internal: remove sys package

This package is replaced by container/stub. Remove and replace it with unexported implementation for the upcoming test suite rewrite.

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

internal/app/hsu.go

@@ -0,0 +1,96 @@
+package app
+
+import (
+	"errors"
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"strconv"
+	"sync"
+
+	"hakurei.app/container"
+	"hakurei.app/hst"
+	"hakurei.app/internal/hlog"
+)
+
+// Hsu caches responses from cmd/hsu.
+type Hsu struct {
+	idOnce sync.Once
+	idErr  error
+	id     int
+
+	kOnce sync.Once
+	k     syscallDispatcher
+}
+
+var ErrHsuAccess = errors.New("current user is not in the hsurc file")
+
+// ensureDispatcher ensures Hsu.k is not nil.
+func (h *Hsu) ensureDispatcher() {
+	h.kOnce.Do(func() {
+		if h.k == nil {
+			h.k = direct{}
+		}
+	})
+}
+
+// ID returns the current user hsurc identifier. ErrHsuAccess is returned if the current user is not in hsurc.
+func (h *Hsu) ID() (int, error) {
+	h.ensureDispatcher()
+	h.idOnce.Do(func() {
+		h.id = -1
+		hsuPath := h.k.mustHsuPath()
+
+		cmd := exec.Command(hsuPath)
+		cmd.Path = hsuPath
+		cmd.Stderr = os.Stderr // pass through fatal messages
+		cmd.Env = make([]string, 0)
+		cmd.Dir = container.FHSRoot
+		var (
+			p         []byte
+			exitError *exec.ExitError
+		)
+
+		const step = "obtain uid from hsu"
+		if p, h.idErr = h.k.cmdOutput(cmd); h.idErr == nil {
+			h.id, h.idErr = strconv.Atoi(string(p))
+			if h.idErr != nil {
+				h.idErr = &hst.AppError{Step: step, Err: h.idErr, Msg: "invalid uid string from hsu"}
+			}
+		} else if errors.As(h.idErr, &exitError) && exitError != nil && exitError.ExitCode() == 1 {
+			// hsu prints an error message in this case
+			h.idErr = &hst.AppError{Step: step, Err: ErrHsuAccess}
+		} else if os.IsNotExist(h.idErr) {
+			h.idErr = &hst.AppError{Step: step, Err: os.ErrNotExist,
+				Msg: fmt.Sprintf("the setuid helper is missing: %s", hsuPath)}
+		}
+	})
+
+	return h.id, h.idErr
+}
+
+// MustID calls [Hsu.ID] and terminates on error.
+func (h *Hsu) MustID() int {
+	id, err := h.ID()
+	if err == nil {
+		return id
+	}
+
+	const fallback = "cannot retrieve user id from setuid wrapper:"
+	if errors.Is(err, ErrHsuAccess) {
+		hlog.Verbose("*"+fallback, err)
+		os.Exit(1)
+		return -0xdeadbeef
+	} else if m, ok := container.GetErrorMessage(err); ok {
+		log.Fatal(m)
+		return -0xdeadbeef
+	} else {
+		log.Fatalln(fallback, err)
+		return -0xdeadbeef
+	}
+}
+
+// HsuUid returns target uid for the stable hsu uid format.
+// No bounds check is performed, a value retrieved from hsu is expected.
+func HsuUid(id, identity int) int { return 1000000 + id*10000 + identity }