Method resolve

src/files/files.cpp:836–901

Result<string> FilesProcess::resolve(const string& path)
{
  // Suppose we have: /1/2/hello_world.txt
  // And we attach: /1/2 as /sandbox
  // Then this function would resolve the following virtual path
  // into the actual path:
  // input: /sandbox/hello_world.txt
  // output: /1/2/hello_world.txt
  //
  // Try and see if this path has been attached. We check for the
  // longest possible prefix match and if found append any suffix to
  // the attached path (provided the path is to a directory).
  vector<string> tokens = strings::split(
      strings::remove(path, stringify(os::PATH_SEPARATOR), strings::SUFFIX),
      stringify(os::PATH_SEPARATOR));

  string suffix;
  while (!tokens.empty()) {
    string prefix = path::join(tokens);

    if (!paths.contains(prefix)) {
      if (suffix.empty()) {
        suffix = tokens.back();
      } else {
        suffix = path::join(tokens.back(), suffix);
      }

      tokens.pop_back();
      continue;
    }

    // Determine the final path: if it's a directory, append the
    // suffix, if it's not a directory and there is a suffix, return
    // 'Not Found'.
    string path = paths[prefix];
    if (os::stat::isdir(path)) {
      path = path::join(path, suffix, os::PATH_SEPARATOR);

      // Canonicalize the absolute path.
      Result<string> realpath = os::realpath(path);
      if (realpath.isError()) {
        return Error(
            "Failed to determine canonical path of '" + path +
            "': " + realpath.error());
      } else if (realpath.isNone()) {
        return None();
      }

      // Make sure the canonicalized absolute path is accessible
      // (i.e., not outside the "chroot").
      if (!strings::startsWith(realpath.get(), paths[prefix])) {
        return Error("'" + path + "' is inaccessible");
      }

      path = realpath.get();
    } else if (suffix != "") {
      // Request is assuming attached path is a directory, but it is
      // not! Rather than 'Bad Request', treat this as 'Not Found'.