symlink

Documentation

Overview

Package symlink provides symlink-related util functions for container extraction.

Index

• func RemoveObsoleteSymlinks(root string) error
• func ResolveInterLayerSymlinks(root, layerDigest, squashedImageDirectory string) error
• func TargetOutsideRoot(path, target string) bool

Functions

func RemoveObsoleteSymlinks

func RemoveObsoleteSymlinks(root string) error

RemoveObsoleteSymlinks removes symlinks that point to a destination file or directory path that does not exist. Note: There are three terms used in this function: symlink, target link, and destination file.

symlink: Refers to the symlink file itself.
target link: The link stored in a symlink file that points to another file (or symlink).
destination file: The last file pointed to by a symlink. That is, if there is a chain of
  symlinks, the destination file is the file pointed to by the last symlink.

Example: In this file system, the symlink, sym3, points to a destination file that doesn't exist

       (b.txt). This function would remove the sym3.txt file.
root
  dir1
    a.txt
    sym1.txt -> ../dir2/sym2.txt
  dir2
    sym2.txt -> ../dir1/a.txt
    sym3.txt -> ../dir1/b.txt (would be removed since b.txt does not exist)

func ResolveInterLayerSymlinks

func ResolveInterLayerSymlinks(root, layerDigest, squashedImageDirectory string) error

ResolveInterLayerSymlinks resolves absolute and relative symlinks in a layer sub-directory with a given layer digest by redirecting the symlink target path to point to the SQUASHED layer's symlink target path if it exists.

The structure of the layered directory before resolving symlinks is as follows:

root
  layer1digest
    dir1
      sample.txt
  layer2digest
    dir2
      relative-symlink.txt -> ../sample.txt    (notice how ../sample.txt wouldn't be found due to the layering approach)
      absolute-symlink.txt -> /dir1/sample.txt (the /dir1/sample.txt target file also wouldn't be found)
  SQUASHED
    dir1
      sample.txt
    dir2
      relative-symlink.txt -> /root/SQUASHED/dir1/sample.txt
      absolute-symlink.txt -> /root/SQUASHED/dir1/sample.txt

After resolving the layer with layer digest of "layer2digest", the file system is as follows:

root
  layer1digest
    dir1
      sample.txt
  layer2digest
    dir2
      relative-symlink.txt -> /root/SQUASHED/dir2/relative-symlink.txt
      absolute-symlink.txt -> /root/SQUASHED/dir2/relative-symlink.txt
  SQUASHED
    dir1
      sample.txt
    dir2
      relative-symlink.txt -> /root/SQUASHED/dir1/sample.txt
      absolute-symlink.txt -> /root/SQUASHED/dir1/sample.txt

func TargetOutsideRoot

func TargetOutsideRoot(path, target string) bool

TargetOutsideRoot checks if the target of a symlink points outside of the root directory of that symlink's path. For example, if a symlink with path `a/symlink.txt“ points to “../../file.text“, then this function would return true because the target file is outside of the root directory.