bot/ftp/ftp.go

// Package ftp implements a FTP client as described in RFC 959.
//
// A textproto.Error is returned for errors at the protocol level.
// This is a stripped down version of
// github.com/jlaffaye/ftp@v0.0.0-20191218041957-e1b8fdd0dcc3
package ftp

import (
	"context"
	"errors"
	"io"
	"net"
	"net/textproto"
	"strconv"
	"strings"
	"time"
)

// EntryType describes the different types of an Entry.
type EntryType int

// The differents types of an Entry
const (
	EntryTypeFile EntryType = iota
	EntryTypeFolder
	EntryTypeLink
)

// ServerConn represents the connection to a remote FTP server.
// A single connection only supports one in-flight data connection.
// It is not safe to be called concurrently.
type ServerConn struct {
	options *dialOptions
	conn    *textproto.Conn
	host    string

	// Server capabilities discovered at runtime
	features      map[string]string
	mlstSupported bool
}

// DialOption represents an option to start a new connection with Dial
type DialOption struct {
	setup func(do *dialOptions)
}

// dialOptions contains all the options set by DialOption.setup
type dialOptions struct {
	context     context.Context
	dialer      net.Dialer
	conn        net.Conn
	disableEPSV bool
	location    *time.Location
}

// Response represents a data-connection
type Response struct {
	conn   net.Conn
	c      *ServerConn
	closed bool
}

// Dial connects to the specified address with optional options
func Dial(addr string, options ...DialOption) (*ServerConn, error) {
	do := &dialOptions{}
	for _, option := range options {
		option.setup(do)
	}

	if do.location == nil {
		do.location = time.UTC
	}

	tconn := do.conn
	if tconn == nil {
		var err error

		ctx := do.context

		if ctx == nil {
			ctx = context.Background()
		}

		tconn, err = do.dialer.DialContext(ctx, "tcp", addr)

		if err != nil {
			return nil, err
		}
	}

	// Use the resolved IP address in case addr contains a domain name
	// If we use the domain name, we might not resolve to the same IP.
	remoteAddr := tconn.RemoteAddr().(*net.TCPAddr)

	var sourceConn io.ReadWriteCloser = tconn
	//	if do.debugOutput != nil {
	//		sourceConn = newDebugWrapper(tconn, do.debugOutput)
	//	}

	c := &ServerConn{
		options:  do,
		features: make(map[string]string),
		conn:     textproto.NewConn(sourceConn),
		host:     remoteAddr.IP.String(),
	}

	_, _, err := c.conn.ReadResponse(StatusReady)
	if err != nil {
		c.Quit()
		return nil, err
	}

	err = c.feat()
	if err != nil {
		c.Quit()
		return nil, err
	}

	if _, mlstSupported := c.features["MLST"]; mlstSupported {
		c.mlstSupported = true
	}

	return c, nil
}

// DialWithTimeout returns a DialOption that configures the ServerConn with specified timeout
func DialWithTimeout(timeout time.Duration) DialOption {
	return DialOption{func(do *dialOptions) {
		do.dialer.Timeout = timeout
	}}
}

// DialWithDisabledEPSV returns a DialOption that configures the ServerConn with EPSV disabled
// Note that EPSV is only used when advertised in the server features.
func DialWithDisabledEPSV(disabled bool) DialOption {
	return DialOption{func(do *dialOptions) {
		do.disableEPSV = disabled
	}}
}

// DialTimeout initializes the connection to the specified ftp server address.
//
// It is generally followed by a call to Login() as most FTP commands require
// an authenticated user.
func DialTimeout(addr string, timeout time.Duration) (*ServerConn, error) {
	return Dial(addr, DialWithTimeout(timeout))
}

// Login authenticates the client with specified user and password.
//
// "anonymous"/"anonymous" is a common user/password scheme for FTP servers
// that allows anonymous read-only accounts.
func (c *ServerConn) Login(user, password string) error {
	code, message, err := c.cmd(-1, "USER %s", user)
	if err != nil {
		return err
	}

	switch code {
	case StatusLoggedIn:
	case StatusUserOK:
		_, _, err = c.cmd(StatusLoggedIn, "PASS %s", password)
		if err != nil {
			return err
		}
	default:
		return errors.New(message)
	}

	// Switch to binary mode
	if _, _, err = c.cmd(StatusCommandOK, "TYPE I"); err != nil {
		return err
	}

	return err
}

// feat issues a FEAT FTP command to list the additional commands supported by
// the remote FTP server.
// FEAT is described in RFC 2389
func (c *ServerConn) feat() error {
	code, message, err := c.cmd(-1, "FEAT")
	if err != nil {
		return err
	}

	if code != StatusSystem {
		// The server does not support the FEAT command. This is not an
		// error: we consider that there is no additional feature.
		return nil
	}

	lines := strings.Split(message, "\n")
	for _, line := range lines {
		if !strings.HasPrefix(line, " ") {
			continue
		}

		line = strings.TrimSpace(line)
		featureElements := strings.SplitN(line, " ", 2)

		command := featureElements[0]

		var commandDesc string
		if len(featureElements) == 2 {
			commandDesc = featureElements[1]
		}

		c.features[command] = commandDesc
	}

	return nil
}

// pasv issues a "PASV" command to get a port number for a data connection.
func (c *ServerConn) pasv() (host string, port int, err error) {
	_, line, err := c.cmd(StatusPassiveMode, "PASV")
	if err != nil {
		return
	}

	// PASV response format : 227 Entering Passive Mode (h1,h2,h3,h4,p1,p2).
	start := strings.Index(line, "(")
	end := strings.LastIndex(line, ")")
	if start == -1 || end == -1 {
		err = errors.New("invalid PASV response format")
		return
	}

	// We have to split the response string
	pasvData := strings.Split(line[start+1:end], ",")

	if len(pasvData) < 6 {
		err = errors.New("invalid PASV response format")
		return
	}

	// Let's compute the port number
	portPart1, err1 := strconv.Atoi(pasvData[4])
	if err1 != nil {
		err = err1
		return
	}

	portPart2, err2 := strconv.Atoi(pasvData[5])
	if err2 != nil {
		err = err2
		return
	}

	// Recompose port
	port = portPart1*256 + portPart2

	// Make the IP address to connect to
	host = strings.Join(pasvData[0:4], ".")
	return
}

// getDataConnPort returns a host, port for a new data connection
func (c *ServerConn) getDataConnPort() (string, int, error) {
	return c.pasv()
}

// openDataConn creates a new FTP data connection.
func (c *ServerConn) openDataConn() (net.Conn, error) {
	host, port, err := c.getDataConnPort()
	if err != nil {
		return nil, err
	}

	addr := net.JoinHostPort(host, strconv.Itoa(port))

	return c.options.dialer.Dial("tcp", addr)
}

// cmd is a helper function to execute a command and check for the expected FTP
// return code
func (c *ServerConn) cmd(expected int, format string, args ...interface{}) (int, string, error) {
	_, err := c.conn.Cmd(format, args...)
	if err != nil {
		return 0, "", err
	}

	return c.conn.ReadResponse(expected)
}

// cmdDataConnFrom executes a command which require a FTP data connection.
// Issues a REST FTP command to specify the number of bytes to skip for the transfer.
func (c *ServerConn) cmdDataConnFrom(offset uint64, format string, args ...interface{}) (net.Conn, error) {
	conn, err := c.openDataConn()
	if err != nil {
		return nil, err
	}

	if offset != 0 {
		_, _, err := c.cmd(StatusRequestFilePending, "REST %d", offset)
		if err != nil {
			conn.Close()
			return nil, err
		}
	}

	_, err = c.conn.Cmd(format, args...)
	if err != nil {
		conn.Close()
		return nil, err
	}

	code, msg, err := c.conn.ReadResponse(-1)
	if err != nil {
		conn.Close()
		return nil, err
	}
	if code != StatusAlreadyOpen && code != StatusAboutToSend {
		conn.Close()
		return nil, &textproto.Error{Code: code, Msg: msg}
	}

	return conn, nil
}

// Retr issues a RETR FTP command to fetch the specified file from the remote
// FTP server.
//
// The returned ReadCloser must be closed to cleanup the FTP data connection.
func (c *ServerConn) Retr(path string) (*Response, error) {
	return c.RetrFrom(path, 0)
}

// RetrFrom issues a RETR FTP command to fetch the specified file from the remote
// FTP server, the server will not send the offset first bytes of the file.
//
// The returned ReadCloser must be closed to cleanup the FTP data connection.
func (c *ServerConn) RetrFrom(path string, offset uint64) (*Response, error) {
	conn, err := c.cmdDataConnFrom(offset, "RETR %s", path)
	if err != nil {
		return nil, err
	}

	return &Response{conn: conn, c: c}, nil
}

// Logout issues a REIN FTP command to logout the current user.
func (c *ServerConn) Logout() error {
	_, _, err := c.cmd(StatusReady, "REIN")
	return err
}

// Quit issues a QUIT FTP command to properly close the connection from the
// remote FTP server.
func (c *ServerConn) Quit() error {
	c.conn.Cmd("QUIT")
	return c.conn.Close()
}

// Read implements the io.Reader interface on a FTP data connection.
func (r *Response) Read(buf []byte) (int, error) {
	return r.conn.Read(buf)
}

// Close implements the io.Closer interface on a FTP data connection.
// After the first call, Close will do nothing and return nil.
func (r *Response) Close() error {
	if r.closed {
		return nil
	}
	err := r.conn.Close()
	_, _, err2 := r.c.conn.ReadResponse(StatusClosingDataConnection)
	if err2 != nil {
		err = err2
	}
	r.closed = true
	return err
}

// SetDeadline sets the deadlines associated with the connection.
func (r *Response) SetDeadline(t time.Time) error {
	return r.conn.SetDeadline(t)
}