clone, fetch and push can all update multiple references in a single
command invocation. Rather than performing sequential iteration
of each reference change inside of the application code, push this
down into the reference database where the implementation can take
advantage of the batch size and optimize itself.

For the local filesystem implementation the obvious optimization
is to write a packed-refs file when the repository is completely
empty. The initial clone, fetch or push into the destination may
have hundreds of new references. Writing all of these as loose
files is not efficient. This optimization is not implemented in
this commit and is left as an exercise for the reader to supply
in a future commit to JGit.

To make the API changes simple, define the BatchRefUpdate type and
implementation using the existing sequential behavior.

Change-Id: I8e1674f091e05e24e3ff56ccbc687a6d18a6a61e

When a command's type is UPDATE, JGit might not yet be sure if it
is a fast-forward or not. Expose a utility method to compute the
exact type by performing the merge base test, allowing the type
to be switched to UPDATE_NONFASTFORWARD if old ObjectId is not
contained in new ObjectId.

BaseReceivePack already does this test when validating the incoming
command list, so provide a package level backdoor to set the type
and avoid needing to redo the merge test later.

Change-Id: If5a6fcc50dc4d6f96e9bb0bb7bba15ebe8b86377

We are working on a publish/subscribe based git protocol, and we want to
reuse several parts of the ReceivePack-like code for reading commands
and processing a pack. In this new implementation, the connection
management will be very different, in particular, there may be multiple
packs received on a single open connection. So, hoist out as much as we
can from ReceivePack, mostly just leaving behind the single-connection
version in that class.

Change-Id: I5567aad6ae77951f73f59c1f91996d934ea88334

Change-Id: I0a86ce0e393dfde9bb27f0b29e036e76c856396e
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
Signed-off-by: Chris Aniszczyk <zx@twitter.com>

Change-Id: I763590a45d75f00a09097ab6f89581a3bbd3c797

Change-Id: I24501f95185878d09b54562e48cb4e7e45dd3968

This allows callers who know in advance whether a command is UPDATE or
UPDATE_NONFASTFORWARD to specify this in the constructor rather than
with a separate method call.

Change-Id: Iae483594a4ff370ff75d17a7b0648c5590b3d1bd

This allows a PreReceiveHook to easily "take over" all of the
ReceiveCommands passed to it, preventing any of them from being handled
within the ReceivePack core.

Change-Id: I2a8c1fc44e8dcadf22cd97a8ec4ee79d4d9d08f1

Per CQ 3448 this is the initial contribution of the JGit project
to eclipse.org.  It is derived from the historical JGit repository
at commit 3a2dd9921c.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>