From 16f6beb72a3fca03f08e4de3e8c8fafcc5f6791f Mon Sep 17 00:00:00 2001
From: c4pp4
Date: Sun, 25 Oct 2026 02:27:13 +0100
Subject: [PATCH 1/1] Fix Dash preview thumbnails

The Dash preview thumbnail generator expands only %s, %u and %o in the
Exec line of the thumbnailers in /usr/share/thumbnailers, so commands
with the %i input path (e.g. ffmpegthumbnailer) fail. The failed
thumbnailer leaves an empty output file, which is taken as a cached
thumbnail ("Unable to load icon ... Unrecognized image file format").
The URI and file names are also not quoted, so a file name with an
apostrophe or spaces breaks the command line.

Expand %i, quote the substituted values, remove the output file of a
failed thumbnailer and generate the thumbnail again when the cached
file is empty.

Signed-off-by: c4pp4
---
 unity-shared/ThumbnailGenerator.cpp    |  4 +++-
 unity-shared/UserThumbnailProvider.cpp | 21 +++++++++++++++++++--
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/unity-shared/ThumbnailGenerator.cpp b/unity-shared/ThumbnailGenerator.cpp
index f3f585d..1124cb2 100644
--- a/unity-shared/ThumbnailGenerator.cpp
+++ b/unity-shared/ThumbnailGenerator.cpp
@@ -155,7 +155,9 @@ bool CheckCache(std::string const& uri_in, std::string& filename_out)
   filename_out += std::to_string(std::hash<std::string>()(uri_in)) + ".png";
 
   glib::Object<GFile> cache_file(g_file_new_for_path(filename_out.c_str()));
-  return g_file_query_exists(cache_file, NULL);
+  glib::Object<GFileInfo> cache_info(g_file_query_info(cache_file, G_FILE_ATTRIBUTE_STANDARD_SIZE, G_FILE_QUERY_INFO_NONE, NULL, NULL));
+  // an empty file is left by a failed thumbnailer, generate the thumbnail again
+  return cache_info && g_file_info_get_size(cache_info) > 0;
 }
 
 ThumbnailNotifier::Ptr ThumbnailGeneratorImpl::GetThumbnail(std::string const& uri, int size)
diff --git a/unity-shared/UserThumbnailProvider.cpp b/unity-shared/UserThumbnailProvider.cpp
index 5e4de6f..8474e03 100644
--- a/unity-shared/UserThumbnailProvider.cpp
+++ b/unity-shared/UserThumbnailProvider.cpp
@@ -20,6 +20,7 @@
  */
 
 #include <Nux/Nux.h>
+#include <glib/gstdio.h>
 #include "UnityCore/GLibWrapper.h"
 #include "UserThumbnailProvider.h"
 #include "ThumbnailGenerator.h"
@@ -58,11 +59,24 @@ bool UserThumbnailer::Run(int size, std::string const& input_file, std::string&
 
   // replace input file name
   pos = tmp_command_line.find("%u");
-  if (pos != std::string::npos) { tmp_command_line.replace(pos, 2, input_file); }
+  if (pos != std::string::npos) { tmp_command_line.replace(pos, 2, glib::String(g_shell_quote(input_file.c_str())).Str()); }
+
+  // replace input file path
+  pos = tmp_command_line.find("%i");
+  if (pos != std::string::npos)
+  {
+    glib::String input_path(g_filename_from_uri(input_file.c_str(), NULL, NULL));
+    if (!input_path)
+    {
+      error_hint = "Input file is not a local file";
+      return false;
+    }
+    tmp_command_line.replace(pos, 2, glib::String(g_shell_quote(input_path)).Str());
+  }
 
   // replace output file name
   pos = tmp_command_line.find("%o");
-  if (pos != std::string::npos) { tmp_command_line.replace(pos, 2, output_file); }
+  if (pos != std::string::npos) { tmp_command_line.replace(pos, 2, glib::String(g_shell_quote(output_file.c_str())).Str()); }
 
   gint exit_status = 0;
   GError* err = NULL;
@@ -71,6 +85,7 @@ bool UserThumbnailer::Run(int size, std::string const& input_file, std::string&
   {
     error_hint = err->message;
     g_error_free (err);
+    g_unlink(output_file.c_str());
     return false;
   }
   else if (exit_status != 0)
@@ -78,6 +93,8 @@ bool UserThumbnailer::Run(int size, std::string const& input_file, std::string&
     std::stringstream ss;
     ss << "Failed to create thumbnail. Program exited with exit_status=" << exit_status;
     error_hint = ss.str();
+    // remove an incomplete thumbnail
+    g_unlink(output_file.c_str());
     return false;
   }
 
-- 
2.55.0