app/dbus: manage dbus proxy and pass address to child

This commit adds code that starts and registers the D-Bus proxy, as well as cleanup code that tracks and closes the daemon once our child exits. A few more flags were added to pass D-Bus config to xdg-dbus-proxy.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

internal/app/dbus.go

@@ -1,14 +1,92 @@
 package app
 
 import (
+	"errors"
 	"fmt"
+	"os"
+	"path"
+	"strconv"
 
+	"git.ophivana.moe/cat/fortify/dbus"
+	"git.ophivana.moe/cat/fortify/internal/acl"
 	"git.ophivana.moe/cat/fortify/internal/state"
+	"git.ophivana.moe/cat/fortify/internal/system"
+	"git.ophivana.moe/cat/fortify/internal/util"
 )
 
-func (a *App) ShareDBus() {
+const dbusSessionBusAddress = "DBUS_SESSION_BUS_ADDRESS"
+
+var dbusAddress string
+
+func (a *App) ShareDBus(c *dbus.Config) {
 	a.setEnablement(state.EnableDBus)
 
-	// TODO: start xdg-dbus-proxy
-	fmt.Println("warn: dbus proxy not implemented")
+	var binPath, address string
+	target := path.Join(system.V.Share, strconv.Itoa(os.Getpid()))
+
+	if b, ok := util.Which("xdg-dbus-proxy"); !ok {
+		state.Fatal("D-Bus: Did not find 'xdg-dbus-proxy' in PATH")
+	} else {
+		binPath = b
+	}
+
+	if addr, ok := os.LookupEnv(dbusSessionBusAddress); !ok {
+		state.Fatal("D-Bus: DBUS_SESSION_BUS_ADDRESS not set")
+	} else {
+		address = addr
+	}
+
+	c.Log = system.V.Verbose
+	p := dbus.New(binPath, address, target)
+	if system.V.Verbose {
+		fmt.Println("D-Bus: sealing proxy", c.Args(address, target))
+	}
+	if err := p.Seal(c); err != nil {
+		state.Fatal("D-Bus: invalid config when sealing proxy,", err)
+	}
+
+	ready := make(chan bool, 1)
+	done := make(chan struct{})
+
+	if system.V.Verbose {
+		fmt.Printf("Starting session bus proxy '%s' for address '%s'\n", dbusAddress, address)
+	}
+	if err := p.Start(&ready); err != nil {
+		state.Fatal("D-Bus: error starting proxy,", err)
+	}
+	if system.V.Verbose {
+		fmt.Println("D-Bus proxy launch:", p)
+	}
+
+	go func() {
+		if err := p.Wait(); err != nil {
+			fmt.Println("warn: D-Bus proxy returned error,", err)
+		} else {
+			if system.V.Verbose {
+				fmt.Println("D-Bus proxy uneventful wait")
+			}
+		}
+		if err := os.Remove(target); err != nil && !errors.Is(err, os.ErrNotExist) {
+			fmt.Println("Error removing dangling D-Bus socket:", err)
+		}
+		done <- struct{}{}
+	}()
+
+	// register early to enable Fatal cleanup
+	state.RegisterDBus(p, &done)
+	dbusAddress = "unix:path=" + target
+
+	if !<-ready {
+		state.Fatal("D-Bus: proxy did not start correctly")
+	}
+
+	a.AppendEnv(dbusSessionBusAddress, dbusAddress)
+	if err := acl.UpdatePerm(target, a.UID(), acl.Read, acl.Write); err != nil {
+		state.Fatal(fmt.Sprintf("Error preparing D-Bus proxy '%s':", dbusAddress), err)
+	} else {
+		state.RegisterRevertPath(target)
+	}
+	if system.V.Verbose {
+		fmt.Printf("Session bus proxy '%s' for address '%s' configured\n", dbusAddress, address)
+	}
 }