Make undigest work with multipart/mixed messages

* test/lisp/mail/undigest.el: New test file (bug#12873).
* lisp/mail/undigest.el (rmail-digest-methods): Install
rmail-digest-parse-mixed-mime.
(rmail-content-type-boundary): New function, to get a specific
Content-type boundary.
(rmail-digest-parse-mixed-mime): New function, to search for a
multipart/digest message inside a multipart/mixed message.

2 files changed, 403 insertions, 1 deletions

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 <https://www.gnu.org/licenses/>.
+
+;;; 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 <digester@digester.com>
+To: Undigester <undigester@undigester.com>
+Date: ddd, dd mmm yy hh:mm:ss zzz
+Subject: Testing you
+
+Testing the undigester.
+
+------- Message sep
+
+From: NN1 <nn1@nn1.com>
+To: Digester <digester@digester.com>
+Date: ddd, dd mmm yy hh:mm:ss zzz
+Subject: Message one
+
+This is message one.
+
+------- Message sep
+
+From: NN2 <nn2@nn2.com>
+To: Digester <digester@digester.com>
+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 <digester@digester.com>
+To: Undigester <undigester@undigester.com>
+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 <nn1@nn1.com>
+Subject: Message One Subject
+
+This is message one.
+
+------------------------------
+
+Date: ddd, dd mmm yy hh:mm:ss zzz
+From: NN2 <nn2@nn2.com>
+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 <digester@digester.com>
+To: Undigester <undigester@undigester.com>
+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 <nn1@nn1.com>
+Subject: Message One Subject
+
+This is message one.
+
+------------------------------
+
+Date: ddd, dd mmm yy hh:mm:ss zzz
+From: NN2 <nn2@nn2.com>
+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 <digester@digester.com>
+To: Undigester <undigester@undigester.com>
+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 <nn1@nn1.com>
+Subject: Message One Subject
+
+This is message one.
+
+------------------------------
+
+Date: ddd, dd mmm yy hh:mm:ss zzz
+From: NN2 <nn2@nn2.com>
+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 <digester@digester.com>
+To: Undigester <undigester@undigester.com>
+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 <nn1@nn1.com>
+To: Digester <digester@digester.com>
+Date: ddd, dd mmm yy hh:mm:ss zzz
+Subject: Message one
+
+Message one.
+
+------- =_aaaaaaaaaa0
+
+From: NN2 <nn2@nn2.com>
+To: Digester <digester@digester.com>
+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 <digester@digester.com>
+To: Undigester <undigester@undigester.com>
+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 <nn1@nn1.com>
+To: Digester <digester@digester.com>
+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 <nn2@nn2.com>
+To: Digester <digester@digester.com>
+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")))))