hst: use hsu userid for share path suffix

The privileged user is identifier to hakurei through its hsu userid. Using the kernel uid here makes little sense and is a leftover design choice from before hsu was implemented.

Closes #7.

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

internal/sys/interface.go

@@ -22,9 +22,9 @@ type State interface {
 	LookupEnv(key string) (string, bool)
 	// TempDir provides [os.TempDir].
 	TempDir() string
-	// LookPath provides [exec.LookPath].
+	// LookPath provides exec.LookPath.
 	LookPath(file string) (string, error)
-	// MustExecutable provides [proc.MustExecutable].
+	// MustExecutable provides [container.MustExecutable].
 	MustExecutable() string
 	// LookupGroup provides [user.LookupGroup].
 	LookupGroup(name string) (*user.Group, error)
@@ -32,9 +32,9 @@ type State interface {
 	ReadDir(name string) ([]fs.DirEntry, error)
 	// Stat provides [os.Stat].
 	Stat(name string) (fs.FileInfo, error)
-	// Open provides [os.Open]
+	// Open provides [os.Open].
 	Open(name string) (fs.File, error)
-	// EvalSymlinks provides [filepath.EvalSymlinks]
+	// EvalSymlinks provides filepath.EvalSymlinks.
 	EvalSymlinks(path string) (string, error)
 	// Exit provides [os.Exit].
 	Exit(code int)
@@ -45,19 +45,28 @@ type State interface {
 	// Paths returns a populated [hst.Paths] struct.
 	Paths() hst.Paths
 	// Uid invokes hsu and returns target uid.
-	// Any errors returned by Uid is already wrapped [fmsg.BaseError].
-	Uid(aid int) (int, error)
+	// Any errors returned by Uid is already wrapped [hlog.BaseError].
+	Uid(identity int) (int, error)
+}
+
+// GetUserID obtains user id from hsu by querying uid of identity 0.
+func GetUserID(os State) (int, error) {
+	if uid, err := os.Uid(0); err != nil {
+		return -1, err
+	} else {
+		return (uid / 10000) - 100, nil
+	}
 }
 
 // CopyPaths is a generic implementation of [hst.Paths].
-func CopyPaths(os State, v *hst.Paths) {
+func CopyPaths(os State, v *hst.Paths, userid int) {
 	if tempDir, err := container.NewAbs(os.TempDir()); err != nil {
 		log.Fatalf("invalid TMPDIR: %v", err)
 	} else {
 		v.TempDir = tempDir
 	}
 
-	v.SharePath = v.TempDir.Append("hakurei." + strconv.Itoa(os.Getuid()))
+	v.SharePath = v.TempDir.Append("hakurei." + strconv.Itoa(userid))
 	hlog.Verbosef("process share directory at %q", v.SharePath)
 
 	r, _ := os.LookupEnv(xdgRuntimeDir)

internal/sys/std.go

@@ -49,11 +49,19 @@ func (s *Std) Printf(format string, v ...any)               { hlog.Verbosef(form
 const xdgRuntimeDir = "XDG_RUNTIME_DIR"
 
 func (s *Std) Paths() hst.Paths {
-	s.pathsOnce.Do(func() { CopyPaths(s, &s.paths) })
+	s.pathsOnce.Do(func() {
+		if userid, err := GetUserID(s); err != nil {
+			hlog.PrintBaseError(err, "cannot obtain user id from hsu:")
+			hlog.BeforeExit()
+			s.Exit(1)
+		} else {
+			CopyPaths(s, &s.paths, userid)
+		}
+	})
 	return s.paths
 }
 
-func (s *Std) Uid(aid int) (int, error) {
+func (s *Std) Uid(identity int) (int, error) {
 	s.uidOnce.Do(func() {
 		s.uidCopy = make(map[int]struct {
 			uid int
@@ -63,7 +71,7 @@ func (s *Std) Uid(aid int) (int, error) {
 
 	{
 		s.uidMu.RLock()
-		u, ok := s.uidCopy[aid]
+		u, ok := s.uidCopy[identity]
 		s.uidMu.RUnlock()
 		if ok {
 			return u.uid, u.err
@@ -77,7 +85,7 @@ func (s *Std) Uid(aid int) (int, error) {
 		uid int
 		err error
 	}{}
-	defer func() { s.uidCopy[aid] = u }()
+	defer func() { s.uidCopy[identity] = u }()
 
 	u.uid = -1
 	hsuPath := internal.MustHsuPath()
@@ -85,7 +93,7 @@ func (s *Std) Uid(aid int) (int, error) {
 	cmd := exec.Command(hsuPath)
 	cmd.Path = hsuPath
 	cmd.Stderr = os.Stderr // pass through fatal messages
-	cmd.Env = []string{"HAKUREI_APP_ID=" + strconv.Itoa(aid)}
+	cmd.Env = []string{"HAKUREI_APP_ID=" + strconv.Itoa(identity)}
 	cmd.Dir = container.FHSRoot
 	var (
 		p         []byte
@@ -95,7 +103,7 @@ func (s *Std) Uid(aid int) (int, error) {
 	if p, u.err = cmd.Output(); u.err == nil {
 		u.uid, u.err = strconv.Atoi(string(p))
 		if u.err != nil {
-			u.err = hlog.WrapErrSuffix(u.err, "cannot parse uid from hsu:")
+			u.err = hlog.WrapErr(u.err, "invalid uid string from hsu")
 		}
 	} else if errors.As(u.err, &exitError) && exitError != nil && exitError.ExitCode() == 1 {
 		u.err = hlog.WrapErr(syscall.EACCES, "") // hsu prints to stderr in this case