// Package safeio reads installation files without following symlinked path components.
package safeio

import (
	"errors"
	"io"
	"os"
	"path/filepath"
	"strings"
)

var ErrUnsafeFile = errors.New("unsafe file")

// ValidateCanonicalPath rejects relative or lexically non-canonical paths before they are opened.
func ValidateCanonicalPath(path string) error {
	if !filepath.IsAbs(path) || filepath.Clean(path) != path || strings.Contains(path, string(filepath.Separator)+".."+string(filepath.Separator)) {
		return ErrUnsafeFile
	}
	return nil
}

func readBoundedRegularFile(file *os.File, maximum int64) ([]byte, error) {
	if maximum < 0 || maximum == int64(^uint64(0)>>1) {
		return nil, ErrUnsafeFile
	}
	info, err := file.Stat()
	if err != nil || !info.Mode().IsRegular() {
		return nil, ErrUnsafeFile
	}
	contents, err := io.ReadAll(io.LimitReader(file, maximum+1))
	if err != nil || int64(len(contents)) > maximum {
		return nil, ErrUnsafeFile
	}
	return contents, nil
}