mirror of
https://github.com/kidfromjupiter/nearby.git
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105 lines
3.6 KiB
C++
105 lines
3.6 KiB
C++
// Copyright 2022 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "fastpair/dataparser/fast_pair_decoder.h"
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#include <algorithm>
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#include <array>
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#include <iterator>
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#include <optional>
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#include <string>
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#include <vector>
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#include "absl/strings/escaping.h"
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namespace nearby {
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namespace fastpair {
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namespace {
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constexpr int kHeaderIndex = 0;
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constexpr int kHeaderLength = 1;
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constexpr int kHeaderLengthBitmask = 0b00011110;
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constexpr int kHeaderLengthOffset = 1;
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constexpr int kHeaderVersionBitmask = 0b11100000;
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constexpr int kHeaderVersionOffset = 5;
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constexpr int kMinModelIdLength = 3;
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constexpr int kMaxModelIdLength = 14;
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} // namespace
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int FastPairDecoder::GetIdLength(const std::vector<uint8_t>* service_data) {
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return service_data->size() == kMinModelIdLength
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? kMinModelIdLength
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: ((*service_data)[kHeaderIndex] & kHeaderLengthBitmask) >>
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kHeaderLengthOffset;
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}
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int FastPairDecoder::GetVersion(const std::vector<uint8_t>* service_data) {
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return service_data->size() == kMinModelIdLength
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? 0
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: ((*service_data)[kHeaderIndex] & kHeaderVersionBitmask) >>
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kHeaderVersionOffset;
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}
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bool IsIdLengthValid(const std::vector<uint8_t>* service_data) {
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int id_length = FastPairDecoder::GetIdLength(service_data);
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return kMinModelIdLength <= id_length && id_length <= kMaxModelIdLength &&
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id_length + kHeaderLength <= static_cast<int>(service_data->size());
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}
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bool FastPairDecoder::HasModelId(const std::vector<uint8_t>* service_data) {
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return service_data != nullptr &&
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(service_data->size() == kMinModelIdLength ||
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// Header byte exists. We support only format version 0. (A different
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// version indicates a breaking change in the format.)
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(service_data->size() > kMinModelIdLength &&
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GetVersion(service_data) == 0 && IsIdLengthValid(service_data)));
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}
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std::optional<std::string> FastPairDecoder::GetHexModelIdFromServiceData(
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const std::vector<uint8_t>* service_data) {
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if (service_data == nullptr || service_data->size() < kMinModelIdLength) {
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return std::nullopt;
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}
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if (service_data->size() == kMinModelIdLength) {
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// If the size is 3, all the bytes are the ID,
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std::vector<uint8_t> bytes = *service_data;
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std::string model_id(bytes.begin(), bytes.end());
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return absl::BytesToHexString(model_id);
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}
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// Otherwise, the first byte is a header which contains the length of the
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// big-endian model ID that follows. The model ID will be trimmed if it
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// contains leading zeros.
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int id_index = 1;
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int end = id_index + GetIdLength(service_data);
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// Ignore leading zeros.
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while ((*service_data)[id_index] == 0 && end - id_index > kMinModelIdLength) {
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id_index++;
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}
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// Copy appropriate bytes to new array.
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int bytes_size = end - id_index;
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std::vector<uint8_t> bytes;
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bytes.reserve(bytes_size);
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for (int i = 0; i < bytes_size; i++) {
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bytes.push_back((*service_data)[i + id_index]);
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}
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std::string model_id(bytes.begin(), bytes.end());
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return absl::BytesToHexString(model_id);
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}
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} // namespace fastpair
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} // namespace nearby
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