app: clean up interactions and handle all application state and setup/teardown

There was an earlier attempt of cleaning up the app package however it ended up creating even more of a mess and the code structure largely still looked like Ego with state setup scattered everywhere and a bunch of ugly hacks had to be implemented to keep track of all of them. In this commit the entire app package is rewritten to track everything that has to do with an app in one thread safe value.

In anticipation of the client/server split also made changes:
- Console messages are cleaned up to be consistent
- State tracking is fully rewritten to be cleaner and usable for multiple process and client/server
- Encapsulate errors to easier identify type of action causing the error as well as additional info
- System-level setup operations is grouped in a way that can be collectively committed/reverted
  and gracefully handles errors returned by each operation
- Resource sharing is made more fine-grained with PID-scoped resources whenever possible,
  a few remnants (X11, Wayland, PulseAudio) will be addressed when a generic proxy is available
- Application setup takes a JSON-friendly config struct and deterministically generates system setup operations

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

main.go

@@ -5,10 +5,7 @@ import (
 	"errors"
 	"flag"
 	"fmt"
-	"io/fs"
 	"os"
-	"strconv"
-	"syscall"
 
 	"git.ophivana.moe/cat/fortify/dbus"
 	"git.ophivana.moe/cat/fortify/internal"
@@ -19,14 +16,6 @@ import (
 
 var (
 	Version = "impure"
-
-	a *app.App
-	s *internal.ExitState
-
-	dbusSession *dbus.Config
-	dbusSystem  *dbus.Config
-
-	launchOptionText string
 )
 
 func tryVersion() {
@@ -40,31 +29,133 @@ func main() {
 	flag.Parse()
 	verbose.Set(flagVerbose)
 
+	if internal.SdBootedV {
+		verbose.Println("system booted with systemd as init system")
+	}
+
 	// launcher payload early exit
-	app.Early(printVersion)
+	if printVersion && printLicense {
+		app.TryShim()
+	}
 
 	// version/license command early exit
 	tryVersion()
 	tryLicense()
 
-	a = app.New(userName, flag.Args(), launchOptionText)
-	s = internal.NewExit(a.User, a.UID(), func() (int, error) {
-		d, err := state.ReadLaunchers(a.RunDir(), a.Uid, false)
-		return len(d), err
-	})
-	a.SealExit(s)
-	internal.SealExit(s)
+	// state query command early exit
+	tryState()
 
-	// parse D-Bus config file if applicable
+	// prepare config
+	var config *app.Config
+
+	if confPath == "nil" {
+		// config from flags
+		config = configFromFlags()
+	} else {
+		// config from file
+		if f, err := os.Open(confPath); err != nil {
+			fatalf("cannot access config file '%s': %s\n", confPath, err)
+		} else {
+			if err = json.NewDecoder(f).Decode(&config); err != nil {
+				fatalf("cannot parse config file '%s': %s\n", confPath, err)
+			}
+		}
+	}
+
+	// invoke app
+	r := 1
+	a := app.New()
+	if err := a.Seal(config); err != nil {
+		logBaseError(err, "fortify: cannot seal app:")
+	} else if err = a.Start(); err != nil {
+		logBaseError(err, "fortify: cannot start app:")
+	} else if r, err = a.Wait(); err != nil {
+		r = 1
+
+		var e *app.BaseError
+		if !app.AsBaseError(err, &e) {
+			fmt.Println("fortify: wait failed:", err)
+		} else {
+			// Wait only returns either *app.ProcessError or *app.StateStoreError wrapped in a *app.BaseError
+			var se *app.StateStoreError
+			if !errors.As(err, &se) {
+				// does not need special handling
+				fmt.Print("fortify: " + e.Message())
+			} else {
+				// inner error are either unwrapped store errors
+				// or joined errors returned by *appSealTx revert
+				// wrapped in *app.BaseError
+				var ej app.RevertCompoundError
+				if !errors.As(se.InnerErr, &ej) {
+					// does not require special handling
+					fmt.Print("fortify: " + e.Message())
+				} else {
+					errs := ej.Unwrap()
+
+					// every error here is wrapped in *app.BaseError
+					for _, ei := range errs {
+						var eb *app.BaseError
+						if !errors.As(ei, &eb) {
+							// unreachable
+							fmt.Println("fortify: invalid error type returned by revert:", ei)
+						} else {
+							// print inner *app.BaseError message
+							fmt.Print("fortify: " + eb.Message())
+						}
+					}
+				}
+			}
+		}
+	}
+	if err := a.WaitErr(); err != nil {
+		fmt.Println("fortify: inner wait failed:", err)
+	}
+	os.Exit(r)
+}
+
+func logBaseError(err error, message string) {
+	var e *app.BaseError
+
+	if app.AsBaseError(err, &e) {
+		fmt.Print("fortify: " + e.Message())
+	} else {
+		fmt.Println(message, err)
+	}
+}
+
+func configFromFlags() (config *app.Config) {
+	// initialise config from flags
+	config = &app.Config{
+		ID:      dbusID,
+		User:    userName,
+		Command: flag.Args(),
+		Method:  launchMethodText,
+	}
+
+	// enablements from flags
+	if mustWayland {
+		config.Confinement.Enablements.Set(state.EnableWayland)
+	}
+	if mustX {
+		config.Confinement.Enablements.Set(state.EnableX)
+	}
+	if mustDBus {
+		config.Confinement.Enablements.Set(state.EnableDBus)
+	}
+	if mustPulse {
+		config.Confinement.Enablements.Set(state.EnablePulse)
+	}
+
+	// parse D-Bus config file from flags if applicable
 	if mustDBus {
 		if dbusConfigSession == "builtin" {
-			dbusSession = dbus.NewConfig(dbusID, true, mpris)
+			config.Confinement.SessionBus = dbus.NewConfig(dbusID, true, mpris)
 		} else {
 			if f, err := os.Open(dbusConfigSession); err != nil {
-				internal.Fatal("Error opening D-Bus proxy config file:", err)
+				fatalf("cannot access session bus proxy config file '%s': %s\n", dbusConfigSession, err)
 			} else {
-				if err = json.NewDecoder(f).Decode(&dbusSession); err != nil {
-					internal.Fatal("Error parsing D-Bus proxy config file:", err)
+				if err = json.NewDecoder(f).Decode(&config.Confinement.SessionBus); err != nil {
+					fatalf("cannot parse session bus proxy config file '%s': %s\n", dbusConfigSession, err)
 				}
 			}
 		}
@@ -72,62 +163,24 @@ func main() {
 		// system bus proxy is optional
 		if dbusConfigSystem != "nil" {
 			if f, err := os.Open(dbusConfigSystem); err != nil {
-				internal.Fatal("Error opening D-Bus proxy config file:", err)
+				fatalf("cannot access system bus proxy config file '%s': %s\n", dbusConfigSystem, err)
 			} else {
-				if err = json.NewDecoder(f).Decode(&dbusSystem); err != nil {
-					internal.Fatal("Error parsing D-Bus proxy config file:", err)
+				if err = json.NewDecoder(f).Decode(&config.Confinement.SystemBus); err != nil {
+					fatalf("cannot parse system bus proxy config file '%s': %s\n", dbusConfigSystem, err)
 				}
 			}
 		}
-	}
 
-	// ensure RunDir (e.g. `/run/user/%d/fortify`)
-	a.EnsureRunDir()
-
-	// state query command early exit
-	tryState()
-
-	// ensure Share (e.g. `/tmp/fortify.%d`)
-	a.EnsureShare()
-
-	// warn about target user home directory ownership
-	if stat, err := os.Stat(a.HomeDir); err != nil {
-		if verbose.Get() {
-			switch {
-			case errors.Is(err, fs.ErrPermission):
-				fmt.Printf("User %s home directory %s is not accessible\n", a.Username, a.HomeDir)
-			case errors.Is(err, fs.ErrNotExist):
-				fmt.Printf("User %s home directory %s does not exis\n", a.Username, a.HomeDir)
-			default:
-				fmt.Printf("Error stat user %s home directory %s: %s\n", a.Username, a.HomeDir, err)
-			}
-		}
-		return
-	} else {
-		// FreeBSD: not cross-platform
-		if u := strconv.Itoa(int(stat.Sys().(*syscall.Stat_t).Uid)); u != a.Uid {
-			fmt.Printf("User %s home directory %s has incorrect ownership (expected UID %s, found %s)", a.Username, a.HomeDir, a.Uid, u)
+		if dbusVerbose {
+			config.Confinement.SessionBus.Log = true
+			config.Confinement.SystemBus.Log = true
 		}
 	}
 
-	// ensure runtime directory ACL (e.g. `/run/user/%d`)
-	a.EnsureRuntime()
-
-	if mustWayland {
-		a.ShareWayland()
-	}
-
-	if mustX {
-		a.ShareX()
-	}
-
-	if mustDBus {
-		a.ShareDBus(dbusSession, dbusSystem, dbusVerbose)
-	}
-
-	if mustPulse {
-		a.SharePulse()
-	}
-
-	a.Run()
+	return
+}
+
+func fatalf(format string, a ...any) {
+	fmt.Printf("fortify: "+format, a...)
+	os.Exit(1)
 }