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The Tor Browser
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optional_blob_encoding.cc (3236B)

      1 /*
      2 *  Copyright (c) 2023 The WebRTC project authors. All Rights Reserved.
      3 *
      4 *  Use of this source code is governed by a BSD-style license
      5 *  that can be found in the LICENSE file in the root of the source
      6 *  tree. An additional intellectual property rights grant can be found
      7 *  in the file PATENTS.  All contributing project authors may
      8 *  be found in the AUTHORS file in the root of the source tree.
      9 */
     10 
     11 #include "logging/rtc_event_log/encoder/optional_blob_encoding.h"
     12 
     13 #include <cstddef>
     14 #include <cstdint>
     15 #include <optional>
     16 #include <string>
     17 #include <vector>
     18 
     19 #include "absl/strings/string_view.h"
     20 #include "rtc_base/bit_buffer.h"
     21 #include "rtc_base/bitstream_reader.h"
     22 #include "rtc_base/checks.h"
     23 
     24 namespace webrtc {
     25 
     26 std::string EncodeOptionalBlobs(
     27    const std::vector<std::optional<std::string>>& blobs) {
     28  if (blobs.empty()) {
     29    return {};
     30  }
     31 
     32  size_t reserve_size_bits = 1;
     33  size_t num_blobs_present = 0;
     34  for (const auto& blob : blobs) {
     35    if (blob.has_value()) {
     36      ++num_blobs_present;
     37      reserve_size_bits +=
     38          (BitBufferWriter::kMaxLeb128Length.bytes() + blob->size()) * 8;
     39    }
     40  }
     41 
     42  if (num_blobs_present == 0) {
     43    return {};
     44  }
     45 
     46  const bool all_blobs_present = num_blobs_present == blobs.size();
     47  if (!all_blobs_present) {
     48    reserve_size_bits += blobs.size();
     49  }
     50 
     51  std::vector<uint8_t> buffer((reserve_size_bits + 7) / 8);
     52  BitBufferWriter writer(buffer.data(), buffer.size());
     53 
     54  // Write present bits if all blobs are not present.
     55  writer.WriteBits(all_blobs_present, 1);
     56  if (!all_blobs_present) {
     57    for (const auto& blob : blobs) {
     58      writer.WriteBits(blob.has_value(), 1);
     59    }
     60  }
     61 
     62  // Byte align the writer.
     63  writer.ConsumeBits(writer.RemainingBitCount() % 8);
     64 
     65  // Write blobs.
     66  for (const auto& blob : blobs) {
     67    if (blob.has_value()) {
     68      writer.WriteLeb128(blob->length());
     69      writer.WriteString(*blob);
     70    }
     71  }
     72 
     73  size_t bytes_written;
     74  size_t bits_written;
     75  writer.GetCurrentOffset(&bytes_written, &bits_written);
     76  RTC_CHECK_EQ(bits_written, 0);
     77  RTC_CHECK_LE(bytes_written, buffer.size());
     78 
     79  return std::string(buffer.data(), buffer.data() + bytes_written);
     80 }
     81 
     82 std::vector<std::optional<std::string>> DecodeOptionalBlobs(
     83    absl::string_view encoded_blobs,
     84    size_t num_of_blobs) {
     85  std::vector<std::optional<std::string>> res(num_of_blobs);
     86  if (encoded_blobs.empty() || num_of_blobs == 0) {
     87    return res;
     88  }
     89 
     90  BitstreamReader reader(encoded_blobs);
     91  const bool all_blobs_present = reader.ReadBit();
     92 
     93  // Read present bits if all blobs are not present.
     94  std::vector<uint8_t> present;
     95  if (!all_blobs_present) {
     96    present.resize(num_of_blobs);
     97    for (size_t i = 0; i < num_of_blobs; ++i) {
     98      present[i] = reader.ReadBit();
     99    }
    100  }
    101 
    102  // Byte align the reader.
    103  reader.ConsumeBits(reader.RemainingBitCount() % 8);
    104 
    105  // Read the blobs.
    106  for (size_t i = 0; i < num_of_blobs; ++i) {
    107    if (!all_blobs_present && !present[i]) {
    108      continue;
    109    }
    110    res[i] = reader.ReadString(reader.ReadLeb128());
    111  }
    112 
    113  // The result is only valid if exactly all bits was consumed during decoding.
    114  if (!reader.Ok() || reader.RemainingBitCount() > 0) {
    115    return {};
    116  }
    117 
    118  return res;
    119 }
    120 
    121 }  // namespace webrtc