nearby/sharing/advertisement.cc

// Copyright 2022 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "sharing/advertisement.h"

#include <stdint.h>

#include <memory>
#include <optional>
#include <string>
#include <utility>
#include <vector>

#include "absl/types/span.h"
#include "sharing/common/nearby_share_enums.h"
#include "sharing/internal/public/logging.h"

namespace nearby {
namespace sharing {
namespace {

// v1 advertisements:
//   - ParseVersion() --> 0
//
// v2 advertisements:
//   - ParseVersion() --> 1
//   - Backwards compatible; no changes in advertisement data--aside from the
//     version number--or parsing logic compared to v1.
//   - Only used by GmsCore at the moment.
constexpr int kMaxSupportedAdvertisementParsedVersionNumber = 1;

// The bit mask for parsing and writing Version.
constexpr uint8_t kVersionBitmask = 0b111;

// The bit mask for parsing and writing Visibility.
constexpr uint8_t kVisibilityBitmask = 0b1;

// The bit mask for parsing and writing Device Type.
constexpr uint8_t kDeviceTypeBitmask = 0b111;

const uint8_t kMinimumSize =
    /* Version(3 bits)|Visibility(1 bit)|Device Type(3 bits)|Reserved(1 bits)=
     */
    1 + sharing::Advertisement::kSaltSize +
    sharing::Advertisement::kMetadataEncryptionKeyHashByteSize;

uint8_t ConvertVersion(int version) {
  return static_cast<uint8_t>((version & kVersionBitmask) << 5);
}

uint8_t ConvertDeviceType(ShareTargetType type) {
  return static_cast<uint8_t>((static_cast<int32_t>(type) & kDeviceTypeBitmask)
                              << 1);
}

uint8_t ConvertHasDeviceName(bool hasDeviceName) {
  return static_cast<uint8_t>((hasDeviceName ? 0 : 1) << 4);
}

int ParseVersion(uint8_t b) { return (b >> 5) & kVersionBitmask; }

bool IsKnownDeviceValue(int32_t value) {
  switch (value) {
    case 0:
    case 1:
    case 2:
    case 3:
      return true;
    default:
      return false;
  }
}

ShareTargetType ParseDeviceType(uint8_t b) {
  int32_t intermediate = static_cast<int32_t>(b >> 1 & kDeviceTypeBitmask);
  if (IsKnownDeviceValue(intermediate)) {
    return static_cast<ShareTargetType>(intermediate);
  }

  return ShareTargetType::kUnknown;
}

bool ParseHasDeviceName(uint8_t b) {
  return ((b >> 4) & kVisibilityBitmask) == 0;
}

}  // namespace

// static
std::unique_ptr<Advertisement> Advertisement::NewInstance(
    std::vector<uint8_t> salt, std::vector<uint8_t> encrypted_metadata_key,
    ShareTargetType device_type, std::optional<std::string> device_name) {
  if (salt.size() != Advertisement::kSaltSize) {
    NL_LOG(ERROR) << "Failed to create advertisement because the salt did "
                     "not match the expected length "
                  << salt.size();
    return nullptr;
  }

  if (encrypted_metadata_key.size() !=
      Advertisement::kMetadataEncryptionKeyHashByteSize) {
    NL_LOG(ERROR) << "Failed to create advertisement because the encrypted "
                     "metadata key did "
                     "not match the expected length "
                  << encrypted_metadata_key.size();
    return nullptr;
  }

  if (device_name.has_value() && device_name->size() > UINT8_MAX) {
    NL_LOG(ERROR) << "Failed to create advertisement because device name "
                     "was over UINT8_MAX: "
                  << device_name->size();
    return nullptr;
  }

  // Using `new` to access a non-public constructor.
  return std::make_unique<Advertisement>(
      /* version= */ 0, std::move(salt), std::move(encrypted_metadata_key),
      device_type, std::move(device_name));
}

std::vector<uint8_t> Advertisement::ToEndpointInfo() {
  int size = kMinimumSize + (device_name_.has_value() ? 1 : 0) +
             (device_name_.has_value() ? device_name_->size() : 0);

  std::vector<uint8_t> endpoint_info;
  endpoint_info.reserve(size);
  endpoint_info.push_back(
      static_cast<uint8_t>(ConvertVersion(version_) |
                           ConvertHasDeviceName(device_name_.has_value()) |
                           ConvertDeviceType(device_type_)));
  endpoint_info.insert(endpoint_info.end(), salt_.begin(), salt_.end());
  endpoint_info.insert(endpoint_info.end(), encrypted_metadata_key_.begin(),
                       encrypted_metadata_key_.end());

  if (device_name_.has_value()) {
    endpoint_info.push_back(static_cast<uint8_t>(device_name_->size() & 0xff));
    endpoint_info.insert(endpoint_info.end(), device_name_->begin(),
                         device_name_->end());
  }

  return endpoint_info;
}

std::unique_ptr<Advertisement> Advertisement::FromEndpointInfo(
    absl::Span<const uint8_t> endpoint_info) {
  if (endpoint_info.size() < kMinimumSize) {
    NL_LOG(ERROR) << "Failed to parse advertisement because it was too short.";
    return nullptr;
  }

  auto iter = endpoint_info.begin();
  uint8_t first_byte = *iter++;

  int version = ParseVersion(first_byte);
  if (version < 0 || version > kMaxSupportedAdvertisementParsedVersionNumber) {
    NL_LOG(ERROR)
        << "Failed to parse advertisement; unsupported version number "
        << version;
    return nullptr;
  }

  bool has_device_name = ParseHasDeviceName(first_byte);
  ShareTargetType device_type = ParseDeviceType(first_byte);

  std::vector<uint8_t> salt(iter, iter + Advertisement::kSaltSize);
  iter += Advertisement::kSaltSize;

  std::vector<uint8_t> encrypted_metadata_key(
      iter, iter + Advertisement::kMetadataEncryptionKeyHashByteSize);
  iter += Advertisement::kMetadataEncryptionKeyHashByteSize;

  int device_name_length = 0;
  if (iter != endpoint_info.end()) device_name_length = *iter++ & 0xff;

  if (endpoint_info.end() - iter < device_name_length ||
      (device_name_length == 0 && has_device_name)) {
    NL_LOG(ERROR)
        << "Failed to parse advertisement because the device name did "
           "not match the expected length "
        << device_name_length;
    return nullptr;
  }

  std::optional<std::string> optional_device_name;
  if (device_name_length > 0) {
    optional_device_name = std::string(iter, iter + device_name_length);
    iter += device_name_length;
  }

  return Advertisement::NewInstance(
      std::move(salt), std::move(encrypted_metadata_key), device_type,
      std::move(optional_device_name));
}

// private
Advertisement::Advertisement(int version, std::vector<uint8_t> salt,
                             std::vector<uint8_t> encrypted_metadata_key,
                             ShareTargetType device_type,
                             std::optional<std::string> device_name)
    : version_(version),
      salt_(std::move(salt)),
      encrypted_metadata_key_(std::move(encrypted_metadata_key)),
      device_type_(device_type),
      device_name_(std::move(device_name)) {}

}  // namespace sharing
}  // namespace nearby