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+# = net/smtp.rb
+#
+# Copyright (c) 1999-2007 Yukihiro Matsumoto.
+#
+# Copyright (c) 1999-2007 Minero Aoki.
+#
+# Written & maintained by Minero Aoki <aamine@loveruby.net>.
+#
+# Documented by William Webber and Minero Aoki.
+#
+# This program is free software. You can re-distribute and/or
+# modify this program under the same terms as Ruby itself.
+#
+# NOTE: You can find Japanese version of this document at:
+# http://www.ruby-lang.org/ja/man/html/net_smtp.html
+#
+# $Id: smtp.rb 46793 2014-07-11 19:22:19Z kosaki $
+#
+# See Net::SMTP for documentation.
+#
+
+require 'net/protocol'
+require 'digest/md5'
+require 'timeout'
+begin
+  require 'openssl'
+rescue LoadError
+end
+
+module Net
+
+  # Module mixed in to all SMTP error classes
+  module SMTPError
+    # This *class* is a module for backward compatibility.
+    # In later release, this module becomes a class.
+  end
+
+  # Represents an SMTP authentication error.
+  class SMTPAuthenticationError < ProtoAuthError
+    include SMTPError
+  end
+
+  # Represents SMTP error code 420 or 450, a temporary error.
+  class SMTPServerBusy < ProtoServerError
+    include SMTPError
+  end
+
+  # Represents an SMTP command syntax error (error code 500)
+  class SMTPSyntaxError < ProtoSyntaxError
+    include SMTPError
+  end
+
+  # Represents a fatal SMTP error (error code 5xx, except for 500)
+  class SMTPFatalError < ProtoFatalError
+    include SMTPError
+  end
+
+  # Unexpected reply code returned from server.
+  class SMTPUnknownError < ProtoUnknownError
+    include SMTPError
+  end
+
+  # Command is not supported on server.
+  class SMTPUnsupportedCommand < ProtocolError
+    include SMTPError
+  end
+
+  #
+  # == What is This Library?
+  #
+  # This library provides functionality to send internet
+  # mail via SMTP, the Simple Mail Transfer Protocol. For details of
+  # SMTP itself, see [RFC2821] (http://www.ietf.org/rfc/rfc2821.txt).
+  #
+  # == What is This Library NOT?
+  #
+  # This library does NOT provide functions to compose internet mails.
+  # You must create them by yourself. If you want better mail support,
+  # try RubyMail or TMail or search for alternatives in
+  # {RubyGems.org}[https://rubygems.org/] or {The Ruby
+  # Toolbox}[https://www.ruby-toolbox.com/].
+  #
+  # FYI: the official documentation on internet mail is: [RFC2822] (http://www.ietf.org/rfc/rfc2822.txt).
+  #
+  # == Examples
+  #
+  # === Sending Messages
+  #
+  # You must open a connection to an SMTP server before sending messages.
+  # The first argument is the address of your SMTP server, and the second
+  # argument is the port number. Using SMTP.start with a block is the simplest
+  # way to do this. This way, the SMTP connection is closed automatically
+  # after the block is executed.
+  #
+  #     require 'net/smtp'
+  #     Net::SMTP.start('your.smtp.server', 25) do |smtp|
+  #       # Use the SMTP object smtp only in this block.
+  #     end
+  #
+  # Replace 'your.smtp.server' with your SMTP server. Normally
+  # your system manager or internet provider supplies a server
+  # for you.
+  #
+  # Then you can send messages.
+  #
+  #     msgstr = <<END_OF_MESSAGE
+  #     From: Your Name <your@mail.address>
+  #     To: Destination Address <someone@example.com>
+  #     Subject: test message
+  #     Date: Sat, 23 Jun 2001 16:26:43 +0900
+  #     Message-Id: <unique.message.id.string@example.com>
+  #
+  #     This is a test message.
+  #     END_OF_MESSAGE
+  #
+  #     require 'net/smtp'
+  #     Net::SMTP.start('your.smtp.server', 25) do |smtp|
+  #       smtp.send_message msgstr,
+  #                         'your@mail.address',
+  #                         'his_address@example.com'
+  #     end
+  #
+  # === Closing the Session
+  #
+  # You MUST close the SMTP session after sending messages, by calling
+  # the #finish method:
+  #
+  #     # using SMTP#finish
+  #     smtp = Net::SMTP.start('your.smtp.server', 25)
+  #     smtp.send_message msgstr, 'from@address', 'to@address'
+  #     smtp.finish
+  #
+  # You can also use the block form of SMTP.start/SMTP#start.  This closes
+  # the SMTP session automatically:
+  #
+  #     # using block form of SMTP.start
+  #     Net::SMTP.start('your.smtp.server', 25) do |smtp|
+  #       smtp.send_message msgstr, 'from@address', 'to@address'
+  #     end
+  #
+  # I strongly recommend this scheme.  This form is simpler and more robust.
+  #
+  # === HELO domain
+  #
+  # In almost all situations, you must provide a third argument
+  # to SMTP.start/SMTP#start. This is the domain name which you are on
+  # (the host to send mail from). It is called the "HELO domain".
+  # The SMTP server will judge whether it should send or reject
+  # the SMTP session by inspecting the HELO domain.
+  #
+  #     Net::SMTP.start('your.smtp.server', 25,
+  #                     'mail.from.domain') { |smtp| ... }
+  #
+  # === SMTP Authentication
+  #
+  # The Net::SMTP class supports three authentication schemes;
+  # PLAIN, LOGIN and CRAM MD5.  (SMTP Authentication: [RFC2554])
+  # To use SMTP authentication, pass extra arguments to
+  # SMTP.start/SMTP#start.
+  #
+  #     # PLAIN
+  #     Net::SMTP.start('your.smtp.server', 25, 'mail.from.domain',
+  #                     'Your Account', 'Your Password', :plain)
+  #     # LOGIN
+  #     Net::SMTP.start('your.smtp.server', 25, 'mail.from.domain',
+  #                     'Your Account', 'Your Password', :login)
+  #
+  #     # CRAM MD5
+  #     Net::SMTP.start('your.smtp.server', 25, 'mail.from.domain',
+  #                     'Your Account', 'Your Password', :cram_md5)
+  #
+  class SMTP
+
+    Revision = %q$Revision: 46793 $.split[1]
+
+    # The default SMTP port number, 25.
+    def SMTP.default_port
+      25
+    end
+
+    # The default mail submission port number, 587.
+    def SMTP.default_submission_port
+      587
+    end
+
+    # The default SMTPS port number, 465.
+    def SMTP.default_tls_port
+      465
+    end
+
+    class << self
+      alias default_ssl_port default_tls_port
+    end
+
+    def SMTP.default_ssl_context
+      OpenSSL::SSL::SSLContext.new
+    end
+
+    #
+    # Creates a new Net::SMTP object.
+    #
+    # +address+ is the hostname or ip address of your SMTP
+    # server.  +port+ is the port to connect to; it defaults to
+    # port 25.
+    #
+    # This method does not open the TCP connection.  You can use
+    # SMTP.start instead of SMTP.new if you want to do everything
+    # at once.  Otherwise, follow SMTP.new with SMTP#start.
+    #
+    def initialize(address, port = nil)
+      @address = address
+      @port = (port || SMTP.default_port)
+      @esmtp = true
+      @capabilities = nil
+      @socket = nil
+      @started = false
+      @open_timeout = 30
+      @read_timeout = 60
+      @error_occurred = false
+      @debug_output = nil
+      @tls = false
+      @starttls = false
+      @ssl_context = nil
+    end
+
+    # Provide human-readable stringification of class state.
+    def inspect
+      "#<#{self.class} #{@address}:#{@port} started=#{@started}>"
+    end
+
+    #
+    # Set whether to use ESMTP or not.  This should be done before
+    # calling #start.  Note that if #start is called in ESMTP mode,
+    # and the connection fails due to a ProtocolError, the SMTP
+    # object will automatically switch to plain SMTP mode and
+    # retry (but not vice versa).
+    #
+    attr_accessor :esmtp
+
+    # +true+ if the SMTP object uses ESMTP (which it does by default).
+    alias :esmtp? :esmtp
+
+    # true if server advertises STARTTLS.
+    # You cannot get valid value before opening SMTP session.
+    def capable_starttls?
+      capable?('STARTTLS')
+    end
+
+    def capable?(key)
+      return nil unless @capabilities
+      @capabilities[key] ? true : false
+    end
+    private :capable?
+
+    # true if server advertises AUTH PLAIN.
+    # You cannot get valid value before opening SMTP session.
+    def capable_plain_auth?
+      auth_capable?('PLAIN')
+    end
+
+    # true if server advertises AUTH LOGIN.
+    # You cannot get valid value before opening SMTP session.
+    def capable_login_auth?
+      auth_capable?('LOGIN')
+    end
+
+    # true if server advertises AUTH CRAM-MD5.
+    # You cannot get valid value before opening SMTP session.
+    def capable_cram_md5_auth?
+      auth_capable?('CRAM-MD5')
+    end
+
+    def auth_capable?(type)
+      return nil unless @capabilities
+      return false unless @capabilities['AUTH']
+      @capabilities['AUTH'].include?(type)
+    end
+    private :auth_capable?
+
+    # Returns supported authentication methods on this server.
+    # You cannot get valid value before opening SMTP session.
+    def capable_auth_types
+      return [] unless @capabilities
+      return [] unless @capabilities['AUTH']
+      @capabilities['AUTH']
+    end
+
+    # true if this object uses SMTP/TLS (SMTPS).
+    def tls?
+      @tls
+    end
+
+    alias ssl? tls?
+
+    # Enables SMTP/TLS (SMTPS: SMTP over direct TLS connection) for
+    # this object.  Must be called before the connection is established
+    # to have any effect.  +context+ is a OpenSSL::SSL::SSLContext object.
+    def enable_tls(context = SMTP.default_ssl_context)
+      raise 'openssl library not installed' unless defined?(OpenSSL)
+      raise ArgumentError, "SMTPS and STARTTLS is exclusive" if @starttls
+      @tls = true
+      @ssl_context = context
+    end
+
+    alias enable_ssl enable_tls
+
+    # Disables SMTP/TLS for this object.  Must be called before the
+    # connection is established to have any effect.
+    def disable_tls
+      @tls = false
+      @ssl_context = nil
+    end
+
+    alias disable_ssl disable_tls
+
+    # Returns truth value if this object uses STARTTLS.
+    # If this object always uses STARTTLS, returns :always.
+    # If this object uses STARTTLS when the server support TLS, returns :auto.
+    def starttls?
+      @starttls
+    end
+
+    # true if this object uses STARTTLS.
+    def starttls_always?
+      @starttls == :always
+    end
+
+    # true if this object uses STARTTLS when server advertises STARTTLS.
+    def starttls_auto?
+      @starttls == :auto
+    end
+
+    # Enables SMTP/TLS (STARTTLS) for this object.
+    # +context+ is a OpenSSL::SSL::SSLContext object.
+    def enable_starttls(context = SMTP.default_ssl_context)
+      raise 'openssl library not installed' unless defined?(OpenSSL)
+      raise ArgumentError, "SMTPS and STARTTLS is exclusive" if @tls
+      @starttls = :always
+      @ssl_context = context
+    end
+
+    # Enables SMTP/TLS (STARTTLS) for this object if server accepts.
+    # +context+ is a OpenSSL::SSL::SSLContext object.
+    def enable_starttls_auto(context = SMTP.default_ssl_context)
+      raise 'openssl library not installed' unless defined?(OpenSSL)
+      raise ArgumentError, "SMTPS and STARTTLS is exclusive" if @tls
+      @starttls = :auto
+      @ssl_context = context
+    end
+
+    # Disables SMTP/TLS (STARTTLS) for this object.  Must be called
+    # before the connection is established to have any effect.
+    def disable_starttls
+      @starttls = false
+      @ssl_context = nil
+    end
+
+    # The address of the SMTP server to connect to.
+    attr_reader :address
+
+    # The port number of the SMTP server to connect to.
+    attr_reader :port
+
+    # Seconds to wait while attempting to open a connection.
+    # If the connection cannot be opened within this time, a
+    # Net::OpenTimeout is raised. The default value is 30 seconds.
+    attr_accessor :open_timeout
+
+    # Seconds to wait while reading one block (by one read(2) call).
+    # If the read(2) call does not complete within this time, a
+    # Net::ReadTimeout is raised. The default value is 60 seconds.
+    attr_reader :read_timeout
+
+    # Set the number of seconds to wait until timing-out a read(2)
+    # call.
+    def read_timeout=(sec)
+      @socket.read_timeout = sec if @socket
+      @read_timeout = sec
+    end
+
+    #
+    # WARNING: This method causes serious security holes.
+    # Use this method for only debugging.
+    #
+    # Set an output stream for debug logging.
+    # You must call this before #start.
+    #
+    #   # example
+    #   smtp = Net::SMTP.new(addr, port)
+    #   smtp.set_debug_output $stderr
+    #   smtp.start do |smtp|
+    #     ....
+    #   end
+    #
+    def debug_output=(arg)
+      @debug_output = arg
+    end
+
+    alias set_debug_output debug_output=
+
+    #
+    # SMTP session control
+    #
+
+    #
+    # Creates a new Net::SMTP object and connects to the server.
+    #
+    # This method is equivalent to:
+    #
+    #   Net::SMTP.new(address, port).start(helo_domain, account, password, authtype)
+    #
+    # === Example
+    #
+    #     Net::SMTP.start('your.smtp.server') do |smtp|
+    #       smtp.send_message msgstr, 'from@example.com', ['dest@example.com']
+    #     end
+    #
+    # === Block Usage
+    #
+    # If called with a block, the newly-opened Net::SMTP object is yielded
+    # to the block, and automatically closed when the block finishes.  If called
+    # without a block, the newly-opened Net::SMTP object is returned to
+    # the caller, and it is the caller's responsibility to close it when
+    # finished.
+    #
+    # === Parameters
+    #
+    # +address+ is the hostname or ip address of your smtp server.
+    #
+    # +port+ is the port to connect to; it defaults to port 25.
+    #
+    # +helo+ is the _HELO_ _domain_ provided by the client to the
+    # server (see overview comments); it defaults to 'localhost'.
+    #
+    # The remaining arguments are used for SMTP authentication, if required
+    # or desired.  +user+ is the account name; +secret+ is your password
+    # or other authentication token; and +authtype+ is the authentication
+    # type, one of :plain, :login, or :cram_md5.  See the discussion of
+    # SMTP Authentication in the overview notes.
+    #
+    # === Errors
+    #
+    # This method may raise:
+    #
+    # * Net::SMTPAuthenticationError
+    # * Net::SMTPServerBusy
+    # * Net::SMTPSyntaxError
+    # * Net::SMTPFatalError
+    # * Net::SMTPUnknownError
+    # * Net::OpenTimeout
+    # * Net::ReadTimeout
+    # * IOError
+    #
+    def SMTP.start(address, port = nil, helo = 'localhost',
+                   user = nil, secret = nil, authtype = nil,
+                   &block)   # :yield: smtp
+      new(address, port).start(helo, user, secret, authtype, &block)
+    end
+
+    # +true+ if the SMTP session has been started.
+    def started?
+      @started
+    end
+
+    #
+    # Opens a TCP connection and starts the SMTP session.
+    #
+    # === Parameters
+    #
+    # +helo+ is the _HELO_ _domain_ that you'll dispatch mails from; see
+    # the discussion in the overview notes.
+    #
+    # If both of +user+ and +secret+ are given, SMTP authentication
+    # will be attempted using the AUTH command.  +authtype+ specifies
+    # the type of authentication to attempt; it must be one of
+    # :login, :plain, and :cram_md5.  See the notes on SMTP Authentication
+    # in the overview.
+    #
+    # === Block Usage
+    #
+    # When this methods is called with a block, the newly-started SMTP
+    # object is yielded to the block, and automatically closed after
+    # the block call finishes.  Otherwise, it is the caller's
+    # responsibility to close the session when finished.
+    #
+    # === Example
+    #
+    # This is very similar to the class method SMTP.start.
+    #
+    #     require 'net/smtp'
+    #     smtp = Net::SMTP.new('smtp.mail.server', 25)
+    #     smtp.start(helo_domain, account, password, authtype) do |smtp|
+    #       smtp.send_message msgstr, 'from@example.com', ['dest@example.com']
+    #     end
+    #
+    # The primary use of this method (as opposed to SMTP.start)
+    # is probably to set debugging (#set_debug_output) or ESMTP
+    # (#esmtp=), which must be done before the session is
+    # started.
+    #
+    # === Errors
+    #
+    # If session has already been started, an IOError will be raised.
+    #
+    # This method may raise:
+    #
+    # * Net::SMTPAuthenticationError
+    # * Net::SMTPServerBusy
+    # * Net::SMTPSyntaxError
+    # * Net::SMTPFatalError
+    # * Net::SMTPUnknownError
+    # * Net::OpenTimeout
+    # * Net::ReadTimeout
+    # * IOError
+    #
+    def start(helo = 'localhost',
+              user = nil, secret = nil, authtype = nil)   # :yield: smtp
+      if block_given?
+        begin
+          do_start helo, user, secret, authtype
+          return yield(self)
+        ensure
+          do_finish
+        end
+      else
+        do_start helo, user, secret, authtype
+        return self
+      end
+    end
+
+    # Finishes the SMTP session and closes TCP connection.
+    # Raises IOError if not started.
+    def finish
+      raise IOError, 'not yet started' unless started?
+      do_finish
+    end
+
+    private
+
+    def tcp_socket(address, port)
+      TCPSocket.open address, port
+    end
+
+    def do_start(helo_domain, user, secret, authtype)
+      raise IOError, 'SMTP session already started' if @started
+      if user or secret
+        check_auth_method(authtype || DEFAULT_AUTH_TYPE)
+        check_auth_args user, secret
+      end
+      s = Timeout.timeout(@open_timeout, Net::OpenTimeout) do
+        tcp_socket(@address, @port)
+      end
+      logging "Connection opened: #{@address}:#{@port}"
+      @socket = new_internet_message_io(tls? ? tlsconnect(s) : s)
+      check_response critical { recv_response() }
+      do_helo helo_domain
+      if starttls_always? or (capable_starttls? and starttls_auto?)
+        unless capable_starttls?
+          raise SMTPUnsupportedCommand,
+              "STARTTLS is not supported on this server"
+        end
+        starttls
+        @socket = new_internet_message_io(tlsconnect(s))
+        # helo response may be different after STARTTLS
+        do_helo helo_domain
+      end
+      authenticate user, secret, (authtype || DEFAULT_AUTH_TYPE) if user
+      @started = true
+    ensure
+      unless @started
+        # authentication failed, cancel connection.
+        s.close if s and not s.closed?
+        @socket = nil
+      end
+    end
+
+    def ssl_socket(socket, context)
+      OpenSSL::SSL::SSLSocket.new socket, context
+    end
+
+    def tlsconnect(s)
+      verified = false
+      s = ssl_socket(s, @ssl_context)
+      logging "TLS connection started"
+      s.sync_close = true
+      s.connect
+      if @ssl_context.verify_mode != OpenSSL::SSL::VERIFY_NONE
+        s.post_connection_check(@address)
+      end
+      verified = true
+      s
+    ensure
+      s.close unless verified
+    end
+
+    def new_internet_message_io(s)
+      io = InternetMessageIO.new(s)
+      io.read_timeout = @read_timeout
+      io.debug_output = @debug_output
+      io
+    end
+
+    def do_helo(helo_domain)
+      res = @esmtp ? ehlo(helo_domain) : helo(helo_domain)
+      @capabilities = res.capabilities
+    rescue SMTPError
+      if @esmtp
+        @esmtp = false
+        @error_occurred = false
+        retry
+      end
+      raise
+    end
+
+    def do_finish
+      quit if @socket and not @socket.closed? and not @error_occurred
+    ensure
+      @started = false
+      @error_occurred = false
+      @socket.close if @socket and not @socket.closed?
+      @socket = nil
+    end
+
+    #
+    # Message Sending
+    #
+
+    public
+
+    #
+    # Sends +msgstr+ as a message.  Single CR ("\r") and LF ("\n") found
+    # in the +msgstr+, are converted into the CR LF pair.  You cannot send a
+    # binary message with this method. +msgstr+ should include both
+    # the message headers and body.
+    #
+    # +from_addr+ is a String representing the source mail address.
+    #
+    # +to_addr+ is a String or Strings or Array of Strings, representing
+    # the destination mail address or addresses.
+    #
+    # === Example
+    #
+    #     Net::SMTP.start('smtp.example.com') do |smtp|
+    #       smtp.send_message msgstr,
+    #                         'from@example.com',
+    #                         ['dest@example.com', 'dest2@example.com']
+    #     end
+    #
+    # === Errors
+    #
+    # This method may raise:
+    #
+    # * Net::SMTPServerBusy
+    # * Net::SMTPSyntaxError
+    # * Net::SMTPFatalError
+    # * Net::SMTPUnknownError
+    # * Net::ReadTimeout
+    # * IOError
+    #
+    def send_message(msgstr, from_addr, *to_addrs)
+      raise IOError, 'closed session' unless @socket
+      mailfrom from_addr
+      rcptto_list(to_addrs) {data msgstr}
+    end
+
+    alias send_mail send_message
+    alias sendmail send_message   # obsolete
+
+    #
+    # Opens a message writer stream and gives it to the block.
+    # The stream is valid only in the block, and has these methods:
+    #
+    # puts(str = '')::       outputs STR and CR LF.
+    # print(str)::           outputs STR.
+    # printf(fmt, *args)::   outputs sprintf(fmt,*args).
+    # write(str)::           outputs STR and returns the length of written bytes.
+    # <<(str)::              outputs STR and returns self.
+    #
+    # If a single CR ("\r") or LF ("\n") is found in the message,
+    # it is converted to the CR LF pair.  You cannot send a binary
+    # message with this method.
+    #
+    # === Parameters
+    #
+    # +from_addr+ is a String representing the source mail address.
+    #
+    # +to_addr+ is a String or Strings or Array of Strings, representing
+    # the destination mail address or addresses.
+    #
+    # === Example
+    #
+    #     Net::SMTP.start('smtp.example.com', 25) do |smtp|
+    #       smtp.open_message_stream('from@example.com', ['dest@example.com']) do |f|
+    #         f.puts 'From: from@example.com'
+    #         f.puts 'To: dest@example.com'
+    #         f.puts 'Subject: test message'
+    #         f.puts
+    #         f.puts 'This is a test message.'
+    #       end
+    #     end
+    #
+    # === Errors
+    #
+    # This method may raise:
+    #
+    # * Net::SMTPServerBusy
+    # * Net::SMTPSyntaxError
+    # * Net::SMTPFatalError
+    # * Net::SMTPUnknownError
+    # * Net::ReadTimeout
+    # * IOError
+    #
+    def open_message_stream(from_addr, *to_addrs, &block)   # :yield: stream
+      raise IOError, 'closed session' unless @socket
+      mailfrom from_addr
+      rcptto_list(to_addrs) {data(&block)}
+    end
+
+    alias ready open_message_stream   # obsolete
+
+    #
+    # Authentication
+    #
+
+    public
+
+    DEFAULT_AUTH_TYPE = :plain
+
+    def authenticate(user, secret, authtype = DEFAULT_AUTH_TYPE)
+      check_auth_method authtype
+      check_auth_args user, secret
+      send auth_method(authtype), user, secret
+    end
+
+    def auth_plain(user, secret)
+      check_auth_args user, secret
+      res = critical {
+        get_response('AUTH PLAIN ' + base64_encode("\0#{user}\0#{secret}"))
+      }
+      check_auth_response res
+      res
+    end
+
+    def auth_login(user, secret)
+      check_auth_args user, secret
+      res = critical {
+        check_auth_continue get_response('AUTH LOGIN')
+        check_auth_continue get_response(base64_encode(user))
+        get_response(base64_encode(secret))
+      }
+      check_auth_response res
+      res
+    end
+
+    def auth_cram_md5(user, secret)
+      check_auth_args user, secret
+      res = critical {
+        res0 = get_response('AUTH CRAM-MD5')
+        check_auth_continue res0
+        crammed = cram_md5_response(secret, res0.cram_md5_challenge)
+        get_response(base64_encode("#{user} #{crammed}"))
+      }
+      check_auth_response res
+      res
+    end
+
+    private
+
+    def check_auth_method(type)
+      unless respond_to?(auth_method(type), true)
+        raise ArgumentError, "wrong authentication type #{type}"
+      end
+    end
+
+    def auth_method(type)
+      "auth_#{type.to_s.downcase}".intern
+    end
+
+    def check_auth_args(user, secret, authtype = DEFAULT_AUTH_TYPE)
+      unless user
+        raise ArgumentError, 'SMTP-AUTH requested but missing user name'
+      end
+      unless secret
+        raise ArgumentError, 'SMTP-AUTH requested but missing secret phrase'
+      end
+    end
+
+    def base64_encode(str)
+      # expects "str" may not become too long
+      [str].pack('m').gsub(/\s+/, '')
+    end
+
+    IMASK = 0x36
+    OMASK = 0x5c
+
+    # CRAM-MD5: [RFC2195]
+    def cram_md5_response(secret, challenge)
+      tmp = Digest::MD5.digest(cram_secret(secret, IMASK) + challenge)
+      Digest::MD5.hexdigest(cram_secret(secret, OMASK) + tmp)
+    end
+
+    CRAM_BUFSIZE = 64
+
+    def cram_secret(secret, mask)
+      secret = Digest::MD5.digest(secret) if secret.size > CRAM_BUFSIZE
+      buf = secret.ljust(CRAM_BUFSIZE, "\0")
+      0.upto(buf.size - 1) do |i|
+        buf[i] = (buf[i].ord ^ mask).chr
+      end
+      buf
+    end
+
+    #
+    # SMTP command dispatcher
+    #
+
+    public
+
+    # Aborts the current mail transaction
+
+    def rset
+      getok('RSET')
+    end
+
+    def starttls
+      getok('STARTTLS')
+    end
+
+    def helo(domain)
+      getok("HELO #{domain}")
+    end
+
+    def ehlo(domain)
+      getok("EHLO #{domain}")
+    end
+
+    def mailfrom(from_addr)
+      if $SAFE > 0
+        raise SecurityError, 'tainted from_addr' if from_addr.tainted?
+      end
+      getok("MAIL FROM:<#{from_addr}>")
+    end
+
+    def rcptto_list(to_addrs)
+      raise ArgumentError, 'mail destination not given' if to_addrs.empty?
+      ok_users = []
+      unknown_users = []
+      to_addrs.flatten.each do |addr|
+        begin
+          rcptto addr
+        rescue SMTPAuthenticationError
+          unknown_users << addr.dump
+        else
+          ok_users << addr
+        end
+      end
+      raise ArgumentError, 'mail destination not given' if ok_users.empty?
+      ret = yield
+      unless unknown_users.empty?
+        raise SMTPAuthenticationError, "failed to deliver for #{unknown_users.join(', ')}"
+      end
+      ret
+    end
+
+    def rcptto(to_addr)
+      if $SAFE > 0
+        raise SecurityError, 'tainted to_addr' if to_addr.tainted?
+      end
+      getok("RCPT TO:<#{to_addr}>")
+    end
+
+    # This method sends a message.
+    # If +msgstr+ is given, sends it as a message.
+    # If block is given, yield a message writer stream.
+    # You must write message before the block is closed.
+    #
+    #   # Example 1 (by string)
+    #   smtp.data(<<EndMessage)
+    #   From: john@example.com
+    #   To: betty@example.com
+    #   Subject: I found a bug
+    #
+    #   Check vm.c:58879.
+    #   EndMessage
+    #
+    #   # Example 2 (by block)
+    #   smtp.data {|f|
+    #     f.puts "From: john@example.com"
+    #     f.puts "To: betty@example.com"
+    #     f.puts "Subject: I found a bug"
+    #     f.puts ""
+    #     f.puts "Check vm.c:58879."
+    #   }
+    #
+    def data(msgstr = nil, &block)   #:yield: stream
+      if msgstr and block
+        raise ArgumentError, "message and block are exclusive"
+      end
+      unless msgstr or block
+        raise ArgumentError, "message or block is required"
+      end
+      res = critical {
+        check_continue get_response('DATA')
+        socket_sync_bak = @socket.io.sync
+        begin
+          @socket.io.sync = false
+          if msgstr
+            @socket.write_message msgstr
+          else
+            @socket.write_message_by_block(&block)
+          end
+        ensure
+          @socket.io.flush
+          @socket.io.sync = socket_sync_bak
+        end
+        recv_response()
+      }
+      check_response res
+      res
+    end
+
+    def quit
+      getok('QUIT')
+    end
+
+    private
+
+    def getok(reqline)
+      res = critical {
+        @socket.writeline reqline
+        recv_response()
+      }
+      check_response res
+      res
+    end
+
+    def get_response(reqline)
+      @socket.writeline reqline
+      recv_response()
+    end
+
+    def recv_response
+      buf = ''
+      while true
+        line = @socket.readline
+        buf << line << "\n"
+        break unless line[3,1] == '-'   # "210-PIPELINING"
+      end
+      Response.parse(buf)
+    end
+
+    def critical
+      return Response.parse('200 dummy reply code') if @error_occurred
+      begin
+        return yield()
+      rescue Exception
+        @error_occurred = true
+        raise
+      end
+    end
+
+    def check_response(res)
+      unless res.success?
+        raise res.exception_class, res.message
+      end
+    end
+
+    def check_continue(res)
+      unless res.continue?
+        raise SMTPUnknownError, "could not get 3xx (#{res.status}: #{res.string})"
+      end
+    end
+
+    def check_auth_response(res)
+      unless res.success?
+        raise SMTPAuthenticationError, res.message
+      end
+    end
+
+    def check_auth_continue(res)
+      unless res.continue?
+        raise res.exception_class, res.message
+      end
+    end
+
+    # This class represents a response received by the SMTP server. Instances
+    # of this class are created by the SMTP class; they should not be directly
+    # created by the user. For more information on SMTP responses, view
+    # {Section 4.2 of RFC 5321}[http://tools.ietf.org/html/rfc5321#section-4.2]
+    class Response
+      # Parses the received response and separates the reply code and the human
+      # readable reply text
+      def self.parse(str)
+        new(str[0,3], str)
+      end
+
+      # Creates a new instance of the Response class and sets the status and
+      # string attributes
+      def initialize(status, string)
+        @status = status
+        @string = string
+      end
+
+      # The three digit reply code of the SMTP response
+      attr_reader :status
+
+      # The human readable reply text of the SMTP response
+      attr_reader :string
+
+      # Takes the first digit of the reply code to determine the status type
+      def status_type_char
+        @status[0, 1]
+      end
+
+      # Determines whether the response received was a Positive Completion
+      # reply (2xx reply code)
+      def success?
+        status_type_char() == '2'
+      end
+
+      # Determines whether the response received was a Positive Intermediate
+      # reply (3xx reply code)
+      def continue?
+        status_type_char() == '3'
+      end
+
+      # The first line of the human readable reply text
+      def message
+        @string.lines.first
+      end
+
+      # Creates a CRAM-MD5 challenge. You can view more information on CRAM-MD5
+      # on Wikipedia: http://en.wikipedia.org/wiki/CRAM-MD5
+      def cram_md5_challenge
+        @string.split(/ /)[1].unpack('m')[0]
+      end
+
+      # Returns a hash of the human readable reply text in the response if it
+      # is multiple lines. It does not return the first line. The key of the
+      # hash is the first word the value of the hash is an array with each word
+      # thereafter being a value in the array
+      def capabilities
+        return {} unless @string[3, 1] == '-'
+        h = {}
+        @string.lines.drop(1).each do |line|
+          k, *v = line[4..-1].chomp.split
+          h[k] = v
+        end
+        h
+      end
+
+      # Determines whether there was an error and raises the appropriate error
+      # based on the reply code of the response
+      def exception_class
+        case @status
+        when /\A4/  then SMTPServerBusy
+        when /\A50/ then SMTPSyntaxError
+        when /\A53/ then SMTPAuthenticationError
+        when /\A5/  then SMTPFatalError
+        else             SMTPUnknownError
+        end
+      end
+    end
+
+    def logging(msg)
+      @debug_output << msg + "\n" if @debug_output
+    end
+
+  end   # class SMTP
+
+  SMTPSession = SMTP # :nodoc:
+
+end