Detect if a message can be encrypted and add an MML tag

* lisp/gnus/message.el (message-all-recipients): Return a list of
pairs, one for each recipient in To, Cc, Bcc.
(message-all-epg-keys-available-p): Check that there is a public key
in epg for each recipient of the current message.
(message-sign-encrypt-if-all-keys-available): Add MML tag to sign and
encrypt current message if there is a public key for every recipient
in current message.

* test/lisp/gnus/message-tests.el (message-all-recipients): Test for
message-all-recipients.

diff --git a/etc/NEWS b/etc/NEWS
index baff9664cf174277a7f61f4755f2817264793859..02b31ecff47669c0d472a41c716b72fff7322c38 100644 (file)
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -337,6 +337,14 @@ or NextCloud hosted files and directories.
 It was obsolete since Emacs 22.1, replaced by customize.
 
 \f
+** Message
+
++++
+*** Messages can now be systematically encrypted
+when the PGP keyring contains a public key for every recipient.  To
+achieve this, add 'message-add-encrypt-tag-if-can-encrypt' to
+'message-send-hook'.
+
 * New Modes and Packages in Emacs 27.1
 
 +++

diff --git a/lisp/gnus/message.el b/lisp/gnus/message.el
index 37b994de99cefa96cf8dcddfbc5d7db3b719393c..fdb296fc24cc97d937b62d797b99ffc6b0763ef7 100644 (file)
--- a/lisp/gnus/message.el
+++ b/lisp/gnus/message.el
@@ -2582,6 +2582,36 @@ PGG manual, depending on the value of `mml2015-use'."
                      (t
                       'message)))))
 
+(defun message-all-recipients ()
+  "Return a list of all recipients in the message, looking at TO, CC and BCC.
+
+Each recipient is in the format of `mail-extract-address-components'."
+  (mapcan (lambda (header)
+            (let ((header-value (message-fetch-field header)))
+              (and
+               header-value
+               (mail-extract-address-components header-value t))))
+          '("To" "Cc" "Bcc")))
+
+(defun message-all-epg-keys-available-p ()
+  "Return non-nil if the pgp keyring has a public key for each recipient."
+  (require 'epa)
+  (let ((context (epg-make-context epa-protocol)))
+    (catch 'break
+      (dolist (recipient (message-all-recipients))
+        (let ((recipient-email (cadr recipient)))
+          (when (and recipient-email (not (epg-list-keys context recipient-email)))
+            (throw 'break nil))))
+      t)))
+
+(defun message-sign-encrypt-if-all-keys-available ()
+  "Add MML tag to encrypt message when there is a key for each recipient.
+
+Consider adding this function to `message-send-hook' to
+systematically send encrypted emails when possible."
+  (when (message-all-epg-keys-available-p)
+    (mml-secure-message-sign-encrypt)))
+
 \f
 
 ;;;

diff --git a/test/lisp/gnus/message-tests.el b/test/lisp/gnus/message-tests.el
index ec1f24702042d52c8c4e3f3689c985724b9109a6..9124dcf77a3567a1f2557c4f48df8903e7a4cc89 100644 (file)
--- a/test/lisp/gnus/message-tests.el
+++ b/test/lisp/gnus/message-tests.el
@@ -29,6 +29,8 @@
 (require 'ert)
 (require 'ert-x)
 
+(require 'cl-lib)
+
 (ert-deftest message-mode-propertize ()
   (with-temp-buffer
     (unwind-protect
@@ -97,6 +99,50 @@
         (should (string= stripped-was
                          (message-strip-subject-trailing-was with-was)))))))
 
+(ert-deftest message-all-recipients ()
+  (ert-with-test-buffer (:name "message")
+    (insert "To: Person 1 <p1@p1.org>, Person 2 <p2@p2.org>\n")
+    (insert "CC: Person 3 <p3@p3.org>, Person 4 <p4@p4.org>\n")
+    (insert "BCC: Person 5 <p5@p5.org>, Person 6 <p6@p6.org>\n")
+    (should (equal (message-all-recipients)
+                   '(("Person 1" "p1@p1.org")
+                     ("Person 2" "p2@p2.org")
+                     ("Person 3" "p3@p3.org")
+                     ("Person 4" "p4@p4.org")
+                     ("Person 5" "p5@p5.org")
+                     ("Person 6" "p6@p6.org"))))))
+
+(ert-deftest message-all-epg-keys-available-p ()
+  (let ((person1 '("Person 1" "p1@p1.org"))
+        (person2 '("Person 2" "p2@p2.org"))
+        (person3 '("Person 3" "p3@p3.org"))
+        (recipients nil)
+        (keyring '("p1@p1.org" "p2@p2.org")))
+    (cl-letf (((symbol-function 'epg-list-keys)
+               (lambda (_ email) (cl-find email keyring :test #'string=)))
+              ((symbol-function 'message-all-recipients)
+               (lambda () recipients)))
+
+      (setq recipients (list))
+      (should (message-all-epg-keys-available-p))
+
+      (setq recipients (list person1))
+      (should (message-all-epg-keys-available-p))
+
+      (setq recipients (list person1 person2))
+      (should (message-all-epg-keys-available-p))
+
+      (setq recipients (list person3))
+      (should-not (message-all-epg-keys-available-p))
+
+      (setq recipients (list person1 person3))
+      (should-not (message-all-epg-keys-available-p))
+
+      (setq recipients (list person3 person1))
+      (should-not (message-all-epg-keys-available-p))
+
+      (setq recipients (list person1 person2 person3))
+      (should-not (message-all-epg-keys-available-p)))))
 
 (provide 'message-mode-tests)