+# given link target, and the directory (basedir) the link is in,
+# return target of link relative to top directory (top tree);
+# return undef if it is not possible (including absolute links).
+sub normalize_link_target {
+ my ($link_target, $basedir, $hash_base) = @_;
+
+ # we can normalize symlink target only if $hash_base is provided
+ return unless $hash_base;
+
+ # absolute symlinks (beginning with '/') cannot be normalized
+ return if (substr($link_target, 0, 1) eq '/');
+
+ # normalize link target to path from top (root) tree (dir)
+ my $path;
+ if ($basedir) {
+ $path = $basedir . '/' . $link_target;
+ } else {
+ # we are in top (root) tree (dir)
+ $path = $link_target;
+ }
+
+ # remove //, /./, and /../
+ my @path_parts;
+ foreach my $part (split('/', $path)) {
+ # discard '.' and ''
+ next if (!$part || $part eq '.');
+ # handle '..'
+ if ($part eq '..') {
+ if (@path_parts) {
+ pop @path_parts;
+ } else {
+ # link leads outside repository (outside top dir)
+ return;
+ }
+ } else {
+ push @path_parts, $part;
+ }
+ }
+ $path = join('/', @path_parts);
+
+ return $path;
+}