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ff43541927
Before this CL, when we encoded a sequence with a non-existent base, we pretended that the delta was 0, and the first delta was based on that. However, in a sequence where the deltas are small, but where the first element is big, that would produce unnecessarily wide deltas. Therefore, we change the behavior in cases where the base is non-existent, to encode the first existent value (if any) as a varint; the delta width may then be smaller. This CL include two piggy-backed changes: 1. Varint encoding/decoding moved to its own file (and an additional flavor added). 2. The unit tests for delta encoding are further parameterized with a random seed. Bug: webrtc:8111 Change-Id: I76fff577c86d019c8334bf74b76bd35db06ff68d Reviewed-on: https://webrtc-review.googlesource.com/c/107860 Reviewed-by: Björn Terelius <terelius@webrtc.org> Commit-Queue: Elad Alon <eladalon@webrtc.org> Cr-Commit-Position: refs/heads/master@{#25395}
110 lines
3.5 KiB
C++
110 lines
3.5 KiB
C++
/*
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* Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "logging/rtc_event_log/encoder/blob_encoding.h"
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#include <algorithm>
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#include "logging/rtc_event_log/encoder/varint.h"
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#include "rtc_base/logging.h"
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namespace webrtc {
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std::string EncodeBlobs(const std::vector<std::string>& blobs) {
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RTC_DCHECK(!blobs.empty());
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size_t result_length_bound = kMaxVarIntLengthBytes * blobs.size();
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for (const auto& blob : blobs) {
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// Providing an input so long that it would cause a wrap-around is an error.
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RTC_DCHECK_GE(result_length_bound + blob.length(), result_length_bound);
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result_length_bound += blob.length();
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}
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std::string result;
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result.reserve(result_length_bound);
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// First, encode all of the lengths.
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for (absl::string_view blob : blobs) {
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result += EncodeVarInt(blob.length());
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}
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// Second, encode the actual blobs.
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for (absl::string_view blob : blobs) {
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result.append(blob.data(), blob.length());
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}
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RTC_DCHECK_LE(result.size(), result_length_bound);
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return result;
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}
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std::vector<absl::string_view> DecodeBlobs(absl::string_view encoded_blobs,
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size_t num_of_blobs) {
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if (encoded_blobs.empty()) {
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RTC_LOG(LS_WARNING) << "Corrupt input; empty input.";
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return std::vector<absl::string_view>();
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}
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if (num_of_blobs == 0u) {
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RTC_LOG(LS_WARNING)
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<< "Corrupt input; number of blobs must be greater than 0.";
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return std::vector<absl::string_view>();
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}
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size_t read_idx = 0;
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// Read the lengths of all blobs.
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std::vector<uint64_t> lengths(num_of_blobs);
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for (size_t i = 0; i < num_of_blobs; ++i) {
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if (read_idx >= encoded_blobs.length()) {
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RTC_DCHECK_EQ(read_idx, encoded_blobs.length());
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RTC_LOG(LS_WARNING) << "Corrupt input; excessive number of blobs.";
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return std::vector<absl::string_view>();
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}
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const size_t read_bytes =
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DecodeVarInt(encoded_blobs.substr(read_idx), &lengths[i]);
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if (read_bytes == 0) {
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RTC_LOG(LS_WARNING) << "Corrupt input; varint decoding failed.";
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return std::vector<absl::string_view>();
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}
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read_idx += read_bytes;
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// Note: It might be that read_idx == encoded_blobs.length(), if this
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// is the last iteration, and all of the blobs are the empty string.
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RTC_DCHECK_LE(read_idx, encoded_blobs.length());
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}
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// Read the blobs themselves.
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std::vector<absl::string_view> blobs(num_of_blobs);
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for (size_t i = 0; i < num_of_blobs; ++i) {
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if (read_idx + lengths[i] < read_idx) { // Wrap-around detection.
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RTC_LOG(LS_WARNING) << "Corrupt input; unreasonably large blob sequence.";
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return std::vector<absl::string_view>();
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}
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if (read_idx + lengths[i] > encoded_blobs.length()) {
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RTC_LOG(LS_WARNING) << "Corrupt input; blob sizes exceed input size.";
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return std::vector<absl::string_view>();
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}
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blobs[i] = encoded_blobs.substr(read_idx, lengths[i]);
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read_idx += lengths[i];
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}
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if (read_idx != encoded_blobs.length()) {
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RTC_LOG(LS_WARNING) << "Corrupt input; unrecognized trailer.";
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return std::vector<absl::string_view>();
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}
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return blobs;
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}
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} // namespace webrtc
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