func Unpack()

in pkg/archive/archive.go [660:788]
88 lines of code
33 McCabe index (conditional complexity)

func Unpack(decompressedArchive io.Reader, dest string, options *TarOptions) error {
	tr := tar.NewReader(decompressedArchive)
	trBuf := pools.BufioReader32KPool.Get(nil)
	defer pools.BufioReader32KPool.Put(trBuf)

	var dirs []*tar.Header
	remappedRootUID, remappedRootGID, err := idtools.GetRootUIDGID(options.UIDMaps, options.GIDMaps)
	if err != nil {
		return err
	}

	// Iterate through the files in the archive.
loop:
	for {
		hdr, err := tr.Next()
		if err == io.EOF {
			// end of tar archive
			break
		}
		if err != nil {
			return err
		}

		// Normalize name, for safety and for a simple is-root check
		// This keeps "../" as-is, but normalizes "/../" to "/". Or Windows:
		// This keeps "..\" as-is, but normalizes "\..\" to "\".
		hdr.Name = filepath.Clean(hdr.Name)

		for _, exclude := range options.ExcludePatterns {
			if strings.HasPrefix(hdr.Name, exclude) {
				continue loop
			}
		}

		// After calling filepath.Clean(hdr.Name) above, hdr.Name will now be in
		// the filepath format for the OS on which the daemon is running. Hence
		// the check for a slash-suffix MUST be done in an OS-agnostic way.
		if !strings.HasSuffix(hdr.Name, string(os.PathSeparator)) {
			// Not the root directory, ensure that the parent directory exists
			parent := filepath.Dir(hdr.Name)
			parentPath := filepath.Join(dest, parent)
			if _, err := os.Lstat(parentPath); err != nil && os.IsNotExist(err) {
				err = idtools.MkdirAllNewAs(parentPath, 0777, remappedRootUID, remappedRootGID)
				if err != nil {
					return err
				}
			}
		}

		path := filepath.Join(dest, hdr.Name)
		rel, err := filepath.Rel(dest, path)
		if err != nil {
			return err
		}
		if strings.HasPrefix(rel, ".."+string(os.PathSeparator)) {
			return breakoutError(fmt.Errorf("%q is outside of %q", hdr.Name, dest))
		}

		// If path exits we almost always just want to remove and replace it
		// The only exception is when it is a directory *and* the file from
		// the layer is also a directory. Then we want to merge them (i.e.
		// just apply the metadata from the layer).
		if fi, err := os.Lstat(path); err == nil {
			if options.NoOverwriteDirNonDir && fi.IsDir() && hdr.Typeflag != tar.TypeDir {
				// If NoOverwriteDirNonDir is true then we cannot replace
				// an existing directory with a non-directory from the archive.
				return fmt.Errorf("cannot overwrite directory %q with non-directory %q", path, dest)
			}

			if options.NoOverwriteDirNonDir && !fi.IsDir() && hdr.Typeflag == tar.TypeDir {
				// If NoOverwriteDirNonDir is true then we cannot replace
				// an existing non-directory with a directory from the archive.
				return fmt.Errorf("cannot overwrite non-directory %q with directory %q", path, dest)
			}

			if fi.IsDir() && hdr.Name == "." {
				continue
			}

			if !(fi.IsDir() && hdr.Typeflag == tar.TypeDir) {
				if err := os.RemoveAll(path); err != nil {
					return err
				}
			}
		}
		trBuf.Reset(tr)

		// if the options contain a uid & gid maps, convert header uid/gid
		// entries using the maps such that lchown sets the proper mapped
		// uid/gid after writing the file. We only perform this mapping if
		// the file isn't already owned by the remapped root UID or GID, as
		// that specific uid/gid has no mapping from container -> host, and
		// those files already have the proper ownership for inside the
		// container.
		if hdr.Uid != remappedRootUID {
			xUID, err := idtools.ToHost(hdr.Uid, options.UIDMaps)
			if err != nil {
				return err
			}
			hdr.Uid = xUID
		}
		if hdr.Gid != remappedRootGID {
			xGID, err := idtools.ToHost(hdr.Gid, options.GIDMaps)
			if err != nil {
				return err
			}
			hdr.Gid = xGID
		}

		if err := createTarFile(path, dest, hdr, trBuf, !options.NoLchown, options.ChownOpts); err != nil {
			return err
		}

		// Directory mtimes must be handled at the end to avoid further
		// file creation in them to modify the directory mtime
		if hdr.Typeflag == tar.TypeDir {
			dirs = append(dirs, hdr)
		}
	}

	for _, hdr := range dirs {
		path := filepath.Join(dest, hdr.Name)

		if err := system.Chtimes(path, hdr.AccessTime, hdr.ModTime); err != nil {
			return err
		}
	}
	return nil
}