// Copyright 2021 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "ash/quick_pair/common/fast_pair/fast_pair_decoder.h"
#include <optional>
#include <vector>
#include "base/containers/span.h"
#include "base/strings/string_number_conversions.h"
#include "base/types/fixed_array.h"
namespace {
constexpr int kMinModelIdLength = 3;
constexpr int kHeaderIndex = 0;
constexpr int kHeaderLengthBitmask = 0b00011110;
constexpr int kHeaderLengthOffset = 1;
constexpr int kHeaderVersionBitmask = 0b11100000;
constexpr int kHeaderVersionOffset = 5;
constexpr int kMaxModelIdLength = 14;
constexpr int kHeaderLength = 1;
} // namespace
namespace ash {
namespace quick_pair {
namespace fast_pair_decoder {
int GetVersion(const std::vector<uint8_t>* service_data) {
return service_data->size() == kMinModelIdLength
? 0
: ((*service_data)[kHeaderIndex] & kHeaderVersionBitmask) >>
kHeaderVersionOffset;
}
int GetIdLength(const std::vector<uint8_t>* service_data) {
return service_data->size() == kMinModelIdLength
? kMinModelIdLength
: ((*service_data)[kHeaderIndex] & kHeaderLengthBitmask) >>
kHeaderLengthOffset;
}
bool IsIdLengthValid(const std::vector<uint8_t>* service_data) {
int id_length = GetIdLength(service_data);
return kMinModelIdLength <= id_length && id_length <= kMaxModelIdLength &&
id_length + kHeaderLength <= static_cast<int>(service_data->size());
}
bool HasModelId(const std::vector<uint8_t>* service_data) {
return service_data != nullptr &&
(service_data->size() == kMinModelIdLength ||
// Header byte exists. We support only format version 0. (A different
// version indicates a breaking change in the format.)
(service_data->size() > kMinModelIdLength &&
GetVersion(service_data) == 0 && IsIdLengthValid(service_data)));
}
std::optional<std::string> GetHexModelIdFromServiceData(
const std::vector<uint8_t>* service_data) {
if (service_data == nullptr || service_data->size() < kMinModelIdLength) {
return std::nullopt;
}
if (service_data->size() == kMinModelIdLength) {
// If the size is 3, all the bytes are the ID,
return base::HexEncode(*service_data);
}
// Otherwise, the first byte is a header which contains the length of the
// big-endian model ID that follows. The model ID will be trimmed if it
// contains leading zeros.
int id_index = 1;
int end = id_index + GetIdLength(service_data);
// Ignore leading zeros.
while ((*service_data)[id_index] == 0 && end - id_index > kMinModelIdLength) {
id_index++;
}
// Copy appropriate bytes to new array.
int bytes_size = end - id_index;
base::FixedArray<uint8_t> bytes(bytes_size);
for (int i = 0; i < bytes_size; i++) {
bytes[i] = (*service_data)[i + id_index];
}
return base::HexEncode(base::span<uint8_t>(bytes));
}
} // namespace fast_pair_decoder
} // namespace quick_pair
} // namespace ash