summaryrefslogtreecommitdiff
path: root/lib/net/pop.rb
blob: f2ba1b9828a106529dc1fe260759c5b45a0e2c0f (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
# = net/pop.rb
#
#--
# Copyright (c) 1999-2004 Yukihiro Matsumoto
# Copyright (c) 1999-2004 Minero Aoki
# 
# written and maintained by Minero Aoki <aamine@loveruby.net>
# 
# This program is free software. You can re-distribute and/or
# modify this program under the same terms as Ruby itself,
# Ruby Distribute License.
# 
# NOTE: You can find Japanese version of this document at:
# http://www.ruby-lang.org/ja/man/index.cgi?cmd=view;name=net%2Fpop.rb
# 
# $Id$
#++
#
# == What is This Library?
# 
# This library provides functionality for retrieving 
# email via POP3, the Post Office Protocol version 3. For details
# of POP3, see [RFC1939] (http://www.ietf.org/rfc/rfc1939.txt).
# 
# == Examples
# 
# === Retrieving Messages 
# 
# This example retrieves messages from the server and deletes them 
# on the server.
# Messages are written to files named 'inbox/1', 'inbox/2', ....
# Replace 'pop.example.com' with your POP3 server address, and
# 'YourAccount' and 'YourPassword' with the appropriate account
# details.
# 
#     require 'net/pop'
# 
#     pop = Net::POP3.new('pop.example.com')
#     pop = pop.enable_ssl(verify, certs) if $use_ssl        # (1)
#     pop.start('YourAccount', 'YourPassword')             # (2)
#     if pop.mails.empty?
#       puts 'no mail.'
#     else
#       i = 0
#       pop.each_mail do |m|   # or "pop.mails.each ..."   # (3)
#         File.open("inbox/#{i}", 'w') {|f|
#           f.write m.pop
#         }
#         m.delete
#         i += 1
#       end
#       puts "#{pop.mails.size} mails popped."
#     end
#     pop.finish                                           # (4)
# 
# 1. optionally enable SSL for this POP connection
# 2. call Net::POP3#start and start POP session
# 3. access messages by using POP3#each_mail and/or POP3#mails
# 4. close POP session by calling POP3#finish or use the block form of #start.
# 
# === Shortened Code
# 
# The example above is very verbose. You can shorten the code by using
# some utility methods. First, the block form of Net::POP3.start can
# be used instead of POP3.new, POP3#start and POP3#finish.
# 
#     require 'net/pop'
# 
#     Net::POP3.start('pop.example.com', 110,
#                     'YourAccount', 'YourPassword') {|pop|
#       if pop.mails.empty?
#         puts 'no mail.'
#       else
#         i = 0
#         pop.each_mail do |m|   # or "pop.mails.each ..."
#           File.open("inbox/#{i}", 'w') {|f|
#             f.write m.pop
#           }
#           m.delete
#           i += 1
#         end
#         puts "#{pop.mails.size} mails popped."
#       end
#     }
# 
# POP3#delete_all alternates #each_mail and m.delete.
# 
#     require 'net/pop'
# 
#     Net::POP3.start('pop.example.com', 110,
#                     'YourAccount', 'YourPassword') {|pop|
#       if pop.mails.empty?
#         puts 'no mail.'
#       else
#         i = 1
#         pop.delete_all do |m|
#           File.open("inbox/#{i}", 'w') {|f|
#             f.write m.pop
#           }
#           i += 1
#         end
#       end
#     }
# 
# And here is an even shorter example.
# 
#     require 'net/pop'
# 
#     i = 0
#     Net::POP3.delete_all('pop.example.com', 110,
#                          'YourAccount', 'YourPassword') do |m|
#       File.open("inbox/#{i}", 'w') {|f|
#         f.write m.pop
#       }
#       i += 1
#     end
# 
# === Memory Space Issues
# 
# All the examples above get each message as one big string.
# This example avoids this.
# 
#     require 'net/pop'
# 
#     i = 1
#     Net::POP3.delete_all('pop.example.com', 110,
#                          'YourAccount', 'YourPassword') do |m|
#       File.open("inbox/#{i}", 'w') {|f|
#         m.pop do |chunk|    # get a message little by little.
#           f.write chunk
#         end
#         i += 1
#       }
#     end
# 
# === Using APOP
# 
# The net/pop library supports APOP authentication.
# To use APOP, use the Net::APOP class instead of the Net::POP3 class.
# You can use the utility method, Net::POP3.APOP(). For example:
# 
#     require 'net/pop'
# 
#     # Use APOP authentication if $isapop == true
#     pop = Net::POP3.APOP($is_apop).new('apop.example.com', 110)
#     pop.start('YourAccount', 'YourPassword') {|pop|
#       # Rest code is same.
#     }
#
# === Using SSL
# The net/pop library supports POP3 over SSL.
# To use SSL:
#
#   Example 1:
#     require 'net/pop'
#     
#     pop = Net::POP3.APOP($is_apop)
#     pop = pop.enable_ssl if $use_ssl
#     pop.start(server, port, account, password) do |pop|
#      ...
#     end 
# 
#   Example 2:
#     require 'net/pop'
#     pop = Net::POP3.new('pop.example.com').enable_ssl
#     pop.start(username, password) do |pop|
#       ...
#     end
#     
#
# === Fetch Only Selected Mail Using `UIDL' POP Command
# 
# If your POP server provides UIDL functionality,
# you can grab only selected mails from the POP server.
# e.g.
# 
#     def need_pop?(id)
#       # determine if we need pop this mail...
#     end
# 
#     Net::POP3.start('pop.example.com', 110,
#                     'Your account', 'Your password') {|pop|
#       pop.mails.select {|m| need_pop?(m.unique_id) }.each do |m|
#         do_something(m.pop)
#       end
#     }
# 
# The POPMail#unique_id() method returns the unique-id of the message as a
# String. Normally the unique-id is a hash of the message.
# 

require 'net/protocol'
require 'digest/md5'
require 'timeout'

begin
  require "openssl"
rescue LoadError
end

module Net

  # Non-authentication POP3 protocol error
  # (reply code "-ERR", except authentication).
  class POPError < ProtocolError; end

  # POP3 authentication error.
  class POPAuthenticationError < ProtoAuthError; end

  # Unexpected response from the server.
  class POPBadResponse < POPError; end


  #
  # Class providing POP3 client functionality.
  #
  # See documentation for the file pop.rb for examples of usage.
  #
  class POP3 < Protocol

    Revision = %q$Revision$.split[1]

    #
    # Class Parameters
    #

    @@usessl = false
    @@verify = nil
    @@certs = nil

    def POP3.default_port
      default_pop3_port()
    end

    # The default port for POP3 connections, port 110
    def POP3.default_pop3_port
      110
    end
    
    # The default port for POP3S connections, port 995
    def POP3.default_pop3s_port
      995
    end

    def POP3.socket_type   #:nodoc: obsolete
      Net::InternetMessageIO
    end

    #
    # Utilities
    #

    # Returns the APOP class if +isapop+ is true; otherwise, returns
    # the POP class.  For example:
    #
    #     # Example 1
    #     pop = Net::POP3::APOP($is_apop).new(addr, port)
    #
    #     # Example 2
    #     Net::POP3::APOP($is_apop).start(addr, port) {|pop|
    #       ....
    #     }
    #
    def POP3.APOP(isapop)
      isapop ? APOP : POP3
    end

    # Starts a POP3 session and iterates over each POPMail object,
    # yielding it to the +block+.
    # This method is equivalent to:
    #
    #     Net::POP3.start(address, port, account, password) {|pop|
    #       pop.each_mail do |m|
    #         yield m
    #       end
    #     }
    #
    # This method raises a POPAuthenticationError if authentication fails.
    #
    #     # Typical usage
    #     Net::POP3.foreach('pop.example.com', 110,
    #                       'YourAccount', 'YourPassword') do |m|
    #       file.write m.pop
    #       m.delete if $DELETE
    #     end
    #
    def POP3.foreach(address, port = nil,
                     account = nil, password = nil,
                     isapop = false, &block)  # :yields: message
      start(address, port, account, password, isapop) {|pop|
        pop.each_mail(&block)
      }
    end

    # Starts a POP3 session and deletes all messages on the server.
    # If a block is given, each POPMail object is yielded to it before
    # being deleted.
    #
    # This method raises a POPAuthenticationError if authentication fails.
    #
    #     # Example
    #     Net::POP3.delete_all('pop.example.com', 110,
    #                          'YourAccount', 'YourPassword') do |m|
    #       file.write m.pop
    #     end
    #
    def POP3.delete_all(address, port = nil,
                        account = nil, password = nil,
                        isapop = false, &block)
      start(address, port, account, password, isapop) {|pop|
        pop.delete_all(&block)
      }
    end

    # Opens a POP3 session, attempts authentication, and quits.
    #
    # This method raises POPAuthenticationError if authentication fails.
    #
    #     # Example 1: normal POP3
    #     Net::POP3.auth_only('pop.example.com', 110,
    #                         'YourAccount', 'YourPassword')
    #
    #     # Example 2: APOP
    #     Net::POP3.auth_only('pop.example.com', 110,
    #                         'YourAccount', 'YourPassword', true)
    #
    def POP3.auth_only(address, port = nil,
                       account = nil, password = nil,
                       isapop = false)
      new(address, port, isapop).auth_only account, password
    end

    # Starts a pop3 session, attempts authentication, and quits.
    # This method must not be called while POP3 session is opened.
    # This method raises POPAuthenticationError if authentication fails.
    def auth_only(account, password)
      raise IOError, 'opening previously opened POP session' if started?
      start(account, password) {
        ;
      }
    end

    #
    # Session management
    #

    # Creates a new POP3 object and open the connection.  Equivalent to 
    # Net::POP3.new(address, port, isapop).start(account, password)
    #
    # If +block+ is provided, yields the newly-opened POP3 object to it,
    # and automatically closes it at the end of the session.
    #
    # Typical usage:
    #
    #    Net::POP3.start(addr, port, account, password) {|pop|
    #      pop.each_mail do |m|
    #        file.write m.pop
    #        m.delete
    #      end
    #    }
    #
    def POP3.start(address, port = nil,
                   account = nil, password = nil,
                   isapop = false, &block)   # :yield: pop
      new(address, port, isapop).start(account, password, &block)
    end

    # Enable SSL for all new instances.
    # +verify+ is the type of verification to do on the Server Cert; Defaults
    # to OpenSSL::SSL::VERIFY_PEER.
    # +certs+ is a file or directory holding CA certs to use to verify the 
    # server cert; Defaults to nil.
    def POP3.enable_ssl(verify = OpenSSL::SSL::VERIFY_PEER, certs = nil)
      @@usessl = true
      @@verify = verify
      @@certs = certs  
    end

    # Disable SSL for all new instances.
    def POP3.disable_ssl
      @@usessl = nil
      @@verify = nil
      @@certs = nil
    end
    
    # Creates a new POP3 object.
    # +addr+ is the hostname or ip address of your POP3 server.
    # The optional +port+ is the port to connect to.
    # The optional +isapop+ specifies whether this connection is going
    # to use APOP authentication; it defaults to +false+.
    # This method does *not* open the TCP connection.
    def initialize(addr, port = nil, isapop = false)
      @address = addr
      @usessl = @@usessl
      @port = port || (@usessl ? POP3.default_pop3s_port : POP3.default_pop3_port)
      @apop = isapop
      @certs = @@certs
      @verify = @@verify
      
      @command = nil
      @socket = nil
      @started = false
      @open_timeout = 30
      @read_timeout = 60
      @debug_output = nil

      @mails = nil
      @n_mails = nil
      @n_bytes = nil
    end

    # Does this instance use APOP authentication?
    def apop?
      @apop
    end

    # does this instance use SSL?
    def use_ssl?
      @usessl
    end
   
    # Enables SSL for this instance.  Must be called before the connection is
    # established to have any effect.
    # +verify+ is the type of verification to do on the Server Cert; Defaults
    # to OpenSSL::SSL::VERIFY_PEER.
    # +certs+ is a file or directory holding CA certs to use to verify the 
    # server cert; Defaults to nil.
    # +port+ is port to establish the SSL connection on; Defaults to 995.
    def enable_ssl(verify = OpenSSL::SSL::VERIFY_PEER, certs = nil, 
                   port = POP3.default_pop3s_port)
      @usessl = true
      @verify = verify
      @certs = certs
      @port = port
    end
    
    def disable_ssl
      @usessl = nil
      @verify = nil
      @certs = nil
    end

    # Provide human-readable stringification of class state.
    def inspect
      "#<#{self.class} #{@address}:#{@port} open=#{@started}>"
    end

    # *WARNING*: This method causes a serious security hole.
    # Use this method only for debugging.
    #
    # Set an output stream for debugging.
    #
    #   # Example
    #   pop = Net::POP.new(addr, port)
    #   pop.set_debug_output $stderr
    #   pop.start(account, passwd) {
    #     ....
    #   }
    #
    def set_debug_output(arg)
      @debug_output = arg
    end

    # The address to connect to.
    attr_reader :address

    # The port number to connect to.
    attr_reader :port

    # Seconds to wait until a connection is opened.
    # If the POP3 object cannot open a connection within this time,
    # it raises a TimeoutError exception.
    attr_accessor :open_timeout

    # Seconds to wait until reading one block (by one read(1) call).
    # If the POP3 object cannot complete a read() within this time,
    # it raises a TimeoutError exception.
    attr_reader :read_timeout

    # Set the read timeout.
    def read_timeout=(sec)
      @command.socket.read_timeout = sec if @command
      @read_timeout = sec
    end

    # +true+ if the POP3 session has started.
    def started?
      @started
    end

    alias active? started?   #:nodoc: obsolete

    # Starts a POP3 session.
    #
    # When called with block, gives a POP3 object to the block and
    # closes the session after block call finishes.
    #
    # This method raises a POPAuthenticationError if authentication fails.
    def start(account, password) # :yield: pop
      raise IOError, 'POP session already started' if @started
      if block_given?
        begin
          do_start account, password
          return yield(self)
        ensure
          do_finish
        end
      else
        do_start account, password
        return self
      end
    end

    def do_start(account, password)
      s = timeout(@open_timeout) { TCPSocket.open(@address, @port) }
      if @usessl
        raise 'SSL extension not installed' unless defined?(OpenSSL)
        sslctx = OpenSSL::SSL::SSLContext.new
        sslctx.verify_mode = @verify
        if @certs
          if File.file?(@certs)
            sslctx.ca_file = @certs
          elsif File.directory?(@certs)
            sslctx.ca_path = @certs
          else
            raise ArgumentError, "certs path is not file/directory: #{@certs}"
          end
        end
        s = OpenSSL::SSL::SSLSocket.new(s, sslctx)
        s.sync_close = true
        s.connect
      end
      
      @socket = InternetMessageIO.new(s)
      
      logging "POP session started: #{@address}:#{@port} (#{@apop ? 'APOP' : 'POP'})"
      @socket.read_timeout = @read_timeout
      @socket.debug_output = @debug_output
      on_connect
      @command = POP3Command.new(@socket)
      if apop?
        @command.apop account, password
      else
        @command.auth account, password
      end
      @started = true
    ensure
      s.close if s and not s.closed?
      do_finish unless @started
    end
    private :do_start

    def on_connect
    end
    private :on_connect

    # Finishes a POP3 session and closes TCP connection.
    def finish
      raise IOError, 'POP session not yet started' unless started?
      do_finish
    end

    def do_finish
      @mails = nil
      @command.quit if @command
    ensure
      @started = false
      @command = nil
      @socket.close if @socket and not @socket.closed?
      @socket = nil
    end
    private :do_finish

    def command
      raise IOError, 'POP session not opened yet' \
                                      if not @socket or @socket.closed?
      @command
    end
    private :command

    #
    # POP protocol wrapper
    #

    # Returns the number of messages on the POP server.
    def n_mails
      return @n_mails if @n_mails
      @n_mails, @n_bytes = command().stat
      @n_mails
    end

    # Returns the total size in bytes of all the messages on the POP server.
    def n_bytes
      return @n_bytes if @n_bytes
      @n_mails, @n_bytes = command().stat
      @n_bytes
    end

    # Returns an array of Net::POPMail objects, representing all the
    # messages on the server.  This array is renewed when the session
    # restarts; otherwise, it is fetched from the server the first time
    # this method is called (directly or indirectly) and cached.
    #
    # This method raises a POPError if an error occurs.
    def mails
      return @mails.dup if @mails
      if n_mails() == 0
        # some popd raises error for LIST on the empty mailbox.
        @mails = []
        return []
      end

      @mails = command().list.map {|num, size|
        POPMail.new(num, size, self, command())
      }
      @mails.dup
    end

    # Yields each message to the passed-in block in turn.
    # Equivalent to:
    # 
    #   pop3.mails.each do |popmail|
    #     ....
    #   end
    #
    # This method raises a POPError if an error occurs.
    def each_mail(&block)  # :yield: message
      mails().each(&block)
    end

    alias each each_mail

    # Deletes all messages on the server.
    #
    # If called with a block, yields each message in turn before deleting it.
    #
    #     # Example
    #     n = 1
    #     pop.delete_all do |m|
    #       File.open("inbox/#{n}") {|f|
    #         f.write m.pop
    #       }
    #       n += 1
    #     end
    #
    # This method raises a POPError if an error occurs.
    def delete_all   # :yield: message
      mails().each do |m|
        yield m if block_given?
        m.delete unless m.deleted?
      end
    end

    # Resets the session.  This clears all "deleted" marks from messages.
    #
    # This method raises a POPError if an error occurs.
    def reset
      command().rset
      mails().each do |m|
        m.instance_eval {
          @deleted = false
        }
      end
    end

    def set_all_uids   #:nodoc: internal use only (called from POPMail#uidl)
      command().uidl.each do |num, uid|
        @mails.find {|m| m.number == num }.uid = uid
      end
    end

    def logging(msg)
      @debug_output << msg if @debug_output
    end

  end   # class POP3

  # class aliases
  POP = POP3
  POPSession  = POP3
  POP3Session = POP3

  #
  # This class is equivalent to POP3, except that it uses APOP authentication.
  #
  class APOP < POP3
    # Always returns true.
    def apop?
      true
    end
  end

  # class aliases
  APOPSession = APOP

  #
  # This class represents a message which exists on the POP server.
  # Instances of this class are created by the POP3 class; they should
  # not be directly created by the user.
  #
  class POPMail

    def initialize(num, len, pop, cmd)   #:nodoc:
      @number = num
      @length = len
      @pop = pop
      @command = cmd
      @deleted = false
      @uid = nil
    end

    # The sequence number of the message on the server.
    attr_reader :number

    # The length of the message in octets.
    attr_reader :length
    alias size length

    # Provide human-readable stringification of class state.
    def inspect
      "#<#{self.class} #{@number}#{@deleted ? ' deleted' : ''}>"
    end

    # This method fetches the message.  If called with a block, the
    # message is yielded to the block one chunk at a time.  If called
    # without a block, the message is returned as a String.  The optional 
    # +dest+ argument will be prepended to the returned String; this
    # argument is essentially obsolete.
    #
    # This method raises a POPError if an error occurs.
    #
    #     # Example without block
    #     POP3.start('pop.example.com', 110,
    #                'YourAccount, 'YourPassword') {|pop|
    #       n = 1
    #       pop.mails.each do |popmail|
    #         File.open("inbox/#{n}", 'w') {|f|
    #           f.write popmail.pop              
    #         }
    #         popmail.delete
    #         n += 1
    #       end
    #     }
    #
    #     # Example with block
    #     POP3.start('pop.example.com', 110,
    #                'YourAccount, 'YourPassword') {|pop|
    #       n = 1
    #       pop.mails.each do |popmail|
    #         File.open("inbox/#{n}", 'w') {|f|
    #           popmail.pop do |chunk|            ####
    #             f.write chunk
    #           end
    #         }
    #         n += 1
    #       end
    #     }
    #
    def pop(dest = '', &block) # :yield: message_chunk
      if block_given?
        @command.retr(@number, &block)
        nil
      else
        @command.retr(@number) do |chunk|
          dest << chunk
        end
        dest
      end
    end

    alias all pop    #:nodoc: obsolete
    alias mail pop   #:nodoc: obsolete

    # Fetches the message header and +lines+ lines of body. 
    # The optional +dest+ argument is obsolete.
    #
    # This method raises a POPError if an error occurs.
    def top(lines, dest = '')
      @command.top(@number, lines) do |chunk|
        dest << chunk
      end
      dest
    end

    # Fetches the message header.     
    # The optional +dest+ argument is obsolete.
    #
    # This method raises a POPError if an error occurs.
    def header(dest = '')
      top(0, dest)
    end

    # Marks a message for deletion on the server.  Deletion does not
    # actually occur until the end of the session; deletion may be
    # cancelled for _all_ marked messages by calling POP3#reset().
    #
    # This method raises a POPError if an error occurs.
    #
    #     # Example
    #     POP3.start('pop.example.com', 110,
    #                'YourAccount, 'YourPassword') {|pop|
    #       n = 1
    #       pop.mails.each do |popmail|
    #         File.open("inbox/#{n}", 'w') {|f|
    #           f.write popmail.pop
    #         }
    #         popmail.delete         ####
    #         n += 1
    #       end
    #     }
    #
    def delete
      @command.dele @number
      @deleted = true
    end

    alias delete! delete    #:nodoc: obsolete

    # True if the mail has been deleted.
    def deleted?
      @deleted
    end

    # Returns the unique-id of the message.
    # Normally the unique-id is a hash string of the message.
    #
    # This method raises a POPError if an error occurs.
    def unique_id
      return @uid if @uid
      @pop.set_all_uids
      @uid
    end

    alias uidl unique_id

    def uid=(uid)   #:nodoc: internal use only
      @uid = uid
    end

  end   # class POPMail


  class POP3Command   #:nodoc: internal use only

    def initialize(sock)
      @socket = sock
      @error_occured = false
      res = check_response(critical { recv_response() })
      @apop_stamp = res.slice(/<.+>/)
    end

    def inspect
      "#<#{self.class} socket=#{@socket}>"
    end

    def auth(account, password)
      check_response_auth(critical {
        check_response_auth(get_response('USER %s', account))
        get_response('PASS %s', password)
      })
    end

    def apop(account, password)
      raise POPAuthenticationError, 'not APOP server; cannot login' \
                                                      unless @apop_stamp
      check_response_auth(critical {
        get_response('APOP %s %s',
                     account,
                     Digest::MD5.hexdigest(@apop_stamp + password))
      })
    end

    def list
      critical {
        getok 'LIST'
        list = []
        @socket.each_list_item do |line|
          m = /\A(\d+)[ \t]+(\d+)/.match(line) or
                  raise POPBadResponse, "bad response: #{line}"
          list.push  [m[1].to_i, m[2].to_i]
        end
        return list
      }
    end

    def stat
      res = check_response(critical { get_response('STAT') })
      m = /\A\+OK\s+(\d+)\s+(\d+)/.match(res) or
              raise POPBadResponse, "wrong response format: #{res}"
      [m[1].to_i, m[2].to_i]
    end

    def rset
      check_response(critical { get_response('RSET') })
    end

    def top(num, lines = 0, &block)
      critical {
        getok('TOP %d %d', num, lines)
        @socket.each_message_chunk(&block)
      }
    end

    def retr(num, &block)
      critical {
        getok('RETR %d', num)
        @socket.each_message_chunk(&block)
      }
    end
    
    def dele(num)
      check_response(critical { get_response('DELE %d', num) })
    end

    def uidl(num = nil)
      if num
        res = check_response(critical { get_response('UIDL %d', num) })
        return res.split(/ /)[1]
      else
        critical {
          getok('UIDL')
          table = {}
          @socket.each_list_item do |line|
            num, uid = line.split
            table[num.to_i] = uid
          end
          return table
        }
      end
    end

    def quit
      check_response(critical { get_response('QUIT') })
    end

    private

    def getok(fmt, *fargs)
      @socket.writeline sprintf(fmt, *fargs)
      check_response(recv_response())
    end

    def get_response(fmt, *fargs)
      @socket.writeline sprintf(fmt, *fargs)
      recv_response()
    end

    def recv_response
      @socket.readline
    end

    def check_response(res)
      raise POPError, res unless /\A\+OK/i =~ res
      res
    end

    def check_response_auth(res)
      raise POPAuthenticationError, res unless /\A\+OK/i =~ res
      res
    end

    def critical
      return '+OK dummy ok response' if @error_occured
      begin
        return yield()
      rescue Exception
        @error_occured = true
        raise
      end
    end

  end   # class POP3Command

end   # module Net