Shawn O. Pearce
01888db892
UploadPack: Fix races in smart HTTP negotiation
Clients cache the set of advertised references at the start of a
negotiation, and keep replaying the same "want SHA1" list to the
server on each negotiation step. If another client pushes into
a branch and moves it by fast-forward, any request to obtain that
branch's prior SHA-1 is still valid, the commit is reachable from
the new position of the reference. Unfortunately the fast-forward
causes smart HTTP negotations to fail, as the server no longer is
advertising that prior SHA-1.
Instead of causing clients to fail out with a "want invalid" error
and forcing the end-user retry, possibly getting into a never ending
try-fail-retry race while other clients are pushing into the same
busy repository, allow the slightly stale want request so long as
it is still reachable.
C Git implemented this same change recently to fix races on the
smart HTTP protocol when the C Git git-http-backend is used.
The new RequestPolicy feature also allows server authors to make
an even more lenient configuration that exports any SHA-1 to the
client. This might be useful in certain settings where a server
has authenticated the client as the "repository owner" and wants
to allow them to grab any content from the server as a complete
unbroken history chain.
The new setAdvertisedRefs() method allows server authors to manually
fix the references that are advertised, possibly bypassing the
getAllRefs() call on the Repository object.
Change-Id: I7cdb563bf9c55c83653f217f6e53c3add55a0541
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Shawn O. Pearce
01888db892
UploadPack: Fix races in smart HTTP negotiation