More work on porting the diff kitten

tools/utils/tar.go

@@ -0,0 +1,101 @@
+// License: GPLv3 Copyright: 2023, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package utils
+
+import (
+	"archive/tar"
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+var _ = fmt.Print
+
+type TarExtractOptions struct {
+	DontPreservePermissions bool
+}
+
+func ExtractAllFromTar(tr *tar.Reader, dest_path string, optss ...TarExtractOptions) (count int, err error) {
+	opts := TarExtractOptions{}
+	if len(optss) > 0 {
+		opts = optss[0]
+	}
+	dest_path, err = filepath.Abs(dest_path)
+	if err != nil {
+		return
+	}
+
+	mode := func(hdr *tar.Header) fs.FileMode {
+		return fs.FileMode(hdr.Mode) & (fs.ModePerm | fs.ModeSetgid | fs.ModeSetuid | fs.ModeSticky)
+	}
+
+	set_metadata := func(chmod func(mode fs.FileMode) error, hdr *tar.Header) (err error) {
+		if !opts.DontPreservePermissions && chmod != nil {
+			perms := mode(hdr)
+			if err = chmod(perms); err != nil {
+				return err
+			}
+		}
+		count++
+		return
+	}
+
+	for {
+		var hdr *tar.Header
+		hdr, err = tr.Next()
+		if errors.Is(err, io.EOF) {
+			break
+		}
+		if err != nil {
+			return count, err
+		}
+		dest := hdr.Name
+		dest = strings.TrimLeft(dest, "/")
+		if !filepath.IsLocal(dest) {
+			continue
+		}
+		dest = filepath.Join(dest_path, dest)
+		switch hdr.Typeflag {
+		case tar.TypeDir:
+			err = os.MkdirAll(dest, 0o700)
+			if err != nil {
+				return
+			}
+			if err = set_metadata(func(m fs.FileMode) error { return os.Chmod(dest, m) }, hdr); err != nil {
+				return
+			}
+		case tar.TypeReg, tar.TypeRegA:
+			var d *os.File
+			if d, err = os.Create(dest); err != nil {
+				return
+			}
+			err = set_metadata(d.Chmod, hdr)
+			if err == nil {
+				_, err = io.Copy(d, tr)
+			}
+			d.Close()
+			if err != nil {
+				return
+			}
+		case tar.TypeLink:
+			if err = os.Link(hdr.Linkname, dest); err != nil {
+				return
+			}
+			if err = set_metadata(func(m fs.FileMode) error { return os.Chmod(dest, m) }, hdr); err != nil {
+				return
+			}
+		case tar.TypeSymlink:
+			if err = os.Symlink(hdr.Linkname, dest); err != nil {
+				return
+			}
+			if err = set_metadata(nil, hdr); err != nil {
+				return
+			}
+		}
+	}
+	return
+}