VirtualFS

VirtualFS is a .NET library for composing multiple file-like data sources into one virtual hierarchy.

The core model is:

• every backend implements IFileSystem
• a RootFileSystem mounts many backends under virtual paths
• callers interact with virtual paths like /assets/logo.png
• reads and writes are dispatched to the mounted backend that owns that path

It behaves more like a small VFS layer than a thin System.IO wrapper.

Status

The project currently targets:

• netstandard2.0
• net472
• net6.0
• net8.0
• net10.0

The test project targets net10.0.

Key Rules

• paths are always rooted
• /foo/ is a directory
• /foo is a file
• trailing / defines directory vs file
• path separator is always /
• mounted filesystems can overlap
• mount priority controls lookup order

Minimal Example

using System.IO;
using VirtualFS;
using VirtualFS.Implementation;
using VirtualFS.Memory;
using VirtualFS.Physical;

var root = new RootFileSystem();

root.Mount(new PhysicalFileSystem(new DirectoryInfo("./content")), "/");
root.Mount(new MemoryFileSystem { Priority = FileSystemMountPriority.High }, "/");

root.Root.FileCreate("runtime.txt").WriteAllText("generated at runtime");

foreach (var entry in root.Root.GetEntries())
{
    Console.WriteLine($"{entry.FullPath} readonly={entry.IsReadOnly}");
}

Documentation

Detailed documentation is split into the docs/ folder:

• Documentation Index
• Architecture
• Usage
• Backends
• Development

Build and Test

The repository includes a Docker-based build/test flow using the official .NET 10 SDK image.

docker build --target test -t virtualfs:test .

The repository CI runs the same Docker target on pushes and pull requests.

License

The project metadata declares the MIT license.