DataParser advertisement for Model Id

PiperOrigin-RevId: 501643615
2026-09-16 15:36:12 -04:00 · 2023-01-12 13:00:10 -08:00
parent 7667420e2b
commit bde4a780c6
7 changed files with 526 additions and 0 deletions
@@ -0,0 +1,105 @@
+// 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 "fastpair/dataparser/fast_pair_decoder.h"
+
+#include <algorithm>
+#include <array>
+#include <iterator>
+#include <string>
+#include <vector>
+
+#include "absl/strings/escaping.h"
+
+namespace nearby {
+namespace fastpair {
+
+namespace {
+
+constexpr int kHeaderIndex = 0;
+constexpr int kHeaderLength = 1;
+constexpr int kHeaderLengthBitmask = 0b00011110;
+constexpr int kHeaderLengthOffset = 1;
+constexpr int kHeaderVersionBitmask = 0b11100000;
+constexpr int kHeaderVersionOffset = 5;
+constexpr int kMinModelIdLength = 3;
+constexpr int kMaxModelIdLength = 14;
+
+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());
+}
+
+int GetVersion(const std::vector<uint8_t>* service_data) {
+  return service_data->size() == kMinModelIdLength
+             ? 0
+             : ((*service_data)[kHeaderIndex] & kHeaderVersionBitmask) >>
+                   kHeaderVersionOffset;
+}
+
+}  // namespace
+
+bool FastPairDecoder::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)));
+}
+
+absl::optional<std::string> FastPairDecoder::GetHexModelIdFromServiceData(
+    const std::vector<uint8_t>* service_data) {
+  if (service_data == nullptr || service_data->size() < kMinModelIdLength) {
+    return absl::nullopt;
+  }
+
+  if (service_data->size() == kMinModelIdLength) {
+    // If the size is 3, all the bytes are the ID,
+    std::vector<uint8_t> bytes = *service_data;
+    std::string model_id(bytes.begin(), bytes.end());
+    return absl::BytesToHexString(model_id);
+  }
+  // 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;
+  std::vector<uint8_t> bytes;
+  bytes.reserve(bytes_size);
+  for (int i = 0; i < bytes_size; i++) {
+    bytes.push_back((*service_data)[i + id_index]);
+  }
+  std::string model_id(bytes.begin(), bytes.end());
+  return absl::BytesToHexString(model_id);
+}
+
+}  // namespace fastpair
+}  // namespace nearby