feat(agent): arbitrary dbus commands via MQTT (thanks @jaynis!)

docs/mqtt.md

@@ -55,6 +55,29 @@ There is a significant discrepancy in permissions between the device running Go
 
 Go Hass Agent runs under a user account on a device. So the above controls will only work where that user has permissions to run the underlying actions on that device. Home Assistant does not currently offer any fine-grained access control for controls like the above. So any Home Assistant user will be able to run any of the controls. This means that a Home Assistant user not associated with the device user running the agent can use the exposed controls to issue potentially disruptive actions on a device that another user is accessing.
 
+## Arbitrary D-BUS commands
+
+The agent subscribes to the MQTT topic `gohassagent/dbus` on the configured MQTT broker and listens for
+JSON messages of the below format, which will be accordingly dispatched to the systems
+[d-bus](https://www.freedesktop.org/wiki/Software/dbus/).
+
+```json
+{
+  "bus": "session",
+  "path": "/org/cinnamon/ScreenSaver",
+  "method": "org.cinnamon.ScreenSaver.Lock",
+  "destination": "org.cinnamon.ScreenSaver",
+  "args": [
+    ""
+  ]
+}
+```
+
+This can be used to trigger arbitrary d-bus commands on the system where the agent runs on,
+by using any MQTT client such as Home Assistants
+[`mqtt.publish`](https://www.home-assistant.io/integrations/mqtt/#service-mqttpublish) service.
+
+
 ## Implementation Details
 
 ### Linux

internal/agent/mqtt_dbus.go

@@ -0,0 +1,64 @@
+// Copyright (c) 2024 Joshua Rich <[email protected]>
+//
+// This software is released under the MIT License.
+// https://opensource.org/licenses/MIT
+
+package agent
+
+import (
+	"context"
+	"encoding/json"
+
+	"github.com/godbus/dbus/v5"
+	"github.com/rs/zerolog/log"
+
+	"github.com/joshuar/go-hass-agent/pkg/linux/dbusx"
+
+	mqttapi "github.com/joshuar/go-hass-anything/v5/pkg/mqtt"
+
+	MQTT "github.com/eclipse/paho.mqtt.golang"
+)
+
+const (
+	dbus_mqtt_topic = "gohassagent/dbus"
+)
+
+type DbusMessage struct {
+	Bus            string          `json:"bus"`
+	Destination    string          `json:"destination"`
+	Path           dbus.ObjectPath `json:"path"`
+	UseSessionPath bool            `json:"useSessionPath"`
+	Method         string          `json:"method"`
+	Args           []any           `json:"args"`
+}
+
+func newDbusSubscription(ctx context.Context) *mqttapi.Subscription {
+	return &mqttapi.Subscription{
+		Callback: func(c MQTT.Client, m MQTT.Message) {
+			var dbusMsg DbusMessage
+
+			if err := json.Unmarshal(m.Payload(), &dbusMsg); err != nil {
+				log.Warn().Err(err).Msg("could not unmarshal dbus MQTT message")
+				return
+			}
+
+			if dbusMsg.UseSessionPath {
+				dbusMsg.Path = dbusx.GetSessionPath(ctx)
+			}
+
+			dbusType, ok := dbusx.DbusTypeMap[dbusMsg.Bus]
+			if !ok {
+				log.Warn().Msg("unsupported dbus type")
+				return
+			}
+
+			log.Info().Str("bus", dbusMsg.Bus).Str("destination", dbusMsg.Destination).Str("path", string(dbusMsg.Path)).Str("method", dbusMsg.Method).Msg("dispatching dbus MQTT message")
+
+			dbusx.NewBusRequest(ctx, dbusType).
+				Path(dbus.ObjectPath(dbusMsg.Path)).
+				Destination(dbusMsg.Destination).
+				Call(dbusMsg.Method, dbusMsg.Args...)
+		},
+		Topic: dbus_mqtt_topic,
+	}
+}

internal/agent/runners.go

@@ -197,8 +197,13 @@ func runMQTTWorker(ctx context.Context) {
 		}
 	}
 	if err := mqtthass.Subscribe(o, c); err != nil {
-		log.Error().Err(err).Msg("Could not activate subscriptions.")
+		log.Error().Err(err).Msg("Could not activate entity subscriptions.")
 	}
+
+	if err := c.Subscribe(newDbusSubscription(ctx)); err != nil {
+		log.Error().Err(err).Msg("Could not activate dbus subscription.")
+	}
+
 	log.Debug().Msg("Listening for events on MQTT.")
 
 	<-ctx.Done()

pkg/linux/dbusx/dbus.go

@@ -23,6 +23,11 @@ const (
 
 var ErrNoBus = errors.New("no D-Bus connection")
 
+var DbusTypeMap = map[string]dbusType{
+	"session": 0,
+	"system": 1,
+}
+
 type dbusType int
 
 type Bus struct {