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>

cli.go

@@ -7,7 +7,10 @@ import (
 )
 
 var (
-	userName string
+	userName   string
+	dbusConfig string
+	dbusID     string
+	mpris      bool
 
 	mustWayland bool
 	mustX       bool
@@ -19,7 +22,10 @@ var (
 )
 
 func init() {
-	flag.StringVar(&userName, "u", "chronos", "Specify a username")
+	flag.StringVar(&userName, "u", "chronos", "Passwd name of user to run as")
+	flag.StringVar(&dbusConfig, "dbus-config", "builtin", "Path to D-Bus proxy config file, or \"builtin\" for defaults")
+	flag.StringVar(&dbusID, "dbus-id", "", "D-Bus ID of application, leave empty to disable own paths, has no effect if custom config is available")
+	flag.BoolVar(&mpris, "mpris", false, "Allow owning MPRIS D-Bus path, has no effect if custom config is available")
 
 	flag.BoolVar(&mustWayland, "wayland", false, "Share Wayland socket")
 	flag.BoolVar(&mustX, "X", false, "Share X11 socket and allow connection")

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
+	var binPath, address string
-	fmt.Println("warn: dbus proxy not implemented")
+	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)
+	}
 }

internal/app/run.go

@@ -166,6 +166,9 @@ func (a *App) commandBuilderMachineCtl() (args []string) {
 	if executable, err := os.Executable(); err != nil {
 		state.Fatal("Error reading executable path:", err)
 	} else {
+		if a.enablements.Has(state.EnableDBus) {
+			innerCommand.WriteString(dbusSessionBusAddress + "=" + "'" + dbusAddress + "' ")
+		}
 		innerCommand.WriteString("exec " + executable + " -V")
 	}
 	args = append(args, innerCommand.String())

internal/state/exit.go

@@ -65,4 +65,23 @@ func BeforeExit() {
 			fmt.Printf("Stripped ACL entry for user '%s' from '%s'\n", u.Username, candidate)
 		}
 	}
+
+	if dbusProxy != nil {
+		if system.V.Verbose {
+			fmt.Println("D-Bus proxy registered, cleaning up")
+		}
+
+		if err := dbusProxy.Close(); err != nil {
+			if errors.Is(err, os.ErrClosed) {
+				if system.V.Verbose {
+					fmt.Println("D-Bus proxy already closed")
+				}
+			} else {
+				fmt.Println("Error closing D-Bus proxy:", err)
+			}
+		}
+
+		// wait for Proxy.Wait to return
+		<-*dbusDone
+	}
 }

internal/state/register.go

@@ -1,9 +1,14 @@
 package state
 
+import "git.ophivana.moe/cat/fortify/dbus"
+
 var (
 	cleanupCandidate  []string
 	enablements       *Enablements
 	xcbActionComplete bool
+
+	dbusProxy *dbus.Proxy
+	dbusDone  *chan struct{}
 )
 
 func RegisterRevertPath(p string) {
@@ -23,3 +28,8 @@ func XcbActionComplete() {
 	}
 	xcbActionComplete = true
 }
+
+func RegisterDBus(p *dbus.Proxy, done *chan struct{}) {
+	dbusProxy = p
+	dbusDone = done
+}

main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"encoding/json"
 	"errors"
 	"flag"
 	"fmt"
@@ -9,6 +10,7 @@ import (
 	"strconv"
 	"syscall"
 
+	"git.ophivana.moe/cat/fortify/dbus"
 	"git.ophivana.moe/cat/fortify/internal/acl"
 	"git.ophivana.moe/cat/fortify/internal/app"
 	"git.ophivana.moe/cat/fortify/internal/state"
@@ -17,7 +19,9 @@ import (
 
 var (
 	Version = "impure"
-	a       *app.App
+
+	a *app.App
+	c *dbus.Config
 )
 
 func tryVersion() {
@@ -41,6 +45,21 @@ func main() {
 	a = app.New(userName, flag.Args())
 	state.Set(*a.User, a.Command(), a.UID())
 
+	// parse D-Bus config file if applicable
+	if mustDBus {
+		if dbusConfig == "builtin" {
+			c = dbus.NewConfig(dbusID, true, mpris)
+		} else {
+			if f, err := os.Open(dbusConfig); err != nil {
+				state.Fatal("Error opening D-Bus proxy config file:", err)
+			} else {
+				if err = json.NewDecoder(f).Decode(&c); err != nil {
+					state.Fatal("Error parsing D-Bus proxy config file:", err)
+				}
+			}
+		}
+	}
+
 	// ensure RunDir (e.g. `/run/user/%d/fortify`)
 	if err := os.Mkdir(system.V.RunDir, 0700); err != nil && !errors.Is(err, fs.ErrExist) {
 		state.Fatal("Error creating runtime directory:", err)
@@ -103,7 +122,7 @@ func main() {
 	}
 
 	if mustDBus {
-		a.ShareDBus()
+		a.ShareDBus(c)
 	}
 
 	if mustPulse {