AnyFS Backend Guide

anyfs-backend is the foundational crate for the AnyFS ecosystem. It provides a trait-based abstraction for filesystem operations, allowing you to:

• Write code that works with any filesystem backend
• Create middleware layers that add cross-cutting functionality
• Build FUSE filesystems with a clean, type-safe API

Who Is This Guide For?

• Backend implementers: You want to create a new filesystem backend (S3, Google Drive, in-memory, etc.)
• Middleware authors: You want to add logging, caching, encryption, or other features as composable layers
• Library users: You want to understand how to use anyfs effectively

What You’ll Learn

Implementing a Backend

Step-by-step guide to implementing a complete filesystem backend, from basic file operations to full POSIX support.

Implementing Middleware

How to create reusable middleware layers using the Tower-inspired Layer pattern.

Quick Example

use anyfs_backend::{Fs, FsError};
use std::path::Path;

// Write a generic function that works with ANY backend
fn copy_file<B: Fs>(fs: &B, src: &Path, dst: &Path) -> Result<(), FsError> {
    let content = fs.read(src)?;
    fs.write(dst, &content)?;
    Ok(())
}

// Use with any backend that implements Fs
fn main() {
    let fs = my_backend::MyFs::new();
    copy_file(&fs, Path::new("/src.txt"), Path::new("/dst.txt")).unwrap();
}

Design Principles

1. Trait-based: All operations are defined as traits, enabling generic code
2. Layered: Traits are organized in layers (Fs → FsFull → FsFuse → FsPosix)
3. Composable: Middleware layers can be stacked to add functionality
4. Thread-safe: All traits require Send + Sync for concurrent access
5. Error-rich: Detailed error types with full context