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package safepath
import (
"os"
"path/filepath"
"github.com/pkg/errors"
)
// evaluatePath evaluates symlinks in the concatenation of path and subpath. If
// err is nil, resolvedBasePath will contain result of resolving all symlinks
// in the given path, and resolvedSubpath will contain a relative path rooted
// at the resolvedBasePath pointing to the concatenation after resolving all
// symlinks.
func evaluatePath(path, subpath string) (resolvedBasePath string, resolvedSubpath string, err error) {
baseResolved, err := filepath.EvalSymlinks(path)
if err != nil {
if errors.Is(err, os.ErrNotExist) {
return "", "", &ErrNotAccessible{Path: path, Cause: err}
}
return "", "", errors.Wrapf(err, "error while resolving symlinks in base directory %q", path)
}
combinedPath := filepath.Join(baseResolved, subpath)
combinedResolved, err := filepath.EvalSymlinks(combinedPath)
if err != nil {
if errors.Is(err, os.ErrNotExist) {
return "", "", &ErrNotAccessible{Path: combinedPath, Cause: err}
}
return "", "", errors.Wrapf(err, "error while resolving symlinks in combined path %q", combinedPath)
}
subpart, err := filepath.Rel(baseResolved, combinedResolved)
if err != nil {
return "", "", &ErrEscapesBase{Base: baseResolved, Subpath: subpath}
}
if !filepath.IsLocal(subpart) {
return "", "", &ErrEscapesBase{Base: baseResolved, Subpath: subpath}
}
return baseResolved, subpart, nil
}
// isLocalTo reports whether path, using lexical analysis only, has all of these properties:
// - is within the subtree rooted at basepath
// - is not empty
// - on Windows, is not a reserved name such as "NUL"
//
// If isLocalTo(path, basepath) returns true, then
//
// filepath.Rel(basepath, path)
//
// will always produce an unrooted path with no `..` elements.
//
// isLocalTo is a purely lexical operation. In particular, it does not account for the effect of any symbolic links that may exist in the filesystem.
//
// Both path and basepath are expected to be absolute paths.
func isLocalTo(path, basepath string) bool {
rel, err := filepath.Rel(basepath, path)
if err != nil {
return false
}
return filepath.IsLocal(rel)
}
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