This is a really quick question: what is the character encoding used in symbolic ref files like .git/HEAD, especially on Windows?
Is it the same as the filesystem's encoding? It sounds improbable, though, since I've heard before that Windows' filesystem encoding is UTF-16 and ASCII control bytes 0x00..0x1F and 0x7F is prohibited in Git ref name (we can't have a byte 0x00 in Git ref). Is it UTF-8 universally? However it does not seem to be documented in git help check-ref-format. Maybe it lies somewhere else? Or is symbolic ref's encoding undefined? However then, how can we clone, push and fetch branches between each other?
There is no specific character encoding used by Git's refs. The format is specified in the git check-ref-format manual page, and it allows a variety of byte values, including values which are not value UTF-8, such as 0xFE and 0xFF.
However, having said that, it is customary to use UTF-8 for ref names, and when ref files are written into the file system on Windows, they will be converted into UTF-16 because Windows can't handle anything else in its file system. The contents of the files, however, remains something containing arbitrary bytes, which, again, are customarily (but need not be) UTF-8.