Re: IMAP and Exchange 2007 - imap-fetch-safe

[Dave Love]

Simon Josefsson <address@hidden> writes:

> Maybe the problem is a condition-case within another condition-case
> work?  I recall problems related to this when run as an async process
> filter.

Yes -- signals from process filters are normally caught; I wasn't
thinking or looking closely enough at what the code does originally.  I
must have had debug-on-error set when testing, but I was sure I'd
actually tried it in fresh Emacs.

> Maybe it is possible to re-write the approach without using
> condition-case, that would likely be easier to debug anyway.

I'm not sure it would be easier, but see the comment in the patch below.
I made it before reading this, and at least the fix over my previous
code is just an extra binding.  It works for me in a fresh Emacs, and
isn't broken in Emacs 22.

> I'd prefer to avoid sending the Exchange bug-workaround approach
> ("1,*:*") to any server that does not need it.  I've seen servers that
> (internally) open up all e-mails in the folder and searches them, but
> for the 1,* approach was able to return data quickly.

Obviously that's a good reason.  Previous comments about efficiency that
I was referred to seemed to be about something different.

> This may be old
> information now, but generally I don't see why imap.el should send poor
> protocol output to all servers just because Exchange is broken.

[It does have workarounds for various other servers, not that I want to
defend Exchange in any way.  Exchange 2007 is doing horrible things like
messing with MIME parts, which I don't think the previous version did,
and I wish I could avoid it.]

Anyhow, per the comment in the patch, is there a good reason -- other
than simplicity? -- to use FETCH rather than UID like other clients?
I'm speaking mostly in ignorance of IMAP...

2009-01-17  Dave Love  <address@hidden>

        * imap.el (imap-fetch-safe): Bind debug-on-error.
        (imap-debug): Add imap-fetch-safe.

Index: imap.el
===================================================================
RCS file: /usr/local/cvsroot/gnus/lisp/imap.el,v
retrieving revision 7.52
diff -u -r7.52 imap.el
--- imap.el     8 Jan 2009 20:51:29 -0000       7.52
+++ imap.el     17 Jan 2009 19:33:31 -0000
@@ -1798,25 +1800,38 @@
 of the UIDS specification, and the cdr is the one which works with
 Exchange 2007 or, potentially, other buggy servers.
 See `imap-enable-exchange-bug-workaround'."
-  ;; We don't unconditionally use the alternative (valid) form, since
-  ;; this is said to be significantly inefficient.  The first time we
-  ;; get here for a given, we'll try the canonical form.  If we get
-  ;; the known error from the buggy server, set the flag
-  ;; buffer-locally (to account for connections to multiple servers),
-  ;; then re-try with the alternative UIDS spec.
+  ;; The first time we get here for a given, we'll try the canonical
+  ;; form.  If we get the known error from the buggy server, set the
+  ;; flag buffer-locally (to account for connections to multiple
+  ;; servers), then re-try with the alternative UIDS spec.  We don't
+  ;; unconditionally use the alternative form, since the
+  ;; currently-used alternatives are seriously inefficient with some
+  ;; servers (although they are valid).
+  ;;
+  ;; FIXME:  Maybe it would be cleaner to have a flag to not signal
+  ;; the error (which otherwise gives a message), and test
+  ;; `imap-failed-tags'.  Also, Other IMAP clients use other forms of
+  ;; request which work with Exchange, e.g. Claws does "UID FETCH 1:*
+  ;; (UID)" rather than "FETCH UID 1,*".  Is there a good reason not
+  ;; to do the same?
   (condition-case data
-      (imap-fetch (if imap-enable-exchange-bug-workaround
-                     (cdr uids)
-                   (car uids))
-                 props receive nouidfetch buffer)
+      ;; Binding `debug-on-error' allows us to get the error from
+      ;; `imap-parse-response' -- it's normally caught by Emacs around
+      ;; execution of a process filter.
+      (let ((debug-on-error t))
+       (imap-fetch (if imap-enable-exchange-bug-workaround
+                       (cdr uids)
+                     (car uids))
+                   props receive nouidfetch buffer))
     (error
      (if (and (not imap-enable-exchange-bug-workaround)
-             (string-match
-              "The specified message set is invalid"
-              (cadr data)))
+             ;; This is the Exchange 2007 response.  It may be more
+             ;; robust just to check for a BAD response to the
+             ;; attempted fetch.
+             (string-match "The specified message set is invalid"
+                           (cadr data)))
         (with-current-buffer (or buffer (current-buffer))
-          (set (make-local-variable
-                'imap-enable-exchange-bug-workaround)
+          (set (make-local-variable 'imap-enable-exchange-bug-workaround)
                t)
           (imap-fetch (cdr uids) props receive nouidfetch))
        (signal (car data) (cdr data))))))
@@ -3023,6 +3038,7 @@
          imap-list-to-message-set
          imap-fetch-asynch
          imap-fetch
+         imap-fetch-safe
          imap-message-put
          imap-message-get
          imap-message-map