Displaying MIME parts internally/externally in Gnus

[Stefan Monnier]

Many attachments come with poor content-type description, in which case Gnus
typically doesn't know what to do with it.  When doing "view externally",
such attachments are actually saved.  I don't know about you, but I don't
consider "saving" as a sort of "viewing" activity.  If I had wanted to save
the attachment I'd have used something more like, say, the "Save"
command instead, don't you think?

Similar problems happen for "view internally".  So I suggest the patch below
which tries harder to show the attachment internally or externally: if the
content-type can't be displayed as requested, it asks the user what kind of
content-type to use instead.

A minor variant of it has been mildly tested (and only on Emacs-CVS), and
it's based on a very shallow understanding of the code, so it's probably
not perfect.

If there's no objection I'll install it, otherwise please tell me what's
wrong with it.


        Stefan


--- gnus-art.el 23 oct 2005 22:29:41 -0400      1.98
+++ gnus-art.el 20 nov 2005 21:33:17 -0500      
@@ -4276,14 +4276,16 @@
         (def-type (and name (mm-default-file-encoding name))))
     (and def-type (cons def-type 0))))
 
-(defun gnus-mime-view-part-as-type (&optional mime-type)
-  "Choose a MIME media type, and view the part as such."
+(defun gnus-mime-view-part-as-type (&optional mime-type pred)
+  "Choose a MIME media type, and view the part as such.
+If non-nil, PRED is a predicate to use during completion to limit the
+available media-types."
   (interactive)
   (unless mime-type
     (setq mime-type (completing-read
                     "View as MIME type: "
                     (mapcar #'list (mailcap-mime-types))
-                    nil nil
+                     pred nil
                     (gnus-mime-view-part-as-type-internal))))
   (gnus-article-check-buffer)
   (let ((handle (get-text-property (point) 'gnus-data)))
@@ -4450,12 +4452,18 @@
         (mm-inlined-types nil)
         (mail-parse-charset gnus-newsgroup-charset)
         (mail-parse-ignored-charsets
-         (save-excursion (set-buffer gnus-summary-buffer)
-                         gnus-newsgroup-ignored-charsets)))
+          (with-current-buffer gnus-summary-buffer
+            gnus-newsgroup-ignored-charsets))
+         (type (mm-handle-media-type handle))
+         (method (mailcap-mime-info type))
+         (mm-enable-external t))
+    (if (not (stringp method))
+        (gnus-mime-view-part-as-type
+         nil (lambda (type) (stringp (mailcap-mime-info type))))
     (when handle
       (if (mm-handle-undisplayer handle)
          (mm-remove-part handle)
-       (mm-display-part handle)))))
+          (mm-display-part handle))))))
 
 (defun gnus-mime-view-part-internally (&optional handle)
   "View the MIME part under point with an internal viewer.
@@ -4467,13 +4475,16 @@
         (mm-inline-large-images t)
         (mail-parse-charset gnus-newsgroup-charset)
         (mail-parse-ignored-charsets
-         (save-excursion (set-buffer gnus-summary-buffer)
+          (with-current-buffer gnus-summary-buffer
                          gnus-newsgroup-ignored-charsets))
         (inhibit-read-only t))
+    (if (not (mm-inlinable-p handle))
+        (gnus-mime-view-part-as-type
+         nil (lambda (type) (mm-inlinable-p handle type)))
     (when handle
       (if (mm-handle-undisplayer handle)
          (mm-remove-part handle)
-       (mm-display-part handle)))))
+          (mm-display-part handle))))))
 
 (defun gnus-mime-action-on-part (&optional action)
   "Do something with the MIME attachment at \(point\)."