Subject: bug#61394: 30.0.50; [PATCH] Image-dired thumb name based on content

From: Manuel Giraud <[email-masked]>
Date: Thu, 09 Feb 2023 20:06:50 +0100

Hi,

Here is a proposal for a modification of how image-dired generates thumb
names.  With this patch, a thumb name will depend on the content of the
associated image.

Pros:
        - the thumb name is unique even if the file is moved or renamed
        - you keep a centralized thumb directory
Cons:
        - none (as it fits my usage :-)

>From 017bb36bdff40383b170e8ee5cff00034595a6ce Mon Sep 17 00:00:00 2001
From: Manuel Giraud <[email-masked]>
Date: Thu, 9 Feb 2023 19:56:37 +0100
Subject: [PATCH] Image-dired thumb name based on content

* lisp/image/image-dired-util.el (image-dired-content-sha1): New
utility that compute the SHA-1 of a part of the content of a file.
(image-dired-thumb-name): Use it.
---
 lisp/image/image-dired-util.el | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/lisp/image/image-dired-util.el b/lisp/image/image-dired-util.el
index c03f9d2e3d3..58c96f7f20b 100644
--- a/lisp/image/image-dired-util.el
+++ b/lisp/image/image-dired-util.el
@@ -57,13 +57,19 @@ image-dired-dir
       (message "Thumbnail directory created: %s" image-dired-dir))
     image-dired-dir))
 
+(defun image-dired-content-sha1 (filename)
+  "Compute the SHA-1 of a part of FILENAME."
+  (with-temp-buffer
+    (let ((file-size (file-attribute-size (file-attributes filename)))
+	  (chunk-size 4096))
+      (insert-file-contents filename nil 0 (min chunk-size file-size))
+      (sha1 (current-buffer)))))
+
 (defun image-dired-thumb-name (file)
   "Return absolute file name for thumbnail FILE.
 Depending on the value of `image-dired-thumbnail-storage', the
 file name of the thumbnail will vary:
-- For `use-image-dired-dir', make a SHA1-hash of the image file's
-  directory name and add that to make the thumbnail file name
-  unique.
+- For `image-dired', make a SHA1-hash of some of the image file.
 - For `per-directory' storage, just add a subdirectory.
 - For `standard' storage, produce the file name according to the
   Thumbnail Managing Standard.  Among other things, an MD5-hash
@@ -85,7 +91,7 @@ image-dired-thumb-name
           ((or (eq 'image-dired image-dired-thumbnail-storage)
                ;; Maintained for backwards compatibility:
                (eq 'use-image-dired-dir image-dired-thumbnail-storage))
-           (expand-file-name (format "%s.jpg" (sha1 file))
+           (expand-file-name (format "%s.jpg" (image-dired-content-sha1 file))
                              (image-dired-dir)))
           ((eq 'per-directory image-dired-thumbnail-storage)
            (expand-file-name (format "%s.thumb.jpg"
-- 
2.39.0

In GNU Emacs 30.0.50 (build 1, x86_64-unknown-openbsd7.2, cairo version
 1.17.6) of 2023-02-09 built on computer
Repository revision: 1518fc5d7c5bedbbe35053696c7ec06020c81b05
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101004
System Description: OpenBSD computer 7.2 GENERIC.MP#933 amd64

Configured using:
 'configure --prefix=/home/manuel/emacs --bindir=/home/manuel/bin
 --with-x-toolkit=no --without-sound --without-compress-install
 CPPFLAGS=-I/usr/local/include LDFLAGS=-L/usr/local/lib'

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON
LCMS2 LIBOTF LIBXML2 MODULES NOTIFY KQUEUE OLDXMENU PDUMPER PNG RSVG
SQLITE3 THREADS TIFF TREE_SITTER WEBP X11 XDBE XIM XINPUT2 XPM ZLIB

Important settings:
  value of $LC_ALL: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Dired by name

Minor modes in effect:
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  magit-auto-revert-mode: t
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  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
/home/manuel/.emacs.d/elpa/ef-themes-0.10.0/theme-loaddefs hides /home/manuel/emacs/share/emacs/30.0.50/lisp/theme-loaddefs
/home/manuel/.emacs.d/elpa/transient-0.3.7/transient hides /home/manuel/emacs/share/emacs/30.0.50/lisp/transient

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Memory information:
((conses 16 890208 177320)
 (symbols 48 60888 5)
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-- 
Manuel Giraud