RefDirectory: Refactor getRef and exactRef to share code

Both getRef and exactRef look for a ref or pseudoref in the $GIT_DIR
directory, with careful error handling to handle non-refs like
.git/config.

Avoid the duplication by factoring out a helper that takes care of
this.  This should make the code easier to understand and manipulate.

Change-Id: I2ea67816d2385e84e2d3394b897e23df5826ba50
Signed-off-by: Jonathan Nieder <jrn@google.com>

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/RefDirectory.java

@@ -319,16 +319,14 @@ public class RefDirectory extends RefDatabase {
 		return loose;
 	}
 
-	/** {@inheritDoc} */
-	@Override
-	public Ref exactRef(String name) throws IOException {
-		RefList<Ref> packed = getPackedRefs();
-		Ref ref;
+	@Nullable
+	private Ref readAndResolve(String name, RefList<Ref> packed) throws IOException {
 		try {
-			ref = readRef(name, packed);
+			Ref ref = readRef(name, packed);
 			if (ref != null) {
 				ref = resolve(ref, 0, null, null, packed);
 			}
+			return ref;
 		} catch (IOException e) {
 			if (name.contains("/") //$NON-NLS-1$
 					|| !(e.getCause() instanceof InvalidObjectIdException)) {
@@ -338,8 +336,14 @@ public class RefDirectory extends RefDatabase {
 			// While looking for a ref outside of refs/ (e.g., 'config'), we
 			// found a non-ref file (e.g., a config file) instead.  Treat this
 			// as a ref-not-found condition.
-			ref = null;
+			return null;
 		}
+	}
+
+	/** {@inheritDoc} */
+	@Override
+	public Ref exactRef(String name) throws IOException {
+		Ref ref = readAndResolve(name, getPackedRefs());
 		fireRefsChanged();
 		return ref;
 	}
@@ -350,19 +354,9 @@ public class RefDirectory extends RefDatabase {
 		final RefList<Ref> packed = getPackedRefs();
 		Ref ref = null;
 		for (String prefix : SEARCH_PATH) {
-			try {
-				ref = readRef(prefix + needle, packed);
-				if (ref != null) {
-					ref = resolve(ref, 0, null, null, packed);
-				}
-				if (ref != null) {
-					break;
-				}
-			} catch (IOException e) {
-				if (!(!needle.contains("/") && "".equals(prefix) && e //$NON-NLS-1$ //$NON-NLS-2$
-						.getCause() instanceof InvalidObjectIdException)) {
-					throw e;
-				}
+			ref = readAndResolve(prefix + needle, packed);
+			if (ref != null) {
+				break;
 			}
 		}
 		fireRefsChanged();