FmiSrl.FtpServer

A lightweight, modern FTP server library for .NET.

Features

• Fully asynchronous operation.
• Supports both Dependency Injection and manual instantiation.
• Extensible authentication and file system providers.
• Built-in support for common FTP commands (USER, PASS, LIST, RETR, STOR, etc.).
• PASV mode support.

Installation

dotnet add package FmiSrl.FtpServer.Server

Usage

With Dependency Injection (Recommended)

To use the FTP server in a modern .NET application (e.g., ASP.NET Core, Worker Service), register it in your Program.cs:

using Microsoft.Extensions.DependencyInjection;
using FmiSrl.FtpServer.Server;
using FmiSrl.FtpServer.Server.DependencyInjection;
using FmiSrl.FtpServer.Server.Services;

var builder = Host.CreateApplicationBuilder(args);

// Configure Options for Providers
builder.Services.Configure<PhysicalFileSystemProviderOptions>(opt =>
{
    opt.RootDirectory = "./my_ftp_root";
});

builder.Services.Configure<SimpleAuthenticationProviderOptions>(opt =>
{
    opt.Username = "admin";
    opt.Password = "secure_password";
});

// Add FTP Server and configure providers via generic DI
builder.Services.AddFtpServer(options =>
{
    options.FtpPort = 21;
    options.ServerName = "My Custom FTP Server";
})
.UseFileSystemProvider<PhysicalFileSystemProvider>()
.UseAuthenticationProvider<SimpleAuthenticationProvider>();

var host = builder.Build();

// Get the server instance and start it
var ftpServer = host.Services.GetRequiredService<FtpServer>();
await ftpServer.StartAsync();

await host.RunAsync();

The server is registered as a Singleton by default.

Without Dependency Injection

You can also use the library in simple console applications or legacy projects without a DI container:

using FmiSrl.FtpServer.Server;
using FmiSrl.FtpServer.Server.Services;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;

var serverOptions = Options.Create(new FtpServerConfigurationOptions
{
    FtpPort = 2121,
    ServerName = "Standalone FTP Server"
});

var fsOptions = Options.Create(new PhysicalFileSystemProviderOptions
{
    RootDirectory = "./ftp_root"
});

var authOptions = Options.Create(new SimpleAuthenticationProviderOptions
{
    Username = "user",
    Password = "password"
});

// Providers are strictly required
var ftpServer = new FtpServer(
    new PhysicalFileSystemProvider(fsOptions),
    new SimpleAuthenticationProvider(authOptions),
    serverOptions,
    NullLogger<FtpServer>.Instance
);

await ftpServer.StartAsync();
Console.WriteLine("Server started. Press any key to stop.");
Console.ReadKey();
await ftpServer.StopAsync();

Configuration

Logging

The library uses Microsoft.Extensions.Logging. When using DI, it will automatically use the configured logging providers (e.g., Serilog, Console, Debug).

When used manually, you can pass any ILogger<FtpServer> implementation to the constructor.

Authentication Provider

Implement the IAuthenticationProvider interface to customize how users are authenticated:

public interface IAuthenticationProvider
{
    Task<bool> AuthenticateAsync(string username, string password);
}

File System Provider

Implement the IFileSystemProvider interface to provide custom storage (e.g., Azure Blob Storage, Database, S3). It provides an FtpAuthenticationContext which includes the currently authenticated username:

using FmiSrl.FtpServer.Server.Abstractions;

public interface IFileSystemProvider
{
    Task<IEnumerable<FileSystemEntry>> GetEntriesAsync(FtpAuthenticationContext authContext, string path);
    Task<Stream> OpenReadAsync(FtpAuthenticationContext authContext, string path);
    Task<Stream> OpenWriteAsync(FtpAuthenticationContext authContext, string path);
    Task DeleteFileAsync(FtpAuthenticationContext authContext, string path);
    Task CreateDirectoryAsync(FtpAuthenticationContext authContext, string path);
    Task DeleteDirectoryAsync(FtpAuthenticationContext authContext, string path);
    Task<bool> FileExistsAsync(FtpAuthenticationContext authContext, string path);
    Task<bool> DirectoryExistsAsync(FtpAuthenticationContext authContext, string path);
    Task RenameAsync(FtpAuthenticationContext authContext, string oldPath, string newPath);
}