@langchain/node-vfs

Node.js Virtual File System backend for DeepAgents.

This package provides an in-memory VFS implementation that enables agents to work with files in an isolated environment without touching the real filesystem. It uses node-vfs-polyfill which implements the upcoming Node.js VFS feature (nodejs/node#61478).

Installation

npm install @langchain/node-vfs deepagents
# or
pnpm add @langchain/node-vfs deepagents

Quick Start

import { VfsSandbox } from "@langchain/node-vfs";
import { createDeepAgent } from "deepagents";
import { ChatAnthropic } from "@langchain/anthropic";

// Create and initialize a VFS sandbox
const sandbox = await VfsSandbox.create({
  initialFiles: {
    "/src/index.js": "console.log('Hello from VFS!')",
  },
});

try {
  const agent = createDeepAgent({
    model: new ChatAnthropic({ model: "claude-sonnet-4-20250514" }),
    systemPrompt: "You are a coding assistant with VFS access.",
    backend: sandbox,
  });

  const result = await agent.invoke({
    messages: [{ role: "user", content: "Run the index.js file" }],
  });
} finally {
  await sandbox.stop();
}

Features

• In-Memory File Storage - Files are stored in a virtual file system using node-vfs-polyfill
• Zero Setup - No Docker, cloud services, or external dependencies required
• Full Command Execution - Execute shell commands with automatic file syncing
• Automatic Cleanup - All resources are cleaned up when sandbox stops
• Initial Files - Pre-populate the sandbox with files at creation time
• Fallback Mode - Automatically falls back to temp directory if VFS is unavailable

API Reference

VfsSandbox

The main class for creating and managing VFS sandboxes.

Static Methods

VfsSandbox.create(options?)

Create and initialize a new VFS sandbox in one step.

const sandbox = await VfsSandbox.create({
  mountPath: "/vfs", // Mount path for the VFS (default: "/vfs")
  timeout: 30000, // Command timeout in ms (default: 30000)
  initialFiles: {
    // Initial files to populate
    "/README.md": "# Hello",
    "/src/index.js": "console.log('Hello')",
  },
});

Instance Methods

sandbox.execute(command)

Execute a shell command in the sandbox.

const result = await sandbox.execute("node src/index.js");
console.log(result.output); // Command output
console.log(result.exitCode); // Exit code (0 = success)

sandbox.uploadFiles(files)

Upload files to the sandbox.

const encoder = new TextEncoder();
await sandbox.uploadFiles([
  ["src/app.js", encoder.encode("console.log('Hi')")],
  ["package.json", encoder.encode('{"name": "test"}')],
]);

sandbox.downloadFiles(paths)

Download files from the sandbox.

const results = await sandbox.downloadFiles(["src/app.js"]);
for (const result of results) {
  if (result.content) {
    console.log(new TextDecoder().decode(result.content));
  }
}

sandbox.stop()

Stop the sandbox and clean up resources.

await sandbox.stop();

Factory Functions

createVfsSandboxFactory(options?)

Create an async factory that creates new sandboxes per invocation.

const factory = createVfsSandboxFactory({
  initialFiles: { "/README.md": "# Hello" },
});

const sandbox = await factory();

createVfsSandboxFactoryFromSandbox(sandbox)

Create a factory that reuses an existing sandbox.

const sandbox = await VfsSandbox.create();
const factory = createVfsSandboxFactoryFromSandbox(sandbox);

Configuration Options

Option	Type	Default	Description
mountPath	string	"/vfs"	Mount path for the virtual file system
timeout	number	30000	Command execution timeout in milliseconds
initialFiles	Record<string, string | Uint8Array>	undefined	Initial files to populate the VFS

Error Handling

The package exports a VfsSandboxError class for typed error handling:

import { VfsSandboxError } from "@langchain/node-vfs";

try {
  await sandbox.execute("some-command");
} catch (error) {
  if (error instanceof VfsSandboxError) {
    switch (error.code) {
      case "NOT_INITIALIZED":
        // Handle uninitialized sandbox
        break;
      case "COMMAND_TIMEOUT":
        // Handle timeout
        break;
    }
  }
}

Error Codes

• NOT_INITIALIZED - Sandbox not initialized
• ALREADY_INITIALIZED - Sandbox already initialized
• INITIALIZATION_FAILED - Failed to initialize VFS
• COMMAND_TIMEOUT - Command execution timed out
• COMMAND_FAILED - Command execution failed
• FILE_OPERATION_FAILED - File operation failed
• NOT_SUPPORTED - VFS not supported in environment

How It Works

The VFS sandbox uses a hybrid approach for maximum compatibility:

1. File Storage - Files are stored in-memory using the VirtualFileSystem from node-vfs-polyfill
2. Command Execution - When executing commands, files are synced to a temp directory, the command runs, and changes are synced back to VFS
3. Fallback Mode - If node-vfs-polyfill is unavailable, falls back to using a temp directory for both storage and execution

This approach provides the benefits of in-memory storage (isolation, speed) while maintaining full shell command execution support.

Future: Native Node.js VFS

This package uses node-vfs-polyfill which implements the upcoming Node.js VFS feature being developed in nodejs/node#61478.

When the official node:vfs module lands in Node.js, this package will be updated to use the native implementation for better performance and compatibility.

License

MIT