From 0fc0d53dee2513b5923553531a8b6a9c5db10975 Mon Sep 17 00:00:00 2001
From: Holger Dürer <me@hdurer.net>
Date: Fri, 5 May 2017 22:19:02 +0100
Subject: Make the image loading asynchronous.

Now that we are also loading avatars there is a lot of image loading to do to show the timeline.
We can do the loading asynchronously to let the user have a look at the toots already while image loading is incrementally proceeding.

We can no longer enforce caching of avatar loading since the variable is consulted when the response parsing happens at which point the dynamic binding we had used so far has gone out of scope again.
---
 lisp/mastodon-media.el | 70 +++++++++++++++++++++++++++++++++-----------------
 1 file changed, 46 insertions(+), 24 deletions(-)

(limited to 'lisp/mastodon-media.el')

diff --git a/lisp/mastodon-media.el b/lisp/mastodon-media.el
index 93ff1b7..289637e 100644
--- a/lisp/mastodon-media.el
+++ b/lisp/mastodon-media.el
@@ -43,25 +43,51 @@
   (image-type-available-p 'imagemagick)
   "A boolean value stating whether to show avatars in timelines.")
 
-(defun mastodon-media--image-from-url (url media-type)
+(defun mastodon-media--process-image-response (status-plist marker image-options region-length image-url)
+  "Callback function processing the url retrieve response for URL.
+
+STATUS-PLIST is the usual plist of status events as per `url-retrieve'.
+IMAGE-OPTIONS are the precomputed options to apply to the image.
+MARKER is the marker to where the response should be visible.
+REGION-LENGTH is the length of the region that should be replaced with the image.
+IMAGE-URL is the URL that was retrieved.
+"
+  (let ((url-buffer (current-buffer))
+        (is-error-response-p (eq :error (car status-plist))))
+    (unwind-protect
+        (let* ((data (unless is-error-response-p
+                       (goto-char (point-min))
+                       (search-forward "\n\n")
+                       (buffer-substring (point) (point-max))))
+               (image (when data
+                        (apply #'create-image data (when image-options 'imagemagick)
+                               t image-options))))
+          (switch-to-buffer (marker-buffer marker))
+          ;; Save narrowing in our buffer
+          (let ((inhibit-read-only t))
+            (save-restriction
+              (widen)
+              (put-text-property marker (+ marker region-length) 'media-state 'loaded)
+              (put-text-property marker (+ marker region-length)
+                                 'display (or
+                                           image
+                                           (format "Failed to load %s" image-url)))
+              ;; We are done with the marker; release it:
+              (set-marker marker nil)))
+          (kill-buffer url-buffer)))))
+
+(defun mastodon-media--load-image-from-url (url media-type start region-length)
   "Takes a URL and MEDIA-TYPE and return an image.
 
 MEDIA-TYPE is a symbol and either 'avatar or 'media-link."
-  ;; TODO: Cache the avatars 
-  (let* ((url-automatic-caching t)
-         (buffer (url-retrieve-synchronously url))
-         (image-options (when (image-type-available-p 'imagemagick)
-                          (case media-type
-                            ('avatar `(:height ,mastodon-avatar-height))
-                            ('media-link `(:max-height ,mastodon-preview-max-height))))))
-    (unwind-protect
-        (let ((data (with-current-buffer buffer
-                      (goto-char (point-min))
-                      (search-forward "\n\n")
-                      (buffer-substring (point) (point-max)))))
-          (apply #'create-image data (when image-options 'imagemagick)
-                 t image-options))
-      (kill-buffer buffer))))
+  ;; TODO: Cache the avatars
+  (let ((image-options (when (image-type-available-p 'imagemagick)
+                         (pcase media-type
+                           ('avatar `(:height ,mastodon-avatar-height))
+                           ('media-link `(:max-height ,mastodon-preview-max-height))))))
+    (url-retrieve url
+                  #'mastodon-media--process-image-response
+                  (list (copy-marker start) image-options region-length url))))
 
 (defun mastodon-media--select-next-media-line ()
   "Find coordinates of the next media to load.
@@ -77,7 +103,7 @@ found."
       ;; do nothing - the loop will proceed
       )
     (when next-pos
-      (case (get-text-property next-pos 'media-type)
+      (pcase (get-text-property next-pos 'media-type)
         ;; Avatars are just one character in the buffer
         ('avatar (list next-pos (+ next-pos 1) 'avatar))
         ;; Media links are 5 character ("[img]")
@@ -101,16 +127,12 @@ not been returned."
              (end (cadr line-details))
              (media-type (caddr line-details))
              (image-url (get-text-property start 'media-url)))
-       
         (if (not (mastodon-media--valid-link-p image-url))
+            ;; mark it at least as not needing loading any more
             (put-text-property start end 'media-state 'invalid-url)
+          ;; proceed to load this image asynchronously
           (put-text-property start end 'media-state 'loading)
-          (let ((image (mastodon-media--image-from-url image-url media-type)))
-            (put-text-property start end 'media-state 'loaded)
-            (put-text-property start end
-                               'display (or
-                                         image
-                                         (format "Failed to load %s" image-url)))))))))
+          (mastodon-media--load-image-from-url image-url media-type start (- end start)))))))
 
 (provide 'mastodon-media)
 ;;; mastodon-media.el ends here
-- 
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