p2p/base/stun_dictionary.cc - src - Git at Google

 /*
  *  Copyright 2020 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */

 #include "p2p/base/stun_dictionary.h"

 #include <algorithm>
 #include <deque>
 #include <utility>

 #include "rtc_base/logging.h"

 namespace cricket {

 namespace {

 StunAttributeValueType GetStunAttributeValueType(int value_type) {
   switch (value_type) {
     case STUN_VALUE_ADDRESS:
       return STUN_VALUE_ADDRESS;
     case STUN_VALUE_XOR_ADDRESS:
       return STUN_VALUE_XOR_ADDRESS;
     case STUN_VALUE_UINT32:
       return STUN_VALUE_UINT32;
     case STUN_VALUE_UINT64:
       return STUN_VALUE_UINT64;
     case STUN_VALUE_BYTE_STRING:
       return STUN_VALUE_BYTE_STRING;
     case STUN_VALUE_ERROR_CODE:
       return STUN_VALUE_ERROR_CODE;
     case STUN_VALUE_UINT16_LIST:
       return STUN_VALUE_UINT16_LIST;
     default:
       return STUN_VALUE_UNKNOWN;
   }
 }

 }  // namespace

 const StunAddressAttribute* StunDictionaryView::GetAddress(int key) const {
   const StunAttribute* attr = GetOrNull(key, STUN_VALUE_ADDRESS);
   if (attr == nullptr) {
     return nullptr;
   }
   return reinterpret_cast<const StunAddressAttribute*>(attr);
 }

 const StunUInt32Attribute* StunDictionaryView::GetUInt32(int key) const {
   const StunAttribute* attr = GetOrNull(key, STUN_VALUE_UINT32);
   if (attr == nullptr) {
     return nullptr;
   }
   return reinterpret_cast<const StunUInt32Attribute*>(attr);
 }

 const StunUInt64Attribute* StunDictionaryView::GetUInt64(int key) const {
   const StunAttribute* attr = GetOrNull(key, STUN_VALUE_UINT64);
   if (attr == nullptr) {
     return nullptr;
   }
   return reinterpret_cast<const StunUInt64Attribute*>(attr);
 }

 const StunByteStringAttribute* StunDictionaryView::GetByteString(
     int key) const {
   const StunAttribute* attr = GetOrNull(key, STUN_VALUE_BYTE_STRING);
   if (attr == nullptr) {
     return nullptr;
   }
   return reinterpret_cast<const StunByteStringAttribute*>(attr);
 }

 const StunUInt16ListAttribute* StunDictionaryView::GetUInt16List(
     int key) const {
   const StunAttribute* attr = GetOrNull(key, STUN_VALUE_UINT16_LIST);
   if (attr == nullptr) {
     return nullptr;
   }
   return reinterpret_cast<const StunUInt16ListAttribute*>(attr);
 }

 const StunAttribute* StunDictionaryView::GetOrNull(
     int key,
     std::optional<StunAttributeValueType> type) const {
   const auto it = attrs_.find(key);
   if (it == attrs_.end()) {
     return nullptr;
   }

   if (type && it->second->value_type() != *type) {
     RTC_LOG(LS_WARNING) << "Get key: " << key << " with type: " << *type
                         << " found different type: "
                         << it->second->value_type();
     return nullptr;
   }
   return (*it).second.get();
 }

 webrtc::RTCErrorOr<
     std::pair<uint64_t, std::deque<std::unique_ptr<StunAttribute>>>>
 StunDictionaryView::ParseDelta(const StunByteStringAttribute& delta) {
   rtc::ByteBufferReader buf(delta.array_view());
   uint16_t magic;
   if (!buf.ReadUInt16(&magic)) {
     return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
                             "Failed to read magic number");
   }
   if (magic != kDeltaMagic) {
     return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
                             "Invalid magic number");
   }

   uint16_t delta_version;
   if (!buf.ReadUInt16(&delta_version)) {
     return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
                             "Failed to read version");
   }

   if (delta_version != kDeltaVersion) {
     return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
                             "Unsupported delta version");
   }

   // Now read all the attributes
   std::deque<std::unique_ptr<StunAttribute>> attrs;
   while (buf.Length()) {
     uint16_t key, length, value_type;
     if (!buf.ReadUInt16(&key)) {
       return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
                               "Failed to read attribute key");
     }
     if (!buf.ReadUInt16(&length)) {
       return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
                               "Failed to read attribute length");
     }
     if (!buf.ReadUInt16(&value_type)) {
       return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
                               "Failed to read value type");
     }

     StunAttributeValueType value_type_enum =
         GetStunAttributeValueType(value_type);
     std::unique_ptr<StunAttribute> attr(
         StunAttribute::Create(value_type_enum, key, length, nullptr));
     if (!attr) {
       return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
                               "Failed to create attribute");
     }
     if (attr->length() != length) {
       return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
                               "Inconsistent attribute length");
     }
     if (!attr->Read(&buf)) {
       return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
                               "Failed to read attribute content");
     }
     attrs.push_back(std::move(attr));
   }

   // The first attribute should be the version...
   if (attrs.empty()) {
     return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
                             "Empty delta!");
   }

   if (attrs[0]->type() != kVersionKey ||
       attrs[0]->value_type() != STUN_VALUE_UINT64) {
     return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
                             "Missing version!");
   }

   uint64_t version_in_delta =
       reinterpret_cast<const StunUInt64Attribute*>(attrs[0].get())->value();
   attrs.pop_front();

   return std::make_pair(std::max(version_in_delta, version_in_delta),
                         std::move(attrs));
 }

 // Apply a delta return an StunUInt64Attribute to ack the update.
 webrtc::RTCErrorOr<
     std::pair<std::unique_ptr<StunUInt64Attribute>, std::vector<uint16_t>>>
 StunDictionaryView::ApplyDelta(const StunByteStringAttribute& delta) {
   auto parsed_delta = ParseDelta(delta);
   if (!parsed_delta.ok()) {
     return webrtc::RTCError(parsed_delta.error());
   }

   uint64_t version_in_delta = parsed_delta.value().first;

   // Check that update does not overflow max_bytes_stored_.
   int new_bytes_stored = bytes_stored_;
   for (auto& attr : parsed_delta.value().second) {
     auto old_version = version_per_key_.find(attr->type());
     if (old_version == version_per_key_.end() ||
         version_in_delta > old_version->second) {
       size_t new_length = attr->length();
       size_t old_length = GetLength(attr->type());
       if (old_version == version_per_key_.end()) {
         new_length += sizeof(int64_t);
       }

       new_bytes_stored = new_bytes_stored + new_length - old_length;
       if (new_bytes_stored <= 0) {
         RTC_LOG(LS_WARNING)
             << "attr: " << attr->type() << " old_length: " << old_length
             << " new_length: " << new_length
             << " bytes_stored_: " << bytes_stored_
             << " new_bytes_stored: " << new_bytes_stored;
         return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER);
       }
       if (new_bytes_stored > max_bytes_stored_) {
         RTC_LOG(LS_INFO) << "attr: " << attr->type()
                          << " old_length: " << old_length
                          << " new_length: " << new_length
                          << " bytes_stored_: " << bytes_stored_
                          << " new_bytes_stored: " << new_bytes_stored;
       }
     }
   }
   if (new_bytes_stored > max_bytes_stored_) {
     RTC_LOG(LS_INFO) << " bytes_stored_: " << bytes_stored_
                      << " new_bytes_stored: " << new_bytes_stored;
     return webrtc::RTCError(webrtc::RTCErrorType::RESOURCE_EXHAUSTED);
   }

   // Apply the update.
   std::vector<uint16_t> keys;
   for (auto& attr : parsed_delta.value().second) {
     if (version_in_delta > version_per_key_[attr->type()]) {
       version_per_key_[attr->type()] = version_in_delta;
       keys.push_back(attr->type());
       if (attr->value_type() == STUN_VALUE_BYTE_STRING && attr->length() == 0) {
         attrs_.erase(attr->type());
       } else {
         int attribute_type = attr->type();
         attrs_[attribute_type] = std::move(attr);
       }
     }
   }
   bytes_stored_ = new_bytes_stored;

   return std::make_pair(std::make_unique<StunUInt64Attribute>(
                             STUN_ATTR_GOOG_DELTA_ACK, version_in_delta),
                         std::move(keys));
 }

 size_t StunDictionaryView::GetLength(int key) const {
   auto attr = GetOrNull(key);
   if (attr != nullptr) {
     return attr->length();
   }
   return 0;
 }

 void StunDictionaryWriter::Disable() {
   disabled_ = true;
 }

 void StunDictionaryWriter::Delete(int key) {
   if (disabled_) {
     return;
   }

   if (dictionary_) {
     if (dictionary_->attrs_.find(key) == dictionary_->attrs_.end()) {
       return;
     }
   }

   // remove any pending updates.
   pending_.erase(
       std::remove_if(pending_.begin(), pending_.end(),
                      [key](const auto& p) { return p.second->type() == key; }),
       pending_.end());

   // Create tombstone.
   auto tombstone = std::make_unique<StunByteStringAttribute>(key);

   // add a pending entry.
   pending_.push_back(std::make_pair(++version_, tombstone.get()));

   // store the tombstone.
   tombstones_[key] = std::move(tombstone);

   if (dictionary_) {
     // remove value
     dictionary_->attrs_.erase(key);
   }
 }

 void StunDictionaryWriter::Set(std::unique_ptr<StunAttribute> attr) {
   if (disabled_) {
     return;
   }
   int key = attr->type();
   // remove any pending updates.
   pending_.erase(
       std::remove_if(pending_.begin(), pending_.end(),
                      [key](const auto& p) { return p.second->type() == key; }),
       pending_.end());

   // remove any existing key.
   tombstones_.erase(key);

   // create pending entry.
   pending_.push_back(std::make_pair(++version_, attr.get()));

   if (dictionary_) {
     // store attribute.
     dictionary_->attrs_[key] = std::move(attr);
   }
 }

 // Create an StunByteStringAttribute containing the pending (e.g not ack:ed)
 // modifications.
 std::unique_ptr<StunByteStringAttribute> StunDictionaryWriter::CreateDelta() {
   if (disabled_) {
     return nullptr;
   }
   if (pending_.empty()) {
     return nullptr;
   }

   rtc::ByteBufferWriter buf;
   buf.WriteUInt16(StunDictionaryView::kDeltaMagic);    // 0,1
   buf.WriteUInt16(StunDictionaryView::kDeltaVersion);  // 2,3

   // max version in Delta.
   buf.WriteUInt16(StunDictionaryView::kVersionKey);  // 4,5
   buf.WriteUInt16(8);                                // 6,7
   buf.WriteUInt16(STUN_VALUE_UINT64);                // 8,9
   buf.WriteUInt64(pending_.back().first);            // 10-17
   // attributes
   for (const auto& attr : pending_) {
     buf.WriteUInt16(attr.second->type());
     buf.WriteUInt16(static_cast<uint16_t>(attr.second->length()));
     buf.WriteUInt16(attr.second->value_type());
     if (!attr.second->Write(&buf)) {
       RTC_LOG(LS_ERROR) << "Failed to write key: " << attr.second->type();
       return nullptr;
     }
   }
   return std::make_unique<StunByteStringAttribute>(STUN_ATTR_GOOG_DELTA,
                                                    buf.Data(), buf.Length());
 }

 // Apply a delta ack, i.e prune list of pending changes.
 void StunDictionaryWriter::ApplyDeltaAck(const StunUInt64Attribute& ack) {
   uint64_t acked_version = ack.value();
   auto entries_to_remove = std::remove_if(
       pending_.begin(), pending_.end(),
       [acked_version](const auto& p) { return p.first <= acked_version; });

   // remove tombstones.
   for (auto it = entries_to_remove; it != pending_.end(); ++it) {
     tombstones_.erase((*it).second->type());
   }
   pending_.erase(entries_to_remove, pending_.end());
 }

 // Check if a key has a pending change (i.e a change
 // that has not been acked).
 bool StunDictionaryWriter::Pending(int key) const {
   for (const auto& attr : pending_) {
     if (attr.second->type() == key) {
       return true;
     }
   }
   return false;
 }

 int StunDictionaryWriter::Pending() const {
   return pending_.size();
 }

 }  // namespace cricket
	/*
	* Copyright 2020 The WebRTC Project Authors. All rights reserved.
	*
	* Use of this source code is governed by a BSD-style license
	* that can be found in the LICENSE file in the root of the source
	* tree. An additional intellectual property rights grant can be found
	* in the file PATENTS. All contributing project authors may
	* be found in the AUTHORS file in the root of the source tree.
	*/

	#include "p2p/base/stun_dictionary.h"

	#include <algorithm>
	#include <deque>
	#include <utility>

	#include "rtc_base/logging.h"

	namespace cricket {

	namespace {

	StunAttributeValueType GetStunAttributeValueType(int value_type) {
	switch (value_type) {
	case STUN_VALUE_ADDRESS:
	return STUN_VALUE_ADDRESS;
	case STUN_VALUE_XOR_ADDRESS:
	return STUN_VALUE_XOR_ADDRESS;
	case STUN_VALUE_UINT32:
	return STUN_VALUE_UINT32;
	case STUN_VALUE_UINT64:
	return STUN_VALUE_UINT64;
	case STUN_VALUE_BYTE_STRING:
	return STUN_VALUE_BYTE_STRING;
	case STUN_VALUE_ERROR_CODE:
	return STUN_VALUE_ERROR_CODE;
	case STUN_VALUE_UINT16_LIST:
	return STUN_VALUE_UINT16_LIST;
	default:
	return STUN_VALUE_UNKNOWN;
	}
	}

	} // namespace

	const StunAddressAttribute* StunDictionaryView::GetAddress(int key) const {
	const StunAttribute* attr = GetOrNull(key, STUN_VALUE_ADDRESS);
	if (attr == nullptr) {
	return nullptr;
	}
	return reinterpret_cast<const StunAddressAttribute*>(attr);
	}

	const StunUInt32Attribute* StunDictionaryView::GetUInt32(int key) const {
	const StunAttribute* attr = GetOrNull(key, STUN_VALUE_UINT32);
	if (attr == nullptr) {
	return nullptr;
	}
	return reinterpret_cast<const StunUInt32Attribute*>(attr);
	}

	const StunUInt64Attribute* StunDictionaryView::GetUInt64(int key) const {
	const StunAttribute* attr = GetOrNull(key, STUN_VALUE_UINT64);
	if (attr == nullptr) {
	return nullptr;
	}
	return reinterpret_cast<const StunUInt64Attribute*>(attr);
	}

	const StunByteStringAttribute* StunDictionaryView::GetByteString(
	int key) const {
	const StunAttribute* attr = GetOrNull(key, STUN_VALUE_BYTE_STRING);
	if (attr == nullptr) {
	return nullptr;
	}
	return reinterpret_cast<const StunByteStringAttribute*>(attr);
	}

	const StunUInt16ListAttribute* StunDictionaryView::GetUInt16List(
	int key) const {
	const StunAttribute* attr = GetOrNull(key, STUN_VALUE_UINT16_LIST);
	if (attr == nullptr) {
	return nullptr;
	}
	return reinterpret_cast<const StunUInt16ListAttribute*>(attr);
	}

	const StunAttribute* StunDictionaryView::GetOrNull(
	int key,
	std::optional<StunAttributeValueType> type) const {
	const auto it = attrs_.find(key);
	if (it == attrs_.end()) {
	return nullptr;
	}

	if (type && it->second->value_type() != *type) {
	RTC_LOG(LS_WARNING) << "Get key: " << key << " with type: " << *type
	<< " found different type: "
	<< it->second->value_type();
	return nullptr;
	}
	return (*it).second.get();
	}

	webrtc::RTCErrorOr<
	std::pair<uint64_t, std::deque<std::unique_ptr<StunAttribute>>>>
	StunDictionaryView::ParseDelta(const StunByteStringAttribute& delta) {
	rtc::ByteBufferReader buf(delta.array_view());
	uint16_t magic;
	if (!buf.ReadUInt16(&magic)) {
	return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
	"Failed to read magic number");
	}
	if (magic != kDeltaMagic) {
	return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
	"Invalid magic number");
	}

	uint16_t delta_version;
	if (!buf.ReadUInt16(&delta_version)) {
	return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
	"Failed to read version");
	}

	if (delta_version != kDeltaVersion) {
	return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
	"Unsupported delta version");
	}

	// Now read all the attributes
	std::deque<std::unique_ptr<StunAttribute>> attrs;
	while (buf.Length()) {
	uint16_t key, length, value_type;
	if (!buf.ReadUInt16(&key)) {
	return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
	"Failed to read attribute key");
	}
	if (!buf.ReadUInt16(&length)) {
	return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
	"Failed to read attribute length");
	}
	if (!buf.ReadUInt16(&value_type)) {
	return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
	"Failed to read value type");
	}

	StunAttributeValueType value_type_enum =
	GetStunAttributeValueType(value_type);
	std::unique_ptr<StunAttribute> attr(
	StunAttribute::Create(value_type_enum, key, length, nullptr));
	if (!attr) {
	return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
	"Failed to create attribute");
	}
	if (attr->length() != length) {
	return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
	"Inconsistent attribute length");
	}
	if (!attr->Read(&buf)) {
	return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
	"Failed to read attribute content");
	}
	attrs.push_back(std::move(attr));
	}

	// The first attribute should be the version...
	if (attrs.empty()) {
	return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
	"Empty delta!");
	}

	if (attrs[0]->type() != kVersionKey \|\|
	attrs[0]->value_type() != STUN_VALUE_UINT64) {
	return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER,
	"Missing version!");
	}

	uint64_t version_in_delta =
	reinterpret_cast<const StunUInt64Attribute*>(attrs[0].get())->value();
	attrs.pop_front();

	return std::make_pair(std::max(version_in_delta, version_in_delta),
	std::move(attrs));
	}

	// Apply a delta return an StunUInt64Attribute to ack the update.
	webrtc::RTCErrorOr<
	std::pair<std::unique_ptr<StunUInt64Attribute>, std::vector<uint16_t>>>
	StunDictionaryView::ApplyDelta(const StunByteStringAttribute& delta) {
	auto parsed_delta = ParseDelta(delta);
	if (!parsed_delta.ok()) {
	return webrtc::RTCError(parsed_delta.error());
	}

	uint64_t version_in_delta = parsed_delta.value().first;

	// Check that update does not overflow max_bytes_stored_.
	int new_bytes_stored = bytes_stored_;
	for (auto& attr : parsed_delta.value().second) {
	auto old_version = version_per_key_.find(attr->type());
	if (old_version == version_per_key_.end() \|\|
	version_in_delta > old_version->second) {
	size_t new_length = attr->length();
	size_t old_length = GetLength(attr->type());
	if (old_version == version_per_key_.end()) {
	new_length += sizeof(int64_t);
	}

	new_bytes_stored = new_bytes_stored + new_length - old_length;
	if (new_bytes_stored <= 0) {
	RTC_LOG(LS_WARNING)
	<< "attr: " << attr->type() << " old_length: " << old_length
	<< " new_length: " << new_length
	<< " bytes_stored_: " << bytes_stored_
	<< " new_bytes_stored: " << new_bytes_stored;
	return webrtc::RTCError(webrtc::RTCErrorType::INVALID_PARAMETER);
	}
	if (new_bytes_stored > max_bytes_stored_) {
	RTC_LOG(LS_INFO) << "attr: " << attr->type()
	<< " old_length: " << old_length
	<< " new_length: " << new_length
	<< " bytes_stored_: " << bytes_stored_
	<< " new_bytes_stored: " << new_bytes_stored;
	}
	}
	}
	if (new_bytes_stored > max_bytes_stored_) {
	RTC_LOG(LS_INFO) << " bytes_stored_: " << bytes_stored_
	<< " new_bytes_stored: " << new_bytes_stored;
	return webrtc::RTCError(webrtc::RTCErrorType::RESOURCE_EXHAUSTED);
	}

	// Apply the update.
	std::vector<uint16_t> keys;
	for (auto& attr : parsed_delta.value().second) {
	if (version_in_delta > version_per_key_[attr->type()]) {
	version_per_key_[attr->type()] = version_in_delta;
	keys.push_back(attr->type());
	if (attr->value_type() == STUN_VALUE_BYTE_STRING && attr->length() == 0) {
	attrs_.erase(attr->type());
	} else {
	int attribute_type = attr->type();
	attrs_[attribute_type] = std::move(attr);
	}
	}
	}
	bytes_stored_ = new_bytes_stored;

	return std::make_pair(std::make_unique<StunUInt64Attribute>(
	STUN_ATTR_GOOG_DELTA_ACK, version_in_delta),
	std::move(keys));
	}

	size_t StunDictionaryView::GetLength(int key) const {
	auto attr = GetOrNull(key);
	if (attr != nullptr) {
	return attr->length();
	}
	return 0;
	}

	void StunDictionaryWriter::Disable() {
	disabled_ = true;
	}

	void StunDictionaryWriter::Delete(int key) {
	if (disabled_) {
	return;
	}

	if (dictionary_) {
	if (dictionary_->attrs_.find(key) == dictionary_->attrs_.end()) {
	return;
	}
	}

	// remove any pending updates.
	pending_.erase(
	std::remove_if(pending_.begin(), pending_.end(),
	[key](const auto& p) { return p.second->type() == key; }),
	pending_.end());

	// Create tombstone.
	auto tombstone = std::make_unique<StunByteStringAttribute>(key);

	// add a pending entry.
	pending_.push_back(std::make_pair(++version_, tombstone.get()));

	// store the tombstone.
	tombstones_[key] = std::move(tombstone);

	if (dictionary_) {
	// remove value
	dictionary_->attrs_.erase(key);
	}
	}

	void StunDictionaryWriter::Set(std::unique_ptr<StunAttribute> attr) {
	if (disabled_) {
	return;
	}
	int key = attr->type();
	// remove any pending updates.
	pending_.erase(
	std::remove_if(pending_.begin(), pending_.end(),
	[key](const auto& p) { return p.second->type() == key; }),
	pending_.end());

	// remove any existing key.
	tombstones_.erase(key);

	// create pending entry.
	pending_.push_back(std::make_pair(++version_, attr.get()));

	if (dictionary_) {
	// store attribute.
	dictionary_->attrs_[key] = std::move(attr);
	}
	}

	// Create an StunByteStringAttribute containing the pending (e.g not ack:ed)
	// modifications.
	std::unique_ptr<StunByteStringAttribute> StunDictionaryWriter::CreateDelta() {
	if (disabled_) {
	return nullptr;
	}
	if (pending_.empty()) {
	return nullptr;
	}

	rtc::ByteBufferWriter buf;
	buf.WriteUInt16(StunDictionaryView::kDeltaMagic); // 0,1
	buf.WriteUInt16(StunDictionaryView::kDeltaVersion); // 2,3

	// max version in Delta.
	buf.WriteUInt16(StunDictionaryView::kVersionKey); // 4,5
	buf.WriteUInt16(8); // 6,7
	buf.WriteUInt16(STUN_VALUE_UINT64); // 8,9
	buf.WriteUInt64(pending_.back().first); // 10-17
	// attributes
	for (const auto& attr : pending_) {
	buf.WriteUInt16(attr.second->type());
	buf.WriteUInt16(static_cast<uint16_t>(attr.second->length()));
	buf.WriteUInt16(attr.second->value_type());
	if (!attr.second->Write(&buf)) {
	RTC_LOG(LS_ERROR) << "Failed to write key: " << attr.second->type();
	return nullptr;
	}
	}
	return std::make_unique<StunByteStringAttribute>(STUN_ATTR_GOOG_DELTA,
	buf.Data(), buf.Length());
	}

	// Apply a delta ack, i.e prune list of pending changes.
	void StunDictionaryWriter::ApplyDeltaAck(const StunUInt64Attribute& ack) {
	uint64_t acked_version = ack.value();
	auto entries_to_remove = std::remove_if(
	pending_.begin(), pending_.end(),
	[acked_version](const auto& p) { return p.first <= acked_version; });

	// remove tombstones.
	for (auto it = entries_to_remove; it != pending_.end(); ++it) {
	tombstones_.erase((*it).second->type());
	}
	pending_.erase(entries_to_remove, pending_.end());
	}

	// Check if a key has a pending change (i.e a change
	// that has not been acked).
	bool StunDictionaryWriter::Pending(int key) const {
	for (const auto& attr : pending_) {
	if (attr.second->type() == key) {
	return true;
	}
	}
	return false;
	}

	int StunDictionaryWriter::Pending() const {
	return pending_.size();
	}

	} // namespace cricket