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Filename : ftp.rb
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#
# = net/ftp.rb - FTP Client Library
#
# Written by Shugo Maeda <shugo@ruby-lang.org>.
#
# Documentation by Gavin Sinclair, sourced from "Programming Ruby" (Hunt/Thomas)
# and "Ruby In a Nutshell" (Matsumoto), used with permission.
#
# This library is distributed under the terms of the Ruby license.
# You can freely distribute/modify this library.
#
# It is included in the Ruby standard library.
#
# See the Net::FTP class for an overview.
#

require "socket"
require "monitor"
require "net/protocol"

module Net

  # :stopdoc:
  class FTPError < StandardError; end
  class FTPReplyError < FTPError; end
  class FTPTempError < FTPError; end
  class FTPPermError < FTPError; end
  class FTPProtoError < FTPError; end
  class FTPConnectionError < FTPError; end
  # :startdoc:

  #
  # This class implements the File Transfer Protocol.  If you have used a
  # command-line FTP program, and are familiar with the commands, you will be
  # able to use this class easily.  Some extra features are included to take
  # advantage of Ruby's style and strengths.
  #
  # == Example
  #
  #   require 'net/ftp'
  #
  # === Example 1
  #
  #   ftp = Net::FTP.new('example.com')
  #   ftp.login
  #   files = ftp.chdir('pub/lang/ruby/contrib')
  #   files = ftp.list('n*')
  #   ftp.getbinaryfile('nif.rb-0.91.gz', 'nif.gz', 1024)
  #   ftp.close
  #
  # === Example 2
  #
  #   Net::FTP.open('example.com') do |ftp|
  #     ftp.login
  #     files = ftp.chdir('pub/lang/ruby/contrib')
  #     files = ftp.list('n*')
  #     ftp.getbinaryfile('nif.rb-0.91.gz', 'nif.gz', 1024)
  #   end
  #
  # == Major Methods
  #
  # The following are the methods most likely to be useful to users:
  # - FTP.open
  # - #getbinaryfile
  # - #gettextfile
  # - #putbinaryfile
  # - #puttextfile
  # - #chdir
  # - #nlst
  # - #size
  # - #rename
  # - #delete
  #
  class FTP
    include MonitorMixin

    # :stopdoc:
    FTP_PORT = 21
    CRLF = "\r\n"
    DEFAULT_BLOCKSIZE = BufferedIO::BUFSIZE
    # :startdoc:

    # When +true+, transfers are performed in binary mode.  Default: +true+.
    attr_reader :binary

    # When +true+, the connection is in passive mode.  Default: +false+.
    attr_accessor :passive

    # When +true+, all traffic to and from the server is written
    # to +$stdout+.  Default: +false+.
    attr_accessor :debug_mode

    # Sets or retrieves the +resume+ status, which decides whether incomplete
    # transfers are resumed or restarted.  Default: +false+.
    attr_accessor :resume

    # Number of seconds to wait for the connection to open. Any number
    # may be used, including Floats for fractional seconds. If the FTP
    # object cannot open a connection in this many seconds, it raises a
    # Net::OpenTimeout exception. The default value is +nil+.
    attr_accessor :open_timeout

    # Number of seconds to wait for one block to be read (via one read(2)
    # call). Any number may be used, including Floats for fractional
    # seconds. If the FTP object cannot read data in this many seconds,
    # it raises a TimeoutError exception. The default value is 60 seconds.
    attr_reader :read_timeout

    # Setter for the read_timeout attribute.
    def read_timeout=(sec)
      @sock.read_timeout = sec
      @read_timeout = sec
    end

    # The server's welcome message.
    attr_reader :welcome

    # The server's last response code.
    attr_reader :last_response_code
    alias lastresp last_response_code

    # The server's last response.
    attr_reader :last_response

    #
    # A synonym for <tt>FTP.new</tt>, but with a mandatory host parameter.
    #
    # If a block is given, it is passed the +FTP+ object, which will be closed
    # when the block finishes, or when an exception is raised.
    #
    def FTP.open(host, user = nil, passwd = nil, acct = nil)
      if block_given?
        ftp = new(host, user, passwd, acct)
        begin
          yield ftp
        ensure
          ftp.close
        end
      else
        new(host, user, passwd, acct)
      end
    end

    #
    # Creates and returns a new +FTP+ object. If a +host+ is given, a connection
    # is made. Additionally, if the +user+ is given, the given user name,
    # password, and (optionally) account are used to log in.  See #login.
    #
    def initialize(host = nil, user = nil, passwd = nil, acct = nil)
      super()
      @binary = true
      @passive = false
      @debug_mode = false
      @resume = false
      @sock = NullSocket.new
      @logged_in = false
      @open_timeout = nil
      @read_timeout = 60
      if host
        connect(host)
        if user
          login(user, passwd, acct)
        end
      end
    end

    # A setter to toggle transfers in binary mode.
    # +newmode+ is either +true+ or +false+
    def binary=(newmode)
      if newmode != @binary
        @binary = newmode
        send_type_command if @logged_in
      end
    end

    # Sends a command to destination host, with the current binary sendmode
    # type.
    #
    # If binary mode is +true+, then "TYPE I" (image) is sent, otherwise "TYPE
    # A" (ascii) is sent.
    def send_type_command # :nodoc:
      if @binary
        voidcmd("TYPE I")
      else
        voidcmd("TYPE A")
      end
    end
    private :send_type_command

    # Toggles transfers in binary mode and yields to a block.
    # This preserves your current binary send mode, but allows a temporary
    # transaction with binary sendmode of +newmode+.
    #
    # +newmode+ is either +true+ or +false+
    def with_binary(newmode) # :nodoc:
      oldmode = binary
      self.binary = newmode
      begin
        yield
      ensure
        self.binary = oldmode
      end
    end
    private :with_binary

    # Obsolete
    def return_code # :nodoc:
      $stderr.puts("warning: Net::FTP#return_code is obsolete and do nothing")
      return "\n"
    end

    # Obsolete
    def return_code=(s) # :nodoc:
      $stderr.puts("warning: Net::FTP#return_code= is obsolete and do nothing")
    end

    # Constructs a socket with +host+ and +port+.
    #
    # If SOCKSSocket is defined and the environment (ENV) defines
    # SOCKS_SERVER, then a SOCKSSocket is returned, else a TCPSocket is
    # returned.
    def open_socket(host, port) # :nodoc:
      return Timeout.timeout(@open_timeout, Net::OpenTimeout) {
        if defined? SOCKSSocket and ENV["SOCKS_SERVER"]
          @passive = true
          sock = SOCKSSocket.open(host, port)
        else
          sock = TCPSocket.open(host, port)
        end
        io = BufferedSocket.new(sock)
        io.read_timeout = @read_timeout
        io
      }
    end
    private :open_socket

    #
    # Establishes an FTP connection to host, optionally overriding the default
    # port. If the environment variable +SOCKS_SERVER+ is set, sets up the
    # connection through a SOCKS proxy. Raises an exception (typically
    # <tt>Errno::ECONNREFUSED</tt>) if the connection cannot be established.
    #
    def connect(host, port = FTP_PORT)
      if @debug_mode
        print "connect: ", host, ", ", port, "\n"
      end
      synchronize do
        @sock = open_socket(host, port)
        voidresp
      end
    end

    #
    # Set the socket used to connect to the FTP server.
    #
    # May raise FTPReplyError if +get_greeting+ is false.
    def set_socket(sock, get_greeting = true)
      synchronize do
        @sock = sock
        if get_greeting
          voidresp
        end
      end
    end

    # If string +s+ includes the PASS command (password), then the contents of
    # the password are cleaned from the string using "*"
    def sanitize(s) # :nodoc:
      if s =~ /^PASS /i
        return s[0, 5] + "*" * (s.length - 5)
      else
        return s
      end
    end
    private :sanitize

    # Ensures that +line+ has a control return / line feed (CRLF) and writes
    # it to the socket.
    def putline(line) # :nodoc:
      if @debug_mode
        print "put: ", sanitize(line), "\n"
      end
      line = line + CRLF
      @sock.write(line)
    end
    private :putline

    # Reads a line from the sock.  If EOF, then it will raise EOFError
    def getline # :nodoc:
      line = @sock.readline # if get EOF, raise EOFError
      line.sub!(/(\r\n|\n|\r)\z/n, "")
      if @debug_mode
        print "get: ", sanitize(line), "\n"
      end
      return line
    end
    private :getline

    # Receive a section of lines until the response code's match.
    def getmultiline # :nodoc:
      line = getline
      buff = line
      if line[3] == ?-
          code = line[0, 3]
        begin
          line = getline
          buff << "\n" << line
        end until line[0, 3] == code and line[3] != ?-
      end
      return buff << "\n"
    end
    private :getmultiline

    # Receives a response from the destination host.
    #
    # Returns the response code or raises FTPTempError, FTPPermError, or
    # FTPProtoError
    def getresp # :nodoc:
      @last_response = getmultiline
      @last_response_code = @last_response[0, 3]
      case @last_response_code
      when /\A[123]/
        return @last_response
      when /\A4/
        raise FTPTempError, @last_response
      when /\A5/
        raise FTPPermError, @last_response
      else
        raise FTPProtoError, @last_response
      end
    end
    private :getresp

    # Receives a response.
    #
    # Raises FTPReplyError if the first position of the response code is not
    # equal 2.
    def voidresp # :nodoc:
      resp = getresp
      if resp[0] != ?2
        raise FTPReplyError, resp
      end
    end
    private :voidresp

    #
    # Sends a command and returns the response.
    #
    def sendcmd(cmd)
      synchronize do
        putline(cmd)
        return getresp
      end
    end

    #
    # Sends a command and expect a response beginning with '2'.
    #
    def voidcmd(cmd)
      synchronize do
        putline(cmd)
        voidresp
      end
    end

    # Constructs and send the appropriate PORT (or EPRT) command
    def sendport(host, port) # :nodoc:
      af = (@sock.peeraddr)[0]
      if af == "AF_INET"
        cmd = "PORT " + (host.split(".") + port.divmod(256)).join(",")
      elsif af == "AF_INET6"
        cmd = sprintf("EPRT |2|%s|%d|", host, port)
      else
        raise FTPProtoError, host
      end
      voidcmd(cmd)
    end
    private :sendport

    # Constructs a TCPServer socket
    def makeport # :nodoc:
      TCPServer.open(@sock.addr[3], 0)
    end
    private :makeport

    # sends the appropriate command to enable a passive connection
    def makepasv # :nodoc:
      if @sock.peeraddr[0] == "AF_INET"
        host, port = parse227(sendcmd("PASV"))
      else
        host, port = parse229(sendcmd("EPSV"))
        #     host, port = parse228(sendcmd("LPSV"))
      end
      return host, port
    end
    private :makepasv

    # Constructs a connection for transferring data
    def transfercmd(cmd, rest_offset = nil) # :nodoc:
      if @passive
        host, port = makepasv
        conn = open_socket(host, port)
        if @resume and rest_offset
          resp = sendcmd("REST " + rest_offset.to_s)
          if resp[0] != ?3
            raise FTPReplyError, resp
          end
        end
        resp = sendcmd(cmd)
        # skip 2XX for some ftp servers
        resp = getresp if resp[0] == ?2
        if resp[0] != ?1
          raise FTPReplyError, resp
        end
      else
        sock = makeport
        begin
          sendport(sock.addr[3], sock.addr[1])
          if @resume and rest_offset
            resp = sendcmd("REST " + rest_offset.to_s)
            if resp[0] != ?3
              raise FTPReplyError, resp
            end
          end
          resp = sendcmd(cmd)
          # skip 2XX for some ftp servers
          resp = getresp if resp[0] == ?2
          if resp[0] != ?1
            raise FTPReplyError, resp
          end
          conn = BufferedSocket.new(sock.accept)
          conn.read_timeout = @read_timeout
          sock.shutdown(Socket::SHUT_WR) rescue nil
          sock.read rescue nil
        ensure
          sock.close
        end
      end
      return conn
    end
    private :transfercmd

    #
    # Logs in to the remote host. The session must have been previously
    # connected.  If +user+ is the string "anonymous" and the +password+ is
    # +nil+, a password of <tt>user@host</tt> is synthesized. If the +acct+
    # parameter is not +nil+, an FTP ACCT command is sent following the
    # successful login.  Raises an exception on error (typically
    # <tt>Net::FTPPermError</tt>).
    #
    def login(user = "anonymous", passwd = nil, acct = nil)
      if user == "anonymous" and passwd == nil
        passwd = "anonymous@"
      end

      resp = ""
      synchronize do
        resp = sendcmd('USER ' + user)
        if resp[0] == ?3
          raise FTPReplyError, resp if passwd.nil?
          resp = sendcmd('PASS ' + passwd)
        end
        if resp[0] == ?3
          raise FTPReplyError, resp if acct.nil?
          resp = sendcmd('ACCT ' + acct)
        end
      end
      if resp[0] != ?2
        raise FTPReplyError, resp
      end
      @welcome = resp
      send_type_command
      @logged_in = true
    end

    #
    # Puts the connection into binary (image) mode, issues the given command,
    # and fetches the data returned, passing it to the associated block in
    # chunks of +blocksize+ characters. Note that +cmd+ is a server command
    # (such as "RETR myfile").
    #
    def retrbinary(cmd, blocksize, rest_offset = nil) # :yield: data
      synchronize do
        with_binary(true) do
          begin
            conn = transfercmd(cmd, rest_offset)
            loop do
              data = conn.read(blocksize)
              break if data == nil
              yield(data)
            end
            conn.shutdown(Socket::SHUT_WR)
            conn.read_timeout = 1
            conn.read
          ensure
            conn.close if conn
          end
          voidresp
        end
      end
    end

    #
    # Puts the connection into ASCII (text) mode, issues the given command, and
    # passes the resulting data, one line at a time, to the associated block. If
    # no block is given, prints the lines. Note that +cmd+ is a server command
    # (such as "RETR myfile").
    #
    def retrlines(cmd) # :yield: line
      synchronize do
        with_binary(false) do
          begin
            conn = transfercmd(cmd)
            loop do
              line = conn.gets
              break if line == nil
              yield(line.sub(/\r?\n\z/, ""), !line.match(/\n\z/).nil?)
            end
            conn.shutdown(Socket::SHUT_WR)
            conn.read_timeout = 1
            conn.read
          ensure
            conn.close if conn
          end
          voidresp
        end
      end
    end

    #
    # Puts the connection into binary (image) mode, issues the given server-side
    # command (such as "STOR myfile"), and sends the contents of the file named
    # +file+ to the server. If the optional block is given, it also passes it
    # the data, in chunks of +blocksize+ characters.
    #
    def storbinary(cmd, file, blocksize, rest_offset = nil) # :yield: data
      if rest_offset
        file.seek(rest_offset, IO::SEEK_SET)
      end
      synchronize do
        with_binary(true) do
          conn = transfercmd(cmd)
          loop do
            buf = file.read(blocksize)
            break if buf == nil
            conn.write(buf)
            yield(buf) if block_given?
          end
          conn.close
          voidresp
        end
      end
    rescue Errno::EPIPE
      # EPIPE, in this case, means that the data connection was unexpectedly
      # terminated.  Rather than just raising EPIPE to the caller, check the
      # response on the control connection.  If getresp doesn't raise a more
      # appropriate exception, re-raise the original exception.
      getresp
      raise
    end

    #
    # Puts the connection into ASCII (text) mode, issues the given server-side
    # command (such as "STOR myfile"), and sends the contents of the file
    # named +file+ to the server, one line at a time. If the optional block is
    # given, it also passes it the lines.
    #
    def storlines(cmd, file) # :yield: line
      synchronize do
        with_binary(false) do
          conn = transfercmd(cmd)
          loop do
            buf = file.gets
            break if buf == nil
            if buf[-2, 2] != CRLF
              buf = buf.chomp + CRLF
            end
            conn.write(buf)
            yield(buf) if block_given?
          end
          conn.close
          voidresp
        end
      end
    rescue Errno::EPIPE
      # EPIPE, in this case, means that the data connection was unexpectedly
      # terminated.  Rather than just raising EPIPE to the caller, check the
      # response on the control connection.  If getresp doesn't raise a more
      # appropriate exception, re-raise the original exception.
      getresp
      raise
    end

    #
    # Retrieves +remotefile+ in binary mode, storing the result in +localfile+.
    # If +localfile+ is nil, returns retrieved data.
    # If a block is supplied, it is passed the retrieved data in +blocksize+
    # chunks.
    #
    def getbinaryfile(remotefile, localfile = File.basename(remotefile),
                      blocksize = DEFAULT_BLOCKSIZE) # :yield: data
      result = nil
      if localfile
        if @resume
          rest_offset = File.size?(localfile)
          f = open(localfile, "a")
        else
          rest_offset = nil
          f = open(localfile, "w")
        end
      elsif !block_given?
        result = ""
      end
      begin
        f.binmode if localfile
        retrbinary("RETR " + remotefile.to_s, blocksize, rest_offset) do |data|
          f.write(data) if localfile
          yield(data) if block_given?
          result.concat(data) if result
        end
        return result
      ensure
        f.close if localfile
      end
    end

    #
    # Retrieves +remotefile+ in ASCII (text) mode, storing the result in
    # +localfile+.
    # If +localfile+ is nil, returns retrieved data.
    # If a block is supplied, it is passed the retrieved data one
    # line at a time.
    #
    def gettextfile(remotefile, localfile = File.basename(remotefile)) # :yield: line
      result = nil
      if localfile
        f = open(localfile, "w")
      elsif !block_given?
        result = ""
      end
      begin
        retrlines("RETR " + remotefile) do |line, newline|
          l = newline ? line + "\n" : line
          f.print(l) if localfile
          yield(line, newline) if block_given?
          result.concat(l) if result
        end
        return result
      ensure
        f.close if localfile
      end
    end

    #
    # Retrieves +remotefile+ in whatever mode the session is set (text or
    # binary).  See #gettextfile and #getbinaryfile.
    #
    def get(remotefile, localfile = File.basename(remotefile),
            blocksize = DEFAULT_BLOCKSIZE, &block) # :yield: data
      if @binary
        getbinaryfile(remotefile, localfile, blocksize, &block)
      else
        gettextfile(remotefile, localfile, &block)
      end
    end

    #
    # Transfers +localfile+ to the server in binary mode, storing the result in
    # +remotefile+. If a block is supplied, calls it, passing in the transmitted
    # data in +blocksize+ chunks.
    #
    def putbinaryfile(localfile, remotefile = File.basename(localfile),
                      blocksize = DEFAULT_BLOCKSIZE, &block) # :yield: data
      if @resume
        begin
          rest_offset = size(remotefile)
        rescue Net::FTPPermError
          rest_offset = nil
        end
      else
        rest_offset = nil
      end
      f = open(localfile)
      begin
        f.binmode
        if rest_offset
          storbinary("APPE " + remotefile, f, blocksize, rest_offset, &block)
        else
          storbinary("STOR " + remotefile, f, blocksize, rest_offset, &block)
        end
      ensure
        f.close
      end
    end

    #
    # Transfers +localfile+ to the server in ASCII (text) mode, storing the result
    # in +remotefile+. If callback or an associated block is supplied, calls it,
    # passing in the transmitted data one line at a time.
    #
    def puttextfile(localfile, remotefile = File.basename(localfile), &block) # :yield: line
      f = open(localfile)
      begin
        storlines("STOR " + remotefile, f, &block)
      ensure
        f.close
      end
    end

    #
    # Transfers +localfile+ to the server in whatever mode the session is set
    # (text or binary).  See #puttextfile and #putbinaryfile.
    #
    def put(localfile, remotefile = File.basename(localfile),
            blocksize = DEFAULT_BLOCKSIZE, &block)
      if @binary
        putbinaryfile(localfile, remotefile, blocksize, &block)
      else
        puttextfile(localfile, remotefile, &block)
      end
    end

    #
    # Sends the ACCT command.
    #
    # This is a less common FTP command, to send account
    # information if the destination host requires it.
    #
    def acct(account)
      cmd = "ACCT " + account
      voidcmd(cmd)
    end

    #
    # Returns an array of filenames in the remote directory.
    #
    def nlst(dir = nil)
      cmd = "NLST"
      if dir
        cmd = cmd + " " + dir
      end
      files = []
      retrlines(cmd) do |line|
        files.push(line)
      end
      return files
    end

    #
    # Returns an array of file information in the directory (the output is like
    # `ls -l`).  If a block is given, it iterates through the listing.
    #
    def list(*args, &block) # :yield: line
      cmd = "LIST"
      args.each do |arg|
        cmd = cmd + " " + arg.to_s
      end
      if block
        retrlines(cmd, &block)
      else
        lines = []
        retrlines(cmd) do |line|
          lines << line
        end
        return lines
      end
    end
    alias ls list
    alias dir list

    #
    # Renames a file on the server.
    #
    def rename(fromname, toname)
      resp = sendcmd("RNFR " + fromname)
      if resp[0] != ?3
        raise FTPReplyError, resp
      end
      voidcmd("RNTO " + toname)
    end

    #
    # Deletes a file on the server.
    #
    def delete(filename)
      resp = sendcmd("DELE " + filename)
      if resp[0, 3] == "250"
        return
      elsif resp[0] == ?5
        raise FTPPermError, resp
      else
        raise FTPReplyError, resp
      end
    end

    #
    # Changes the (remote) directory.
    #
    def chdir(dirname)
      if dirname == ".."
        begin
          voidcmd("CDUP")
          return
        rescue FTPPermError => e
          if e.message[0, 3] != "500"
            raise e
          end
        end
      end
      cmd = "CWD " + dirname
      voidcmd(cmd)
    end

    #
    # Returns the size of the given (remote) filename.
    #
    def size(filename)
      with_binary(true) do
        resp = sendcmd("SIZE " + filename)
        if resp[0, 3] != "213"
          raise FTPReplyError, resp
        end
        return resp[3..-1].strip.to_i
      end
    end

    MDTM_REGEXP = /^(\d\d\d\d)(\d\d)(\d\d)(\d\d)(\d\d)(\d\d)/  # :nodoc:

    #
    # Returns the last modification time of the (remote) file.  If +local+ is
    # +true+, it is returned as a local time, otherwise it's a UTC time.
    #
    def mtime(filename, local = false)
      str = mdtm(filename)
      ary = str.scan(MDTM_REGEXP)[0].collect {|i| i.to_i}
      return local ? Time.local(*ary) : Time.gm(*ary)
    end

    #
    # Creates a remote directory.
    #
    def mkdir(dirname)
      resp = sendcmd("MKD " + dirname)
      return parse257(resp)
    end

    #
    # Removes a remote directory.
    #
    def rmdir(dirname)
      voidcmd("RMD " + dirname)
    end

    #
    # Returns the current remote directory.
    #
    def pwd
      resp = sendcmd("PWD")
      return parse257(resp)
    end
    alias getdir pwd

    #
    # Returns system information.
    #
    def system
      resp = sendcmd("SYST")
      if resp[0, 3] != "215"
        raise FTPReplyError, resp
      end
      return resp[4 .. -1]
    end

    #
    # Aborts the previous command (ABOR command).
    #
    def abort
      line = "ABOR" + CRLF
      print "put: ABOR\n" if @debug_mode
      @sock.send(line, Socket::MSG_OOB)
      resp = getmultiline
      unless ["426", "226", "225"].include?(resp[0, 3])
        raise FTPProtoError, resp
      end
      return resp
    end

    #
    # Returns the status (STAT command).
    #
    def status
      line = "STAT" + CRLF
      print "put: STAT\n" if @debug_mode
      @sock.send(line, Socket::MSG_OOB)
      return getresp
    end

    #
    # Returns the raw last modification time of the (remote) file in the format
    # "YYYYMMDDhhmmss" (MDTM command).
    #
    # Use +mtime+ if you want a parsed Time instance.
    #
    def mdtm(filename)
      resp = sendcmd("MDTM " + filename)
      if resp[0, 3] == "213"
        return resp[3 .. -1].strip
      end
    end

    #
    # Issues the HELP command.
    #
    def help(arg = nil)
      cmd = "HELP"
      if arg
        cmd = cmd + " " + arg
      end
      sendcmd(cmd)
    end

    #
    # Exits the FTP session.
    #
    def quit
      voidcmd("QUIT")
    end

    #
    # Issues a NOOP command.
    #
    # Does nothing except return a response.
    #
    def noop
      voidcmd("NOOP")
    end

    #
    # Issues a SITE command.
    #
    def site(arg)
      cmd = "SITE " + arg
      voidcmd(cmd)
    end

    #
    # Closes the connection.  Further operations are impossible until you open
    # a new connection with #connect.
    #
    def close
      if @sock and not @sock.closed?
        begin
          @sock.shutdown(Socket::SHUT_WR) rescue nil
          orig, self.read_timeout = self.read_timeout, 3
          @sock.read rescue nil
        ensure
          @sock.close
          self.read_timeout = orig
        end
      end
    end

    #
    # Returns +true+ iff the connection is closed.
    #
    def closed?
      @sock == nil or @sock.closed?
    end

    # handler for response code 227
    # (Entering Passive Mode (h1,h2,h3,h4,p1,p2))
    #
    # Returns host and port.
    def parse227(resp) # :nodoc:
      if resp[0, 3] != "227"
        raise FTPReplyError, resp
      end
      if m = /\((?<host>\d+(,\d+){3}),(?<port>\d+,\d+)\)/.match(resp)
        return parse_pasv_ipv4_host(m["host"]), parse_pasv_port(m["port"])
      else
        raise FTPProtoError, resp
      end
    end
    private :parse227

    # handler for response code 228
    # (Entering Long Passive Mode)
    #
    # Returns host and port.
    def parse228(resp) # :nodoc:
      if resp[0, 3] != "228"
        raise FTPReplyError, resp
      end
      if m = /\(4,4,(?<host>\d+(,\d+){3}),2,(?<port>\d+,\d+)\)/.match(resp)
        return parse_pasv_ipv4_host(m["host"]), parse_pasv_port(m["port"])
      elsif m = /\(6,16,(?<host>\d+(,(\d+)){15}),2,(?<port>\d+,\d+)\)/.match(resp)
        return parse_pasv_ipv6_host(m["host"]), parse_pasv_port(m["port"])
      else
        raise FTPProtoError, resp
      end
    end
    private :parse228

    def parse_pasv_ipv4_host(s)
      return s.tr(",", ".")
    end
    private :parse_pasv_ipv4_host

    def parse_pasv_ipv6_host(s)
      return s.split(/,/).map { |i|
        "%02x" % i.to_i
      }.each_slice(2).map(&:join).join(":")
    end
    private :parse_pasv_ipv6_host

    def parse_pasv_port(s)
      return s.split(/,/).map(&:to_i).inject { |x, y|
        (x << 8) + y
      }
    end
    private :parse_pasv_port

    # handler for response code 229
    # (Extended Passive Mode Entered)
    #
    # Returns host and port.
    def parse229(resp) # :nodoc:
      if resp[0, 3] != "229"
        raise FTPReplyError, resp
      end
      if m = /\((?<d>[!-~])\k<d>\k<d>(?<port>\d+)\k<d>\)/.match(resp)
        return @sock.peeraddr[3], m["port"].to_i
      else
        raise FTPProtoError, resp
      end
    end
    private :parse229

    # handler for response code 257
    # ("PATHNAME" created)
    #
    # Returns host and port.
    def parse257(resp) # :nodoc:
      if resp[0, 3] != "257"
        raise FTPReplyError, resp
      end
      if resp[3, 2] != ' "'
        return ""
      end
      dirname = ""
      i = 5
      n = resp.length
      while i < n
        c = resp[i, 1]
        i = i + 1
        if c == '"'
          if i > n or resp[i, 1] != '"'
            break
          end
          i = i + 1
        end
        dirname = dirname + c
      end
      return dirname
    end
    private :parse257

    # :stopdoc:
    class NullSocket
      def read_timeout=(sec)
      end

      def closed?
        true
      end

      def close
      end

      def method_missing(mid, *args)
        raise FTPConnectionError, "not connected"
      end
    end

    class BufferedSocket < BufferedIO
      [:addr, :peeraddr, :send, :shutdown].each do |method|
        define_method(method) { |*args|
          @io.__send__(method, *args)
        }
      end

      def read(len = nil)
        if len
          s = super(len, "", true)
          return s.empty? ? nil : s
        else
          result = ""
          while s = super(DEFAULT_BLOCKSIZE, "", true)
            break if s.empty?
            result << s
          end
          return result
        end
      end

      def gets
        line = readuntil("\n", true)
        return line.empty? ? nil : line
      end

      def readline
        line = gets
        if line.nil?
          raise EOFError, "end of file reached"
        end
        return line
      end
    end
    # :startdoc:
  end
end


# Documentation comments:
#  - sourced from pickaxe and nutshell, with improvements (hopefully)