  getBuf(const std::string& hex, size_t headroom = 0, size_t tailroom = 0) {
    auto data = unhexlify(hex);
    return IOBuf::copyBuffer(data.data(), data.size(), headroom, tailroom);
  }
  getBuf(const std::string& hex, size_t headroom = 0, size_t tailroom = 0) {
    auto data = unhexlify(hex);
    return IOBuf::copyBuffer(data.data(), data.size(), headroom, tailroom);
  }