stepwriter: Add OS that replicates the current logic

installer/stepwriter/os.go

@@ -0,0 +1,168 @@
+// SPDX-FileCopyrightText: Fabio Forni <development@redaril.me>
+// SPDX-License-Identifier: MPL-2.0
+
+package stepwriter
+
+import (
+	"errors"
+	"fmt"
+	"io/fs"
+	"os"
+	"os/exec"
+	"path/filepath"
+
+	"github.com/livingsilver94/backee/installer"
+	"github.com/livingsilver94/backee/privilege"
+	"github.com/livingsilver94/backee/service"
+)
+
+func init() {
+	privilege.RegisterInterfaceImpl(symlinkWriter{})
+	privilege.RegisterInterfaceImpl(fileCopyWriter{})
+	privilege.RegisterInterfaceImpl(privilegedPathWriter{})
+}
+
+type OS struct{}
+
+func (OS) Setup(script string) error {
+	return runScript(script)
+}
+
+func (OS) InstallPackages(fullCmd []string) error {
+	return runProcess(fullCmd[0], fullCmd[1:]...)
+}
+
+func (OS) SymlinkFile(dst service.FilePath, src string) error {
+	return writePossiblyPrivilegedPath(dst, &symlinkWriter{SrcPath: src})
+}
+
+func (OS) CopyFile(dst service.FilePath, src installer.FileCopy) error {
+	return writePossiblyPrivilegedPath(dst, &fileCopyWriter{})
+}
+
+func (OS) Finalize(script string) error {
+	return runScript(script)
+}
+
+type fileWriter interface {
+	writeFile(dst string) error
+}
+
+func writePath(dst service.FilePath, wr fileWriter) error {
+	err := os.MkdirAll(filepath.Dir(dst.Path), 0755)
+	if err != nil {
+		return err
+	}
+	err = wr.writeFile(dst.Path)
+	if err != nil {
+		return err
+	}
+	if dst.Mode != 0 {
+		return os.Chmod(dst.Path, fs.FileMode(dst.Mode))
+	}
+	return nil
+}
+
+func writePathPrivileged(dst service.FilePath, wr fileWriter) error {
+	var r privilege.Runner = privilegedPathWriter{Dst: dst, Wr: wr}
+	return privilege.Run(r)
+}
+
+func writePossiblyPrivilegedPath(dst service.FilePath, wr fileWriter) error {
+	err := writePath(dst, wr)
+	if err != nil {
+		if !errors.Is(err, fs.ErrPermission) {
+			return err
+		}
+		err = writePathPrivileged(dst, wr)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+type symlinkWriter struct {
+	SrcPath string
+}
+
+func (w symlinkWriter) writeFile(dst string) error {
+	err := os.Symlink(w.SrcPath, dst)
+	if err != nil {
+		if !errors.Is(err, fs.ErrExist) {
+			return err
+		}
+		eq, errEq := w.isSymlinkEqual(dst)
+		if errEq != nil {
+			return errEq
+		}
+		if !eq {
+			return err
+		}
+	}
+	return nil
+}
+
+func (w *symlinkWriter) isSymlinkEqual(dst string) (bool, error) {
+	eq, err := filepath.EvalSymlinks(dst)
+	if err != nil {
+		return false, err
+	}
+	return eq == w.SrcPath, nil
+}
+
+type fileCopyWriter struct {
+	FileCopy installer.FileCopy
+}
+
+func (w fileCopyWriter) writeFile(dst string) error {
+	file, err := os.Create(dst)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+	_, err = w.FileCopy.WriteTo(file)
+	return err
+}
+
+type privilegedPathWriter struct {
+	Dst service.FilePath
+	Wr  fileWriter
+}
+
+func (p privilegedPathWriter) RunPrivileged() error {
+	return writePath(p.Dst, p.Wr)
+}
+
+func runProcess(name string, arg ...string) error {
+	cmd := exec.Command(name, arg...)
+	cmd.Stdout = nil
+	cmd.Stderr = os.Stderr
+	return cmd.Run()
+}
+
+type UnixID struct {
+	UID uint32
+	GID uint32
+}
+
+func PathOwner(path string) (UnixID, error) {
+	return PathOwnerFS(os.DirFS(path), ".")
+}
+
+func parentPathOwner(path string) (UnixID, error) {
+	for {
+		if len(path) == 1 {
+			return UnixID{}, fmt.Errorf("parent directory of %s: %w", path, fs.ErrNotExist)
+		}
+		id, err := PathOwner(path)
+		if err != nil {
+			if !errors.Is(err, fs.ErrNotExist) {
+				return UnixID{}, err
+			}
+			path = filepath.Dir(path)
+			continue
+		}
+		return id, nil
+	}
+}

installer/stepwriter/os_unix.go

@@ -0,0 +1,46 @@
+//go:build unix
+
+// SPDX-FileCopyrightText: Fabio Forni <development@redaril.me>
+// SPDX-License-Identifier: MPL-2.0
+
+package stepwriter
+
+import (
+	"fmt"
+	"io/fs"
+	"syscall"
+)
+
+func runScript(script string) error {
+	return runProcess(
+		"sh",
+		"-e", // Stop script on first error.
+		"-c", // Run the following script string.
+		script,
+	)
+}
+
+func PathOwnerFS(sys fs.FS, path string) (UnixID, error) {
+	info, err := fs.Stat(sys, path)
+	if err != nil {
+		return UnixID{}, err
+	}
+	stat := info.Sys().(*syscall.Stat_t)
+	return UnixID{UID: stat.Uid, GID: stat.Gid}, nil
+}
+
+func RunAsUnixID(f func() error, id UnixID) error {
+	oldUID := syscall.Geteuid()
+	oldGID := syscall.Getegid()
+	err := syscall.Setegid(int(id.GID))
+	if err != nil {
+		return fmt.Errorf("setting GID %d: %w", id.GID, err)
+	}
+	defer syscall.Setegid(oldGID)
+	err = syscall.Seteuid(int(id.UID))
+	if err != nil {
+		return fmt.Errorf("setting UID %d: %w", id.UID, err)
+	}
+	defer syscall.Seteuid(oldUID)
+	return f()
+}

installer/stepwriter/os_unix_test.go

@@ -0,0 +1,40 @@
+//go:build unix
+
+// SPDX-FileCopyrightText: Fabio Forni <development@redaril.me>
+// SPDX-License-Identifier: MPL-2.0
+
+package stepwriter_test
+
+import (
+	"syscall"
+	"testing"
+	"testing/fstest"
+
+	"github.com/livingsilver94/backee/installer/stepwriter"
+)
+
+func TestUnixIDsFS(t *testing.T) {
+	const expUID = 123
+	const expGID = 456
+	fs := fstest.MapFS{
+		"file.txt": &fstest.MapFile{Sys: &syscall.Stat_t{Uid: expUID, Gid: expGID}},
+	}
+
+	id, err := stepwriter.PathOwnerFS(fs, "file.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if id.UID != expUID || id.GID != expGID {
+		t.Fatalf("expected UID %d and GID %d. Got %d and %d", expUID, expGID, id.UID, id.GID)
+	}
+}
+
+func TestRunAs(t *testing.T) {
+	f := func() error { return nil }
+	uid := syscall.Getuid()
+	gid := syscall.Getgid()
+	err := stepwriter.RunAsUnixID(f, stepwriter.UnixID{UID: uint32(uid), GID: uint32(gid)})
+	if err != nil {
+		t.Fatal(err)
+	}
+}

installer/stepwriter/os_windows.go

@@ -0,0 +1,27 @@
+//go:build windows
+
+// SPDX-FileCopyrightText: Fabio Forni <development@redaril.me>
+// SPDX-License-Identifier: MPL-2.0
+
+package stepwriter
+
+import (
+	"io/fs"
+)
+
+func runScript(script string) error {
+	return runProcess(
+		"powershell",
+		"-NoLogo",  // Hide copyright banner.
+		"-Command", // Run the following script string.
+		script,
+	)
+}
+
+func PathOwnerFS(sys fs.FS, path string) (UnixID, error) {
+	return UnixID{}, nil
+}
+
+func RunAsUnixID(f func() error, id UnixID) error {
+	return f()
+}