Externalize the error message and make it more specific. Also emit
an error log.

Change-Id: Ie7b1c90c54673bfb8e133fb0aa19a117d4ca6587
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Add a new exception type that server implementations can throw when a
client attempts to make an unauthorized LFS operation, which will result
in HTTP 401 Unauthorized being returned to the client.

An example of this is a Gerrit server that rejects a request to perform
an LFS operation on a ref that is not visible to the caller.

As defined in the LFS spec [1] the request may include authentication,
and per RFC 2616 [2], "401 response indicates that authorization has been
refused for those credentials".

[1] https://github.com/git-lfs/git-lfs/blob/master/docs/api/batch.md
[2] https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html

Change-Id: I2aa22e2144df5fb7972df0e3285b77b08ecc63f2
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

The class AtomicObjectOutputStream should be available to all lfs
related classes, not only to the server side. Move the class from
org.eclipse.jgit.lfs.server.fs to org.eclipse.jgit.lfs.internal to
achieve that.

Change-Id: I028e1c9ec7c21f316340b21d558b9a6b77e2060d

Adds a JGit built-in implementation of the "git lfs clean" filter. This
filter should do the same as the one described in [1]. But since this
filter is written in Java and can be called by JGit without forking new
processes it should be much faster

[1]
https://github.com/github/git-lfs/blob/master/docs/man/git-lfs-clean.1.ronn

Change-Id: If60e387e97870245b4bd765eda6717eb84cffb1d

Instead of returning null, LfsProtocolServlet#getLargeFileRepository
should throw LfsUnavailable.

If null is returned, throw a generic LfsException.

Handle LfsException as an internal server error and return HTTP 500.

Change-Id: I33e2a19fcc0fde8aaf0f703860c8fa8ce2de2db5
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

Instead of hard-coding the message strings, define them in a properties
file. This will allow them to be translated.

Change-Id: I77556881579e66b2c13d187759c7efdddfee87ae
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

The Large File Storage extension specified by GitHub [1] uses SHA-256 to
compute the ID of large files stored by the extension. Hence implement a
SHA-256 abstraction similar to the SHA-1 abstraction used by JGit.

[1] https://git-lfs.github.com/

Bug: 470333
Change-Id: I3a95954543c8570d73929e55f4a884b55dbf1b7a
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>