Fixed the check for surrogates in mqtt3 similar to the fix applied in mqtt5 version.

Signed-off-by: Ilia Beliaev <silhlol@gmail.com>

Author: silh

org.eclipse.paho.client.mqttv3.test/src/test/java/org/eclipse/paho/client/mqttv3/test/MqttDataTypesTest.java

@@ -1,7 +1,6 @@
 package org.eclipse.paho.client.mqttv3.test;
 
 import java.io.*;
-import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 
 import org.eclipse.paho.client.mqttv3.MqttException;
@@ -72,6 +71,25 @@ public void TestEncodeInvalidUTF8StringInDifferentRange() throws MqttException {
 		encodeAndDecodeString(invalidString);
 	}
 
+	@Test
+	public void TestEncodeAndDecodeUTF8StringWithSurrogates() throws MqttException {
+		String testString = "\uD801\uDC37";
+		String decodedUTF8 = encodeAndDecodeString(testString);
+		Assert.assertEquals(testString, decodedUTF8);
+	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void TestEncodeAndDecodeUTF8StringWithTrailingHighSurrogate() throws MqttException {
+		String testString = "\uD801";
+		encodeAndDecodeString(testString);
+	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void TestEncodeAndDecodeUTF8StringWithLowSurrogate() throws MqttException {
+		String testString = "\uDC37";
+		encodeAndDecodeString(testString);
+	}
+
 	@Test
 	public void TestEncodeAndDecodeUTF8String() throws MqttException {
 		String testString = "Answer to life the universe and everything";
@@ -91,14 +109,11 @@ public void TestEncodeAndDecodeChineseUTF8String() throws MqttException {
 
 	}
 
-	@Test(expected = IllegalArgumentException.class)
+	@Test
 	public void TestEncodeAndDecodeEmojiString() throws MqttException {
 		String testString = "👁🐝Ⓜ️️";
-		// System.out.println(String.format("'%s' is %d bytes, %d chars long",
-		// testString, testString.getBytes().length, testString.length()));
 		String decodedUTF8 = encodeAndDecodeString(testString);
 		Assert.assertEquals(testString, decodedUTF8);
-
 	}
 
 	@Test

org.eclipse.paho.client.mqttv3/src/main/java/org/eclipse/paho/client/mqttv3/internal/wire/MqttWireMessage.java

@@ -54,7 +54,7 @@ public abstract class MqttWireMessage {
 	private static final String[] PACKET_NAMES = {"reserved", "CONNECT", "CONNACK", "PUBLISH", "PUBACK", "PUBREC",
 			"PUBREL", "PUBCOMP", "SUBSCRIBE", "SUBACK", "UNSUBSCRIBE", "UNSUBACK", "PINGREQ", "PINGRESP",
 			"DISCONNECT"};
-	
+
 
 	private static final long FOUR_BYTE_INT_MAX = 4294967295L;
 	private static final int VARIABLE_BYTE_INT_MAX = 268435455;
@@ -388,31 +388,27 @@ private static void validateUTF8String(String input) throws IllegalArgumentExcep
 				} else {
 					char c2 = input.charAt(i);
 					if (Character.isLowSurrogate(c2)) {
-						isBad = true; /* No low surrogate */
-					} else {
 						int ch = ((((int) c) & 0x3ff) << 10) | (c2 & 0x3ff);
 						if ((ch & 0xffff) == 0xffff || (ch & 0xffff) == 0xfffe) {
 							isBad = true; /* Noncharacter in base plane */
 						}
+					} else {
+						isBad = true; /* No low surrogate */
 					}
 				}
-			} else {
-				if (Character.isISOControl(c) || Character.isLowSurrogate(c)) {
-					isBad = true; /* Control character or no high surrogate */
-				} else if (c >= 0xfdd0 && (c == 0xfffe || c >= 0xfdd0 || c <= 0xfddf)) {
-					isBad = true; /* Noncharacter in other nonbase plane */
-				}
+			} else if (Character.isISOControl(c) // Control character
+					|| Character.isLowSurrogate(c) // or no high surrogate
+					|| c >= 0xfdd0 && (c <= 0xfddf || c >= 0xfffe)) { // non-character in other nonbase plane
+				isBad = true;
 			}
 			if (isBad) {
-				throw new IllegalArgumentException(String.format("Invalid UTF-8 char: [%x]", (int) c));
+				throw new IllegalArgumentException(String.format("Invalid UTF-8 char: [%04x]", (int) c));
 			}
 		}
 	}
-	
+
 	public static void validateVariableByteInt(int value) throws IllegalArgumentException {
-		if (value >= 0 && value <= VARIABLE_BYTE_INT_MAX) {
-			return;
-		} else {
+		if (value < 0 || value > VARIABLE_BYTE_INT_MAX) {
 			throw new IllegalArgumentException("This property must be a number between 0 and " + VARIABLE_BYTE_INT_MAX);
 		}