dbus: handle bizarre dbus proxy behaviour

There is a strange behaviour in xdg-dbus-proxy where if any interface string when stripped of a single ".*" suffix does not contain a '.' byte anywhere, the program will exit with code 1 without any output. This checks for such conditions to make the failure less confusing.

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

dbus/proxy.go

@@ -2,6 +2,7 @@ package dbus
 
 import (
 	"context"
+	"fmt"
 	"io"
 	"os/exec"
 	"sync"
@@ -14,6 +15,15 @@ import (
 // Overriding ProxyName will only affect Proxy instance created after the change.
 var ProxyName = "xdg-dbus-proxy"
 
+type BadInterfaceError struct {
+	Interface string
+	Segment   string
+}
+
+func (e *BadInterfaceError) Error() string {
+	return fmt.Sprintf("bad interface string %q in %s bus configuration", e.Interface, e.Segment)
+}
+
 // Proxy holds the state of a xdg-dbus-proxy process, and should never be copied.
 type Proxy struct {
 	helper helper.Helper
@@ -66,9 +76,15 @@ func Finalise(sessionBus, systemBus ProxyPair, session, system *Config) (final *
 
 	var args []string
 	if session != nil {
+		if err = session.checkInterfaces("session"); err != nil {
+			return
+		}
 		args = append(args, session.Args(sessionBus)...)
 	}
 	if system != nil {
+		if err = system.checkInterfaces("system"); err != nil {
+			return
+		}
 		args = append(args, system.Args(systemBus)...)
 	}