AppImage
appimage-extract(-and-run) don't preserve file timestamps
I wanted to fix this issue myself, seemed easy enough. Probably in runtime.c where this line is:
chmod(prefixed_path_to_extract, st.st_mode);
Don't just apply permissions but also timestamps. However, since AppImageKit doesn't seem to be able to be compiled on modern systems, I can't add this myself.
As for why:
Not restoring timestamps breaks code that checks cache validity through timestamps. For example in one of my applications that I ship as an AppImage, I bundle LibVLC and its plugins into the AppImage. Before the creation of the image, I generate the usr/lib/vlc/plugins/plugins.dat file. This speeds up VLC plugin loading. However, if the timestamps of the plugins changes, which happens when running the AppImage with --appimage-extract-and-run, LibVLC prints countless error messages about every plugin. One example:
main libvlc error: stale plugins cache: modified /tmp/appimage_extracted_1e2e0dbe8053a3543648ca6c3c5a71fb/usr/lib/vlc/plugins/packetizer/libpacketizer_h264_plugin.so
As a result, the cache isn't used at all. This is not the end of the world, since it's a soft error, but still it would be nice if timestamps were preserved when extracting.
Agree that extracting should obey creation timestamps, sounds reasonable to me. What about modification timestamps? How is this normally done by unarchiving programs?
What do others think?
According to stat, both cp -a as well as tar preserve modification time. They only change access time and "change" time. ("Change" time seems to be the time the file's metadata, like access permissions, were changed.)
Example:
$ stat some_file
File: some_file
Size: 72965 Blocks: 144 IO Block: 4096 regular file
Device: 22h/34d Inode: 254422 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 1000/ realnc) Gid: ( 1000/ realnc)
Access: 2021-09-24 00:09:33.648484504 +0300
Modify: 2019-04-06 03:41:26.000000000 +0300
Change: 2021-09-24 00:09:33.648484504 +0300
Birth: -
"Access" and "Change" times were updated to current time. "Modify" time was preserved. Indeed, if I run the AppImage normally without extracting it, and while the application is open I either cp -a /mnt/.mount_Application-ID to somewhere else, or do tar cf app.tar /mnt/.mount_Application-ID and then untar it and run the application from the copy, it works correctly. Modification time is what matters.
I think we should mirror the behavior of
tar, do you agree?
Yes. I looked at some other formats as well, and they all do the same thing as tar.
Great, so we know what we should do. Pull requests would be highly welcome!