reftable: fix seeking to refs in reflog implementation

Small reftables omit the log index. Currently,
ReftableWriter#shouldHaveIndex does this if there is a single-block
log, but other writers could decide on different criteria.

In the case that the log index is missing, we have to linearly search
for the right block. It is never appropriate to use binary search on
blocks for log data, as the blocks are compressed and therefore
irregularly sized.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Change-Id: Id59874edf6bf45c7dec502d9465888e077ffe198

2 files changed, 71 insertions, 0 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/reftable/ReftableTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/reftable/ReftableTest.java
index a142166983..db9a4d0ac1 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/reftable/ReftableTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/reftable/ReftableTest.java
@@ -472,6 +472,51 @@ public class ReftableTest {
 	}
 
 	@Test
+	public void reflogSeek() throws IOException {
+		PersonIdent who = new PersonIdent("Log", "Ger", 1500079709, -8 * 60);
+		String msg = "test";
+		String msgNext = "test next";
+
+		ByteArrayOutputStream buffer = new ByteArrayOutputStream();
+		ReftableWriter writer = new ReftableWriter()
+				.setMinUpdateIndex(1)
+				.setMaxUpdateIndex(1)
+				.begin(buffer);
+
+		writer.writeLog(MASTER, 1, who, ObjectId.zeroId(), id(1), msg);
+		writer.writeLog(NEXT, 1, who, ObjectId.zeroId(), id(2), msgNext);
+
+		writer.finish();
+		byte[] table = buffer.toByteArray();
+
+		ReftableReader t = read(table);
+		try (LogCursor c = t.seekLog(MASTER, Long.MAX_VALUE)) {
+			assertTrue(c.next());
+			assertEquals(c.getReflogEntry().getComment(), msg);
+		}
+		try (LogCursor c = t.seekLog(MASTER, 0)) {
+			assertFalse(c.next());
+		}
+		try (LogCursor c = t.seekLog(MASTER, 1)) {
+			assertTrue(c.next());
+			assertEquals(c.getUpdateIndex(), 1);
+			assertEquals(c.getReflogEntry().getComment(), msg);
+		}
+		try (LogCursor c = t.seekLog(NEXT, Long.MAX_VALUE)) {
+			assertTrue(c.next());
+			assertEquals(c.getReflogEntry().getComment(), msgNext);
+		}
+		try (LogCursor c = t.seekLog(NEXT, 0)) {
+			assertFalse(c.next());
+		}
+		try (LogCursor c = t.seekLog(NEXT, 1)) {
+			assertTrue(c.next());
+			assertEquals(c.getUpdateIndex(), 1);
+			assertEquals(c.getReflogEntry().getComment(), msgNext);
+		}
+	}
+
+	@Test
 	public void onlyReflog() throws IOException {
 		PersonIdent who = new PersonIdent("Log", "Ger", 1500079709, -8 * 60);
 		String msg = "test";
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/ReftableReader.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/ReftableReader.java
index bf3a9aeca0..226e675e41 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/ReftableReader.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftable/ReftableReader.java
@@ -255,6 +255,32 @@ public class ReftableReader extends Reftable {
 			block.seekKey(key);
 			return block;
 		}
+		if (blockType == LOG_BLOCK_TYPE) {
+			// No index. Log blocks are irregularly sized, so we can't do binary search
+			// between blocks. Scan over blocks instead.
+			BlockReader block = readBlock(startPos, endPos);
+
+			for (;;) {
+				if (block == null || block.type() != LOG_BLOCK_TYPE) {
+					return null;
+				}
+
+				int result = block.seekKey(key);
+				if (result <= 0) {
+					// == 0 : we found the key.
+					// < 0 : the key is before this block. Either the ref name is there
+					// but only at a newer updateIndex, or it is absent. We leave it to
+					// logcursor to distinguish between both cases.
+					return block;
+				}
+
+				long pos = block.endPosition();
+				if (pos >= endPos) {
+					return null;
+				}
+				block = readBlock(pos, endPos);
+			}
+		}
 		return binarySearch(blockType, key, startPos, endPos);
 	}