✨ 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/client.ts

@@ -0,0 +1,83 @@
+import * as Stream from "./stream"
+import * as Setup from "./setup"
+import * as Control from "./control"
+import { Objects } from "./objects"
+import { Connection } from "./connection"
+
+export interface ClientConfig {
+	url: string
+
+	// Parameters used to create the MoQ session
+	role: Setup.Role
+
+	// If set, the server fingerprint will be fetched from this URL.
+	// This is required to use self-signed certificates with Chrome (May 2023)
+	fingerprint?: string
+}
+
+export class Client {
+	#fingerprint: Promise<WebTransportHash | undefined>
+
+	readonly config: ClientConfig
+
+	constructor(config: ClientConfig) {
+		this.config = config
+
+		this.#fingerprint = this.#fetchFingerprint(config.fingerprint).catch((e) => {
+			console.warn("failed to fetch fingerprint: ", e)
+			return undefined
+		})
+	}
+
+	async connect(): Promise<Connection> {
+		// Helper function to make creating a promise easier
+		const options: WebTransportOptions = {}
+
+		const fingerprint = await this.#fingerprint
+		if (fingerprint) options.serverCertificateHashes = [fingerprint]
+
+		const quic = new WebTransport(this.config.url, options)
+		await quic.ready
+
+		const stream = await quic.createBidirectionalStream()
+
+		const writer = new Stream.Writer(stream.writable)
+		const reader = new Stream.Reader(new Uint8Array(), stream.readable)
+
+		const setup = new Setup.Stream(reader, writer)
+
+		// Send the setup message.
+		await setup.send.client({ versions: [Setup.Version.DRAFT_04], role: this.config.role })
+
+		// Receive the setup message.
+		// TODO verify the SETUP response.
+		const server = await setup.recv.server()
+
+		if (server.version != Setup.Version.DRAFT_04) {
+			throw new Error(`unsupported server version: ${server.version}`)
+		}
+
+		const control = new Control.Stream(reader, writer)
+		const objects = new Objects(quic)
+
+		return new Connection(quic, control, objects)
+	}
+
+	async #fetchFingerprint(url?: string): Promise<WebTransportHash | undefined> {
+		if (!url) return
+
+		// TODO remove this fingerprint when Chrome WebTransport accepts the system CA
+		const response = await fetch(url)
+		const hexString = await response.text()
+
+		const hexBytes = new Uint8Array(hexString.length / 2)
+		for (let i = 0; i < hexBytes.length; i += 1) {
+			hexBytes[i] = parseInt(hexString.slice(2 * i, 2 * i + 2), 16)
+		}
+
+		return {
+			algorithm: "sha-256",
+			value: hexBytes,
+		}
+	}
+}