AdvertisedRequestValidator: fix WantNotValidException caused by race

Fetch with protocol V2 failed under the following conditions
- fetch uses bidirectional protocol (git, ssh) which uses a shortcut
  to determine invalid wants
- not all wants are advertised
- race condition: wanted ref is updated during fetch by another thread
  after the thread serving upload-pack determined wants and before it
  checks not advertised wants

Fix this by calling
`new ReachableCommitRequestValidator().checkWants(up, wants)`
instead of throwing WantNotValidException in [1]
if this race happened in the same way like it's done for unidirectional
protocols (http) [2].

[1] https://github.com/eclipse-jgit/jgit/blob/stable-6.10/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java#L2002
[2] https://github.com/eclipse-jgit/jgit/blob/stable-6.10/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java#L2000

Bug: jgit-48
Change-Id: I32f28502923815dc49781aab5d810c9afbe7e7e6

1 files changed, 2 insertions, 3 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java
index 160e2e6e3d..3238020722 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java
@@ -1916,10 +1916,9 @@ public class UploadPack implements Closeable {
 		@Override
 		public void checkWants(UploadPack up, List<ObjectId> wants)
 				throws PackProtocolException, IOException {
-			if (!up.isBiDirectionalPipe())
+			if (!up.isBiDirectionalPipe() || !wants.isEmpty()) {
 				new ReachableCommitRequestValidator().checkWants(up, wants);
-			else if (!wants.isEmpty())
-				throw new WantNotValidException(wants.iterator().next());
+			}
 		}
 	}