Exiv2

Under MacOS X, if an image has a file size greater than 1MB, writeMetadata() destroys the image's resource fork.

This leads to all types of strange effects. One example, from a typical designer workflow: You save a file in Photoshop as EPS, and tell the MacOS X Finder to open that specific file with Photoshop rather than Illustator. You don't set this globally, as you only want Photoshop to (re-)open those EPS files originally created by Photoshop, and all other EPS files with a vector graphics tool such as Illustrator. If you then adjust the metadata using the Exiv2 library, the file no longer opens automatically with Photoshop, but with the standard vector tool. This happens because the information that you want to open that specific file with Photoshop was stored in the resource fork which has been destroyed by Exiv2.

Since files which are at most 1MB are written "in place", those don't suffer from the problem. However, a file greater than 1MB is written to a temp file (that has no resource fork), which is then moved (renamed) over the old file. That's why the resource fork is lost here.

This issue is partly connected with bug #812 (see also http://dev.exiv2.org/boards/3/topics/1103), where the "tempfile+move" mechanism destroyed hard links. However, although the solution of #812 would also be applicable here, I don't think it is a good idea to use the "in place" mechanism for all files under MacOS X. That would lead to huge memory consumption when writing metadata to big image files.

Instead, the temporary file mechanism of BasicIo::temporary() should be improved to copy the original file's extended attributes (which contain the resource fork, among others) into the newly created temporary file.