Prevent panicing when parsing invalid messages

irc/message.go

@@ -19,7 +19,13 @@ func parseMessage(line string) *Message {
 
 	if strings.HasPrefix(line, ":") {
 		cmdStart = strings.Index(line, " ") + 1
-		msg.Prefix = line[1 : cmdStart-1]
+
+		if cmdStart > 0 {
+			msg.Prefix = line[1 : cmdStart-1]
+		} else {
+			// Invalid message
+			return &msg
+		}
 
 		if i := strings.Index(msg.Prefix, "!"); i > 0 {
 			msg.Nick = msg.Prefix[:i]

irc/message_test.go

@@ -71,3 +71,10 @@ func TestParseMessage(t *testing.T) {
 		assert.Equal(t, tc.expected, parseMessage(tc.input))
 	}
 }
+
+func TestBadMessagePanic(t *testing.T) {
+	parseMessage(":user\r\n")
+	parseMessage(":\r\n")
+	parseMessage(":")
+	parseMessage("")
+}