aboutsummaryrefslogtreecommitdiff
path: root/email/email.scm
blob: 53840dbc8030fd30278222e38ad077a4bacb2cfa (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
;;; guile-email --- Guile email parser
;;; Copyright © 2018 Arun Isaac <arunisaac@systemreboot.net>
;;;
;;; 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 iconv)
  #:use-module (ice-9 match)
  #:use-module (ice-9 peg)
  #:use-module (ice-9 regex)
  #: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)
                #:select (get-line-with-delimiter
                          read-objects read-while
                          acons* alist-delete*))
  #: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)))

;;; Quoted characters

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

;;; Folding white space and comments

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

(define-printable-ascii-character-pattern ctext "(" ")" "\\")

(define-peg-pattern comment none
  (and "(" (* (and (? fws) ccontent)) ")"))

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

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

;;; Atom

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

(define-peg-pattern atom body
  (and (? cfws) (+ atext) (? cfws)))

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

(define-peg-pattern dot-atom body
  (and (? cfws) dot-atom-text (? cfws)))

;;; Quoted strings

(define-printable-ascii-character-pattern 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

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

(define-peg-pattern phrase body
  (+ word))

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

;;; Date and time specification

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

(define-peg-pattern day-of-week all
  (and (ignore (? fws)) day-name))

;; TODO: Remove workaround guile peg bug for ignore
(define-peg-pattern day all
  (and (ignore (? fws)) digit (? digit) (ignore (and fws))))

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

;; TODO: Remove workaround guile peg bug for ignore
(define-peg-pattern year all
  (and (ignore (and fws)) digit digit digit digit (ignore (and fws))))

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

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

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

(define-peg-pattern seconds all
  (and digit digit))

(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))

;; TODO: Remove workaround guile peg bug for ignore
(define-peg-pattern zone all
  (and (ignore (and fws)) zone-sign zone-hours zone-minutes))

(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

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

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

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

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

(define-peg-pattern domain body
  (or dot-atom domain-literal))

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

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

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

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

(define-peg-pattern mailbox-list all
  (and mailbox (* (and (ignore ",") mailbox))))

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

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

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

(define-peg-pattern address-list all
  (and address (* (and (ignore ",") address))))

;;; Fields

(define-syntax-rule (define-field-pattern name header pattern)
  (define-peg-pattern name all
    (and (ignore (string-ci header)) (ignore ":") pattern crlf)))

;;; Origination date field

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

;;; Originator fields

(define-field-pattern from "From" (or mailbox-list address-list))
(define-field-pattern sender "Sender" (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)))

;;; Identification fields

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

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

(define-peg-pattern id-right body
  (or 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))
(define-field-pattern references "References" (+ 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))))

;;; Resent fields

(define-field-pattern resent-date "Resent-Date" date-time)
(define-field-pattern resent-from "Resent-From" (or mailbox-list address-list))
(define-field-pattern resent-sender "Resent-Sender" (or mailbox address))
(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)))
(define-field-pattern resent-msg-id "Resent-Message-ID" msg-id)

;;; Trace fields

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

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

(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 optional-field all
  (and field-name (ignore ":") unstructured crlf))

;;; 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
         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)))
   'post))

(define (body->mime-entities body boundary)
  "Split BODY into a list of mime entities separated by BOUNDARY (as
explained in RFC2045), and return that list."
  (define (read-till-boundary port)
    (read-while port get-line-with-delimiter
                (negate (cut string-prefix? (string-append "--" boundary) <>))))

  (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-input-string body
    (lambda (port)
      (read-till-boundary port)
      (read-objects read-mime-entity port))))

(define (email->headers+body email)
  "Split EMAIL into headers and body. Return as multiple values."
  (call-with-input-string email
    (lambda (port)
      (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 headers
                (read-while port get-line-with-delimiter identity))))))

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

(define post-process-content-type
  (match-lambda*
    (`(content (type ,type)
               (subtype ,subtype)
               . ,parameters)
     (let ((type (string->lcase-symbol type))
           (subtype (string->lcase-symbol subtype)))
       `(content-type
         ,(acons* 'type type
                  'subtype subtype
                  (let ((parameters
                         (map (match-lambda
                                (`(parameter (attribute ,attribute)
                                             (value ,value))
                                 (cons (string->lcase-symbol attribute) value)))
                              (flatten-and-filter '(parameter) parameters))))
                    (if (and (eq? type 'text)
                             (not (assoc-ref parameters 'charset)))
                        ;; UTF-8 is specified as the default charset in RFC6657
                        (acons 'charset "utf-8" parameters)
                        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 (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\"))"
  (cond
   ((string-match "([^<]*)<([^>]*)>" address)
    => (lambda (match-record)
         (let ((name (string-trim-both (match:substring match-record 1)))
               (address (match:substring match-record 2)))
           (if (string-null? name)
               `((address . ,address))
               `((name . ,name)
                 (address . ,address))))))
   (else `((address . ,address)))))

(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."
  (let ((content-type (assoc-ref headers 'content-type)))
    (case (assoc-ref content-type 'type)
      ((multipart)
       (map parse-mime-entity
            (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
  (let ((default-headers
          (acons* 'content-type '((type . text)
                                  (subtype . plain)
                                  ;; UTF-8 is specified as the default
                                  ;; charset in RFC6657
                                  (charset . "utf-8"))
                  'content-transfer-encoding '#{7bit}#)))
    (append (alist-delete* (append (if (assoc-ref headers 'content-type)
                                       (list 'content-type) (list))
                                   (if (assoc-ref headers 'content-transfer-encoding)
                                       (list 'content-transfer-encoding) (list)))
                           default-headers)
            headers)))

(define (parse-mime-entity text)
  (let-values (((headers body) (email->headers+body text)))
    (let ((headers
           (pre-post-order
            (peg:tree
             (match-pattern mime-entity-fields text))
            `((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-headers
                                        (map (match-lambda
                                               ((mime-entity-field value)
                                                (cons mime-entity-field value))
                                               ((mime-entity-field . values)
                                                (cons mime-entity-field values)))
                                             mime-entity-fields))))
              (*text* . ,(lambda (_ 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 a <email> record."
  (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."
  (define (trim-address address)
    (string-trim-right
     (string-trim (string-trim-both address) #\<)
     #\>))

  (pre-post-order
   (peg:tree
    (match-pattern fields headers))
   `((date-time . ,(lambda node
                     (match-let
                         ((`((day ,day) (month ,month) (year ,year)
                             (hours ,hours) (minutes ,minutes) (seconds ,seconds)
                             (zone-sign ,zone-sign) (zone-hours ,zone-hours) (zone-minutes ,zone-minutes))
                           (flatten-and-filter
                            '(day month year hours minutes seconds
                                  zone-sign zone-hours zone-minutes)
                            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")))
                                  (string->number year)
                                  (* (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 . ,(match-lambda*
                   (`(mailbox (display-name ,name) ,address)
                    `((name . ,(decode-mime-encoded-word
                                (string-trim-both name)))
                      (address . ,(trim-address address))))
                   (`(mailbox ,address)
                    `((address . ,(trim-address address))))
                   (_ (error "Failed to parse 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)
     (fields . ,(lambda (_ . fields)
                  (add-default-headers
                   (filter-map (match-lambda
                                 ((field value)
                                  (cons field value))
                                 ((field . values)
                                  (cons field values))
                                 (_ #f))
                               fields))))
     (*text* . ,(lambda (_ value) value))
     (*default* . ,(lambda tree tree)))))

(define* (decode-body body encoding #:optional charset)
  (let ((octets
         (case encoding
           ((base64)
            (base64-decode 
             (string-filter
              (char-set-union
               (ucs-range->char-set (char->integer #\a) (1+ (char->integer #\z)))
               (ucs-range->char-set (char->integer #\A) (1+ (char->integer #\Z)))
               (ucs-range->char-set (char->integer #\0) (1+ (char->integer #\9)))
               (char-set #\+ #\/ #\=))
              body)))
           ((quoted-printable) (quoted-printable-decode body))
           ((#{7bit}# #{8bit}# binary) body)
           (else (error "Body decoding failed. Unknown encoding" encoding)))))
    (if charset
        (case encoding
          ((base64 quoted-printable) (bytevector->string octets charset))
          ((#{7bit}# #{8bit}# binary) octets))
        octets)))

(define (read-next-email-in-mbox port)
  ;; Read and discard From_ line
  (get-line-with-delimiter port)
  ;; Read the actual email
  (read-while port get-line-with-delimiter
              (negate (cut string-prefix? "From " <>))))

(define (mbox->emails port)
  (read-objects read-next-email-in-mbox port))