PacketLineIn: Add helper methods to check for END and DELIM

These methods will allow clients to check for END and DELIM without
doing a reference comparison on the String objects, which raises
warnings from Error Prone.

Change-Id: I9e7e59843553ed4488ee8e864033198bbb60d67c
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

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

@@ -44,7 +44,8 @@
 package org.eclipse.jgit.transport;
 
 import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNotSame;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.fail;
 
@@ -142,21 +143,21 @@ public class PacketLineInTest {
 		init("0004");
 		final String act = in.readString();
 		assertEquals("", act);
-		assertNotSame(PacketLineIn.END, act);
+		assertFalse(PacketLineIn.isEnd(act));
 		assertEOF();
 	}
 
 	@Test
 	public void testReadString_End() throws IOException {
 		init("0000");
-		assertSame(PacketLineIn.END, in.readString());
+		assertTrue(PacketLineIn.isEnd(in.readString()));
 		assertEOF();
 	}
 
 	@Test
 	public void testReadString_Delim() throws IOException {
 		init("0001");
-		assertSame(PacketLineIn.DELIM, in.readString());
+		assertTrue(PacketLineIn.isDelim(in.readString()));
 		assertEOF();
 	}
 
@@ -183,14 +184,14 @@ public class PacketLineInTest {
 		init("0004");
 		final String act = in.readStringRaw();
 		assertEquals("", act);
-		assertNotSame(PacketLineIn.END, act);
+		assertFalse(PacketLineIn.isEnd(act));
 		assertEOF();
 	}
 
 	@Test
 	public void testReadStringRaw_End() throws IOException {
 		init("0000");
-		assertSame(PacketLineIn.END, in.readStringRaw());
+		assertTrue(PacketLineIn.isEnd(in.readString()));
 		assertEOF();
 	}
 

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

@@ -224,6 +224,30 @@ public class PacketLineIn {
 		return s;
 	}
 
+	/**
+	 * Check if a string is the delimiter marker.
+	 *
+	 * @param s
+	 *            the string to check
+	 * @return true if the given string is {@link #DELIM}, otherwise false.
+	 * @since 5.4
+	 */
+	public static boolean isDelim(String s) {
+		return s == DELIM;
+	}
+
+	/**
+	 * Check if a string is the packet end marker.
+	 *
+	 * @param s
+	 *            the string to check
+	 * @return true if the given string is {@link #END}, otherwise false.
+	 * @since 5.4
+	 */
+	public static boolean isEnd(String s) {
+		return s == END;
+	}
+
 	void discardUntilEnd() throws IOException {
 		for (;;) {
 			int n = readLength();