Implement the no-done capability

Smart HTTP clients may request both multi_ack_detailed and no-done in
the same request to prevent the client from needing to send a "done"
line to the server in response to a server's "ACK %s ready".

For smart HTTP, this can save 1 full HTTP RPC in the fetch exchange,
improving overall latency when incrementally updating a client that
has not diverged very far from the remote repository.

Unfortuantely this capability cannot be enabled for the traditional
bi-directional connections.  multi_ack_detailed has the client sending
more "have" lines at the same time that the server is creating the
"ACK %s ready" and writing out the PACK stream, resulting in some race
conditions and/or deadlock, depending on how the pipe buffers are
implemented.  For very small updates, a server might actually be able
to send "ACK %s ready", then the PACK, and disconnect before the
client even finishes sending its first batch of "have" lines.  This
may cause the client to fail with a broken pipe exception.  To avoid
all of these potential problems, "no-done" is restricted only to the
smart HTTP variant of the protocol.

Change-Id: Ie0d0a39320202bc096fec2e97cb58e9efd061b2d
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

1 files changed, 64 insertions, 3 deletions

diff --git a/org.eclipse.jgit.http.test/tst/org/eclipse/jgit/http/test/SmartClientSmartServerTest.java b/org.eclipse.jgit.http.test/tst/org/eclipse/jgit/http/test/SmartClientSmartServerTest.java
index c3590a44fb..cd127cdeaf 100644
--- a/org.eclipse.jgit.http.test/tst/org/eclipse/jgit/http/test/SmartClientSmartServerTest.java
+++ b/org.eclipse.jgit.http.test/tst/org/eclipse/jgit/http/test/SmartClientSmartServerTest.java
@@ -292,8 +292,6 @@ public class SmartClientSmartServerTest extends HttpTestCase {
 				.getRequestHeader(HDR_CONTENT_LENGTH));
 		assertNull("not chunked", service
 				.getRequestHeader(HDR_TRANSFER_ENCODING));
-		assertNull("no compression (too small)", service
-				.getRequestHeader(HDR_CONTENT_ENCODING));
 
 		assertEquals(200, service.getStatus());
 		assertEquals("application/x-git-upload-pack-result", service
@@ -301,7 +299,70 @@ public class SmartClientSmartServerTest extends HttpTestCase {
 	}
 
 	@Test
-	public void testFetchUpdateExisting() throws Exception {
+	public void testFetch_FewLocalCommits() throws Exception {
+		// Bootstrap by doing the clone.
+		//
+		TestRepository dst = createTestRepository();
+		Transport t = Transport.open(dst.getRepository(), remoteURI);
+		try {
+			t.fetch(NullProgressMonitor.INSTANCE, mirror(master));
+		} finally {
+			t.close();
+		}
+		assertEquals(B, dst.getRepository().getRef(master).getObjectId());
+		List<AccessEvent> cloneRequests = getRequests();
+
+		// Only create a few new commits.
+		TestRepository.BranchBuilder b = dst.branch(master);
+		for (int i = 0; i < 4; i++)
+			b.commit().tick(3600 /* 1 hour */).message("c" + i).create();
+
+		// Create a new commit on the remote.
+		//
+		b = new TestRepository(remoteRepository).branch(master);
+		RevCommit Z = b.commit().message("Z").create();
+
+		// Now incrementally update.
+		//
+		t = Transport.open(dst.getRepository(), remoteURI);
+		try {
+			t.fetch(NullProgressMonitor.INSTANCE, mirror(master));
+		} finally {
+			t.close();
+		}
+		assertEquals(Z, dst.getRepository().getRef(master).getObjectId());
+
+		List<AccessEvent> requests = getRequests();
+		requests.removeAll(cloneRequests);
+		assertEquals(2, requests.size());
+
+		AccessEvent info = requests.get(0);
+		assertEquals("GET", info.getMethod());
+		assertEquals(join(remoteURI, "info/refs"), info.getPath());
+		assertEquals(1, info.getParameters().size());
+		assertEquals("git-upload-pack", info.getParameter("service"));
+		assertEquals(200, info.getStatus());
+		assertEquals("application/x-git-upload-pack-advertisement",
+				info.getResponseHeader(HDR_CONTENT_TYPE));
+
+		// We should have needed one request to perform the fetch.
+		//
+		AccessEvent service = requests.get(1);
+		assertEquals("POST", service.getMethod());
+		assertEquals(join(remoteURI, "git-upload-pack"), service.getPath());
+		assertEquals(0, service.getParameters().size());
+		assertNotNull("has content-length",
+				service.getRequestHeader(HDR_CONTENT_LENGTH));
+		assertNull("not chunked",
+				service.getRequestHeader(HDR_TRANSFER_ENCODING));
+
+		assertEquals(200, service.getStatus());
+		assertEquals("application/x-git-upload-pack-result",
+				service.getResponseHeader(HDR_CONTENT_TYPE));
+	}
+
+	@Test
+	public void testFetch_TooManyLocalCommits() throws Exception {
 		// Bootstrap by doing the clone.
 		//
 		TestRepository dst = createTestRepository();