error(`server SETUP type must be 0x41, got ${type}`)
+
+		const version = await this.r.u53()
+		const params = await this.parameters()
+
+		return {
+			version,
+			params,
+		}
+	}
+
+	private async parameters(): Promise<Parameters | undefined> {
+		const count = await this.r.u53()
+		if (count == 0) return undefined
+
+		const params = new Map<bigint, Uint8Array>()
+
+		for (let i = 0; i < count; i++) {
+			const id = await this.r.u62()
+			const size = await this.r.u53()
+			const value = await this.r.read(size)
+
+			if (params.has(id)) {
+				throw new Error(`duplicate parameter id: ${id}`)
+			}
+
+			params.set(id, value)
+		}
+
+		return params
+	}
+
+	role(raw: Uint8Array | undefined): Role {
+		if (!raw) throw new Error("missing role parameter")
+		if (raw.length != 1) throw new Error("multi-byte varint not supported")
+
+		switch (raw[0]) {
+			case 1:
+				return "publisher"
+			case 2:
+				return "subscriber"
+			case 3:
+				return "both"
+			default:
+				throw new Error(`invalid role: ${raw[0]}`)
+		}
+	}
+}
+
+export class Encoder {
+	w: Writer
+
+	constructor(w: Writer) {
+		this.w = w
+	}
+
+	async client(c: Client) {
+		await this.w.u53(0x40)
+		await this.w.u53(c.versions.length)
+		for (const v of c.versions) {
+			await this.w.u53(v)
+		}
+
+		// I hate it
+		const params = c.params ?? new Map()
+		params.set(0n, new Uint8Array([c.role == "publisher" ? 1 : c.role == "subscriber" ? 2 : 3]))
+		await this.parameters(params)
+	}
+
+	async server(s: Server) {
+		await this.w.u53(0x41)
+		await this.w.u53(s.version)
+		await this.parameters(s.params)
+	}
+
+	private async parameters(p: Parameters | undefined) {
+		if (!p) {
+			await this.w.u8(0)
+			return
+		}
+
+		await this.w.u53(p.size)
+		for (const [id, value] of p) {
+			await this.w.u62(id)
+			await this.w.u53(value.length)
+			await this.w.write(value)
+		}
+	}
+}