Make illegal characters detection even more strict

The previous implementation allowed for high surrogates followed by
non-low surrogates. We now assure that every high surrogate is followed
by a low surrogate (under the assumption that the last byte in an XMPP
stream can not be a unicode surrogate pair).

OF-391

git-svn-id: http://svn.igniterealtime.org/svn/repos/openfire/trunk@13996 b35dd754-fafc-0310-a699-88a17e54d16e

src/java/org/jivesoftware/openfire/net/MXParser.java

@@ -370,12 +370,12 @@ public class MXParser extends org.xmlpull.mxp1.MXParser {
 	 * Note that when MXParser is being modified to handle multibyte chars correctly, this method needs to change (as
 	 * then, there are more codepoints to check).
 	 * 
-	 * Also note that the current implementations allows high surrogates followed by non low surrogates.
 	 */
     @Override
     protected char more() throws IOException, XmlPullParserException {
-    	final char codePoint  = super.more(); // note - this does NOT return a codepoint now, but simply a (single byte) character!
+    	final char codePoint  = super.more(); // note - this does NOT return a codepoint now, but simply a (double byte) character!
 		boolean validCodepoint = false;
+		boolean isLowSurrogate = Character.isLowSurrogate(codePoint);
 		if ((codePoint == 0x0) ||  // 0x0 is not allowed, but flash clients insist on sending this as the very first character of a stream. We should stop allowing this codepoint after the first byte has been parsed.
 				(codePoint == 0x9) ||
 				(codePoint == 0xA) ||
@@ -384,12 +384,15 @@ public class MXParser extends org.xmlpull.mxp1.MXParser {
 				((codePoint >= 0xE000) && (codePoint <= 0xFFFD))) {
 			validCodepoint = true;
 		}
-		else if (Character.isLowSurrogate(codePoint)) {
-			if (highSurrogateSeen) {
+		else if (highSurrogateSeen) {
+			if (isLowSurrogate) {
 				validCodepoint = true;
 			} else {
-				throw new XmlPullParserException("Low surrogate '0x " + String.format("%x", (int) codePoint) + " without preceeding high surrogate");
+				throw new XmlPullParserException("High surrogate followed by non low surrogate '0x" + String.format("%x", (int) codePoint) + "'");
+			}
 		}
+		else if (isLowSurrogate) {
+			throw new XmlPullParserException("Low surrogate '0x " + String.format("%x", (int) codePoint) + " without preceeding high surrogate");
 		}
 		else if (Character.isHighSurrogate(codePoint)) {
 			highSurrogateSeen = true;