Re: master ef14acf: Make nnml handle invalid non-ASCII headers more consistently

[Eli Zaretskii]

> From: Florian Weimer <fweimer@redhat.com>
> Cc: Lars Ingebrigtsen <larsi@gnus.org>, ding@gnus.org
> Date: Fri, 16 Dec 2022 23:42:21 +0100
> 
> * Lars Ingebrigtsen:
> 
> > branch: master
> > commit ef14acfb68bb5b0ce42221e9681b93562f8085eb
> > Author: Lars Ingebrigtsen <larsi@gnus.org>
> > Commit: Lars Ingebrigtsen <larsi@gnus.org>
> >
> >     Make nnml handle invalid non-ASCII headers more consistently
> >     
> >     * lisp/gnus/nnml.el (nnml--encode-headers): New function to
> >     RFC2047-encode invalid Subject/From headers (bug#45925).  This
> >     will make them be displayed more consistently in the Summary
> >     buffer (but still "wrong" sometimes, since there's not that much
> >     we can guess at at this stage, charset wise).
> >     (nnml-parse-head): Use it.
> > ---
> >  lisp/gnus/nnml.el | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> >
> > diff --git a/lisp/gnus/nnml.el b/lisp/gnus/nnml.el
> > index ebececa..3cdfc74 100644
> > --- a/lisp/gnus/nnml.el
> > +++ b/lisp/gnus/nnml.el
> > @@ -769,8 +769,24 @@ article number.  This function is called narrowed to 
> > an article."
> >        (let ((headers (nnheader-parse-head t)))
> >     (setf (mail-header-chars  headers) chars)
> >     (setf (mail-header-number headers) number)
> > +   ;; If there's non-ASCII raw characters in the data,
> > +   ;; RFC2047-encode them to avoid having arbitrary data in the
> > +   ;; .overview file.
> > +   (nnml--encode-headers headers)
> >     headers))))
> 
> Unfortunately, this change in particular causes Gnus to stops storing
> messages into nnmail after receiving a message with this header:
> 
> From: =?utf-8?b?572X5YuH5YiaKFlvbmdnYW5nIEx1bykgdmlhIEVsZnV0aWxzLWRldmVs?=
>  <elfutils-devel@sourceware.org>
> 
> The logged error message is:
> 
> Mail source (maildir :path …) failed: (error Invalid data for rfc2047 
> encoding: 罗勇刚(Yonggang Luo) via Elfutils-devel 
> <elfutils-devel@sourceware.org>)
> 
> On an older Emacs without this change, it seems that the original header
> is written to the .overview file, which sidestep the problem that not
> all strings are encodable by the rfc2047 functions.

Thanks.  I guess this From header is invalid because there's no space
between the "罗勇刚" and the "(Yonggang Luo)" parts?

Does the naïve patch below solve the problem?

diff --git a/lisp/gnus/nnml.el b/lisp/gnus/nnml.el
index 40e4b9e..7aa445e 100644
--- a/lisp/gnus/nnml.el
+++ b/lisp/gnus/nnml.el
@@ -776,17 +776,22 @@ nnml-parse-head
        (nnml--encode-headers headers)
        headers))))
 
+;; RFC2047-encode Subject and From, but leave invalid headers unencoded.
 (defun nnml--encode-headers (headers)
   (let ((subject (mail-header-subject headers))
        (rfc2047-encoding-type 'mime))
     (unless (string-match "\\`[[:ascii:]]*\\'" subject)
-      (setf (mail-header-subject headers)
-           (mail-encode-encoded-word-string subject t))))
+      (let ((encoded-subject
+             (ignore-errors (mail-encode-encoded-word-string subject t))))
+        (if encoded-subject
+            (setf (mail-header-subject headers) encoded-subject)))))
   (let ((from (mail-header-from headers))
        (rfc2047-encoding-type 'address-mime))
     (unless (string-match "\\`[[:ascii:]]*\\'" from)
-      (setf (mail-header-from headers)
-           (rfc2047-encode-string from t)))))
+      (let ((encoded-from
+             (ignore-errors (rfc2047-encode-string from t))))
+        (if encoded-from
+            (setf (mail-header-from headers) encoded-from))))))
 
 (defun nnml-get-nov-buffer (group &optional incrementalp)
   (let ((buffer (gnus-get-buffer-create