ftpserver

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Published: Sep 10, 2021 License: MIT Imports: 26 Imported by: 6

README

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

Features
  • 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 sleep, no panic, no global sync (only around control/transfer connection per client)
  • 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 {
	afero.Fs
}

// 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

	// GetLastDataChannel returns the last data channel mode
	GetLastDataChannel() DataChannel
}

// 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
	// ActiveConnectionsCheck defines the security requirements for active connections
	ActiveConnectionsCheck DataConnectionRequirement
	// PasvConnectionsCheck defines the security requirements for passive connections
	PasvConnectionsCheck DataConnectionRequirement
}
Extensions

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)
}
// 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.

Documentation

Overview

Package ftpserver provides all the tools to build your own FTP server: The core library and the driver.

Index

Constants

View Source
const (
	// 100 Series - The requested action is being initiated, expect another reply before
	// proceeding with a new command.
	StatusFileStatusOK = 150 // RFC 959, 4.2.1

	// 200 Series - The requested action has been successfully completed.
	StatusOK                 = 200 // RFC 959, 4.2.1
	StatusNotImplemented     = 202 // RFC 959, 4.2.1
	StatusSystemStatus       = 211 // RFC 959, 4.2.1
	StatusDirectoryStatus    = 212 // RFC 959, 4.2.1
	StatusFileStatus         = 213 // RFC 959, 4.2.1
	StatusHelpMessage        = 214 // RFC 959, 4.2.1
	StatusSystemType         = 215 // RFC 959, 4.2.1
	StatusServiceReady       = 220 // RFC 959, 4.2.1
	StatusClosingControlConn = 221 // RFC 959, 4.2.1
	StatusClosingDataConn    = 226 // RFC 959, 4.2.1
	StatusEnteringPASV       = 227 // RFC 959, 4.2.1
	StatusEnteringEPSV       = 229 // RFC 2428, 3
	StatusUserLoggedIn       = 230 // RFC 959, 4.2.1
	StatusAuthAccepted       = 234 // RFC 2228, 3
	StatusFileOK             = 250 // RFC 959, 4.2.1
	StatusPathCreated        = 257 // RFC 959, 4.2.1

	// 300 Series - The command has been accepted, but the requested action is on hold,
	// pending receipt of further information.
	StatusUserOK            = 331 // RFC 959, 4.2.1
	StatusFileActionPending = 350 // RFC 959, 4.2.1

	// 400 Series - The command was not accepted and the requested action did not take place,
	// but the error condition is temporary and the action may be requested again.
	StatusServiceNotAvailable      = 421 // RFC 959, 4.2.1
	StatusCannotOpenDataConnection = 425 // RFC 959, 4.2.1
	StatusTransferAborted          = 426 // RFC 959, 4.2.1
	StatusFileActionNotTaken       = 450 // RFC 959, 4.2.1

	// 500 Series - Syntax error, command unrecognized and the requested action did not take
	// place. This may include errors such as command line too long.
	StatusSyntaxErrorNotRecognised = 500 // RFC 959, 4.2.1
	StatusSyntaxErrorParameters    = 501 // RFC 959, 4.2.1
	StatusCommandNotImplemented    = 502 // RFC 959, 4.2.1
	StatusBadCommandSequence       = 503 // RFC 959, 4.2.1
	StatusNotImplementedParam      = 504 // RFC 959, 4.2.1
	StatusNotLoggedIn              = 530 // RFC 959, 4.2.1
	StatusActionNotTaken           = 550 // RFC 959, 4.2.1
	StatusActionAborted            = 552 // RFC 959, 4.2.1
	StatusActionNotTakenNoFile     = 553 // RFC 959, 4.2.1
)

Status codes as documented by: https://tools.ietf.org/html/rfc959 https://tools.ietf.org/html/rfc2428 https://tools.ietf.org/html/rfc2228

Variables

View Source
var (
	// ErrStorageExceeded defines the error mapped to the FTP 552 reply code.
	// As for RFC 959 this error is checked for STOR, APPE
	ErrStorageExceeded = errors.New("storage limit exceeded")
	// ErrFileNameNotAllowed defines the error mapped to the FTP 553 reply code.
	// As for RFC 959 this error is checked for STOR, APPE, RNTO
	ErrFileNameNotAllowed = errors.New("filename not allowed")
)
View Source
var ErrNoAvailableListeningPort = errors.New("could not find any port to listen to")

ErrNoAvailableListeningPort is returned when no port could be found to accept incoming connection

View Source
var (
	// ErrNotListening is returned when we are performing an action that is only valid while listening
	ErrNotListening = errors.New("we aren't listening")
)
View Source
var ErrRemoteAddrFormat = errors.New("remote address has a bad format")

ErrRemoteAddrFormat is returned when the remote address has a bad format

Functions

This section is empty.

Types

type ClientContext

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

	// GetLastDataChannel returns the last data channel mode
	GetLastDataChannel() DataChannel
}

ClientContext is implemented on the server side to provide some access to few data around the client

type ClientDriver

type ClientDriver interface {
	afero.Fs
}

ClientDriver is the base FS implementation that allows to manipulate files

type ClientDriverExtensionAllocate

type ClientDriverExtensionAllocate interface {

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

ClientDriverExtensionAllocate is an extension to support the "ALLO" - file allocation - command

type ClientDriverExtensionAvailableSpace added in v0.12.0

type ClientDriverExtensionAvailableSpace interface {
	GetAvailableSpace(dirName string) (int64, error)
}

ClientDriverExtensionAvailableSpace is an extension to implement to support the AVBL ftp command

type ClientDriverExtensionFileList added in v0.9.0

type ClientDriverExtensionFileList interface {

	// ReadDir reads the directory named by name and return a list of directory entries.
	ReadDir(name string) ([]os.FileInfo, error)
}

ClientDriverExtensionFileList is a convenience extension to allow to return file listing without requiring to implement the methods Open/Readdir for your custom afero.File

type ClientDriverExtensionHasher added in v0.12.0

type ClientDriverExtensionHasher interface {
	ComputeHash(name string, algo HASHAlgo, startOffset, endOffset int64) (string, error)
}

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 ClientDriverExtensionRemoveDir added in v0.9.0

type ClientDriverExtensionRemoveDir interface {
	RemoveDir(name string) error
}

ClientDriverExtensionRemoveDir is an extension to implement if you need to distinguish between the FTP command DELE (remove a file) and RMD (remove a dir). If you don't implement this extension they will be both mapped to the Remove method defined in your afero.Fs implementation

type ClientDriverExtensionSymlink interface {

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

ClientDriverExtensionSymlink is an extension to support the "SITE SYMLINK" - symbolic link creation - command

type ClientDriverExtentionFileTransfer added in v0.9.0

type ClientDriverExtentionFileTransfer interface {

	// GetHandle return an handle to upload or download a file based on flags:
	// os.O_RDONLY indicates a download
	// os.O_WRONLY indicates an upload and can be combined with os.O_APPEND (resume) or
	// os.O_CREATE (upload to new file/truncate)
	//
	// offset is the argument of a previous REST command, if any, or 0
	GetHandle(name string, flags int, offset int64) (FileTransfer, error)
}

ClientDriverExtentionFileTransfer is a convenience extension to allow to transfer files without requiring to implement the methods Create/Open/OpenFile for your custom afero.File.

type CommandDescription

type CommandDescription struct {
	Open            bool                               // Open to clients without auth
	TransferRelated bool                               // This is a command that can open a transfer connection
	SpecialAction   bool                               // Command to handle even if there is a transfer in progress
	Fn              func(*clientHandler, string) error // Function to handle it
}

CommandDescription defines which function should be used and if it should be open to anyone or only logged in users

type DataChannel added in v0.15.0

type DataChannel int

DataChannel is the enumerable that represents the data channel (active or passive)

const (
	DataChannelPassive DataChannel = iota + 1
	DataChannelActive
)

Supported data channel types

type DataConnectionRequirement added in v0.16.0

type DataConnectionRequirement int

DataConnectionRequirement is the enumerable that represents the supported protection mode for data channels

const (
	// IPMatchRequired requires matching peer IP addresses of control and data connection
	IPMatchRequired DataConnectionRequirement = iota
	// IPMatchDisabled disables checking peer IP addresses of control and data connection
	IPMatchDisabled
)

Supported data connection requirements

type FileTransfer added in v0.9.0

type FileTransfer interface {
	io.Reader
	io.Writer
	io.Seeker
	io.Closer
}

FileTransfer defines the inferface for file transfers.

type FileTransferError added in v0.9.0

type FileTransferError interface {
	TransferError(err error)
}

FileTransferError is a FileTransfer extension used to notify errors.

type FtpServer

type FtpServer struct {
	Logger log.Logger // Go-Kit logger
	// contains filtered or unexported fields
}

FtpServer is where everything is stored We want to keep it as simple as possible

func NewFtpServer

func NewFtpServer(driver MainDriver) *FtpServer

NewFtpServer creates a new FtpServer instance

func (*FtpServer) Addr

func (server *FtpServer) Addr() string

Addr shows the listening address

func (*FtpServer) Listen

func (server *FtpServer) Listen() error

Listen starts the listening It's not a blocking call

func (*FtpServer) ListenAndServe

func (server *FtpServer) ListenAndServe() error

ListenAndServe simply chains the Listen and Serve method calls

func (*FtpServer) Serve

func (server *FtpServer) Serve() error

Serve accepts and processes any new incoming client

func (*FtpServer) Stop

func (server *FtpServer) Stop() error

Stop closes the listener

type HASHAlgo added in v0.12.0

type HASHAlgo int

HASHAlgo is the enumerable that represents the supported HASH algorithms

const (
	HASHAlgoCRC32 HASHAlgo = iota
	HASHAlgoMD5
	HASHAlgoSHA1
	HASHAlgoSHA256
	HASHAlgoSHA512
)

Supported hash algorithms

type MainDriver

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)
}

MainDriver handles the authentication and ClientHandlingDriver selection

type MainDriverExtensionPassiveWrapper added in v0.16.0

type MainDriverExtensionPassiveWrapper interface {
	// WrapPassiveListener is called after creating the listener for passive
	// data connections.
	// You can wrap the passed listener or just return it unmodified.
	// Returning an error will cause the passive connection to fail
	WrapPassiveListener(listener net.Listener) (net.Listener, error)
}

MainDriverExtensionPassiveWrapper is an extension that allows to wrap the listener used for passive connection

type MainDriverExtensionTLSVerifier added in v0.13.0

type MainDriverExtensionTLSVerifier interface {
	// VerifyConnection is called when receiving the "USER" command.
	// If it returns a non-nil error, the client will receive a 530 error and it will be disconnected.
	// If it returns a non-nil ClientDriver and a nil error the client will be authenticated.
	// If it returns a nil ClientDriver and a nil error the user password is required
	VerifyConnection(cc ClientContext, user string, tlsConn *tls.Conn) (ClientDriver, error)
}

MainDriverExtensionTLSVerifier is an extension that allows to verify the TLS connection estabilished on the control channel

type PortRange

type PortRange struct {
	Start int // Range start
	End   int // Range end
}

PortRange is a range of ports

type PublicIPResolver

type PublicIPResolver func(ClientContext) (string, error)

PublicIPResolver takes a ClientContext for a connection and returns the public IP to use in the response to the PASV command, or an error if a public IP cannot be determined.

type 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
	// ActiveConnectionsCheck defines the security requirements for active connections
	ActiveConnectionsCheck DataConnectionRequirement
	// PasvConnectionsCheck defines the security requirements for passive connections
	PasvConnectionsCheck DataConnectionRequirement
}

Settings defines all the server settings nolint: maligned

type TLSRequirement added in v0.12.0

type TLSRequirement int

TLSRequirement is the enumerable that represents the supported TLS mode

const (
	ClearOrEncrypted TLSRequirement = iota
	MandatoryEncryption
	ImplicitEncryption
)

TLS modes

type TransferType added in v0.12.0

type TransferType int

TransferType is the enumerable that represents the supported transfer types

const (
	TransferTypeASCII TransferType = iota
	TransferTypeBinary
)

Supported transfer type

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