sane-sandboxed: reduce forking (use out vars)

pkgs/additional/sane-sandboxed/sane-sandboxed

@@ -135,16 +135,16 @@ usage() {
 
 ## UTILITIES/BOILERPLATE
 
-# `relativeTo base-dir path`
+# `relativeToPwd out-var path`
 # if `path` is absolute, returns `path`
-# otherwise, joins `path` onto `base-dir`
-relativeTo() {
-  local base="$1"
+# otherwise, joins `path` onto `$PWD`
+relativeToPwd() {
+  local outvar="$1"
   local path="$2"
   if [ "${path:0:1}" == "/" ]; then
-    echo "$path"
+    declare -g "$outvar"="$path"
   else
-    echo "$base/$path"
+    declare -g "$outvar"="$PWD/path"
   fi
 }
 
@@ -252,6 +252,19 @@ contains() {
   return 1
 }
 
+# `derefOnce outvar path`: assume `path` is a symlink and set `outvar` to its target.
+# the result is always an absolute path (relative symlinks are transformed).
+derefOnce() {
+  local outVar="$1"
+  local source="$2"
+  local target="$(readlink "$source")"
+  # make absolute
+  if [ "${target:0:1}" != "/" ]; then
+    target="$(dirname "$source")/$target"
+  fi
+  declare -g "$outVar"="$target"
+}
+
 
 ## HELPERS
 
@@ -300,17 +313,19 @@ tryPath() {
   if [ "$how" = "existing" ]; then
     # the caller wants to access either a file, or a directory (possibly a symlink to such a thing)
     if [ -e "$path" ]; then
-      paths+=("$(relativeTo "$PWD" "$path")")
-      true
+      relativeToPwd _absPath "$path"
+      paths+=("$_absPath")
+      return 0
     fi
-    false
+    return 1
   elif [ "$how" = "existingFile" ]; then
     # the caller wants to access a file, and explicitly *not* a directory (though it could be a symlink *to a file*)
     if [ -f "$path" ]; then
-      paths+=("$(relativeTo "$PWD" "$path")")
-      true
+      relativeToPwd _absPath "$path"
+      paths+=("$_absPath")
+      return 0
     fi
-    false
+    return 1
   elif [ "$how" = "parent" ]; then
     # the caller wants access to the entire directory containing this directory regardless of the file's existence.
     parent _tryPathParent "$path"
@@ -456,7 +471,8 @@ parseArgs() {
       (--sane-sandbox-path)
         local path="$1"
         shift
-        paths+=("$(relativeTo "$PWD" "$path")")
+        relativeToPwd _absPath "$path"
+        paths+=("$_absPath")
         ;;
       (--sane-sandbox-add-pwd)
         paths+=("$PWD")
@@ -800,12 +816,10 @@ canonicalizePaths() {
 }
 expandLink() {
   if [ -L "$1" ]; then
-    local target="$(readlink "$1")"
-    # make absolute
-    target="$(relativeTo "$(dirname "$1")" "$target")"
+    derefOnce _linkTarget "$1"
     # add + expand the symlink further, but take care to avoid infinite recursion
-    normPath _canonTarget "$target"
-    if ! $(contains "$_canonTarget" "${paths[@]}"); then
+    normPath _canonTarget "$_linkTarget"
+    if ! contains "$_canonTarget" "${paths[@]}"; then
       paths+=("$_canonTarget")
       expandLink "$_canonTarget"
     fi
@@ -837,7 +851,7 @@ removeSubpaths() {
   # remove duplicated paths.
   local canonicalizedPaths=()
   for path in "${toplevelPaths[@]}"; do
-    if ! $(contains "$path" "${canonicalizedPaths[@]}"); then
+    if ! contains "$path" "${canonicalizedPaths[@]}"; then
       canonicalizedPaths+=("$path")
     fi
   done