Add support for tree filters when fetching

Teach the FilterSpec serialization code about tree filters so they can
be communicated over the wire and understood by the server.

While we're here, harden the FilterSpec serialization code to throw
IllegalStateException if we encounter a FilterSpec that cannot be
expressed as a "filter" line.  The only public API for creating a
Filterspec is to pass in a "filter" line to be parsed, so these should
not appear in practice.

Change-Id: I9664844059ffbc9c36eb829e2d860f198b9403a0
Signed-off-by: Jonathan Nieder <jrn@google.com>

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

@@ -297,6 +297,38 @@ public class UploadPackTest {
 		}
 	}
 
+	@Test
+	public void testFetchWithTreeZeroFilter() throws Exception {
+		InMemoryRepository server2 = newRepo("server2");
+		try (TestRepository<InMemoryRepository> remote2 = new TestRepository<>(
+				server2)) {
+			RevBlob blob1 = remote2.blob("foobar");
+			RevBlob blob2 = remote2.blob("fooba");
+			RevTree tree = remote2.tree(remote2.file("1", blob1),
+					remote2.file("2", blob2));
+			RevCommit commit = remote2.commit(tree);
+			remote2.update("master", commit);
+
+			server2.getConfig().setBoolean("uploadpack", null, "allowfilter",
+					true);
+
+			testProtocol = new TestProtocol<>((Object req, Repository db) -> {
+				UploadPack up = new UploadPack(db);
+				return up;
+			}, null);
+			uri = testProtocol.register(ctx, server2);
+
+			try (Transport tn = testProtocol.open(uri, client, "server2")) {
+				tn.setFilterSpec(FilterSpec.withTreeDepthLimit(0));
+				tn.fetch(NullProgressMonitor.INSTANCE,
+						Collections.singletonList(new RefSpec(commit.name())));
+				assertFalse(client.getObjectDatabase().has(tree.toObjectId()));
+				assertFalse(client.getObjectDatabase().has(blob1.toObjectId()));
+				assertFalse(client.getObjectDatabase().has(blob2.toObjectId()));
+			}
+		}
+	}
+
 	@Test
 	public void testFetchWithNonSupportingServer() throws Exception {
 		InMemoryRepository server2 = newRepo("server2");

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

@@ -10,6 +10,8 @@
 
 package org.eclipse.jgit.transport;
 
+import static org.eclipse.jgit.transport.GitProtocolConstants.OPTION_FILTER;
+
 import java.text.MessageFormat;
 
 import org.eclipse.jgit.annotations.Nullable;
@@ -146,14 +148,16 @@ public final class FilterSpec {
 	 */
 	@Nullable
 	public String filterLine() {
-		if (blobLimit == 0) {
-			return GitProtocolConstants.OPTION_FILTER + " blob:none"; //$NON-NLS-1$
-		}
-
-		if (blobLimit > 0) {
-			return GitProtocolConstants.OPTION_FILTER + " blob:limit=" + blobLimit; //$NON-NLS-1$
-		}
-
+		if (isNoOp()) {
 			return null;
+		} else if (blobLimit == 0 && treeDepthLimit == -1) {
+			return OPTION_FILTER + " blob:none"; //$NON-NLS-1$
+		} else if (blobLimit > 0 && treeDepthLimit == -1) {
+			return OPTION_FILTER + " blob:limit=" + blobLimit; //$NON-NLS-1$
+		} else if (blobLimit == -1 && treeDepthLimit >= 0) {
+			return OPTION_FILTER + " tree:" + treeDepthLimit; //$NON-NLS-1$
+		} else {
+			throw new IllegalStateException();
+		}
 	}
 }