system/dbus: use well-known address in spec

The session bus still performs non-standard formatting since it makes no sense for hakurei to start the session bus.

Signed-off-by: Ophestra <cat@gensokyo.uk>

system/dbus/dbus.go

@@ -8,8 +8,31 @@ import (
 )
 
 const (
+	/*SessionBusAddress is the name of the environment variable where the address of the login session message bus is given in.
+
+	If that variable is not set, applications may also try to read the address from the X Window System root window property _DBUS_SESSION_BUS_ADDRESS.
+	The root window property must have type STRING. The environment variable should have precedence over the root window property.
+
+	The address of the login session message bus is given in the DBUS_SESSION_BUS_ADDRESS environment variable.
+	If DBUS_SESSION_BUS_ADDRESS is not set, or if it's set to the string "autolaunch:",
+	the system should use platform-specific methods of locating a running D-Bus session server,
+	or starting one if a running instance cannot be found.
+	Note that this mechanism is not recommended for attempting to determine if a daemon is running.
+	It is inherently racy to attempt to make this determination, since the bus daemon may be started just before or just after the determination is made.
+	Therefore, it is recommended that applications do not try to make this determination for their functionality purposes, and instead they should attempt to start the server.
+
+	This package diverges from the specification, as the caller is unlikely to be an X client, or be in a position to autolaunch a dbus server.
+	So a fallback address with a socket located in the well-known default XDG_RUNTIME_DIR formatting is used.*/
 	SessionBusAddress = "DBUS_SESSION_BUS_ADDRESS"
+
+	/*SystemBusAddress is the name of the environment variable where the address of the system message bus is given in.
+
+	If that variable is not set, applications should try to connect to the well-known address unix:path=/var/run/dbus/system_bus_socket.
+	Implementations of the well-known system bus should listen on an address that will result in that connection being successful.*/
 	SystemBusAddress = "DBUS_SYSTEM_BUS_ADDRESS"
+
+	// FallbackSystemBusAddress is used when [SystemBusAddress] is not set.
+	FallbackSystemBusAddress = "unix:path=/var/run/dbus/system_bus_socket"
 )
 
 var (
@@ -30,7 +53,7 @@ func Address() (session, system string) {
 		// resolve upstream system bus address
 		if addr, ok := os.LookupEnv(SystemBusAddress); !ok {
 			// fall back to default hardcoded value
-			addresses[1] = "unix:path=/run/dbus/system_bus_socket"
+			addresses[1] = FallbackSystemBusAddress
 		} else {
 			addresses[1] = addr
 		}