athost / proxy.js

import { createServer } from "node:http";
import { Readable } from "node:stream";
import { parseArgs } from "node:util";

const { values } = parseArgs({
	args: process.argv.slice(2),
	options: {
		port: { type: "string", default: "3000" },
		did: { type: "string" },
		rkey: { type: "string" },
	},
});

const did = values.did,
	collection = "com.jakelazaroff.athost",
	rkey = values.rkey;

if (!did) {
	console.error("--did is required.");
	process.exit(1);
}

if (!rkey) {
	console.error("--rkey is required.");
	process.exit(1);
}

const doc = await resolveDid(did);
const pds = doc.service[0].serviceEndpoint;

/** @type {Error | undefined} */
let error;

let record = await getRecord(pds, did, collection, rkey);
let files = untar(await getBlob(pds, did, record.value.assets.ref.$link));
let updating = false;

async function updateRecord() {
	if (updating) return;
	try {
		updating = true;
		record = await getRecord(pds, did, collection, rkey);
		files = untar(await getBlob(pds, did, record.value.assets.ref.$link));
		error = undefined;
	} catch (e) {
		error = e;
	} finally {
		updating = false;
	}
}

/**
 *
 * @param {number} status
 * @param {string} message
 */
function fail(res, status, message) {
	res.statusCode = status;
	res.end(message);
}

const server = createServer(async (req, res) => {
	process.stdout.write(`${req.method} ${req.url} `);
	const start = performance.now();

	let err;
	try {
		if (req.method !== "GET") return fail(res, 405, "Method not supported");
		queueMicrotask(updateRecord);

		if (error) return fail(res, 502, "Bad gateway");

		let path = req.url.slice(1);
		let asset = files[req.url.slice(1)];
		let status = 200;

		// if there's no matching file, try to treat it as a folder and use an index.html inside it
		if (!asset) {
			path = req.url.slice(1).split("/").filter(Boolean).concat("index.html").join("/");
			asset = files[path];
		}

		// if there's *still* no matching file, return a generic 404
		if (!asset) return fail(res, 404, "Not found");

		res.statusCode = status;
		res.setHeader("content-type", getMimeType(path));
		res.setHeader("content-length", asset.size);

		const stream = Readable.fromWeb(asset.stream());
		await new Promise((resolve, reject) => {
			stream.pipe(res);
			stream.on("error", reject);
			stream.on("end", resolve);
			res.on("error", reject);
		});
	} finally {
		const ms = performance.now() - start;
		process.stdout.write(`${res.statusCode} - ${Math.round(ms)}ms\n`);
		if (err) console.error(err);
	}
});

const port = Number.parseInt(values.port) || 3000;
server.listen(port, () => {
	console.log(`Server running at http://localhost:${port}`);
	console.log(`Proxying to at://${did}/${collection}/${rkey}`);
	console.log("");
});

/** @param {string} did */
async function resolveDid(did) {
	let url;
	if (did.startsWith("did:web:")) url = `https://${did.slice(8)}/.well-known/did.json`;
	else if (did.startsWith("did:plc:")) url = `https://plc.directory/${did}`;
	else throw new Error(`Unsupported did: ${did}`);

	const res = await fetch(url);
	const doc = await res.json();
	return doc;
}

/**
 * @param {string} pds
 * @param {string} did
 * @param {string} collection
 * @param {string} rkey
 */
async function getRecord(pds, did, collection, rkey) {
	const url = new URL(`${pds}/xrpc/com.atproto.repo.getRecord`);
	url.searchParams.set("repo", did);
	url.searchParams.set("collection", collection);
	url.searchParams.set("rkey", rkey);
	const response = await fetch(url);
	return await response.json();
}

/**
 * @param {string} pds
 * @param {string} did
 * @param {string} collection
 * @param {string} rkey
 */
async function getBlob(pds, did, cid) {
	const url = new URL(`${pds}/xrpc/com.atproto.sync.getBlob`);
	url.searchParams.set("did", did);
	url.searchParams.set("cid", cid);

	const res = await fetch(url);
	return new Uint8Array(await res.arrayBuffer());
}

/** @param {Uint8Array} data */
function untar(data) {
	/** @type {Record<string, File>} */
	const files = {};
	let offset = 0;

	while (offset < data.length) {
		// check if we've hit the end (two empty 512-byte blocks)
		if (data[offset] === 0) break;

		// read header (512 bytes)
		const header = data.slice(offset, offset + 512);

		// type flag (156)
		const typeflag = String.fromCharCode(header[156]);

		// file size (124-135, octal string)
		const sizeBytes = header.slice(124, 136);
		const sizeStr = new TextDecoder().decode(sizeBytes).trim().replace(/\0/g, "");
		const size = Number.parseInt(sizeStr, 8) || 0;

		offset += 512;
		const paddedSize = Math.ceil(size / 512) * 512;

		// kkip directories and other non-file entries
		if (typeflag === "5" || typeflag === "x" || typeflag === "g") {
			offset += paddedSize;
			continue;
		}

		// file name (first 100 bytes, null-terminated)
		const nameBytes = header.slice(0, 100);
		const nameEnd = nameBytes.indexOf(0);
		const name = new TextDecoder().decode(nameBytes.slice(0, nameEnd > 0 ? nameEnd : 100));

		if (!name) {
			offset += paddedSize;
			continue;
		}

		// read content
		const content = data.slice(offset, offset + size);
		offset += paddedSize;

		files[name] = new File([content], name.split("/").pop() || name);
	}

	return files;
}

/** @param {string} filename */
function getMimeType(filename) {
	const ext = filename.split(".").pop()?.toLowerCase();
	const mimeTypes = {
		txt: "text/plain",
		html: "text/html",
		css: "text/css",
		js: "text/javascript",
		json: "application/json",
		png: "image/png",
		jpg: "image/jpeg",
		jpeg: "image/jpeg",
		gif: "image/gif",
		svg: "image/svg+xml",
		pdf: "application/pdf",
		zip: "application/zip",
		xml: "application/xml",
	};
	return mimeTypes[ext] || "application/octet-stream";
}