absl::string_view host_address, Envoy::Http::ResponseHeaderMap& headers) {

  const auto upstream_value_header = headers.get(factory_.name_);

  if (upstream_value_header.size() != 1) {

    ENVOY_LOG(trace, "Header {} not exist or occurs multiple times", factory_.name_);

    return false;

  }

  const bool host_changed =

      !upstream_address_.has_value() || host_address != upstream_address_.value();

  const std::string new_header =

      absl::StrCat(Envoy::Base64::encode(host_address), ";", OriginUpstreamValuePartFlag,

                   Envoy::Base64::encode(upstream_value_header[0]->value().getStringView()));

  headers.setReferenceKey(factory_.name_, new_header);

  return host_changed;

}

    : name_(config.header().name()) {}

EnvelopeSessionStateFactory::parseAddress(Envoy::Http::RequestHeaderMap& headers) const {

  const auto hdr = headers.get(name_);

  if (hdr.empty()) {

    return absl::nullopt;

  }

  const absl::InlinedVector<absl::string_view, 2> parts =

      absl::StrSplit(hdr[0]->value().getStringView(), ';', absl::SkipEmpty());

  if (parts.empty()) {

    return absl::nullopt;

  }

  std::string upstream_host = Base64::decode(parts[0]);

  absl::string_view upstream_value;

  const auto other_parts_view = absl::Span<const absl::string_view>(parts).subspan(1);

  for (absl::string_view part : other_parts_view) {

    if (absl::StartsWith(part, OriginUpstreamValuePartFlag)) {

      upstream_value = part.substr(OriginUpstreamValuePartFlag.size());

      break;

    }

  }

  const std::string decoded = Envoy::Base64::decode(upstream_value);

  if (decoded.empty()) {

    ENVOY_LOG(info, "Header {} contains invalid 'UV' part or there is no 'UV' part", name_);

    return absl::nullopt;

  }

  headers.setReferenceKey(name_, decoded);

  return !upstream_host.empty() ? absl::make_optional(std::move(upstream_host)) : absl::nullopt;

}