Programming language: Go
License: MIT License
Tags: Networking    

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Golang FTP Server library

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This library allows to easily build a simple and fully-featured FTP server using afero as the backend filesystem.

If you're interested in a fully featured FTP server, you should use sftpgo (fully featured SFTP/FTP server) or ftpserver (basic FTP server).

Current status of the project


  • Uploading and downloading files
  • Directory listing (LIST + MLST)
  • File and directory deletion and renaming
  • TLS support (AUTH + PROT)
  • File download/upload resume support (REST)
  • Passive socket connections (PASV and EPSV commands)
  • Active socket connections (PORT and EPRT commands)
  • IPv6 support (EPSV + EPRT)
  • Small memory footprint
  • Clean code: No sync, no sleep, no panic
  • Uses only the standard library except for:
    • afero for generic file systems handling
    • go-kit log (optional) for logging
  • Supported extensions:
    • AUTH - Control session protection
    • AUTH TLS - TLS session
    • PROT - Transfer protection
    • EPRT/EPSV - IPv6 support
    • MDTM - File Modification Time
    • SIZE - Size of a file
    • REST - Restart of interrupted transfer
    • MLST - Simple file listing for machine processing
    • MLSD - Directory listing for machine processing
    • HASH - Hashing of files
    • AVLB - Available space
    • COMB - Combine files

Quick test

The easiest way to test this library is to use ftpserver.

The driver

The simplest way to get a good understanding of how the driver shall be implemented, you can have a look at the tests driver.

The base API

The API is directly based on afero.

// MainDriver handles the authentication and ClientHandlingDriver selection
type MainDriver interface {
    // GetSettings returns some general settings around the server setup
    GetSettings() (*Settings, error)

    // ClientConnected is called to send the very first welcome message
    ClientConnected(cc ClientContext) (string, error)

    // ClientDisconnected is called when the user disconnects, even if he never authenticated
    ClientDisconnected(cc ClientContext)

    // AuthUser authenticates the user and selects an handling driver
    AuthUser(cc ClientContext, user, pass string) (ClientDriver, error)

    // GetTLSConfig returns a TLS Certificate to use
    // The certificate could frequently change if we use something like "let's encrypt"
    GetTLSConfig() (*tls.Config, error)

// ClientDriver is the base FS implementation that allows to manipulate files
type ClientDriver interface {

// ClientContext is implemented on the server side to provide some access to few data around the client
type ClientContext interface {
    // Path provides the path of the current connection
    Path() string

    // SetDebug activates the debugging of this connection commands
    SetDebug(debug bool)

    // Debug returns the current debugging status of this connection commands
    Debug() bool

    // Client's ID on the server
    ID() uint32

    // Client's address
    RemoteAddr() net.Addr

    // Servers's address
    LocalAddr() net.Addr

    // Client's version can be empty
    GetClientVersion() string

    // Close closes the connection and disconnects the client.
    Close() error

    // HasTLSForControl returns true if the control connection is over TLS
    HasTLSForControl() bool

    // HasTLSForTransfers returns true if the transfer connection is over TLS
    HasTLSForTransfers() bool

    // GetLastCommand returns the last received command
    GetLastCommand() string

// Settings define all the server settings
type Settings struct {
    Listener                 net.Listener     // (Optional) To provide an already initialized listener
    ListenAddr               string           // Listening address
    PublicHost               string           // Public IP to expose (only an IP address is accepted at this stage)
    PublicIPResolver         PublicIPResolver // (Optional) To fetch a public IP lookup
    PassiveTransferPortRange *PortRange       // (Optional) Port Range for data connections. Random if not specified
    ActiveTransferPortNon20  bool             // Do not impose the port 20 for active data transfer (#88, RFC 1579)
    IdleTimeout              int              // Maximum inactivity time before disconnecting (#58)
    ConnectionTimeout        int              // Maximum time to establish passive or active transfer connections
    DisableMLSD              bool             // Disable MLSD support
    DisableMLST              bool             // Disable MLST support
    DisableMFMT              bool             // Disable MFMT support (modify file mtime)
    Banner                   string           // Banner to use in server status response
    TLSRequired              TLSRequirement   // defines the TLS mode
    DisableLISTArgs          bool             // Disable ls like options (-a,-la etc.) for directory listing
    DisableSite              bool             // Disable SITE command
    DisableActiveMode        bool             // Disable Active FTP
    EnableHASH               bool             // Enable support for calculating hash value of files
    DisableSTAT              bool             // Disable Server STATUS, STAT on files and directories will still work
    DisableSYST              bool             // Disable SYST
    EnableCOMB               bool             // Enable COMB support
    DefaultTransferType      TransferType     // Transfer type to use if the client don't send the TYPE command


There are a few extensions to the base afero APIs so that you can perform some operations that aren't offered by afero.

Pre-allocate some space

// ClientDriverExtensionAllocate is an extension to support the "ALLO" - file allocation - command
type ClientDriverExtensionAllocate interface {

    // AllocateSpace reserves the space necessary to upload files
    AllocateSpace(size int) error

Get available space

// ClientDriverExtensionAvailableSpace is an extension to implement to support
// the AVBL ftp command
type ClientDriverExtensionAvailableSpace interface {
    GetAvailableSpace(dirName string) (int64, error)

Create symbolic link

// ClientDriverExtensionSymlink is an extension to support the "SITE SYMLINK" - symbolic link creation - command
type ClientDriverExtensionSymlink interface {

    // Symlink creates a symlink
    Symlink(oldname, newname string) error

    // SymlinkIfPossible allows to get the source of a symlink (but we don't need for now)
    // ReadlinkIfPossible(name string) (string, error)

Compute file hash

// ClientDriverExtensionHasher is an extension to implement if you want to handle file digests
// yourself. You have to set EnableHASH to true for this extension to be called
type ClientDriverExtensionHasher interface {
    ComputeHash(name string, algo HASHAlgo, startOffset, endOffset int64) (string, error)

History of the project

I wanted to make a system which would accept files through FTP and redirect them to something else. Go seemed like the obvious choice and it seemed there was a lot of libraries available but it turns out none of them were in a useable state.