Method _read

src/files/files.cpp:620–713

Future<Try<tuple<size_t, string>, FilesError>> FilesProcess::_read(
    size_t offset,
    Option<size_t> length,
    const string& path)
{
  Result<string> resolvedPath = resolve(path);

  if (resolvedPath.isError()) {
    return FilesError(FilesError::Type::INVALID, resolvedPath.error() + ".\n");
  } else if (!resolvedPath.isSome()) {
    return FilesError(FilesError::Type::NOT_FOUND);
  }

  // Don't read directories.
  if (os::stat::isdir(resolvedPath.get())) {
    return FilesError(FilesError::Type::INVALID, "Cannot read a directory.\n");
  }

  // TODO(benh): Cache file descriptors so we aren't constantly
  // opening them and paging the data in from disk.
  Try<int_fd> fd = os::open(resolvedPath.get(), O_RDONLY | O_CLOEXEC);
  if (fd.isError()) {
    string error = strings::format(
        "Failed to open file at '%s': %s",
        resolvedPath.get(),
        fd.error()).get();
    LOG(WARNING) << error;
    return FilesError(FilesError::Type::UNKNOWN, error + ".\n");
  }

  Try<off_t> lseek = os::lseek(fd.get(), 0, SEEK_END);
  if (lseek.isError()) {
    string error = strings::format(
        "Failed to open file at '%s': %s",
        resolvedPath.get(),
        os::strerror(errno)).get();

    LOG(WARNING) << error;
    os::close(fd.get());
    return FilesError(FilesError::Type::UNKNOWN, error + ".\n");
  }

  const off_t size = lseek.get();

  if (offset >= static_cast<size_t>(size)) {
    os::close(fd.get());
    return std::make_tuple(size, "");
  }

  if (length.isNone()) {
    length = size - offset;
  }

  // Return the size of file if length is 0.
  if (length == 0) {
    os::close(fd.get());
    return std::make_tuple(size, "");
  }