I'm using XSLT 2 (Saxon 9.x) with Java and having the following problem ...
doc-available('file:///C:/Users/filename.xml')
returns false
However ...
unparsed-text-available('file:///C:/Users/filename.xml')
returns true
The file is a well-formed XML and exists.
If I use relative paths, then both functions return true.
Also tried file:/C:/Users/filename.xml but with the same problem.
I have also removed the Windows firewall, but that has no effect.
The same code works in Oxygen.
doc-available() can return false for two reasons: the file doesn't exist, or it can't be parsed as well-formed XML. You've eliminated the first possibility using unparsed-text; that leaves the second. I can't see any reason why a relative URI should work and not an absolute URI. (Well, actually I can, like the relative URI is actually fetching the file from a different location than the absolute URI.)
Essentially there are so many variables affecting the outcome that it's very hard to tell you what the cause is in your particular case.