diff --git a/lisp/mail/undigest.el b/lisp/mail/undigest.el
index 03e77a83ce3..c6d29bc4e77 100644
--- a/lisp/mail/undigest.el
+++ b/lisp/mail/undigest.el
@@ -41,7 +41,8 @@ You may need to customize it for local needs."
(defconst rmail-digest-methods
- '(rmail-digest-parse-mime
+ '(rmail-digest-parse-mixed-mime
+ rmail-digest-parse-mime
rmail-digest-parse-rfc1153strict
rmail-digest-parse-rfc1153sloppy
rmail-digest-parse-rfc934)
@@ -52,6 +53,53 @@ A function returns nil if it cannot parse the digest. If it can, it
returns a list of cons pairs containing the start and end positions of
each undigestified message as markers.")
+(defun rmail-content-type-boundary (type)
+ "If Content-type is of type TYPE, return its boundary; otherwise, return nil."
+ (goto-char (point-min))
+ (let ((head-end (save-excursion (search-forward "\n\n" nil t) (point))))
+ (when (re-search-forward
+ (concat "^Content-type: " type ";"
+ "\\s-* boundary=\"?\\([^\";\n]+\\)[\";\n]")
+ head-end t)
+ (match-string 1))))
+
+(defun rmail-digest-parse-mixed-mime ()
+ "Like `rmail-digest-parse-mime', but for multipart/mixed messages."
+ (when-let ((boundary (rmail-content-type-boundary "multipart/mixed")))
+ (let ((global-sep (concat "\n--" boundary))
+ (digest (concat "^Content-type: multipart/digest;"
+ "\\s-* boundary=\"?\\([^\";\n]+\\)[\";\n]"))
+ result)
+ (search-forward global-sep nil t)
+ (while (not (or result (eobp)))
+ ;; For each part, see if it is a multipart/digest.
+ (let* ((limit (save-excursion (search-forward global-sep nil 'move)
+ (point)))
+ (beg (and (re-search-forward digest limit t)
+ (match-beginning 0)))
+ digest-sep)
+ (when (and beg
+ (setq digest-sep (concat "\n--" (match-string 1)))
+ ;; Search for 1st sep.
+ (search-forward digest-sep nil t))
+ ;; Skip body part headers.
+ (search-forward "\n\n" nil t)
+ ;; Push the 1st message.
+ (push (cons (copy-marker beg) (copy-marker (point-marker) t))
+ result)
+ ;; Push the rest of the messages.
+ (let ((start (make-marker))
+ done)
+ (while (and (search-forward digest-sep limit 'move) (not done))
+ (move-marker start (match-beginning 0))
+ (and (looking-at "--$") (setq done t))
+ (search-forward "\n\n")
+ (push (cons (copy-marker start)
+ (copy-marker (point-marker) t))
+ result))))
+ (goto-char limit)))
+ (nreverse result))))
+
(defun rmail-digest-parse-mime ()
(goto-char (point-min))
(when (let ((head-end (progn (search-forward "\n\n" nil t) (point))))
diff --git a/test/lisp/mail/undigest-tests.el b/test/lisp/mail/undigest-tests.el
new file mode 100644
index 00000000000..24059aa349a
--- /dev/null
+++ b/test/lisp/mail/undigest-tests.el
@@ -0,0 +1,354 @@
+;;; undigest.el --- Tests for undigest.el -*- lexical-binding:t -*-
+
+;; Copyright (C) 2022 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs 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 General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs. If not, see .
+
+;;; Code:
+
+(require 'ert)
+(require 'rmail)
+(require 'undigest)
+
+;;; Variables:
+;; Some digests for testing.
+(defvar rmail-rfc934-digest "From tester Fri Jan 24 00:00:00 2022
+From: Digester
+To: Undigester
+Date: ddd, dd mmm yy hh:mm:ss zzz
+Subject: Testing you
+
+Testing the undigester.
+
+------- Message sep
+
+From: NN1
+To: Digester
+Date: ddd, dd mmm yy hh:mm:ss zzz
+Subject: Message one
+
+This is message one.
+
+------- Message sep
+
+From: NN2
+To: Digester
+Date: ddd, dd mmm yy hh:mm:ss zzz
+Subject: Message two
+
+This is message two.
+"
+
+ "RFC 934 digest.")
+
+(defvar rmail-rfc1153-digest-strict "From tester Fri Jan 24 00:00:00 2022
+Date: ddd, dd mmm yy hh:mm:ss zzz
+From: Digester
+To: Undigester
+Date: ddd, dd mmm yy hh:mm:ss zzz
+Subject: Testing you
+
+Some mailing list information.
+
+Today's Topics:
+
+ 1. Message One Subject (Sender)
+ 2. Message Two Subject (Sender)
+
+----------------------------------------------------------------------
+
+Date: ddd, dd mmm yy hh:mm:ss zzz
+From: NN1
+Subject: Message One Subject
+
+This is message one.
+
+------------------------------
+
+Date: ddd, dd mmm yy hh:mm:ss zzz
+From: NN2
+Subject: Message Two Subject
+
+This is message two.
+
+------------------------------
+
+End of Digest.
+************************************
+"
+ "RFC 1153 strict style digest.")
+
+(defvar rmail-rfc1153-digest-less-strict "From tester Fri Jan 24 00:00:00 2022
+From: Digester
+To: Undigester
+Date: ddd, dd mmm yy hh:mm:ss zzz
+Subject: Testing you
+
+Some mailing list information.
+
+Today's Topics:
+
+ 1. Message One Subject (Sender)
+ 2. Message Two Subject (Sender)
+
+----------------------------------------------------------------------
+
+Date: ddd, dd mmm yy hh:mm:ss zzz
+From: NN1
+Subject: Message One Subject
+
+This is message one.
+
+------------------------------
+
+Date: ddd, dd mmm yy hh:mm:ss zzz
+From: NN2
+Subject: Message Two Subject
+
+This is message two.
+
+------------------------------
+
+Subject: Digest Footer
+
+End of Sbcl-help Digest, Vol 158, Issue 4
+*****************************************
+"
+ "RFC 1153 style digest, with a Subject header.")
+
+(defvar rmail-rfc1153-digest-sloppy "From tester Fri Jan 24 00:00:00 2022
+From: Digester
+To: Undigester
+Date: ddd, dd mmm yy hh:mm:ss zzz
+Subject: Testing you
+
+Some mailing list information.
+
+Today's Topics:
+
+ 1. Message One Subject (Sender)
+ 2. Message Two Subject (Sender)
+
+----------------------------------------------------------------------
+
+Date: ddd, dd mmm yy hh:mm:ss zzz
+From: NN1
+Subject: Message One Subject
+
+This is message one.
+
+------------------------------
+
+Date: ddd, dd mmm yy hh:mm:ss zzz
+From: NN2
+Subject: Message Two Subject
+
+This is message two.
+
+------------------------------
+
+Subject: Digest Footer
+
+______________________________________________
+Some blurb.
+
+End of Digest.
+************************************
+"
+ "RFC 1153 sloppy style digest.")
+
+(defvar rmail-rfc1521-mime-digest "From tester Fri Jan 24 00:00:00 2022
+From: Digester
+To: Undigester
+Date: ddd, dd mmm yy hh:mm:ss zzz
+Subject: Test digest
+MIME-Version: 1.0
+Content-Type: multipart/digest; boundary=\"----- =_aaaaaaaaaa0\"
+
+------- =_aaaaaaaaaa0
+Content-Type: message/rfc822
+
+From: NN1
+To: Digester
+Date: ddd, dd mmm yy hh:mm:ss zzz
+Subject: Message one
+
+Message one.
+
+------- =_aaaaaaaaaa0
+
+From: NN2
+To: Digester
+Date: ddd, dd mmm yy hh:mm:ss zzz
+Subject: Message two
+
+Message two.
+
+------- =_aaaaaaaaaa0
+"
+ "RFC 1521 style MIME digest.")
+
+(defvar rmail-multipart-mixed-digest
+ "From tester Fri Jan 24 00:00:00 2022
+From: Digester
+To: Undigester
+Date: ddd, dd mmm yy hh:mm:ss zzz
+Subject: Test digest
+Content-Type: multipart/mixed; boundary=\"===============2529375068597856000==\"
+MIME-Version: 1.0
+
+--===============2529375068597856000==
+Content-Type: text/plain;
+MIME-Version: 1.0
+Content-Description: Today's Topics
+
+Some message.
+
+--===============2529375068597856000==
+Content-Type: multipart/digest; boundary=\"===============6060050777038710134==\"
+MIME-Version: 1.0
+
+--===============6060050777038710134==
+Content-Type: message/rfc822
+MIME-Version: 1.0
+
+From: NN1
+To: Digester
+Date: ddd, dd mmm yy hh:mm:ss zzz
+Subject: Message one
+
+Message one.
+
+--===============6060050777038710134==
+Content-Type: message/rfc822
+MIME-Version: 1.0
+
+From: NN2
+To: Digester
+Date: ddd, dd mmm yy hh:mm:ss zzz
+Subject: Message two
+
+Message two.
+
+--===============6060050777038710134==--
+
+--===============2529375068597856000==
+Content-Type: text/plain;
+MIME-Version: 1.0
+Content-Description: Digest Footer
+
+The footer.
+
+--===============2529375068597856000==--"
+ "RFC 1521 digest inside a multipart/mixed message.")
+
+;;; Utils:
+(defun rmail-message-content (message)
+ "Return the content of the message numbered MESSAGE."
+ (rmail-show-message message)
+ (let ((beg (rmail-msgbeg rmail-current-message))
+ (end (rmail-msgend rmail-current-message)))
+ (with-current-buffer rmail-view-buffer
+ (save-excursion
+ (goto-char beg)
+ (search-forward "\n\n" end nil)
+ (buffer-substring-no-properties (match-end 0) end)))))
+
+;;; Tests:
+(ert-deftest rmail-undigest-test-rfc934-digest ()
+ "Test that we can undigest a RFC 934 digest."
+ (let ((file (make-temp-file "undigest-test-")))
+ (with-temp-file file
+ (insert rmail-rfc934-digest)
+ (write-region nil nil file)
+ (rmail file)
+ (undigestify-rmail-message)
+ (should (= rmail-total-messages 4))
+ (should (string= (rmail-message-content 2) "Testing the undigester.\n\n"))
+ (should (string= (rmail-message-content 3) "This is message one.\n\n"))
+ (should (string= (rmail-message-content 4) "This is message two.\n")))))
+
+(ert-deftest rmail-undigest-test-rfc1153-digest-strict ()
+ "Test that we can undigest a strict RFC 1153 digest."
+ :expected-result :failed
+ (let ((file (make-temp-file "undigest-test-")))
+ (with-temp-file file
+ (insert rmail-rfc1153-digest-strict)
+ (write-region nil nil file)
+ (rmail file)
+ (should
+ (condition-case nil
+ (progn
+ ;; This throws an error, because the Trailer is not recognized
+ ;; as a valid RFC 822 (or later) message.
+ (undigestify-rmail-message)
+ (should (string= (rmail-message-content 2) "Testing the undigester.\n\n"))
+ (should (string= (rmail-message-content 3) "This is message one.\n\n"))
+ (should (string= (rmail-message-content 4) "This is message two.\n"))
+ t)
+ (error nil))))))
+
+(ert-deftest rmail-undigest-test-rfc1153-less-strict-digest ()
+ "Test that we can undigest a RFC 1153 with a Subject header in its footer."
+ (let ((file (make-temp-file "undigest-test-")))
+ (with-temp-file file
+ (insert rmail-rfc1153-digest-less-strict)
+ (write-region nil nil file)
+ (rmail file)
+ (undigestify-rmail-message)
+ (should (= rmail-total-messages 5))
+ (should (string= (rmail-message-content 3) "This is message one.\n\n"))
+ (should (string= (rmail-message-content 4) "This is message two.\n\n")))))
+
+(ert-deftest rmail-undigest-test-rfc1153-sloppy-digest ()
+ "Test that we can undigest a sloppy RFC 1153 digest."
+ (let ((file (make-temp-file "undigest-test-")))
+ (with-temp-file file
+ (insert rmail-rfc1153-digest-sloppy)
+ (write-region nil nil file)
+ (rmail file)
+ (undigestify-rmail-message)
+ (should (= rmail-total-messages 5))
+ (should (string= (rmail-message-content 3) "This is message one.\n\n"))
+ (should (string= (rmail-message-content 4) "This is message two.\n\n")))))
+
+;; This fails because `rmail-digest-parse-mime' combines the preamble with the
+;; first message of the digest. And then, it doesn't get rid of the last
+;; separator.
+(ert-deftest rmail-undigest-test-rfc1521-mime-digest ()
+ "Test that we can undigest a RFC 1521 MIME digest."
+ :expected-result :failed
+ (let ((file (make-temp-file "undigest-test-")))
+ (with-temp-file file
+ (insert rmail-rfc1521-mime-digest)
+ (write-region nil nil file)
+ (rmail file)
+ (undigestify-rmail-message)
+ (should (= rmail-total-messages 3))
+ (should (string= (rmail-message-content 2) "Message one.\n\n"))
+ (should (string= (rmail-message-content 3) "Message two.\n\n")))))
+
+(ert-deftest rmail-undigest-test-multipart-mixed-digest ()
+ "Test that we can undigest a digest inside a multipart/mixed digest."
+ (let ((file (make-temp-file "undigest-test-")))
+ (with-temp-file file
+ (insert rmail-multipart-mixed-digest)
+ (write-region nil nil file)
+ (rmail file)
+ (undigestify-rmail-message)
+ (should (= rmail-total-messages 4))
+ (should (string= (rmail-message-content 2) "Message one.\n\n"))
+ (should (string= (rmail-message-content 3) "Message two.\n\n")))))