summaryrefslogtreecommitdiff
path: root/lib/net/smtp.rb
blob: c066bacbe4d8eef998276b05e242ff8d1ea3df1e (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
# = 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
#
# $Id$
#
# 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

  #
  # = Net::SMTP
  #
  # == 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. You can get both libraries from RAA.
  # (http://www.ruby-lang.org/en/raa.html)
  #
  # 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$Revision$.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_occured = 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
    # TimeoutError is raised.
    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
    # TimeoutError is raised.
    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
    # * IOError
    # * TimeoutError
    #
    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
    # * IOError
    # * TimeoutError
    #
    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(@open_timeout) { tcp_socket(@address, @port) }
      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_occured = false
        retry
      end
      raise
    end

    def do_finish
      quit if @socket and not @socket.closed? and not @error_occured
    ensure
      @started = false
      @error_occured = 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
    # * IOError
    # * TimeoutError
    #
    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
    # * IOError
    # * TimeoutError
    #
    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

    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')
        if msgstr
          @socket.write_message msgstr
        else
          @socket.write_message_by_block(&block)
        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(&block)
      return '200 dummy reply code' if @error_occured
      begin
        return yield()
      rescue Exception
        @error_occured = 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})"
      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

    class Response
      def Response.parse(str)
        new(str[0,3], str)
      end

      def initialize(status, string)
        @status = status
        @string = string
      end

      attr_reader :status
      attr_reader :string

      def status_type_char
        @status[0, 1]
      end

      def success?
        status_type_char() == '2'
      end

      def continue?
        status_type_char() == '3'
      end

      def message
        @string.lines.first
      end

      def cram_md5_challenge
        @string.split(/ /)[1].unpack('m')[0]
      end

      def capabilities
        return {} unless @string[3, 1] == '-'
        h = {}
        @string.lines.drop(1).each do |line|
          k, *v = line[4..-1].chomp.split(nil)
          h[k] = v
        end
        h
      end

      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

end