path: root/email/email.scm

;;; 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 all
  (and (ignore (? cfws))
       (ignore"<") addr-spec (ignore">")
       (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))

;; TODO: Do not discard the internal structure of received
(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)
    (if (string-prefix? (string-append "--" boundary "--")
			(get-line-with-delimiter port))
	(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 (extract-value _ value) value)

  (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)))
     (angle-addr . ,extract-value)
     (mailbox . ,(match-lambda*
		   (`(mailbox (display-name ,name) ,address)
		    `((name . ,(decode-mime-encoded-word
				(string-trim-both name)))
		      (address . ,address)))
		   (`(mailbox ,address)
		    `((address . ,(string-trim-both 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
				 (('trace . _) #f)
				 ((field value)
				  (cons field value))
				 ((field . values)
				  (cons field values))
				 (_ #f))
			       fields))))
     (*text* . ,extract-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))