Sprucing up org-download

My interest in org-download was renewed today with this thread on org-mode's mailing list.

org-download allows you to drag-and-drop an image from e.g. Firefox or your own file system to an org-mode buffer. When I originally wrote it, I was taking a Chemistry course on edX, which included homework and exams with a lot of images. Doing the homework in a literate style with org-mode, I wanted the problems to be completely self-contained, and for that I needed to save all the images from the website, preferably quickly, to an org-mode buffer. With a few hacks and some advice and contributions from more experienced hackers, org-download came to be.

Today's commits

The main contribution from today's commits was adding the code that un-aliases images that point to HTML. I see a lot of these from the people that I'm following on my Twitter, @_abo_abo. Here's the code:

(defcustom org-download-img-regex-list
  '("<img +src=\"" "<img +\\(class=\"[^\"]+\"\\)? *src=\"")
  "This regex is used to unalias links that look like images.
The html to which the links points will be searched for these
regexes, one by one, until one succeeds.  The found image address
will be used."
  :group 'org-download)

and in (org-download-image link):

(unless (image-type-from-file-name link)
    (with-current-buffer
        (url-retrieve-synchronously link t)
      (let ((regexes org-download-img-regex-list)
            lnk)
        (while (and (not lnk) regexes)
          (goto-char (point-min))
          (when (re-search-forward (pop regexes) nil t)
            (backward-char)
            (setq lnk (read (current-buffer)))))
        (if lnk
            (setq link lnk)
          (error "link %s does not point to an image" link)))))

Here, image-type-from-file-name is a built-in from image.el that decides if link looks like an image file or not.

As you can see, since I intend to use link right after to be transformed right now, I'm using url-retrieve-synchronously, instead of the asynchronous url-retrieve. The other one is used by default to download the actual image.

Note the use of the while / pop combination for traversing a list. I've seen it used in some places in the Emacs core, and I think it's pretty neat.

Arranging the regular expressions into a list is necessary to give priority to some regexes. For instance, the first element of org-download-img-regex-list should match e.g. an actual referred image on Twitter, while the second element will match at least a profile picture in the case when there is no referred image.

Visual demo

I think that I might have over-engineered the custom options of org-download a bit. Just to keep you motivated enough to figure them out, here's a link to a Youtube demo of the fast clickety-clicking (the mouse usage), that comes after some clackety-clacking (the customization).