Enhance Parser decode

* Avoid using expected IndexOutOfBound exception
* Add few more error checks
* Add few malformated message error test cases

src/test/java/com/github/nkzawa/socketio/parser/Helpers.java

@@ -15,6 +15,7 @@ import static org.junit.Assert.assertThat;
 public class Helpers {
 
     private static Parser.Encoder encoder = new Parser.Encoder();
+    private static Packet<String> errorPacket = new Packet<String>(Parser.ERROR, "parser error");
 
     public static void test(final Packet obj) {
         encoder.encode(obj, new Parser.Encoder.Callback() {
@@ -33,6 +34,18 @@ public class Helpers {
         });
     }
 
+    public static void testDecodeError(final String errorMessage) {
+        Parser.Decoder decoder = new Parser.Decoder();
+        decoder.on(Parser.Decoder.EVENT_DECODED, new Emitter.Listener() {
+            @Override
+            public void call(Object... args) {
+                Packet packet = (Packet)args[0];
+                assertPacket(errorPacket, packet);
+            }
+        });
+        decoder.add(errorMessage);
+    }
+
     public static void testBin(final Packet obj) {
         final Object originalData = obj.data;
         encoder.encode(obj, new Parser.Encoder.Callback() {

src/test/java/com/github/nkzawa/socketio/parser/ParserTest.java

@@ -11,7 +11,6 @@ public class ParserTest {
 
     private static Parser.Encoder encoder = new Parser.Encoder();
 
-
     @Test
     public void encodeConnection() {
         Packet packet = new Packet(Parser.CONNECT);
@@ -47,4 +46,22 @@ public class ParserTest {
         packet.nsp = "/";
         Helpers.test(packet);
     }
+
+    @Test
+    public void decodeInError() throws JSONException {
+        // Random string
+        Helpers.testDecodeError("asdf");
+        // Unknown type
+        Helpers.testDecodeError(Parser.types.length + "asdf");
+        // Binary event with no `-`
+        Helpers.testDecodeError(Parser.BINARY_EVENT + "asdf");
+        // Binary ack with no `-`
+        Helpers.testDecodeError(Parser.BINARY_ACK + "asdf");
+        // Binary event with no attachment
+        Helpers.testDecodeError(String.valueOf(Parser.BINARY_EVENT));
+        // event non numeric id
+        Helpers.testDecodeError(Parser.EVENT + "2sd");
+        // event with invalid json data
+        Helpers.testDecodeError(Parser.EVENT + "2[\"a\",1,{asdf}]");
+    }
 }