[PATCH 08/11] emacs: Support caching in notmuch-get-bodypart-{binary, text}

[Austin Clements]

Quoth Mark Walters on Apr 24 at 11:46 am:
> 
> On Mon, 21 Apr 2014, Austin Clements <amdragon at MIT.EDU> wrote:
> > (The actual code change here is small, but requires re-indenting
> > existing code.)
> > ---
> >  emacs/notmuch-lib.el | 52 ++++++++++++++++++++++++++++++----------------------
> >  1 file changed, 30 insertions(+), 22 deletions(-)
> >
> > diff --git a/emacs/notmuch-lib.el b/emacs/notmuch-lib.el
> > index fc67b14..fee8512 100644
> > --- a/emacs/notmuch-lib.el
> > +++ b/emacs/notmuch-lib.el
> > @@ -503,33 +503,39 @@ (defun notmuch-parts-filter-by-type (parts type)
> >     (lambda (part) (notmuch-match-content-type (plist-get part :content-type) type))
> >     parts))
> >  
> > -(defun notmuch-get-bodypart-binary (msg part process-crypto)
> > +(defun notmuch-get-bodypart-binary (msg part process-crypto &optional cache)
> >    "Return the unprocessed content of PART in MSG as a unibyte string.
> >  
> >  This returns the \"raw\" content of the given part after content
> >  transfer decoding, but with no further processing (see the
> >  discussion of --format=raw in man notmuch-show).  In particular,
> >  this does no charset conversion."
> > -  (let ((args `("show" "--format=raw"
> > -		,(format "--part=%d" (plist-get part :id))
> > -		,@(when process-crypto '("--decrypt"))
> > -		,(notmuch-id-to-query (plist-get msg :id)))))
> > -    (with-temp-buffer
> > -      ;; Emacs internally uses a UTF-8-like multibyte string
> > -      ;; representation by default (regardless of the coding system,
> > -      ;; which only affects how it goes from outside data to this
> > -      ;; internal representation).  This *almost* never matters.
> > -      ;; Annoyingly, it does matter if we use this data in an image
> > -      ;; descriptor, since Emacs will use its internal data buffer
> > -      ;; directly and this multibyte representation corrupts binary
> > -      ;; image formats.  Since the caller is asking for binary data, a
> > -      ;; unibyte string is a more appropriate representation anyway.
> > -      (set-buffer-multibyte nil)
> > -      (let ((coding-system-for-read 'no-conversion))
> > -	(apply #'call-process notmuch-command nil '(t nil) nil args)
> > -	(buffer-string)))))
> > -
> > -(defun notmuch-get-bodypart-text (msg part process-crypto)
> > +  (let ((data (plist-get part :binary-content)))
> > +    (when (not data)
> > +      (let ((args `("show" "--format=raw"
> > +		    ,(format "--part=%d" (plist-get part :id))
> > +		    ,@(when process-crypto '("--decrypt"))
> > +		    ,(notmuch-id-to-query (plist-get msg :id)))))
> > +	(with-temp-buffer
> > +	  ;; Emacs internally uses a UTF-8-like multibyte string
> > +	  ;; representation by default (regardless of the coding
> > +	  ;; system, which only affects how it goes from outside data
> > +	  ;; to this internal representation).  This *almost* never
> > +	  ;; matters.  Annoyingly, it does matter if we use this data
> > +	  ;; in an image descriptor, since Emacs will use its internal
> > +	  ;; data buffer directly and this multibyte representation
> > +	  ;; corrupts binary image formats.  Since the caller is
> > +	  ;; asking for binary data, a unibyte string is a more
> > +	  ;; appropriate representation anyway.
> > +	  (set-buffer-multibyte nil)
> > +	  (let ((coding-system-for-read 'no-conversion))
> > +	    (apply #'call-process notmuch-command nil '(t nil) nil args)
> > +	    (setq data (buffer-string)))))
> > +      (when cache
> > +	(plist-put part :binary-content data)))
> > +    data))
> 
> I am a little puzzled by this but that could be lack of familiarity with
> elisp. As far as I can see plist-put will sometimes modify the original
> plist and sometimes return a new plist. If the latter happens then I
> think it works out as if we hadn't cached anything as the part passed to
> the function is unmodified. That might not matter in this case (though I
> find the lack of determinism disturbing).
> 
> Or is something else going on?

No, your familiarity with Elisp serves you well.  I'm completely
cheating here.  According to the specification of plist-put, it's
allowed to return a new list but in reality this only happens when the
original plist is nil.  We lean on this already all over the
notmuch-emacs code, but maybe that doesn't excuse me adding one more
cheat.

I could add a comment here explaining what's going on, I could
manually do the list insertion in a way that's guaranteed to mutate it
in place, or I could add a nil :binary-content property when parts are
created (since plist-put is guaranteed to mutate existing keys in
place).

> Best wishes
> 
> Mark
> 
> 
> 
> > +
> > +(defun notmuch-get-bodypart-text (msg part process-crypto &optional cache)
> >    "Return the text content of PART in MSG.
> >  
> >  This returns the content of the given part as a multibyte Lisp
> > @@ -546,7 +552,9 @@ (defun notmuch-get-bodypart-text (msg part process-crypto)
> >  	     (npart (apply #'notmuch-call-notmuch-sexp args)))
> >  	(setq content (plist-get npart :content))
> >  	(when (not content)
> > -	  (error "Internal error: No :content from %S" args))))
> > +	  (error "Internal error: No :content from %S" args)))
> > +      (when cache
> > +	(plist-put part :content content)))
> >      content))
> >  
> >  ;; Workaround: The call to `mm-display-part' below triggers a bug in