dbus: add SetPropertiesSubscriber method

dbus/dbus.go

@@ -16,6 +16,7 @@
 package dbus
 
 import (
+	"encoding/hex"
 	"fmt"
 	"os"
 	"strconv"
@@ -60,6 +61,27 @@ func PathBusEscape(path string) string {
 	return string(n)
 }
 
+// pathBusUnescape is the inverse of PathBusEscape.
+func pathBusUnescape(path string) string {
+	if path == "_" {
+		return ""
+	}
+	n := []byte{}
+	for i := 0; i < len(path); i++ {
+		c := path[i]
+		if c == '_' && i+2 < len(path) {
+			res, err := hex.DecodeString(path[i+1 : i+3])
+			if err == nil {
+				n = append(n, res...)
+			}
+			i += 2
+		} else {
+			n = append(n, c)
+		}
+	}
+	return string(n)
+}
+
 // Conn is a connection to systemd's dbus endpoint.
 type Conn struct {
 	// sysconn/sysobj are only used to call dbus methods
@@ -74,13 +96,18 @@ type Conn struct {
 		jobs map[dbus.ObjectPath]chan<- string
 		sync.Mutex
 	}
-	subscriber struct {
+	subStateSubscriber struct {
 		updateCh chan<- *SubStateUpdate
 		errCh    chan<- error
 		sync.Mutex
 		ignore      map[dbus.ObjectPath]int64
 		cleanIgnore int64
 	}
+	propertiesSubscriber struct {
+		updateCh chan<- *PropertiesUpdate
+		errCh    chan<- error
+		sync.Mutex
+	}
 }
 
 // New establishes a connection to any available bus and authenticates.
@@ -152,7 +179,7 @@ func NewConnection(dialBus func() (*dbus.Conn, error)) (*Conn, error) {
 		sigobj:  systemdObject(sigconn),
 	}
 
-	c.subscriber.ignore = make(map[dbus.ObjectPath]int64)
+	c.subStateSubscriber.ignore = make(map[dbus.ObjectPath]int64)
 	c.jobListener.jobs = make(map[dbus.ObjectPath]chan<- string)
 
 	// Setup the listeners on jobs so that we can get completions

dbus/dbus_test.go

@@ -67,6 +67,25 @@ func TestPathBusEscape(t *testing.T) {
 
 }
 
+func TestPathBusUnescape(t *testing.T) {
+	for in, want := range map[string]string{
+		"_":                      "",
+		"foo_2eservice":          "foo.service",
+		"foobar":                 "foobar",
+		"woof_40woof_2eservice":  "[email protected]",
+		"_30123456":              "0123456",
+		"account_5fdb_2eservice": "account_db.service",
+		"got_2ddashes":           "got-dashes",
+		"foobar_":                "foobar_",
+		"foobar_2":               "foobar_2",
+	} {
+		got := pathBusUnescape(in)
+		if got != want {
+			t.Errorf("bad result for pathBusUnescape(%s): got %q, want %q", in, got, want)
+		}
+	}
+}
+
 // TestNew ensures that New() works without errors.
 func TestNew(t *testing.T) {
 	_, err := New()

dbus/methods.go

@@ -584,3 +584,8 @@ func (c *Conn) Reload() error {
 func unitPath(name string) dbus.ObjectPath {
 	return dbus.ObjectPath("/org/freedesktop/systemd1/unit/" + PathBusEscape(name))
 }
+
+// unitName returns the unescaped base element of the supplied escaped path
+func unitName(dpath dbus.ObjectPath) string {
+	return pathBusUnescape(path.Base(string(dpath)))
+}

dbus/methods_test.go

@@ -1524,3 +1524,20 @@ func TestReload(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestUnitName(t *testing.T) {
+	for _, unit := range []string{
+		"",
+		"foo.service",
+		"foobar",
+		"[email protected]",
+		"0123456",
+		"account_db.service",
+		"got-dashes",
+	} {
+		got := unitName(unitPath(unit))
+		if got != unit {
+			t.Errorf("bad result for unitName(%s): got %q, want %q", unit, got, unit)
+		}
+	}
+}

dbus/subscription.go

@@ -70,7 +70,8 @@ func (c *Conn) dispatch() {
 				c.jobComplete(signal)
 			}
 
-			if c.subscriber.updateCh == nil {
+			if c.subStateSubscriber.updateCh == nil &&
+				c.propertiesSubscriber.updateCh == nil {
 				continue
 			}
 
@@ -84,6 +85,12 @@ func (c *Conn) dispatch() {
 			case "org.freedesktop.DBus.Properties.PropertiesChanged":
 				if signal.Body[0].(string) == "org.freedesktop.systemd1.Unit" {
 					unitPath = signal.Path
+
+					if len(signal.Body) >= 2 {
+						if changed, ok := signal.Body[1].(map[string]dbus.Variant); ok {
+							c.sendPropertiesUpdate(unitPath, changed)
+						}
+					}
 				}
 			}
 
@@ -169,15 +176,19 @@ type SubStateUpdate struct {
 // is full, it attempts to write an error to errCh; if errCh is full, the error
 // passes silently.
 func (c *Conn) SetSubStateSubscriber(updateCh chan<- *SubStateUpdate, errCh chan<- error) {
-	c.subscriber.Lock()
-	defer c.subscriber.Unlock()
-	c.subscriber.updateCh = updateCh
-	c.subscriber.errCh = errCh
+	c.subStateSubscriber.Lock()
+	defer c.subStateSubscriber.Unlock()
+	c.subStateSubscriber.updateCh = updateCh
+	c.subStateSubscriber.errCh = errCh
 }
 
 func (c *Conn) sendSubStateUpdate(unitPath dbus.ObjectPath) {
-	c.subscriber.Lock()
-	defer c.subscriber.Unlock()
+	c.subStateSubscriber.Lock()
+	defer c.subStateSubscriber.Unlock()
+
+	if c.subStateSubscriber.updateCh == nil {
+		return
+	}
 
 	if c.shouldIgnore(unitPath) {
 		return
@@ -186,7 +197,7 @@ func (c *Conn) sendSubStateUpdate(unitPath dbus.ObjectPath) {
 	info, err := c.GetUnitPathProperties(unitPath)
 	if err != nil {
 		select {
-		case c.subscriber.errCh <- err:
+		case c.subStateSubscriber.errCh <- err:
 		default:
 		}
 	}
@@ -196,10 +207,10 @@ func (c *Conn) sendSubStateUpdate(unitPath dbus.ObjectPath) {
 
 	update := &SubStateUpdate{name, substate}
 	select {
-	case c.subscriber.updateCh <- update:
+	case c.subStateSubscriber.updateCh <- update:
 	default:
 		select {
-		case c.subscriber.errCh <- errors.New("update channel full!"):
+		case c.subStateSubscriber.errCh <- errors.New("update channel full!"):
 		default:
 		}
 	}
@@ -222,7 +233,7 @@ func (c *Conn) sendSubStateUpdate(unitPath dbus.ObjectPath) {
 // the properties).
 
 func (c *Conn) shouldIgnore(path dbus.ObjectPath) bool {
-	t, ok := c.subscriber.ignore[path]
+	t, ok := c.subStateSubscriber.ignore[path]
 	return ok && t >= time.Now().UnixNano()
 }
 
@@ -231,20 +242,62 @@ func (c *Conn) updateIgnore(path dbus.ObjectPath, info map[string]interface{}) {
 
 	// unit is unloaded - it will trigger bad systemd dbus behavior
 	if info["LoadState"].(string) == "not-found" {
-		c.subscriber.ignore[path] = time.Now().UnixNano() + ignoreInterval
+		c.subStateSubscriber.ignore[path] = time.Now().UnixNano() + ignoreInterval
 	}
 }
 
 // without this, ignore would grow unboundedly over time
 func (c *Conn) cleanIgnore() {
 	now := time.Now().UnixNano()
-	if c.subscriber.cleanIgnore < now {
-		c.subscriber.cleanIgnore = now + cleanIgnoreInterval
+	if c.subStateSubscriber.cleanIgnore < now {
+		c.subStateSubscriber.cleanIgnore = now + cleanIgnoreInterval
 
-		for p, t := range c.subscriber.ignore {
+		for p, t := range c.subStateSubscriber.ignore {
 			if t < now {
-				delete(c.subscriber.ignore, p)
+				delete(c.subStateSubscriber.ignore, p)
 			}
 		}
 	}
 }
+
+// PropertiesUpdate holds a map of a unit's changed properties
+type PropertiesUpdate struct {
+	UnitName string
+	Changed  map[string]dbus.Variant
+}
+
+// SetPropertiesSubscriber writes to updateCh when any unit's properties
+// change. Every property change reported by systemd will be sent; that is, no
+// transitions will be "missed" (as they might be with SetSubStateSubscriber).
+// However, state changes will only be written to the channel with non-blocking
+// writes.  If updateCh is full, it attempts to write an error to errCh; if
+// errCh is full, the error passes silently.
+func (c *Conn) SetPropertiesSubscriber(updateCh chan<- *PropertiesUpdate, errCh chan<- error) {
+	c.propertiesSubscriber.Lock()
+	defer c.propertiesSubscriber.Unlock()
+	c.propertiesSubscriber.updateCh = updateCh
+	c.propertiesSubscriber.errCh = errCh
+}
+
+// we don't need to worry about shouldIgnore() here because
+// sendPropertiesUpdate doesn't call GetProperties()
+func (c *Conn) sendPropertiesUpdate(unitPath dbus.ObjectPath, changedProps map[string]dbus.Variant) {
+	c.propertiesSubscriber.Lock()
+	defer c.propertiesSubscriber.Unlock()
+
+	if c.propertiesSubscriber.updateCh == nil {
+		return
+	}
+
+	update := &PropertiesUpdate{unitName(unitPath), changedProps}
+
+	select {
+	case c.propertiesSubscriber.updateCh <- update:
+	default:
+		select {
+		case c.propertiesSubscriber.errCh <- errors.New("update channel is full"):
+		default:
+		}
+		return
+	}
+}

dbus/subscription_test.go

@@ -151,3 +151,59 @@ func TestSubStateSubscription(t *testing.T) {
 		}
 	}
 }
+
+// TestPropertiesSubscription exercises the basics of property change event subscriptions
+func TestPropertiesSubscription(t *testing.T) {
+	target := "subscribe-events.service"
+
+	conn, err := New()
+	defer conn.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = conn.Subscribe()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	updateCh := make(chan *PropertiesUpdate)
+	errCh := make(chan error)
+	conn.SetPropertiesSubscriber(updateCh, errCh)
+
+	setupUnit(target, conn, t)
+	linkUnit(target, conn, t)
+
+	reschan := make(chan string)
+	_, err = conn.StartUnit(target, "replace", reschan)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	job := <-reschan
+	if job != "done" {
+		t.Fatal("Couldn't start", target)
+	}
+
+	timeout := make(chan bool, 1)
+	go func() {
+		time.Sleep(3 * time.Second)
+		close(timeout)
+	}()
+
+	for {
+		select {
+		case update := <-updateCh:
+			if update.UnitName == target {
+				subState, ok := update.Changed["SubState"].Value().(string)
+				if ok && subState == "running" {
+					return // success
+				}
+			}
+		case err := <-errCh:
+			t.Fatal(err)
+		case <-timeout:
+			t.Fatal("Reached timeout")
+		}
+	}
+}