system: move system access packages

These packages loosely belong in the "system" package and "system" provides high level wrappers for all of them.

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

system/dbus/dbus.go

@@ -0,0 +1,40 @@
+// Package dbus wraps xdg-dbus-proxy and implements configuration and sandboxing of the underlying helper process.
+package dbus
+
+import (
+	"fmt"
+	"os"
+	"sync"
+)
+
+const (
+	SessionBusAddress = "DBUS_SESSION_BUS_ADDRESS"
+	SystemBusAddress  = "DBUS_SYSTEM_BUS_ADDRESS"
+)
+
+var (
+	addresses   [2]string
+	addressOnce sync.Once
+)
+
+func Address() (session, system string) {
+	addressOnce.Do(func() {
+		// resolve upstream session bus address
+		if addr, ok := os.LookupEnv(SessionBusAddress); !ok {
+			// fall back to default format
+			addresses[0] = fmt.Sprintf("unix:path=/run/user/%d/bus", os.Getuid())
+		} else {
+			addresses[0] = addr
+		}
+
+		// 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"
+		} else {
+			addresses[1] = addr
+		}
+	})
+
+	return addresses[0], addresses[1]
+}