Index out of range panic upon encountering an empty string (#27)

* Index out of range panic upon encountering an empty string

* Added unit test for the empty value case

cmd/rabtap/json_message_formatter.go

@@ -20,12 +20,15 @@ var (
 )
 
 // Format validates and formats a message in JSON format. The body can be a
-// simple JSON object or an array of JSON objecs. If the message is not valid
-// JSON, it will returned unformatted as-is.
+// simple JSON object or an array of JSON objects. If the message is not valid
+// JSON, it will be returned unformatted as-is.
 func (s JSONMessageFormatter) Format(message rabtap.TapMessage) string {
 
 	var formatted []byte
 	originalMessage := strings.TrimSpace(string(message.AmqpMessage.Body))
+	if len(originalMessage) == 0 {
+		return string(message.AmqpMessage.Body)
+	}
 	if originalMessage[0] == '[' {
 		// try to unmarshal array to JSON objects
 		var arrayJSONObj []map[string]interface{}

cmd/rabtap/json_message_formatter_test.go

@@ -48,3 +48,13 @@ func TestJSONFormatterValidObject(t *testing.T) {
 	formattedMessage := JSONMessageFormatter{}.Format(rabtap.NewTapMessage(&message, time.Now()))
 	assert.Equal(t, "{\n  \"a\": 1\n}", formattedMessage)
 }
+
+func TestJSONFormatterEmptyValue(t *testing.T) {
+	// An empty buffer effectively should be returned unmodified
+	message := amqp.Delivery{
+		Body: []byte(""),
+	}
+	formattedMessage := JSONMessageFormatter{}.Format(rabtap.NewTapMessage(&message, time.Now()))
+	// message is expected to be returned untouched
+	assert.Equal(t, "", formattedMessage)
+}