aboutsummaryrefslogtreecommitdiff
path: root/email/email.scm
blob: a29a53236330c8113873dcf44362b914282b25b3 (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
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
;;; guile-email --- Guile email parser
;;; Copyright © 2018, 2019, 2020, 2021, 2023 Arun Isaac <arunisaac@systemreboot.net>
;;; Copyright © 2021 Mathieu Othacehe <othacehe@gnu.org>
;;; Copyright © 2023 Andrew Whatson <whatson@tailcall.au>
;;;
;;; This file is part of guile-email.
;;;
;;; guile-email is free software; you can redistribute it and/or modify
;;; it under the terms of the GNU Affero General Public License as
;;; published by the Free Software Foundation; either version 3 of the
;;; License, or (at your option) any later version.
;;;
;;; guile-email is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
;;; Affero General Public License for more details.
;;;
;;; You should have received a copy of the GNU Affero General Public
;;; License along with guile-email.  If not, see
;;; <http://www.gnu.org/licenses/>.

(define-module (email email)
  #:use-module (ice-9 binary-ports)
  #:use-module (ice-9 iconv)
  #:use-module (ice-9 match)
  #:use-module (ice-9 peg)
  #:use-module (ice-9 regex)
  #:use-module (rnrs bytevectors)
  #:use-module ((rnrs io ports) #:select (call-with-port))
  #:use-module (rnrs io simple)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-2)
  #:use-module (srfi srfi-9)
  #:use-module (srfi srfi-11)
  #:use-module (srfi srfi-19)
  #:use-module (srfi srfi-26)
  #:use-module (sxml transform)
  #:use-module (email base64)
  #:use-module (email quoted-printable)
  #:use-module (email utils)
  #:export (<email>
            make-email
            email?
            email-headers
            email-body
            <mime-entity>
            make-mime-entity
            mime-entity?
            mime-entity-headers
            mime-entity-body
            email->headers+body
            parse-email
            parse-email-headers
            parse-email-body
            parse-email-address
            interpret-address
            mbox->emails))

(define (flatten-and-filter terms tree)
  (filter list? (keyword-flatten terms tree)))

(define-record-type <email>
  (make-email headers body)
  email?
  (headers email-headers)
  (body email-body))

(define-record-type <mime-entity>
  (make-mime-entity headers body)
  mime-entity?
  (headers mime-entity-headers)
  (body mime-entity-body))

(define string->lcase-symbol
  (compose string->symbol string-downcase))

;;; PEG parser implementing the ABNF grammar specified in RFC5322
;;; (Internet Message Format), RFC6854 (Update to Internet Message
;;; Format to Allow Group Syntax in the "From:" and "Sender:" Header
;;; Fields)

;;; Obsolete syntax has not been implemented.

;;; Core ABNF rules from RFC5234

(define-peg-pattern alpha body
  (or (range #\A #\Z) (range #\a #\z)))

;; Though line endings should be crlf (\r\n), we also tolerate bare
;; line feeds (\n)
(define-peg-pattern crlf none
  (or "\r\n" "\n"))

(define-peg-pattern digit body
  (range #\0 #\9))

(define-peg-pattern dquote body
  "\"")

;; Printable ASCII characters and UTF-8 characters > \x7f (RFC6532)
(define-peg-pattern vchar body
  (and (not-followed-by (or (range #\Nul #\Space)
                            "\x7f"))
       peg-any))

(define-peg-pattern wsp body
  (or " " "\t"))

(define-peg-pattern lwsp body
  (* (or wsp (and crlf wsp))))

(define-syntax-rule (define-printable-ascii-character-pattern name . exceptions)
  (define-peg-pattern name body
    (and (not-followed-by (or . exceptions))
         vchar)))

(define-syntax-rule (define-printable-ascii-character-pattern-with-obsolete
                      name obsolete-pattern . exceptions)
  (define-peg-pattern name body
    (or (and (not-followed-by (or . exceptions))
             vchar)
        obsolete-pattern)))

;;; Quoted characters

(define-peg-pattern obs-qp body
  (and "\\" (or "\x00" obs-no-ws-ctl "\n" "\r")))

(define-peg-pattern quoted-pair body
  (or (and (ignore "\\") (or vchar wsp))
      obs-qp))

;;; Folding white space and comments

(define-peg-pattern obs-fws body
  (and (+ wsp) (* (and crlf (+ wsp)))))

(define-peg-pattern fws body
  (or (and (? (and (* wsp) crlf)) (+ wsp))
      obs-fws))

(define-peg-pattern obs-no-ws-ctl body
  (and (not-followed-by (or "\t" "\n" "\r"))
       (or (range #\soh #\us)
           "\x7f")))

(define-peg-pattern obs-ctext body
  obs-no-ws-ctl)

(define-printable-ascii-character-pattern-with-obsolete ctext obs-ctext
  "(" ")" "\\")

(define-syntax-rule (define-comment-pattern name capture-type)
  (define-peg-pattern name capture-type
    (and (ignore "(") (* (and (? fws) ccontent)) (ignore ")"))))

(define-comment-pattern comment none)

(define-peg-pattern ccontent body
  (or ctext quoted-pair comment))

(define-syntax-rule (define-cfws-pattern name comment)
  (define-peg-pattern name body
    (or (and (+ (and (? fws) comment))
             (? fws))
        fws)))

(define-cfws-pattern cfws comment)

;;; Atom

(define-printable-ascii-character-pattern atext
  "\"" "(" ")" "," "." ":" ";" "<" ">" "@" "[" "\\" "]")

(define-syntax define-atom-pattern
  (syntax-rules ()
    ((define-atom-pattern name)
     (define-peg-pattern name body
       (and (ignore (? cfws)) (+ atext) (ignore (? cfws)))))
    ((define-atom-pattern name cfws)
     (define-peg-pattern name body
       (and (? cfws) (+ atext) (? cfws))))
    ((define-atom-pattern name cfws atext)
     (define-peg-pattern name body
       (and (? cfws) (+ atext) (? cfws))))))

(define-atom-pattern atom)

(define-peg-pattern dot-atom-text body
  (and (+ atext) (* (and "." (+ atext)))))

(define-syntax-rule (define-dot-atom-pattern name cfws)
  (define-peg-pattern name body
    (and (ignore (? cfws)) dot-atom-text (ignore (? cfws)))))

(define-dot-atom-pattern dot-atom cfws)

;;; Quoted strings

(define-peg-pattern obs-qtext body
  obs-no-ws-ctl)

(define-printable-ascii-character-pattern-with-obsolete qtext obs-qtext
  "\\" "\"")

(define-peg-pattern qcontent body
  (or qtext quoted-pair))

;; TODO: Remove workaround guile peg bug for ignore
(define-peg-pattern quoted-string body
  (and (? cfws) (ignore (and dquote))
       (* (and (? fws) qcontent))
       (? fws)
       (ignore (and dquote)) (? cfws)))

;;; Miscellaneous tokens

;; According to RFC5322§3.2.3, the leading and trailing cfws in atom
;; are semantically not part of it, and should be ignored. But, to
;; support obs-phrase, we need to capture it. Hence, we define a set
;; of cfws-captured-* patterns needed by obs-phrase.

(define-syntax-rule (define-word-pattern name atom)
  (define-peg-pattern name body
    (or atom quoted-string)))

(define-word-pattern word atom)
(define-atom-pattern cfws-captured-atom cfws)
(define-word-pattern cfws-captured-word cfws-captured-atom)

(define-syntax-rule (define-phrase-pattern name word)
  (define-peg-pattern name body
    (and word (* (or word "." cfws)))))

(define-phrase-pattern obs-phrase cfws-captured-word)

;; We set phrase to be the same as obs-phrase since, according to
;; their definitions in RFC5322, all phrases are obs-phrases.
(define-peg-pattern phrase body
  obs-phrase)

(define-peg-pattern obs-phrase-list body
  (and (? (or phrase cfws))
       (* (and "," (or phrase cfws)))))

(define-peg-pattern obs-utext body
  (or "\x00" obs-no-ws-ctl vchar))

(define-peg-pattern obs-unstruct body
  (* (or (and (* "\n") (* "\r")
              (* (and obs-utext (* "\n") (* "\r"))))
         fws)))

;; ABNF modified to ignore leading whitespace
;; ABNF modified to allow for blank lines in folded field
(define-peg-pattern unstructured body
  (or (and (ignore (? fws))
           (* (and (? fws) (? vchar)))
           (ignore (* wsp)))
      obs-unstruct))

;;; Date and time specification

(define-peg-pattern day-name body
  (or "Mon" "Tue" "Wed" "Thu" "Fri" "Sat" "Sun"))

(define-peg-pattern obs-day-of-week body
  (and (ignore (? cfws)) day-name (ignore (? cfws))))

;; We set day-of-week to be the same as obs-day-of-week since,
;; according to their definitions in RFC5322, all days-of-week are
;; obs-days-of-week.
(define-peg-pattern day-of-week all
  obs-day-of-week)

(define-peg-pattern obs-day body
  (and (ignore (? cfws)) digit (? digit) (ignore (? cfws))))

;; We set day to be the same as obs-day since, according to their
;; definitions in RFC5322, all days are obs-days.
(define-peg-pattern day all
  obs-day)

(define-peg-pattern month all
  (or "Jan" "Feb" "Mar" "Apr" "May" "Jun"
      "Jul" "Aug" "Sep" "Oct" "Nov" "Dec"))

(define-peg-pattern obs-year body
  (and (ignore (? cfws)) (and digit digit) (* digit) (ignore (? cfws))))

;; We set year to be the same as obs-year since, according to their
;; definitions in RFC5322, all years are obs-years.
(define-peg-pattern year all
  obs-year)

(define-peg-pattern date all
  (and day month year))

(define-peg-pattern obs-hour body
  (and (ignore (? cfws)) digit digit (ignore (? cfws))))

;; We set hours to be the same as obs-hour since, according to their
;; definitions in RFC5322, all hours are obs-hours.
(define-peg-pattern hours all
  obs-hour)

(define-peg-pattern obs-minute body
  (and (ignore (? cfws)) digit digit (ignore (? cfws))))

;; We set minutes to be the same as obs-minute since, according to
;; their definitions in RFC5322, all minutes are obs-minutes.
(define-peg-pattern minutes all
  obs-minute)

(define-peg-pattern obs-second body
  (and (ignore (? cfws)) digit digit (ignore (? cfws))))

;; We set seconds to be the same as obs-second since, according to
;; their definitions in RFC5322, all seconds are obs-seconds.
(define-peg-pattern seconds all
  obs-second)

(define-peg-pattern time-of-day all
  (and hours (ignore ":") minutes (? (and (ignore ":") seconds))))

;; zone-sign, zone-hours and zone-minutes do not exist in the ABNF
;; specified in RFC5322. But, we have it here since it eases parsing
;; the zone and converting it to a number of seconds as required by
;; the make-date procedure of SRFI-19.
(define-peg-pattern zone-sign all
  (or "+" "-"))

(define-peg-pattern zone-hours all
  (and digit digit))

(define-peg-pattern zone-minutes all
  (and digit digit))

(define-peg-pattern obs-zone body
  (or "UT" "GMT"
      "EST" "EDT" "CST" "CDT"
      "MST" "MDT" "PST" "PDT"
      (and (not-followed-by (or "j" "J"))
           (or (range #\a #\z)
               (range #\A #\Z)))))

(define-peg-pattern zone all
  (or (and zone-sign zone-hours zone-minutes)
      obs-zone))

(define-peg-pattern time all
  (and time-of-day zone))

(define-peg-pattern date-time all
  (and (? (and day-of-week (ignore ","))) date time (? cfws)))

;;; Address specification

;; People tend to put strange characters in their display names, and
;; MUAs tend to pass on these non-standard names without any
;; quoting. Tolerate such names.

;; Tolerate non-standard ( and ) in atext.
(define-peg-pattern liberal-atext body
  (or atext "(" ")"))

(define-atom-pattern liberal-cfws-captured-atom cfws liberal-atext)
(define-word-pattern liberal-cfws-captured-word liberal-cfws-captured-atom)
(define-phrase-pattern liberal-phrase liberal-cfws-captured-word)

(define-peg-pattern display-name all
  liberal-phrase)

(define-peg-pattern obs-local-part body
  (and word (* (and "." word))))

(define-peg-pattern local-part body
  (or obs-local-part dot-atom quoted-string))

(define-peg-pattern obs-dtext body
  (or obs-no-ws-ctl quoted-pair))

(define-printable-ascii-character-pattern-with-obsolete dtext obs-dtext "[" "]" "\\")

(define-peg-pattern domain-literal body
  (and (? cfws) "[" (* (and (? fws) dtext)) (? fws) "]" (? cfws)))

(define-syntax-rule (define-obs-domain-pattern name atom)
  (define-peg-pattern name body
    (and atom (* (and "." atom)))))

(define-obs-domain-pattern obs-domain atom)

(define-syntax-rule (define-domain-pattern name obs-domain dot-atom)
  (define-peg-pattern name body
    (or obs-domain dot-atom domain-literal)))

(define-domain-pattern domain obs-domain dot-atom)

(define-syntax-rule (define-addr-spec-pattern name domain)
  (define-peg-pattern name body
    (and local-part "@" domain)))

(define-addr-spec-pattern addr-spec domain)

(define-peg-pattern obs-domain-list body
  (and (* (or cfws ",")) "@" domain
       (* (and "," (? cfws) (? (and "@" domain))))))

(define-peg-pattern obs-route none
  (and obs-domain-list ":"))

(define-peg-pattern obs-angle-addr body
  (and (ignore (and (? cfws) "<"))
       obs-route addr-spec
       (ignore (and ">" (? cfws)))))

(define-syntax-rule (define-angle-addr-pattern
                      name opening-bracket closing-bracket)
  (define-peg-pattern name body
    (or (and (ignore (? cfws))
             opening-bracket addr-spec closing-bracket
             (ignore (? cfws)))
        obs-angle-addr)))

(define-angle-addr-pattern angle-addr "<" ">")

;; When handling email addresses, we need to drop the angle
;; brackets. But in the Received field we need to include the angle
;; brackes. So, we define unbracketed-angle-addr, a variant of
;; angle-addr in which the angle brackets are ignored.

(define-angle-addr-pattern
  unbracketed-angle-addr (ignore "<") (ignore ">"))

(define-peg-pattern name-addr body
  (and (? display-name) unbracketed-angle-addr))

;; In order to support emacs message mode parens style email
;; addresses, we need to capture comments in address fields and
;; process them as names. But, we need to ignore comments in other
;; parts of the email. In order to facilitate this, we define a set of
;; captured-* patterns which are used in address fields.

(define-atom-pattern captured-atom captured-cfws)
(define-comment-pattern captured-comment all)
(define-cfws-pattern captured-cfws captured-comment)
(define-dot-atom-pattern captured-dot-atom captured-cfws)
(define-obs-domain-pattern captured-obs-domain captured-atom)
(define-domain-pattern captured-domain captured-obs-domain captured-dot-atom)
(define-addr-spec-pattern captured-addr-spec captured-domain)

(define-peg-pattern mailbox all
  (or name-addr captured-addr-spec))

(define-peg-pattern obs-mbox-list body
  (and (* (and (? cfws) ",")) mailbox
       (* (and "," (? (or mailbox cfws))))))

;; We set mailbox-list to be the same as obs-mbox-list since,
;; according to their definitions in RFC5322, all mailbox-lists are
;; obs-mbox-lists.
(define-peg-pattern mailbox-list all
  obs-mbox-list)

(define-peg-pattern group all
  (and display-name (ignore ":")
       (? group-list) (ignore ";") (? cfws)))

(define-peg-pattern obs-group-list body
  (and (+ (and (? cfws) ","))
       (? cfws)))

(define-peg-pattern group-list all
  (or mailbox-list cfws obs-group-list))

(define-peg-pattern address body
  (or mailbox group))

(define-peg-pattern obs-addr-list body
  (and (* (and (? cfws) ",")) address
       (* (and "," (? (or address cfws))))))

;; We set address-list to be the same as obs-addr-list since,
;; according to their definitions in RFC5322, all address-lists are
;; obs-address-lists.
(define-peg-pattern address-list all
  obs-addr-list)

;;; Fields

;; We have compressed the current field pattern and the obsolete field
;; pattern into a single PEG pattern.
(define-syntax define-field-pattern
  (syntax-rules ()
    ((define-field-pattern name header pattern)
     (define-peg-pattern name all
       (and (ignore (string-ci header))
            (ignore (and (* wsp) ":"))
            pattern crlf)))
    ((define-field-pattern name header pattern obsolete-pattern)
     (define-peg-pattern name all
       (and (ignore (string-ci header))
            (ignore (and (* wsp) ":"))
            (or pattern obsolete-pattern) crlf)))))

;;; Origination date field

(define-field-pattern orig-date "Date" date-time)

;;; Originator fields

(define-field-pattern from "From" mailbox-list (or mailbox-list address-list))
(define-field-pattern sender "Sender" mailbox (or mailbox address))
(define-field-pattern reply-to "Reply-To" address-list)

;; Destination address fields

(define-field-pattern to "To" address-list)
(define-field-pattern cc "Cc" address-list)
(define-field-pattern bcc "Bcc"
  (? (or address-list cfws))
  (or address-list (and (* (and (? cfws) ",")) (? cfws))))

;;; Identification fields

(define-peg-pattern no-fold-literal body
  (and "[" (* dtext) "]"))

(define-peg-pattern obs-id-left body
  local-part)

(define-peg-pattern id-left body
  (or obs-id-left dot-atom-text))

(define-peg-pattern obs-id-right body
  domain)

(define-peg-pattern id-right body
  (or obs-id-right dot-atom-text no-fold-literal))

(define-peg-pattern msg-id all
  (and (ignore (? cfws)) (ignore "<")
       id-left "@" id-right
       (ignore ">") (ignore (? cfws))))

(define-field-pattern message-id "Message-ID" msg-id)
(define-field-pattern in-reply-to "In-Reply-To"
  (+ msg-id)
  (* (or phrase msg-id)))
(define-field-pattern references "References"
  (+ msg-id)
  (* (or phrase msg-id)))

;;; Informational fields

(define-field-pattern subject "Subject" unstructured)
(define-field-pattern comments "Comments" unstructured)
(define-field-pattern keywords "Keywords"
  (and phrase (* (and "," phrase)))
  obs-phrase-list)

;;; Resent fields

(define-field-pattern resent-date "Resent-Date" date-time)
(define-field-pattern resent-from "Resent-From"
  (or mailbox-list address-list)
  mailbox-list)
(define-field-pattern resent-sender "Resent-Sender"
  (or mailbox address)
  mailbox)
(define-field-pattern resent-to "Resent-To" address-list)
(define-field-pattern resent-cc "Resent-Cc" address-list)
(define-field-pattern resent-bcc "Resent-Bcc"
  (? (or address-list cfws))
  (or address-list
      (and (* (and (? cfws) ",")) (? cfws))))
(define-field-pattern resent-msg-id "Resent-Message-ID" msg-id)
(define-field-pattern obs-resent-rply "Resent-Reply-To" address-list)

;;; Trace fields

;; word is given last priority in the ordered choice
(define-peg-pattern received-token all
  (or angle-addr addr-spec domain word))

(define-field-pattern received "Received"
  (and (* received-token) (ignore ";") date-time)
  (* received-token))

(define-peg-pattern path body
  (or angle-addr (and (? cfws) (ignore "<") (? cfws) (ignore ">") (? cfws))))

(define-field-pattern return "Return-Path" path)

(define-peg-pattern trace all
  (and (? return) (+ received)))

;;; Optional fields

(define-printable-ascii-character-pattern ftext ":")

(define-peg-pattern field-name all
  (+ ftext))

(define-peg-pattern obs-optional body
  (and field-name (ignore (and (* wsp) ":")) unstructured crlf))

(define-peg-pattern optional-field all
  (or (and field-name (ignore ":") unstructured crlf)
      obs-optional))

;;; MIME version

;; I have prepended optional cfws to account for leading whitespace.
(define-field-pattern mime-version "MIME-Version"
  (and (ignore (? cfws)) (+ digit) "." (+ digit)))

;;; Content type

;; TODO: What is <"> in RFC2045?
(define-peg-pattern tspecials body
  (or "(" ")" "<" ">" "@"
      "," ";" ":" "\\"
      "/" "[" "]" "?" "="))

;; TODO: What is a CTL in RFC2045?
(define-peg-pattern token body
  (+ (and (not-followed-by (or " " crlf tspecials))
          peg-any)))

;; TODO: Implement iana-token, ietf-token and x-token
(define-peg-pattern iana-token body
  token)

(define-peg-pattern ietf-token body
  token)

(define-peg-pattern x-token body
  token)

(define-peg-pattern extension-token body
  (or ietf-token x-token))

(define-peg-pattern discrete-type body
  (or "text" "image" "audio" "video"
      "application" extension-token))

(define-peg-pattern composite-type body
  (or "message" "multipart" extension-token))

(define-peg-pattern type all
  (or discrete-type composite-type))

(define-peg-pattern subtype all
  (or extension-token iana-token))

(define-peg-pattern attribute all
  token)

;; quoted-string is given higher precedence
(define-peg-pattern value all
  (or quoted-string token))

(define-peg-pattern parameter all
  (and attribute (ignore "=") value))

;; I have prepended optional cfws to account for leading whitespace.
(define-field-pattern content "Content-Type"
  (and (ignore (? cfws)) type (ignore "/") subtype
       (* (and (ignore ";") (ignore (? cfws)) parameter))))

;;; Content Disposition as defined in RFC2183

(define-peg-pattern disposition-type body
  (or "inline" "attachment" extension-token))

(define-peg-pattern quoted-date-time all
  quoted-string)

(define-syntax-rule (define-parameter-pattern name header pattern)
  (define-peg-pattern name all
    (and (ignore header) (ignore "=") pattern)))

(define-parameter-pattern filename-parm "filename" value)
(define-parameter-pattern creation-date-parm "creation-date" quoted-date-time)
(define-parameter-pattern modification-date-parm "modification-date" quoted-date-time)
(define-parameter-pattern read-date-parm "read-date" quoted-date-time)
(define-parameter-pattern size-parm "size" (+ digit))

(define-peg-pattern disposition-parm body
  (or filename-parm creation-date-parm modification-date-parm
      read-date-parm size-parm parameter))

;; I have prepended optional cfws to account for leading whitespace.
(define-field-pattern disposition "Content-Disposition"
  (and (ignore (? cfws)) disposition-type
       (* (and (ignore ";") (ignore (? cfws)) disposition-parm))))

;;; Content transfer encoding

(define-peg-pattern mechanism body
  (or "7bit" "8bit" "binary"
      "quoted-printable" "base64"
      ietf-token x-token))

(define-field-pattern encoding "Content-Transfer-Encoding"
  (and (ignore (? cfws)) mechanism))

;;; Fields

;; The ABNF specified for fields in RFC5322 does not make sense. With
;; it, all headers are eaten up by optional-field. So, as a temporary
;; workaround, I am going with the following much simpler (but
;; possibly incorrect) ABNF.

;; TODO: Try to understand and implement the actual ABNF specified by
;; RFC5322.
(define-peg-pattern fields all
  (* (or trace
         resent-date
         resent-from
         resent-sender
         resent-to
         resent-cc
         resent-bcc
         resent-msg-id
         obs-resent-rply
         orig-date
         from
         sender
         reply-to
         to
         cc
         bcc
         message-id
         in-reply-to
         references
         subject
         comments
         keywords
         mime-version
         content
         disposition
         encoding
         optional-field)))

(define-peg-pattern mime-extension-field-name all
  (and "Content-" (+ ftext)))

(define-peg-pattern mime-extension-field all
  (and mime-extension-field-name (ignore ":") unstructured crlf))

(define-peg-pattern mime-entity-fields all
  (* (or content
         disposition
         encoding
         mime-extension-field
         optional-field)))

(define (decode-mime-encoded-word word)
  (regexp-substitute/global
   #f "=\\?([^?]*)\\?([^?]*)\\?([^?]*)\\?=" word
   'pre (lambda (match-record)
          (let ((charset (match:substring match-record 1))
                (encoding (string->lcase-symbol (match:substring match-record 2)))
                (encoded-text (match:substring match-record 3)))
            (bytevector->string
             ((case encoding
                ((b) base64-decode)
                ((q) q-encoding-decode)
                (else (error "Encoding of MIME word unknown" word)))
              encoded-text)
             charset 'substitute)))
   'post))

(define (body->mime-entities body boundary)
  "Split bytevector BODY into a list of mime entities separated by
BOUNDARY (as explained in RFC2045), and return that list."
  (define (read-till-boundary port)
    (read-bytes-till
     port
     ;; TODO: Look for the boundary sequence only at the beginning of
     ;; a line.
     ;; Boundary is always an ASCII string.
     (string->bytevector (string-append "--" boundary) "us-ascii")))

  (define (read-mime-entity port)
    (let ((line (get-line-with-delimiter port)))
      ;; The eof-object? check returns #t only when the message is
      ;; prematurely truncated. It is invoked only to handle truncated
      ;; messages gracefully without raising an error.
      (if (or (eof-object? line)
              (string-prefix? (string-append "--" boundary "--") line))
          (eof-object)
          (read-till-boundary port))))

  (call-with-port (open-bytevector-input-port body)
    (lambda (port)
      (read-till-boundary port)
      (read-objects read-mime-entity port))))

(define (email->headers+body email)
  "Split EMAIL bytevector into headers and body. Return as multiple
values. The returned headers is a string and body is a bytevector."
  (call-with-port (open-bytevector-input-port email)
    (lambda (port)
      ;; Email headers must strictly be ASCII characters. But for the
      ;; sake of supporting Emacs message mode parens style addresses
      ;; that may use non-ASCII characters, typically for the full
      ;; name, we relax this requirement. We assume an encoding of
      ;; UTF-8, and hope that everything turns out fine. Since UTF-8
      ;; is a superset of ASCII, this should not affect standards
      ;; conforming headers. If encoding is neither UTF-8 nor ASCII,
      ;; we use the substitute conversion strategy and proceed without
      ;; raising an error.
      (set-port-encoding! port "utf-8")
      (set-port-conversion-strategy! port 'substitute)
      (let ((headers (read-while port get-line-with-delimiter
                                 (lambda (line)
                                   (not (or (string= line "\n")
                                            (string= line "\r\n")))))))
        (get-line-with-delimiter port)
        (values (if (eof-object? headers) "" headers)
                (get-bytevector-all port))))))

(define (post-process-mailbox . args)
  (define process-name
    (compose decode-mime-encoded-word string-trim-both))

  (match args
    ;; name-addr email address
    (`(mailbox (display-name ,name) ,address)
     `((name . ,(process-name name))
       (address . ,(string-trim-both address))))
    ;; addr-spec email address
    (`(mailbox ,(? string? address))
     `((address . ,(string-trim-both address))))
    ;; emacs message mode parens style email address
    (`(mailbox ,(? list? address-parts))
     `((name . ,(match-let ((`((captured-comment ,name))
                             (flatten-and-filter '(captured-comment) address-parts)))
                  (process-name name)))
       (address . ,(string-trim-both
                    (string-join (drop-right address-parts 1) "")))))
    (_ (error "Failed to parse mailbox"))))

(define (post-process-content-transfer-encoding _ value)
  (list 'content-transfer-encoding (string->lcase-symbol value)))

(define (post-process-content-type . args)
  (define (valid-charset? charset)
    (catch #t
      (lambda ()
        (bytevector->string (make-bytevector 1 0) charset)
        #t)
      (const #f)))

  (match args
    (`(content (type ,type)
               (subtype ,subtype)
               . ,parameters)
     (let ((type (string->lcase-symbol type))
           (subtype (string->lcase-symbol subtype))
           (parameters
            (map (match-lambda
                   (`(parameter (attribute ,attribute)
                                (value ,value))
                    (cons (string->lcase-symbol attribute) value)))
                 (flatten-and-filter '(parameter) parameters))))
       `(content-type
         ,(acons*
           'type type
           'subtype subtype
           (cond
            ((and (eq? type 'text)
                  (or
                   ;; RFC6657 specifies UTF-8 as the default charset for
                   ;; text/* media types.
                   (not (assoc-ref parameters 'charset))
                   ;; RFC2045 recommends that the default be assumed
                   ;; when a syntactically invalid Content-Type header
                   ;; is encountered. In this implementation, we are
                   ;; only checking for the validity of the
                   ;; charset. Should we check for the validity of the
                   ;; entire Content-Type header? If so, how?
                   (not (valid-charset? (assoc-ref parameters 'charset)))))
             (alist-combine parameters (acons* 'charset "utf-8")))
            (else parameters))))))))

(define post-process-content-disposition
  (match-lambda*
    (`(disposition ,type . ,parameters)
     `(content-disposition
       ,(acons 'type (string->lcase-symbol type)
               (map (match-lambda
                      (('filename-parm ('value filename))
                       (cons 'filename (basename filename)))
                      (((? (lambda (date-parm)
                             (member date-parm '(creation-date-parm modification-date-parm read-date-parm)))
                           date-parm) value)
                       ;; TODO: Convert to SRFI-19 datetime
                       (cons date-parm value))
                      (('size-parm value)
                       (cons 'size (string->number value)))
                      (`(parameter (attribute ,attribute)
                                   (value ,value))
                       (cons (string->lcase-symbol attribute) value)))
                    (flatten-and-filter
                     '(filename-parm creation-date-parm modification-date-parm
                                     read-date-parm size-parm parameter)
                     parameters)))))))

(define post-process-optional-field
  (match-lambda*
    (`(optional-field
       (field-name ,field-name)
       ,field-value)
     (list (string->lcase-symbol field-name)
           field-value))
    (`(optional-field (field-name ,field-name))
     (list field-name ""))))

(define* (macro-process-address-list _ . addresses)
  (flatten-and-filter '(address mailbox) addresses))

(define (post-process-fields fields)
  (map (match-lambda
         ((field value)
          (cons field value))
         ((field . values)
          (cons field values))
         ;; If the Subject header is blank, treat it as having the
         ;; null string as value.
         ('subject '(subject . ""))
         (_ #f))
       fields))

(define (parse-email-address address)
  "Parse ADDRESS as an email address and return an association list
with keys being the symbols name and address, and values being the
display-name and addr-spec respectively. display-name and addr-spec
are as defined in RFC5322.

For example,
(parse-email-address \"Foo <foo@example.org>\")
=> ((name . \"Foo\") (address . \"foo@example.org\"))
(parse-email-address \"foo@example.org\")
=> ((address . \"foo@example.org\"))"
  (pre-post-order
   (peg:tree (match-pattern mailbox address))
   `((mailbox . ,post-process-mailbox)
     (*text* . ,(lambda (_ text) text))
     (*default* . ,(lambda tree tree)))))

(define interpret-address
  (match-lambda
    ((('name . name)
      ('address . address))
     (format #f "~a <~a>" name address))
    ((('address . address)) address)))

(define (parse-email-body headers body)
  "Parse BODY as email body where HEADERS is an association list of
header keys and values as returned by parse-email-headers. Return a
list of <mime-entity> records if the body is a multipart
message. Else, return a single <mime-entity> record."
  (match body
    ((? string? body)
     (parse-email-body headers (string->bytevector body "utf-8")))
    ((? bytevector? body)
     (let ((content-type (assoc-ref headers 'content-type)))
       (case (assoc-ref content-type 'type)
         ((multipart)
          (map (cut parse-mime-entity headers <>)
               (body->mime-entities body (assoc-ref content-type 'boundary))))
         ((text)
          (string-trim-both
           (decode-body body (assoc-ref headers 'content-transfer-encoding)
                        (assoc-ref content-type 'charset))))
         (else (decode-body body (assoc-ref headers 'content-transfer-encoding))))))))

(define (add-default-headers headers)
  ;; Default Content-Type and Content-Transfer-Encoding headers as
  ;; specified in RFC2045
  (alist-combine (acons* 'content-type '((type . text)
                                         (subtype . plain)
                                         ;; UTF-8 is specified as the default
                                         ;; charset in RFC6657
                                         (charset . "utf-8"))
                         'content-transfer-encoding '#{7bit}#)
                 headers))

(define (handle-invalid-headers headers)
  ;; §6.4 of RFC2045 specifies that any entity with an unrecognized
  ;; Content-Transfer-Encoding must be treated as if it has a
  ;; Content-Type of "application/octet-stream", regardless of what
  ;; the Content-Type header field actually says.
  (if (memq (assq-ref headers 'content-transfer-encoding)
            (list '7bit '8bit 'binary 'quoted-printable 'base64))
      headers
      (alist-combine headers
                     '((content-type (type . application)
                                     (subtype . octet-stream))
                       (content-transfer-encoding . binary)))))

(define (add-default-mime-entity-headers parent-headers headers)
  ;; Default Content-Type and Content-Transfer-Encoding headers as
  ;; specified in RFC2045 and RFC2046
  (let ((parent-content-type (assoc-ref parent-headers 'content-type)))
    (alist-combine
     (acons* 'content-type
             `(,@(if (and (eq? (assoc-ref parent-content-type 'type) 'multipart)
                          (eq? (assoc-ref parent-content-type 'subtype) 'digest))
                     '((type . message)
                       (subtype . rfc822))
                     '((type . text)
                       (subtype . plain)))
               ;; UTF-8 is specified as the default
               ;; charset in RFC6657
               (charset . "utf-8"))
             'content-transfer-encoding '#{7bit}#)
     headers)))

(define (parse-mime-entity parent-headers bv)
  (let-values (((headers body) (email->headers+body bv)))
    (let ((headers
           (pre-post-order
            (peg:tree
             (match-pattern mime-entity-fields headers))
            `((content . ,post-process-content-type)
              (encoding . ,post-process-content-transfer-encoding)
              (disposition . ,post-process-content-disposition)
              (optional-field . ,post-process-optional-field)
              (mime-entity-fields . ,(lambda (_ . mime-entity-fields)
                                       (add-default-mime-entity-headers
                                        parent-headers
                                        (post-process-fields mime-entity-fields))))
              (*text* . ,(match-lambda*
                           ;; Handle MIME entities that have no
                           ;; headers.
                           ((_ 'mime-entity-fields)
                            (add-default-mime-entity-headers parent-headers '()))
                           ((_ text) text)))
              (*default* . ,(lambda tree tree))))))
      (make-mime-entity headers (parse-email-body headers body)))))

(define (parse-email email)
  "Parse string EMAIL and return result as an <email> record."
  (match email
    ((? string? email)
     (parse-email (string->bytevector email "utf-8")))
    ((? bytevector? email)
     (let-values (((headers body) (email->headers+body email)))
       (let ((headers-alist (parse-email-headers headers)))
         (make-email headers-alist (parse-email-body headers-alist body)))))))

(define (parse-email-headers headers)
  "Parse string HEADERS as email headers and return an association
list of header keys and values."
  (pre-post-order
   (peg:tree
    (match-pattern fields headers))
   `((received . ,(match-lambda*
                    (('received tokens (? date? timestamp))
                     (list 'received (string-join tokens) timestamp))
                    (('received tokens ...)
                     (list 'received (string-join tokens)))))
     (received-token . ,(match-lambda*
                          (`(received-token ,token) token)))
     (date-time . ,(lambda node
                     (match-let*
                         (;; Seconds are optional; provide a default
                          ;; binding which will be shadowed by match.
                          (seconds "0")
                          ((('day day) ('month month) ('year year)
                            ('hours hours) ('minutes minutes)
                            . (or (('seconds seconds) ('zone . zone))
                                  (('zone . zone))))
                           (flatten-and-filter
                            '(day month year hours minutes seconds zone)
                            node)))
                       (make-date 0
                                  (string->number seconds)
                                  (string->number minutes)
                                  (string->number hours)
                                  (string->number day)
                                  (1+ (list-index
                                       (cut equal? <> month)
                                       (list "Jan" "Feb" "Mar" "Apr" "May" "Jun"
                                             "Jul" "Aug" "Sep" "Oct" "Nov" "Dec")))
                                  (let ((year (string->number year)))
                                    (cond
                                     ((and (>= year 0) (<= year 49))
                                      (+ year 2000))
                                     ((and (>= year 50) (<= year 999))
                                      (+ year 1900))
                                     (else year)))
                                  (match zone
                                    (((or "UT" "GMT")) 0)
                                    (("EDT") (* -4 3600))
                                    (((or "EST" "CDT")) (* -5 3600))
                                    (((or "CST" "MDT")) (* -6 3600))
                                    (((or "MST" "PDT")) (* -7 3600))
                                    (("PST") (* -8 3600))
                                    (`((zone-sign ,zone-sign)
                                       (zone-hours ,zone-hours)
                                       (zone-minutes ,zone-minutes))
                                     (* (case (string->symbol zone-sign)
                                          ((+) 1)
                                          ((-) -1))
                                        (+ (* 60 60 (string->number zone-hours))
                                           (* 60 (string->number zone-minutes))))))))))
     (orig-date . ,(lambda (_ date) (list 'date date)))
     (mailbox . ,post-process-mailbox)
     (address-list *macro* . ,macro-process-address-list)
     (mailbox-list *macro* . ,macro-process-address-list)
     (optional-field . ,post-process-optional-field)
     (msg-id . ,(match-lambda* (`(msg-id ,msg-id) msg-id)))
     (content . ,post-process-content-type)
     (encoding . ,post-process-content-transfer-encoding)
     (disposition . ,post-process-content-disposition)
     (subject . ,(match-lambda* (`(subject ,subject)
                                 `(subject ,(decode-mime-encoded-word subject)))))
     (keywords . ,(lambda (_ value)
                    (cons 'keywords (string-split value #\,))))
     (fields . ,(lambda (_ . fields)
                  (handle-invalid-headers
                   (add-default-headers (post-process-fields fields)))))
     (*text* . ,(lambda (_ value) value))
     (*default* . ,(lambda tree tree)))))

(define* (decode-body body encoding #:optional charset)
  (let ((decoded-octets
         (case encoding
           ((base64) (base64-decode body))
           ((quoted-printable) (quoted-printable-decode
                                (bytevector->string body "us-ascii")))
           ((#{7bit}# #{8bit}# binary) body)
           (else (error "Body decoding failed. Unknown encoding" encoding)))))
    (if charset
        (bytevector->string decoded-octets charset 'substitute)
        decoded-octets)))

(define (read-next-email-in-mbox port)
  "Read next email from PORT and return as a bytevector.  PORT is an
input port reading an mbox file."
  ;; Read and discard From_ line
  (get-line-with-delimiter port)
  ;; Read the actual email
  (let ((email (read-bytes-till
                port (string->bytevector "\nFrom " "us-ascii"))))
    (read-char port)
    email))

(define (mbox->emails port)
  "Read all emails from PORT and return as a list of bytevectors.
PORT is an input port reading an mbox file."
  (read-objects read-next-email-in-mbox port))