feat(dbus): add GetUnitProperty interface

Author: yichengq

dbus/methods.go

@@ -167,6 +167,28 @@ func (c *Conn) GetUnitProperties(unit string) (map[string]interface{}, error) {
 	return c.getProperties(unit, "org.freedesktop.systemd1.Unit")
 }
 
+func (c *Conn) getProperty(unit string, dbusInterface string, propertyName string) (*Property, error) {
+	var err error
+	var prop dbus.Variant
+
+	path := ObjectPath("/org/freedesktop/systemd1/unit/" + unit)
+	if !path.IsValid() {
+		return nil, errors.New("invalid unit name: " + unit)
+	}
+
+	obj := c.sysconn.Object("org.freedesktop.systemd1", path)
+	err = obj.Call("org.freedesktop.DBus.Properties.Get", 0, dbusInterface, propertyName).Store(&prop)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Property{Name: propertyName, Value: prop}, nil
+}
+
+func (c *Conn) GetUnitProperty(unit string, propertyName string) (*Property, error) {
+	return c.getProperty(unit, "org.freedesktop.systemd1.Unit", propertyName)
+}
+
 // GetUnitTypeProperties returns the extra properties for a unit, specific to the unit type.
 // Valid values for unitType: Service, Socket, Target, Device, Mount, Automount, Snapshot, Timer, Swap, Path, Slice, Scope
 // return "dbus.Error: Unknown interface" if the unitType is not the correct type of the unit

dbus/methods_test.go

@@ -21,6 +21,7 @@ import (
 	"math/rand"
 	"os"
 	"path/filepath"
+	"reflect"
 	"testing"
 )
 
@@ -142,6 +143,20 @@ func TestGetUnitProperties(t *testing.T) {
 	if names[0] != "system.slice" {
 		t.Fatal("unexpected wants for /")
 	}
+
+	prop, err := conn.GetUnitProperty(unit, "Wants")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if prop.Name != "Wants" {
+		t.Fatal("unexpected property name")
+	}
+
+	val := prop.Value.Value().([]string)
+	if !reflect.DeepEqual(val, names) {
+		t.Fatal("unexpected property value")
+	}
 }
 
 // TestGetUnitPropertiesRejectsInvalidName attempts to get the properties for a
@@ -153,7 +168,11 @@ func TestGetUnitPropertiesRejectsInvalidName(t *testing.T) {
 	unit := "//invalid#$^/"
 
 	_, err := conn.GetUnitProperties(unit)
+	if err == nil {
+		t.Fatal("Expected an error, got nil")
+	}
 
+	_, err = conn.GetUnitProperty(unit, "Wants")
 	if err == nil {
 		t.Fatal("Expected an error, got nil")
 	}