Teach UploadPack "filter" in protocol v2 fetch

If the configuration variable uploadpack.allowfilter is true, advertise
that "filter" is supported, and support it if the client sends such an
argument.

Change-Id: I7de66c0a0ada46ff71c5ba124d4ffa7c47254c3b
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>

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

 		assertTrue(pckIn.readString() == PacketLineIn.END);
 	}
 
+	@Test
+	public void testV2CapabilitiesAllowFilter() throws Exception {
+		server.getConfig().setBoolean("uploadpack", null, "allowfilter", true);
+		ByteArrayInputStream recvStream =
+			uploadPackV2Setup(null, null, PacketLineIn.END);
+		PacketLineIn pckIn = new PacketLineIn(recvStream);
+
+		assertThat(pckIn.readString(), is("version 2"));
+		assertThat(
+			Arrays.asList(pckIn.readString(), pckIn.readString()),
+			// TODO(jonathantanmy) This check overspecifies the
+			// order of the capabilities of "fetch".
+			hasItems("ls-refs", "fetch=filter shallow"));
+		assertTrue(pckIn.readString() == PacketLineIn.END);
+	}
+
 	@Test
 	@SuppressWarnings("boxing")
 	public void testV2EmptyRequest() throws Exception {
 			PacketLineIn.END);
 	}
 
+	@Test
+	public void testV2FetchFilter() throws Exception {
+		RevBlob big = remote.blob("foobar");
+		RevBlob small = remote.blob("fooba");
+		RevTree tree = remote.tree(remote.file("1", big),
+				remote.file("2", small));
+		RevCommit commit = remote.commit(tree);
+		remote.update("master", commit);
+
+		server.getConfig().setBoolean("uploadpack", null, "allowfilter", true);
+
+		ByteArrayInputStream recvStream = uploadPackV2(
+			"command=fetch\n",
+			PacketLineIn.DELIM,
+			"want " + commit.toObjectId().getName() + "\n",
+			"filter blob:limit=5\n",
+			"done\n",
+			PacketLineIn.END);
+		PacketLineIn pckIn = new PacketLineIn(recvStream);
+		assertThat(pckIn.readString(), is("packfile"));
+		parsePack(recvStream);
+
+		assertFalse(client.hasObject(big.toObjectId()));
+		assertTrue(client.hasObject(small.toObjectId()));
+	}
+
+	@Test
+	public void testV2FetchFilterWhenNotAllowed() throws Exception {
+		RevCommit commit = remote.commit().message("0").create();
+		remote.update("master", commit);
+
+		server.getConfig().setBoolean("uploadpack", null, "allowfilter", false);
+
+		thrown.expect(PackProtocolException.class);
+		thrown.expectMessage("unexpected filter blob:limit=5");
+		uploadPackV2(
+			"command=fetch\n",
+			PacketLineIn.DELIM,
+			"want " + commit.toObjectId().getName() + "\n",
+			"filter blob:limit=5\n",
+			"done\n",
+			PacketLineIn.END);
+	}
+
 	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

 		}
 
 		boolean includeTag = false;
+		boolean filterReceived = false;
 		while ((line = pckIn.readString()) != PacketLineIn.END) {
 			if (line.startsWith("want ")) { //$NON-NLS-1$
 				wantIds.add(ObjectId.fromString(line.substring(5)));
 					throw new PackProtocolException(
 							JGitText.get().deepenSinceWithDeepen);
 				}
+			} else if (transferConfig.isAllowFilter()
+					&& line.startsWith(OPTION_FILTER + ' ')) {
+				if (filterReceived) {
+					throw new PackProtocolException(JGitText.get().tooManyFilters);
+				}
+				filterReceived = true;
+				parseFilter(line.substring(OPTION_FILTER.length() + 1));
 			} else {
 				throw new PackProtocolException(MessageFormat
 						.format(JGitText.get().unexpectedPacketLine, line));
 		ArrayList<String> caps = new ArrayList<>();
 		caps.add("version 2"); //$NON-NLS-1$
 		caps.add(COMMAND_LS_REFS);
-		caps.add(COMMAND_FETCH + '=' + OPTION_SHALLOW);
+		caps.add(
+				COMMAND_FETCH + '=' +
+				(transferConfig.isAllowFilter() ? OPTION_FILTER + ' ' : "") + //$NON-NLS-1$
+				OPTION_SHALLOW);
 		return caps;
 	}