Fix balanced match for empty string (fixes issue #23)

README.html

@@ -917,6 +917,9 @@ Files are no longer hosted at LuaForge.
 
 <tr valign="top"><td>&nbsp;&nbsp;<b>3.0-beta3</b></td><td><ul>
 <li>Fix maven sample code.</li>
+<li>Add sample code for Android Application that uses luaj.</li>
+<li>Add sample code for Applet that uses luaj.</li>
+<li>Fix balanced match for empty string (fixes issue #23).</li>
 
 </ul></td></tr>
 </table></td></tr></table>

src/core/org/luaj/vm2/LuaString.java

@@ -387,6 +387,12 @@ public class LuaString extends LuaValue {
 		return this;
 	}
 	
+	/** Take a substring using Java zero-based indexes for begin and end or range.
+	 * @param beginIndex  The zero-based index of the first character to include.
+	 * @param endIndex  The zero-based index of position after the last character.
+	 * @return LuaString which is a substring whose first character is at offset 
+	 * beginIndex and extending for (endIndex - beginIndex ) characters.
+	 */
 	public LuaString substring( int beginIndex, int endIndex ) {
 		return valueOf( m_bytes, m_offset + beginIndex, endIndex - beginIndex );
 	}

src/core/org/luaj/vm2/lib/StringLib.java

@@ -1155,19 +1155,20 @@ public class StringLib extends TwoArgFunction {
 			if ( poff == plen || poff + 1 == plen ) {
 				error( "unbalanced pattern" );
 			}
-			if ( s.luaByte( soff ) != p.luaByte( poff ) )
+			final int slen = s.length();
+			if ( soff >= slen )
 				return -1;
-			else {
+			final int b = p.luaByte( poff );
-				int b = p.luaByte( poff );
+			if ( s.luaByte( soff ) != b )
-				int e = p.luaByte( poff + 1 );
+				return -1;
+			final int e = p.luaByte( poff + 1 );
 			int cont = 1;
-				while ( ++soff < s.length() ) {
+			while ( ++soff < slen ) {
 				if ( s.luaByte( soff ) == e ) {
 					if ( --cont == 0 ) return soff + 1;
 				}
 				else if ( s.luaByte( soff ) == b ) cont++;
 			}
-			}
 			return -1;
 		}
 	}

test/junit/org/luaj/vm2/StringTest.java

@@ -349,4 +349,33 @@ public class StringTest extends TestCase {
 		assertEquals(1, sub.indexOfAny(CdEFGHIJ));
 		assertEquals(-1, sub.indexOfAny(EFGHIJKL));
 	}
+	
+	public void testMatchShortPatterns() {
+		LuaValue[] args = { LuaString.valueOf("%bxy") };
+		LuaString _ = LuaString.valueOf("");
+
+		LuaString a = LuaString.valueOf("a");
+		LuaString ax = LuaString.valueOf("ax");
+		LuaString axb = LuaString.valueOf("axb");
+		LuaString axby = LuaString.valueOf("axby");
+		LuaString xbya = LuaString.valueOf("xbya");
+		LuaString bya = LuaString.valueOf("bya");
+		LuaString xby = LuaString.valueOf("xby");
+		LuaString axbya = LuaString.valueOf("axbya");
+		LuaValue nil = LuaValue.NIL;
+		
+		assertEquals(nil, _.invokemethod("match", args));
+		assertEquals(nil, a.invokemethod("match", args));
+		assertEquals(nil, ax.invokemethod("match", args));
+		assertEquals(nil, axb.invokemethod("match", args));
+		assertEquals(xby, axby.invokemethod("match", args));
+		assertEquals(xby, xbya.invokemethod("match", args));
+		assertEquals(nil, bya.invokemethod("match", args));
+		assertEquals(xby, xby.invokemethod("match", args));
+		assertEquals(xby, axbya.invokemethod("match", args));
+		assertEquals(xby, axbya.substring(0,4).invokemethod("match", args));
+		assertEquals(nil, axbya.substring(0,3).invokemethod("match", args));
+		assertEquals(xby, axbya.substring(1,5).invokemethod("match", args));
+		assertEquals(nil, axbya.substring(2,5).invokemethod("match", args));
+	}
 }