@anymux/union

Union/overlay file system for AnyMux. Layer multiple file systems with configurable read/write precedence.

Installation

pnpm add @anymux/union

Usage

import { UnionFileSystem } from "@anymux/union";
import { MemoryFileSystem } from "@anymux/file-system/mem-fs";

const base = new MemoryFileSystem();
const overlay = new MemoryFileSystem();

// Writes go to overlay; reads check overlay first, then base
const fs = new UnionFileSystem([
  { fs: overlay, writable: true },
  { fs: base, writable: false },
]);

await base.writeFile("/config.txt", "default");
await fs.writeFile("/config.txt", "custom"); // written to overlay

const content = await fs.readFile("/config.txt", "utf-8"); // "custom"

API Overview

Implements IFileSystem by composing multiple file systems into a layered stack.

• Read operations — search layers top-to-bottom, return first match
• Write operations — directed to the first writable layer
• Directory listings — merged across all layers, deduplicating entries
• Copy-on-write semantics when modifying files from read-only layers

License

MIT