Decompression caching and preview links

src/decompress.js

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+'use strict';
+
+import {Worker} from 'node:worker_threads';
+import path from 'node:path';
+import os from 'node:os';
+import {fileURLToPath} from 'node:url';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
+/** Round-robin pool of worker threads for off-main-thread cluster decompression. */
+class DecompressPool {
+	#workers = [];
+	#next = 0;
+	#pending = new Map(); // id -> {resolve, reject}
+	#nextId = 0;
+	#active = 0;
+
+	constructor(size = Math.max(1, os.cpus().length - 1)) {
+		for (let i = 0; i < size; i++) this.#spawn();
+	}
+
+	#spawn() {
+		const worker = new Worker(path.join(__dirname, 'decompress-worker.js'));
+		worker.on('message', ({id, data, error}) => {
+			const task = this.#pending.get(id);
+			if (!task) return;
+			this.#pending.delete(id);
+			// No work left in flight -> safe to let the process exit again.
+			if (--this.#active === 0) for (const w of this.#workers) w.unref();
+			error ? task.reject(new Error(error)) : task.resolve(Buffer.from(data));
+		});
+		worker.unref(); // idle workers must never keep a short script/server alive
+		this.#workers.push(worker);
+	}
+
+	/** Decompresses `{compType, body}` on the next worker in rotation. `body` must be a Uint8Array/Buffer view. */
+	run({compType, body}) {
+		const worker = this.#workers[this.#next];
+		this.#next = (this.#next + 1) % this.#workers.length;
+		const id = this.#nextId++;
+		const owned = new Uint8Array(body);
+		if (this.#active++ === 0) for (const w of this.#workers) w.ref();
+		return new Promise((resolve, reject) => {
+			this.#pending.set(id, {resolve, reject});
+			worker.postMessage({id, compType, body: owned}, [owned.buffer]);
+		});
+	}
+}
+
+export const decompressPool = new DecompressPool();