config: Set a default port for the monitor.

Port 9331 has been allocated for use by influx-spout.

See https://github.com/prometheus/prometheus/wiki/Default-port-allocations

config/config.go

@@ -101,11 +101,18 @@ func NewConfigFromFile(fileName string) (*Config, error) {
 	if conf.Name == "" {
 		conf.Name = pathToConfigName(fileName)
 	}
-	if conf.Mode == "listener" && conf.Port == 0 {
-		conf.Port = 10001
-	} else if conf.Mode == "listener_http" && conf.Port == 0 {
-		conf.Port = 13337
+
+	if conf.Port == 0 {
+		switch conf.Mode {
+		case "listener":
+			conf.Port = 10001
+		case "listener_http":
+			conf.Port = 13337
+		case "monitor":
+			conf.Port = 9331
+		}
 	}
+
 	return conf, nil
 }
 

config/config_small_test.go

@@ -120,6 +120,12 @@ func TestDefaultPortHTTPListener(t *testing.T) {
 	assert.Equal(t, 13337, conf.Port)
 }
 
+func TestDefaultPortMonitor(t *testing.T) {
+	conf, err := parseConfig(`mode = "monitor"`)
+	require.NoError(t, err)
+	assert.Equal(t, 9331, conf.Port)
+}
+
 func TestNoMode(t *testing.T) {
 	_, err := parseConfig("")
 	assert.EqualError(t, err, "mode not specified in config")