Teach UploadPack "thin-pack" in "fetch"

Add support for the "thin-pack" parameter in the "fetch" command in
the fetch-pack/upload-pack protocol v2.

Change-Id: I39a37b2b66a16929137d35c718a3acf2afb6b0b5
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/transport/UploadPackTest.java

@@ -13,6 +13,7 @@ import java.util.HashMap;
 import java.util.Map;
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
+import java.io.IOException;
 import java.io.StringWriter;
 import org.eclipse.jgit.errors.TransportException;
 import org.eclipse.jgit.internal.storage.dfs.DfsGarbageCollector;
@@ -750,6 +751,36 @@ public class UploadPackTest {
 		assertTrue(client.hasObject(barChild.toObjectId()));
 	}
 
+	@Test
+	public void testV2FetchThinPack() throws Exception {
+		String commonInBlob = "abcdefghijklmnopqrstuvwxyz";
+
+		RevBlob parentBlob = remote.blob(commonInBlob + "a");
+		RevCommit parent = remote.commit(remote.tree(remote.file("foo", parentBlob)));
+		RevBlob childBlob = remote.blob(commonInBlob + "b");
+		RevCommit child = remote.commit(remote.tree(remote.file("foo", childBlob)), parent);
+		remote.update("branch1", child);
+
+		// Pretend that we have parent to get a thin pack based on it.
+		ByteArrayInputStream recvStream = uploadPackV2(
+			"command=fetch\n",
+			PacketLineIn.DELIM,
+			"want " + child.toObjectId().getName() + "\n",
+			"have " + parent.toObjectId().getName() + "\n",
+			"thin-pack\n",
+			"done\n",
+			PacketLineIn.END);
+		PacketLineIn pckIn = new PacketLineIn(recvStream);
+
+		assertThat(pckIn.readString(), is("packfile"));
+
+		// Verify that we received a thin pack by trying to apply it
+		// against the client repo, which does not have parent.
+		thrown.expect(IOException.class);
+		thrown.expectMessage("pack has unresolved deltas");
+		parsePack(recvStream);
+	}
+
 	private static class RejectAllRefFilter implements RefFilter {
 		@Override
 		public Map<String, Ref> filter(Map<String, Ref> refs) {

org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java

@@ -954,6 +954,8 @@ public class UploadPack {
 				peerHas.add(ObjectId.fromString(line.substring(5)));
 			} else if (line.equals("done")) {
 				doneReceived = true;
+			} else if (line.equals(OPTION_THIN_PACK)) {
+				options.add(OPTION_THIN_PACK);
 			}
 			// else ignore it
 		}