DfsReader: check object type during open

Do not open an OBJ_TREE if the caller is expecting an OBJ_BLOB or
OBJ_COMMIT; instead throw IncorrectObjectTypeException.  This better
matches behavior of WindowCursor, the ObjectReader implementation of
the local file based object store.

Change-Id: I3fb0e77f54895b123679a405e1b6ba5b95752ff0

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsInserter.java

@@ -69,6 +69,7 @@ import java.util.zip.Inflater;
 import java.util.zip.InflaterInputStream;
 
 import org.eclipse.jgit.errors.CorruptObjectException;
+import org.eclipse.jgit.errors.IncorrectObjectTypeException;
 import org.eclipse.jgit.errors.LargeObjectException;
 import org.eclipse.jgit.internal.JGitText;
 import org.eclipse.jgit.internal.storage.file.PackIndex;
@@ -570,6 +571,9 @@ public class DfsInserter extends ObjectInserter {
 			if (type == OBJ_OFS_DELTA || type == OBJ_REF_DELTA)
 				throw new IOException(MessageFormat.format(
 						DfsText.get().cannotReadBackDelta, Integer.toString(type)));
+			if (typeHint != OBJ_ANY && type != typeHint) {
+				throw new IncorrectObjectTypeException(objectId.copy(), typeHint);
+			}
 
 			long sz = c & 0x0f;
 			int ptr = 1;

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsReader.java

@@ -222,20 +222,21 @@ public final class DfsReader extends ObjectReader implements ObjectReuseAsIs {
 		ObjectLoader ldr;
 		if (last != null) {
 			ldr = last.get(this, objectId);
-			if (ldr != null)
-				return ldr;
+			if (ldr != null) {
+				return checkType(ldr, objectId, typeHint);
+			}
 		}
 
 		PackList packList = db.getPackList();
 		boolean noGarbage = avoidUnreachable;
 		ldr = openImpl(packList, objectId, noGarbage);
 		if (ldr != null) {
-			return ldr;
+			return checkType(ldr, objectId, typeHint);
 		}
 		if (packList.dirty()) {
 			ldr = openImpl(db.scanPacks(packList), objectId, noGarbage);
 			if (ldr != null) {
-				return ldr;
+				return checkType(ldr, objectId, typeHint);
 			}
 		}
 
@@ -245,6 +246,14 @@ public final class DfsReader extends ObjectReader implements ObjectReuseAsIs {
 		throw new MissingObjectException(objectId.copy(), typeHint);
 	}
 
+	private static ObjectLoader checkType(ObjectLoader ldr, AnyObjectId id,
+			int typeHint) throws IncorrectObjectTypeException {
+		if (typeHint != OBJ_ANY && ldr.getType() != typeHint) {
+			throw new IncorrectObjectTypeException(id.copy(), typeHint);
+		}
+		return ldr;
+	}
+
 	private ObjectLoader openImpl(PackList packList, AnyObjectId objectId,
 			boolean noGarbage) throws IOException {
 		for (DfsPackFile pack : packList.packs) {