Stream output to a local file - Denoland

You can stream output to a local file in a sandbox. This avoids buffering entire large artifacts in memory.

If you generate something sizable inside the sandbox (like big.txt below), you can pipe it out chunk-by-chunk over a ReadableStream, converting Node’s fs.WriteStream to a Web WritableStream for efficient transfer.

import { Sandbox } from "@deno/sandbox";
import fs from "node:fs";
import { Writable } from "node:stream";

await using sandbox = await Sandbox.create();

// Create a large file in the sandbox
await sandbox.fs.writeTextFile("big.txt", "#".repeat(5_000_000));

// Stream it out to a local file
const child = await sandbox.spawn("cat", {
  args: ["big.txt"],
  stdout: "piped",
});
const file = fs.createWriteStream("./big-local-copy.txt");
await child.stdout.pipeTo(Writable.toWeb(file));

const status = await child.status;
console.log("done:", status);

This pattern keeps memory usage flat, works well for logs or big binaries, and lets you persist sandbox results on the host without temporary files or stdout truncation.