osVFS
=====

This provides an application level virtual file system (VFS) for Python with
an API almost identical to the Python os module. For 99% of all Python
applications, the only modifications required to use a VFS are to replace os
and open with your vfs as follows;

import vfs;
os=vfs.fakeroot_filesystem(os,'/tmp') # replace with vfs of your choice
open=os.file

Note that it is preferable to use os.file() instead of open() when possible,
as this clarifys which filesystem you are opening the file from.


Problems with protocols
=======================

Proper VFS requires fetching of mtimes, symbolic links, inodes (for
mirroring of hardlinks only), and directorys. It is also handy to be
able to obtain sizes. It is possible to simply fetch and cache
directory listings, but unfortunately these are formatted differently
for different protocols, so they will need to be translated.

Much of the low-level posix filesystem interface relies on meaningful
device/inode numbers. However, most of the Python os API can be implemented
without them, instead dummy numbers are used by things like os.stat().

ftp: much info can only be retrieved by directory listings, but
fortunately these are systematicly structured for easy parsing and
interpretation. Some info can be obtained by special ftp commands
(size, mtime?), but these are not always supported. The sad news is
talking through a http proxy means you are actualy using http, and
hence get the crippled http listings (see below).

http: some info can be extracted from directory listings, but these
are painfuly html formated, and different httpds/proxys format them
differently. http traditionaly supports fetching of metadata through
"HEAD" fetches, but all desired attributes are not required to be
sent. I'm not sure that all info can always be fetched, making true
mirroring not always possible. Particularly tricky is symbolic
links...

rsync: rsync is built for mirroring, but that doesn't necisarily mean
dynamic mirroring. rsync will fetch files and build directory
structures, with full support for symbolic and hard links. However,
I'm not sure it can be used to fetch directory listings or file
attributes without fetching the whole file. This means it cannot be
used to fetch directory listings only. UPDATE: looks like rsync can be
used for listing remote files... checking it out soon.

webDAV: good potential. Extends http to include all the info that is
missing for a VFS, then adds some.

rsync over http: as defined/used by rproxy. nice. Can user client-side
delta calculation without changing the protocol.

Other: not widely used.