Project import generated by Copybara.

PiperOrigin-RevId: 237361882
Change-Id: I109a68f44db867b20f8c6a7732b0ce657133e52a
diff --git a/quic/core/quic_dispatcher.cc b/quic/core/quic_dispatcher.cc
new file mode 100644
index 0000000..14da558
--- /dev/null
+++ b/quic/core/quic_dispatcher.cc
@@ -0,0 +1,1354 @@
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/third_party/quiche/src/quic/core/quic_dispatcher.h"
+
+#include <utility>
+
+#include "base/macros.h"
+#include "net/third_party/quiche/src/quic/core/chlo_extractor.h"
+#include "net/third_party/quiche/src/quic/core/crypto/crypto_protocol.h"
+#include "net/third_party/quiche/src/quic/core/crypto/quic_random.h"
+#include "net/third_party/quiche/src/quic/core/quic_time_wait_list_manager.h"
+#include "net/third_party/quiche/src/quic/core/quic_types.h"
+#include "net/third_party/quiche/src/quic/core/quic_utils.h"
+#include "net/third_party/quiche/src/quic/core/stateless_rejector.h"
+#include "net/third_party/quiche/src/quic/platform/api/quic_bug_tracker.h"
+#include "net/third_party/quiche/src/quic/platform/api/quic_flag_utils.h"
+#include "net/third_party/quiche/src/quic/platform/api/quic_flags.h"
+#include "net/third_party/quiche/src/quic/platform/api/quic_logging.h"
+#include "net/third_party/quiche/src/quic/platform/api/quic_ptr_util.h"
+#include "net/third_party/quiche/src/quic/platform/api/quic_stack_trace.h"
+#include "net/third_party/quiche/src/quic/platform/api/quic_string.h"
+#include "net/third_party/quiche/src/quic/platform/api/quic_string_piece.h"
+
+namespace quic {
+
+typedef QuicBufferedPacketStore::BufferedPacket BufferedPacket;
+typedef QuicBufferedPacketStore::BufferedPacketList BufferedPacketList;
+typedef QuicBufferedPacketStore::EnqueuePacketResult EnqueuePacketResult;
+
+namespace {
+
+// An alarm that informs the QuicDispatcher to delete old sessions.
+class DeleteSessionsAlarm : public QuicAlarm::Delegate {
+ public:
+  explicit DeleteSessionsAlarm(QuicDispatcher* dispatcher)
+      : dispatcher_(dispatcher) {}
+  DeleteSessionsAlarm(const DeleteSessionsAlarm&) = delete;
+  DeleteSessionsAlarm& operator=(const DeleteSessionsAlarm&) = delete;
+
+  void OnAlarm() override { dispatcher_->DeleteSessions(); }
+
+ private:
+  // Not owned.
+  QuicDispatcher* dispatcher_;
+};
+
+// Collects packets serialized by a QuicPacketCreator in order
+// to be handed off to the time wait list manager.
+class PacketCollector : public QuicPacketCreator::DelegateInterface,
+                        public QuicStreamFrameDataProducer {
+ public:
+  explicit PacketCollector(QuicBufferAllocator* allocator)
+      : send_buffer_(allocator) {}
+  ~PacketCollector() override = default;
+
+  // QuicPacketCreator::DelegateInterface methods:
+  void OnSerializedPacket(SerializedPacket* serialized_packet) override {
+    // Make a copy of the serialized packet to send later.
+    packets_.emplace_back(
+        new QuicEncryptedPacket(CopyBuffer(*serialized_packet),
+                                serialized_packet->encrypted_length, true));
+    serialized_packet->encrypted_buffer = nullptr;
+    DeleteFrames(&(serialized_packet->retransmittable_frames));
+    serialized_packet->retransmittable_frames.clear();
+  }
+
+  char* GetPacketBuffer() override {
+    // Let QuicPacketCreator to serialize packets on stack buffer.
+    return nullptr;
+  }
+
+  void OnUnrecoverableError(QuicErrorCode error,
+                            const QuicString& error_details,
+                            ConnectionCloseSource source) override {}
+
+  void SaveStatelessRejectFrameData(QuicStringPiece reject) {
+    struct iovec iovec;
+    iovec.iov_base = const_cast<char*>(reject.data());
+    iovec.iov_len = reject.length();
+    send_buffer_.SaveStreamData(&iovec, 1, 0, iovec.iov_len);
+  }
+
+  // QuicStreamFrameDataProducer
+  WriteStreamDataResult WriteStreamData(QuicStreamId id,
+                                        QuicStreamOffset offset,
+                                        QuicByteCount data_length,
+                                        QuicDataWriter* writer) override {
+    if (send_buffer_.WriteStreamData(offset, data_length, writer)) {
+      return WRITE_SUCCESS;
+    }
+    return WRITE_FAILED;
+  }
+  bool WriteCryptoData(EncryptionLevel level,
+                       QuicStreamOffset offset,
+                       QuicByteCount data_length,
+                       QuicDataWriter* writer) override {
+    return send_buffer_.WriteStreamData(offset, data_length, writer);
+  }
+
+  std::vector<std::unique_ptr<QuicEncryptedPacket>>* packets() {
+    return &packets_;
+  }
+
+ private:
+  std::vector<std::unique_ptr<QuicEncryptedPacket>> packets_;
+  // This is only needed until the packets are encrypted. Once packets are
+  // encrypted, the stream data is no longer required.
+  QuicStreamSendBuffer send_buffer_;
+};
+
+// Helper for statelessly closing connections by generating the
+// correct termination packets and adding the connection to the time wait
+// list manager.
+class StatelessConnectionTerminator {
+ public:
+  StatelessConnectionTerminator(QuicConnectionId connection_id,
+                                QuicFramer* framer,
+                                QuicConnectionHelperInterface* helper,
+                                QuicTimeWaitListManager* time_wait_list_manager)
+      : connection_id_(connection_id),
+        framer_(framer),
+        collector_(helper->GetStreamSendBufferAllocator()),
+        creator_(connection_id, framer, &collector_),
+        time_wait_list_manager_(time_wait_list_manager) {
+    framer_->set_data_producer(&collector_);
+  }
+
+  ~StatelessConnectionTerminator() {
+    // Clear framer's producer.
+    framer_->set_data_producer(nullptr);
+  }
+
+  // Generates a packet containing a CONNECTION_CLOSE frame specifying
+  // |error_code| and |error_details| and add the connection to time wait.
+  void CloseConnection(QuicErrorCode error_code,
+                       const QuicString& error_details,
+                       bool ietf_quic) {
+    QuicConnectionCloseFrame* frame = new QuicConnectionCloseFrame;
+    frame->error_code = error_code;
+    frame->error_details = error_details;
+    if (!creator_.AddSavedFrame(QuicFrame(frame), NOT_RETRANSMISSION)) {
+      QUIC_BUG << "Unable to add frame to an empty packet";
+      delete frame;
+      return;
+    }
+    creator_.Flush();
+    DCHECK_EQ(1u, collector_.packets()->size());
+    time_wait_list_manager_->AddConnectionIdToTimeWait(
+        connection_id_, ietf_quic,
+        QuicTimeWaitListManager::SEND_TERMINATION_PACKETS,
+        quic::ENCRYPTION_NONE, collector_.packets());
+  }
+
+  // Generates a series of termination packets containing the crypto handshake
+  // message |reject|.  Adds the connection to time wait list with the
+  // generated packets.
+  void RejectConnection(QuicStringPiece reject, bool ietf_quic) {
+    QuicStreamOffset offset = 0;
+    collector_.SaveStatelessRejectFrameData(reject);
+    while (offset < reject.length()) {
+      QuicFrame frame;
+      if (framer_->transport_version() < QUIC_VERSION_47) {
+        if (!creator_.ConsumeData(
+                QuicUtils::GetCryptoStreamId(framer_->transport_version()),
+                reject.length(), offset, offset,
+                /*fin=*/false,
+                /*needs_full_padding=*/true, NOT_RETRANSMISSION, &frame)) {
+          QUIC_BUG << "Unable to consume data into an empty packet.";
+          return;
+        }
+        offset += frame.stream_frame.data_length;
+      } else {
+        if (!creator_.ConsumeCryptoData(ENCRYPTION_NONE,
+                                        reject.length() - offset, offset,
+                                        NOT_RETRANSMISSION, &frame)) {
+          QUIC_BUG << "Unable to consume crypto data into an empty packet.";
+          return;
+        }
+        offset += frame.crypto_frame->data_length;
+      }
+      if (offset < reject.length()) {
+        DCHECK(!creator_.HasRoomForStreamFrame(
+            QuicUtils::GetCryptoStreamId(framer_->transport_version()), offset,
+            frame.stream_frame.data_length));
+      }
+      creator_.Flush();
+    }
+    time_wait_list_manager_->AddConnectionIdToTimeWait(
+        connection_id_, ietf_quic,
+        QuicTimeWaitListManager::SEND_TERMINATION_PACKETS, ENCRYPTION_NONE,
+        collector_.packets());
+    DCHECK(time_wait_list_manager_->IsConnectionIdInTimeWait(connection_id_));
+  }
+
+ private:
+  QuicConnectionId connection_id_;
+  QuicFramer* framer_;  // Unowned.
+  // Set as the visitor of |creator_| to collect any generated packets.
+  PacketCollector collector_;
+  QuicPacketCreator creator_;
+  QuicTimeWaitListManager* time_wait_list_manager_;
+};
+
+// Class which extracts the ALPN from a CHLO packet.
+class ChloAlpnExtractor : public ChloExtractor::Delegate {
+ public:
+  void OnChlo(QuicTransportVersion version,
+              QuicConnectionId connection_id,
+              const CryptoHandshakeMessage& chlo) override {
+    QuicStringPiece alpn_value;
+    if (chlo.GetStringPiece(kALPN, &alpn_value)) {
+      alpn_ = QuicString(alpn_value);
+    }
+  }
+
+  QuicString&& ConsumeAlpn() { return std::move(alpn_); }
+
+ private:
+  QuicString alpn_;
+};
+
+// Class which sits between the ChloExtractor and the StatelessRejector
+// to give the QuicDispatcher a chance to apply policy checks to the CHLO.
+class ChloValidator : public ChloAlpnExtractor {
+ public:
+  ChloValidator(QuicCryptoServerStream::Helper* helper,
+                const QuicSocketAddress& client_address,
+                const QuicSocketAddress& peer_address,
+                const QuicSocketAddress& self_address,
+                StatelessRejector* rejector)
+      : helper_(helper),
+        client_address_(client_address),
+        peer_address_(peer_address),
+        self_address_(self_address),
+        rejector_(rejector),
+        can_accept_(false),
+        error_details_("CHLO not processed") {}
+
+  // ChloExtractor::Delegate implementation.
+  void OnChlo(QuicTransportVersion version,
+              QuicConnectionId connection_id,
+              const CryptoHandshakeMessage& chlo) override {
+    // Extract the ALPN
+    ChloAlpnExtractor::OnChlo(version, connection_id, chlo);
+    if (helper_->CanAcceptClientHello(chlo, client_address_, peer_address_,
+                                      self_address_, &error_details_)) {
+      can_accept_ = true;
+      rejector_->OnChlo(
+          version, connection_id,
+          helper_->GenerateConnectionIdForReject(version, connection_id), chlo);
+    }
+  }
+
+  bool can_accept() const { return can_accept_; }
+
+  const QuicString& error_details() const { return error_details_; }
+
+ private:
+  QuicCryptoServerStream::Helper* helper_;  // Unowned.
+  // client_address_ and peer_address_ could be different values for proxy
+  // connections.
+  QuicSocketAddress client_address_;
+  QuicSocketAddress peer_address_;
+  QuicSocketAddress self_address_;
+  StatelessRejector* rejector_;  // Unowned.
+  bool can_accept_;
+  QuicString error_details_;
+};
+
+}  // namespace
+
+QuicDispatcher::QuicDispatcher(
+    const QuicConfig* config,
+    const QuicCryptoServerConfig* crypto_config,
+    QuicVersionManager* version_manager,
+    std::unique_ptr<QuicConnectionHelperInterface> helper,
+    std::unique_ptr<QuicCryptoServerStream::Helper> session_helper,
+    std::unique_ptr<QuicAlarmFactory> alarm_factory,
+    uint8_t expected_connection_id_length)
+    : config_(config),
+      crypto_config_(crypto_config),
+      compressed_certs_cache_(
+          QuicCompressedCertsCache::kQuicCompressedCertsCacheSize),
+      helper_(std::move(helper)),
+      session_helper_(std::move(session_helper)),
+      alarm_factory_(std::move(alarm_factory)),
+      delete_sessions_alarm_(
+          alarm_factory_->CreateAlarm(new DeleteSessionsAlarm(this))),
+      buffered_packets_(this, helper_->GetClock(), alarm_factory_.get()),
+      current_packet_(nullptr),
+      version_manager_(version_manager),
+      framer_(GetSupportedVersions(),
+              /*unused*/ QuicTime::Zero(),
+              Perspective::IS_SERVER,
+              expected_connection_id_length),
+      last_error_(QUIC_NO_ERROR),
+      new_sessions_allowed_per_event_loop_(0u),
+      accept_new_connections_(true) {
+  framer_.set_visitor(this);
+}
+
+QuicDispatcher::~QuicDispatcher() {
+  session_map_.clear();
+  closed_session_list_.clear();
+}
+
+void QuicDispatcher::InitializeWithWriter(QuicPacketWriter* writer) {
+  DCHECK(writer_ == nullptr);
+  writer_.reset(writer);
+  time_wait_list_manager_.reset(CreateQuicTimeWaitListManager());
+}
+
+void QuicDispatcher::ProcessPacket(const QuicSocketAddress& self_address,
+                                   const QuicSocketAddress& peer_address,
+                                   const QuicReceivedPacket& packet) {
+  current_self_address_ = self_address;
+  current_peer_address_ = peer_address;
+  // GetClientAddress must be called after current_peer_address_ is set.
+  current_client_address_ = GetClientAddress();
+  current_packet_ = &packet;
+  // ProcessPacket will cause the packet to be dispatched in
+  // OnUnauthenticatedPublicHeader, or sent to the time wait list manager
+  // in OnUnauthenticatedHeader.
+  framer_.ProcessPacket(packet);
+  // TODO(rjshade): Return a status describing if/why a packet was dropped,
+  //                and log somehow.  Maybe expose as a varz.
+  // TODO(wub): Consider invalidate the current_* variables so processing of the
+  //            next packet does not use them incorrectly.
+}
+
+bool QuicDispatcher::OnUnauthenticatedPublicHeader(
+    const QuicPacketHeader& header) {
+  current_connection_id_ = header.destination_connection_id;
+
+  // Port zero is only allowed for unidirectional UDP, so is disallowed by QUIC.
+  // Given that we can't even send a reply rejecting the packet, just drop the
+  // packet.
+  if (current_peer_address_.port() == 0) {
+    return false;
+  }
+
+  // The dispatcher requires the connection ID to be present in order to
+  // look up the matching QuicConnection, so we error out if it is absent.
+  if (header.destination_connection_id_included != CONNECTION_ID_PRESENT) {
+    return false;
+  }
+
+  // Packets with connection IDs for active connections are processed
+  // immediately.
+  QuicConnectionId connection_id = header.destination_connection_id;
+  auto it = session_map_.find(connection_id);
+  if (it != session_map_.end()) {
+    DCHECK(!buffered_packets_.HasBufferedPackets(connection_id));
+    it->second->ProcessUdpPacket(current_self_address_, current_peer_address_,
+                                 *current_packet_);
+    return false;
+  }
+
+  if (buffered_packets_.HasChloForConnection(connection_id)) {
+    BufferEarlyPacket(connection_id, header.form != GOOGLE_QUIC_PACKET,
+                      header.version);
+    return false;
+  }
+
+  // Check if we are buffering packets for this connection ID
+  if (temporarily_buffered_connections_.find(connection_id) !=
+      temporarily_buffered_connections_.end()) {
+    // This packet was received while the a CHLO for the same connection ID was
+    // being processed.  Buffer it.
+    BufferEarlyPacket(connection_id, header.form != GOOGLE_QUIC_PACKET,
+                      header.version);
+    return false;
+  }
+
+  if (!OnUnauthenticatedUnknownPublicHeader(header)) {
+    return false;
+  }
+
+  // If the packet is a public reset for a connection ID that is not active,
+  // there is nothing we must do or can do.
+  if (header.reset_flag) {
+    return false;
+  }
+
+  if (time_wait_list_manager_->IsConnectionIdInTimeWait(connection_id)) {
+    // This connection ID is already in time-wait state.
+    time_wait_list_manager_->ProcessPacket(
+        current_self_address_, current_peer_address_,
+        header.destination_connection_id, header.form, GetPerPacketContext());
+    return false;
+  }
+
+  // The packet has an unknown connection ID.
+
+  // Unless the packet provides a version, assume that we can continue
+  // processing using our preferred version.
+  ParsedQuicVersion version = GetSupportedVersions().front();
+  if (header.version_flag) {
+    ParsedQuicVersion packet_version = header.version;
+    if (framer_.supported_versions() != GetSupportedVersions()) {
+      // Reset framer's version if version flags change in flight.
+      framer_.SetSupportedVersions(GetSupportedVersions());
+    }
+    if (!framer_.IsSupportedVersion(packet_version)) {
+      if (ShouldCreateSessionForUnknownVersion(framer_.last_version_label())) {
+        return true;
+      }
+      if (!crypto_config()->validate_chlo_size() ||
+          current_packet_->length() >= kMinPacketSizeForVersionNegotiation) {
+        // Since the version is not supported, send a version negotiation
+        // packet and stop processing the current packet.
+        time_wait_list_manager()->SendVersionNegotiationPacket(
+            connection_id, header.form != GOOGLE_QUIC_PACKET,
+            GetSupportedVersions(), current_self_address_,
+            current_peer_address_, GetPerPacketContext());
+      }
+      return false;
+    }
+    version = packet_version;
+  }
+  // Set the framer's version and continue processing.
+  framer_.set_version(version);
+  return true;
+}
+
+bool QuicDispatcher::OnUnauthenticatedHeader(const QuicPacketHeader& header) {
+  QuicConnectionId connection_id = header.destination_connection_id;
+  // Packet's connection ID is unknown.  Apply the validity checks.
+  QuicPacketFate fate = ValidityChecks(header);
+  if (fate == kFateProcess) {
+    // Execute stateless rejection logic to determine the packet fate, then
+    // invoke ProcessUnauthenticatedHeaderFate.
+    MaybeRejectStatelessly(connection_id, header.form, header.version);
+  } else {
+    // If the fate is already known, process it without executing stateless
+    // rejection logic.
+    ProcessUnauthenticatedHeaderFate(fate, connection_id, header.form,
+                                     header.version);
+  }
+
+  return false;
+}
+
+void QuicDispatcher::ProcessUnauthenticatedHeaderFate(
+    QuicPacketFate fate,
+    QuicConnectionId connection_id,
+    PacketHeaderFormat form,
+    ParsedQuicVersion version) {
+  switch (fate) {
+    case kFateProcess: {
+      ProcessChlo(form, version);
+      break;
+    }
+    case kFateTimeWait:
+      // MaybeRejectStatelessly or OnExpiredPackets might have already added the
+      // connection to time wait, in which case it should not be added again.
+      if (!GetQuicReloadableFlag(quic_use_cheap_stateless_rejects) ||
+          !time_wait_list_manager_->IsConnectionIdInTimeWait(connection_id)) {
+        // Add this connection_id to the time-wait state, to safely reject
+        // future packets.
+        QUIC_DLOG(INFO) << "Adding connection ID " << connection_id
+                        << "to time-wait list.";
+        QUIC_CODE_COUNT(quic_reject_fate_time_wait);
+        StatelesslyTerminateConnection(
+            connection_id, form, version, QUIC_HANDSHAKE_FAILED,
+            "Reject connection",
+            quic::QuicTimeWaitListManager::SEND_STATELESS_RESET);
+      }
+      DCHECK(time_wait_list_manager_->IsConnectionIdInTimeWait(connection_id));
+      time_wait_list_manager_->ProcessPacket(
+          current_self_address_, current_peer_address_, connection_id, form,
+          GetPerPacketContext());
+
+      // Any packets which were buffered while the stateless rejector logic was
+      // running should be discarded.  Do not inform the time wait list manager,
+      // which should already have a made a decision about sending a reject
+      // based on the CHLO alone.
+      buffered_packets_.DiscardPackets(connection_id);
+      break;
+    case kFateBuffer:
+      // This packet is a non-CHLO packet which has arrived before the
+      // corresponding CHLO, *or* this packet was received while the
+      // corresponding CHLO was being processed.  Buffer it.
+      BufferEarlyPacket(connection_id, form != GOOGLE_QUIC_PACKET, version);
+      break;
+    case kFateDrop:
+      // Do nothing with the packet.
+      break;
+  }
+}
+
+QuicDispatcher::QuicPacketFate QuicDispatcher::ValidityChecks(
+    const QuicPacketHeader& header) {
+  // To have all the checks work properly without tears, insert any new check
+  // into the framework of this method in the section for checks that return the
+  // check's fate value.  The sections for checks must be ordered with the
+  // highest priority fate first.
+
+  // Checks that return kFateDrop.
+
+  // Checks that return kFateTimeWait.
+
+  // All packets within a connection sent by a client before receiving a
+  // response from the server are required to have the version negotiation flag
+  // set.  Since this may be a client continuing a connection we lost track of
+  // via server restart, send a rejection to fast-fail the connection.
+  if (!header.version_flag) {
+    QUIC_DLOG(INFO)
+        << "Packet without version arrived for unknown connection ID "
+        << header.destination_connection_id;
+    return kFateTimeWait;
+  }
+
+  // initial packet number of 0 is always invalid.
+  if (!header.packet_number.IsInitialized()) {
+    return kFateTimeWait;
+  }
+  if (GetQuicRestartFlag(quic_enable_accept_random_ipn)) {
+    QUIC_RESTART_FLAG_COUNT_N(quic_enable_accept_random_ipn, 1, 2);
+    // Accepting Initial Packet Numbers in 1...((2^31)-1) range... check
+    // maximum accordingly.
+    if (header.packet_number > MaxRandomInitialPacketNumber()) {
+      return kFateTimeWait;
+    }
+  } else {
+    // Count those that would have been accepted if FLAGS..random_ipn
+    // were true -- to detect/diagnose potential issues prior to
+    // enabling the flag.
+    if ((header.packet_number >
+         QuicPacketNumber(kMaxReasonableInitialPacketNumber)) &&
+        (header.packet_number <= MaxRandomInitialPacketNumber())) {
+      QUIC_CODE_COUNT_N(had_possibly_random_ipn, 1, 2);
+    }
+    // Check that the sequence number is within the range that the client is
+    // expected to send before receiving a response from the server.
+    if (header.packet_number >
+        QuicPacketNumber(kMaxReasonableInitialPacketNumber)) {
+      return kFateTimeWait;
+    }
+  }
+  return kFateProcess;
+}
+
+void QuicDispatcher::CleanUpSession(SessionMap::iterator it,
+                                    QuicConnection* connection,
+                                    bool should_close_statelessly,
+                                    ConnectionCloseSource source) {
+  write_blocked_list_.erase(connection);
+  if (should_close_statelessly) {
+    DCHECK(connection->termination_packets() != nullptr &&
+           !connection->termination_packets()->empty());
+  }
+  QuicTimeWaitListManager::TimeWaitAction action =
+      QuicTimeWaitListManager::SEND_STATELESS_RESET;
+  if (connection->termination_packets() != nullptr &&
+      !connection->termination_packets()->empty()) {
+    action = QuicTimeWaitListManager::SEND_TERMINATION_PACKETS;
+  } else if (connection->transport_version() > QUIC_VERSION_43) {
+    if (!connection->IsHandshakeConfirmed()) {
+      QUIC_CODE_COUNT(quic_v44_add_to_time_wait_list_with_handshake_failed);
+      action = QuicTimeWaitListManager::SEND_TERMINATION_PACKETS;
+      // This serializes a connection close termination packet with error code
+      // QUIC_HANDSHAKE_FAILED and adds the connection to the time wait list.
+      StatelesslyTerminateConnection(
+          connection->connection_id(), IETF_QUIC_LONG_HEADER_PACKET,
+          connection->version(), QUIC_HANDSHAKE_FAILED,
+          "Connection is closed by server before handshake confirmed",
+          // Although it is our intention to send termination packets, the
+          // |action| argument is not used by this call to
+          // StatelesslyTerminateConnection().
+          action);
+      session_map_.erase(it);
+      return;
+    }
+    QUIC_CODE_COUNT(quic_v44_add_to_time_wait_list_with_stateless_reset);
+  }
+  time_wait_list_manager_->AddConnectionIdToTimeWait(
+      it->first, connection->transport_version() > QUIC_VERSION_43, action,
+      connection->encryption_level(), connection->termination_packets());
+  session_map_.erase(it);
+}
+
+void QuicDispatcher::StopAcceptingNewConnections() {
+  accept_new_connections_ = false;
+}
+
+std::unique_ptr<QuicPerPacketContext> QuicDispatcher::GetPerPacketContext()
+    const {
+  return nullptr;
+}
+
+void QuicDispatcher::DeleteSessions() {
+  if (GetQuicReloadableFlag(
+          quic_connection_do_not_add_to_write_blocked_list_if_disconnected) &&
+      !write_blocked_list_.empty()) {
+    QUIC_RELOADABLE_FLAG_COUNT_N(
+        quic_connection_do_not_add_to_write_blocked_list_if_disconnected, 2, 2);
+    for (const std::unique_ptr<QuicSession>& session : closed_session_list_) {
+      if (write_blocked_list_.erase(session->connection()) != 0) {
+        QUIC_BUG << "QuicConnection was in WriteBlockedList before destruction";
+      }
+    }
+  }
+  closed_session_list_.clear();
+}
+
+void QuicDispatcher::OnCanWrite() {
+  // The socket is now writable.
+  writer_->SetWritable();
+
+  // Move every blocked writer in |write_blocked_list_| to a temporary list.
+  const size_t num_blocked_writers_before = write_blocked_list_.size();
+  WriteBlockedList temp_list;
+  temp_list.swap(write_blocked_list_);
+  DCHECK(write_blocked_list_.empty());
+
+  // Give each blocked writer a chance to write what they indended to write.
+  // If they are blocked again, they will call |OnWriteBlocked| to add
+  // themselves back into |write_blocked_list_|.
+  while (!temp_list.empty()) {
+    QuicBlockedWriterInterface* blocked_writer = temp_list.begin()->first;
+    temp_list.erase(temp_list.begin());
+    blocked_writer->OnBlockedWriterCanWrite();
+  }
+  const size_t num_blocked_writers_after = write_blocked_list_.size();
+  if (num_blocked_writers_after != 0) {
+    if (num_blocked_writers_before == num_blocked_writers_after) {
+      QUIC_CODE_COUNT(quic_zero_progress_on_can_write);
+    } else {
+      QUIC_CODE_COUNT(quic_blocked_again_on_can_write);
+    }
+  }
+}
+
+bool QuicDispatcher::HasPendingWrites() const {
+  return !write_blocked_list_.empty();
+}
+
+void QuicDispatcher::Shutdown() {
+  while (!session_map_.empty()) {
+    QuicSession* session = session_map_.begin()->second.get();
+    session->connection()->CloseConnection(
+        QUIC_PEER_GOING_AWAY, "Server shutdown imminent",
+        ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
+    // Validate that the session removes itself from the session map on close.
+    DCHECK(session_map_.empty() ||
+           session_map_.begin()->second.get() != session);
+  }
+  DeleteSessions();
+}
+
+void QuicDispatcher::OnConnectionClosed(QuicConnectionId connection_id,
+                                        QuicErrorCode error,
+                                        const QuicString& error_details,
+                                        ConnectionCloseSource source) {
+  auto it = session_map_.find(connection_id);
+  if (it == session_map_.end()) {
+    QUIC_BUG << "ConnectionId " << connection_id
+             << " does not exist in the session map.  Error: "
+             << QuicErrorCodeToString(error);
+    QUIC_BUG << QuicStackTrace();
+    return;
+  }
+
+  QUIC_DLOG_IF(INFO, error != QUIC_NO_ERROR)
+      << "Closing connection (" << connection_id
+      << ") due to error: " << QuicErrorCodeToString(error)
+      << ", with details: " << error_details;
+
+  QuicConnection* connection = it->second->connection();
+  if (ShouldDestroySessionAsynchronously()) {
+    // Set up alarm to fire immediately to bring destruction of this session
+    // out of current call stack.
+    if (closed_session_list_.empty()) {
+      delete_sessions_alarm_->Update(helper()->GetClock()->ApproximateNow(),
+                                     QuicTime::Delta::Zero());
+    }
+    closed_session_list_.push_back(std::move(it->second));
+  }
+  const bool should_close_statelessly =
+      (error == QUIC_CRYPTO_HANDSHAKE_STATELESS_REJECT);
+  CleanUpSession(it, connection, should_close_statelessly, source);
+}
+
+void QuicDispatcher::OnWriteBlocked(
+    QuicBlockedWriterInterface* blocked_writer) {
+  if (!blocked_writer->IsWriterBlocked()) {
+    // It is a programming error if this ever happens. When we are sure it is
+    // not happening, replace it with a DCHECK.
+    QUIC_BUG
+        << "Tried to add writer into blocked list when it shouldn't be added";
+    // Return without adding the connection to the blocked list, to avoid
+    // infinite loops in OnCanWrite.
+    return;
+  }
+
+  write_blocked_list_.insert(std::make_pair(blocked_writer, true));
+}
+
+void QuicDispatcher::OnRstStreamReceived(const QuicRstStreamFrame& frame) {}
+
+void QuicDispatcher::OnStopSendingReceived(const QuicStopSendingFrame& frame) {}
+
+void QuicDispatcher::OnConnectionAddedToTimeWaitList(
+    QuicConnectionId connection_id) {
+  QUIC_DLOG(INFO) << "Connection " << connection_id
+                  << " added to time wait list.";
+}
+
+void QuicDispatcher::StatelesslyTerminateConnection(
+    QuicConnectionId connection_id,
+    PacketHeaderFormat format,
+    ParsedQuicVersion version,
+    QuicErrorCode error_code,
+    const QuicString& error_details,
+    QuicTimeWaitListManager::TimeWaitAction action) {
+  if (format != IETF_QUIC_LONG_HEADER_PACKET) {
+    QUIC_DVLOG(1) << "Statelessly terminating " << connection_id
+                  << " based on a non-ietf-long packet, action:" << action
+                  << ", error_code:" << error_code
+                  << ", error_details:" << error_details;
+    time_wait_list_manager_->AddConnectionIdToTimeWait(
+        connection_id, format != GOOGLE_QUIC_PACKET, action, ENCRYPTION_NONE,
+        nullptr);
+    return;
+  }
+
+  // If the version is known and supported by framer, send a connection close.
+  if (framer_.IsSupportedVersion(version)) {
+    QUIC_DVLOG(1)
+        << "Statelessly terminating " << connection_id
+        << " based on an ietf-long packet, which has a supported version:"
+        << version << ", error_code:" << error_code
+        << ", error_details:" << error_details;
+    // Set framer_ to the packet's version such that the connection close can be
+    // processed by the client.
+    ParsedQuicVersion original_version = framer_.version();
+    framer_.set_version(version);
+
+    StatelessConnectionTerminator terminator(
+        connection_id, &framer_, helper_.get(), time_wait_list_manager_.get());
+    // This also adds the connection to time wait list.
+    terminator.CloseConnection(error_code, error_details, true);
+
+    // Restore framer_ to the original version, as if nothing changed in it.
+    framer_.set_version(original_version);
+    return;
+  }
+
+  QUIC_DVLOG(1)
+      << "Statelessly terminating " << connection_id
+      << " based on an ietf-long packet, which has an unsupported version:"
+      << version << ", error_code:" << error_code
+      << ", error_details:" << error_details;
+  // Version is unknown or unsupported by framer, send a version negotiation
+  // with an empty version list, which can be understood by the client.
+  std::vector<std::unique_ptr<QuicEncryptedPacket>> termination_packets;
+  termination_packets.push_back(QuicFramer::BuildVersionNegotiationPacket(
+      connection_id, /*ietf_quic=*/true,
+      ParsedQuicVersionVector{UnsupportedQuicVersion()}));
+  time_wait_list_manager()->AddConnectionIdToTimeWait(
+      connection_id, /*ietf_quic=*/true,
+      QuicTimeWaitListManager::SEND_TERMINATION_PACKETS, ENCRYPTION_NONE,
+      &termination_packets);
+}
+
+void QuicDispatcher::OnPacket() {}
+
+void QuicDispatcher::OnError(QuicFramer* framer) {
+  QuicErrorCode error = framer->error();
+  SetLastError(error);
+  QUIC_DLOG(INFO) << QuicErrorCodeToString(error);
+}
+
+bool QuicDispatcher::ShouldCreateSessionForUnknownVersion(
+    QuicVersionLabel /*version_label*/) {
+  return false;
+}
+
+bool QuicDispatcher::OnProtocolVersionMismatch(
+    ParsedQuicVersion /*received_version*/,
+    PacketHeaderFormat /*form*/) {
+  QUIC_BUG_IF(
+      !time_wait_list_manager_->IsConnectionIdInTimeWait(
+          current_connection_id_) &&
+      !ShouldCreateSessionForUnknownVersion(framer_.last_version_label()))
+      << "Unexpected version mismatch: "
+      << QuicVersionLabelToString(framer_.last_version_label());
+
+  // Keep processing after protocol mismatch - this will be dealt with by the
+  // time wait list or connection that we will create.
+  return true;
+}
+
+void QuicDispatcher::OnPublicResetPacket(
+    const QuicPublicResetPacket& /*packet*/) {
+  DCHECK(false);
+}
+
+void QuicDispatcher::OnVersionNegotiationPacket(
+    const QuicVersionNegotiationPacket& /*packet*/) {
+  DCHECK(false);
+}
+
+void QuicDispatcher::OnDecryptedPacket(EncryptionLevel level) {
+  DCHECK(false);
+}
+
+bool QuicDispatcher::OnPacketHeader(const QuicPacketHeader& /*header*/) {
+  DCHECK(false);
+  return false;
+}
+
+void QuicDispatcher::OnCoalescedPacket(const QuicEncryptedPacket& /*packet*/) {
+  DCHECK(false);
+}
+
+bool QuicDispatcher::OnStreamFrame(const QuicStreamFrame& /*frame*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnCryptoFrame(const QuicCryptoFrame& /*frame*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnAckFrameStart(QuicPacketNumber /*largest_acked*/,
+                                     QuicTime::Delta /*ack_delay_time*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnAckRange(QuicPacketNumber /*start*/,
+                                QuicPacketNumber /*end*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnAckTimestamp(QuicPacketNumber /*packet_number*/,
+                                    QuicTime /*timestamp*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnAckFrameEnd(QuicPacketNumber /*start*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnStopWaitingFrame(const QuicStopWaitingFrame& /*frame*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnPaddingFrame(const QuicPaddingFrame& /*frame*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnPingFrame(const QuicPingFrame& /*frame*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnRstStreamFrame(const QuicRstStreamFrame& /*frame*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnConnectionCloseFrame(
+    const QuicConnectionCloseFrame& /*frame*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnApplicationCloseFrame(
+    const QuicApplicationCloseFrame& /*frame*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnMaxStreamIdFrame(const QuicMaxStreamIdFrame& frame) {
+  return true;
+}
+
+bool QuicDispatcher::OnStreamIdBlockedFrame(
+    const QuicStreamIdBlockedFrame& frame) {
+  return true;
+}
+
+bool QuicDispatcher::OnStopSendingFrame(const QuicStopSendingFrame& /*frame*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnPathChallengeFrame(
+    const QuicPathChallengeFrame& /*frame*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnPathResponseFrame(
+    const QuicPathResponseFrame& /*frame*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnGoAwayFrame(const QuicGoAwayFrame& /*frame*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnWindowUpdateFrame(
+    const QuicWindowUpdateFrame& /*frame*/) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnBlockedFrame(const QuicBlockedFrame& frame) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnNewConnectionIdFrame(
+    const QuicNewConnectionIdFrame& frame) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnRetireConnectionIdFrame(
+    const QuicRetireConnectionIdFrame& frame) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnNewTokenFrame(const QuicNewTokenFrame& frame) {
+  DCHECK(false);
+  return false;
+}
+
+bool QuicDispatcher::OnMessageFrame(const QuicMessageFrame& frame) {
+  DCHECK(false);
+  return false;
+}
+
+void QuicDispatcher::OnPacketComplete() {
+  DCHECK(false);
+}
+
+bool QuicDispatcher::IsValidStatelessResetToken(QuicUint128 token) const {
+  DCHECK(false);
+  return false;
+}
+
+void QuicDispatcher::OnAuthenticatedIetfStatelessResetPacket(
+    const QuicIetfStatelessResetPacket& packet) {
+  DCHECK(false);
+}
+
+void QuicDispatcher::OnExpiredPackets(
+    QuicConnectionId connection_id,
+    BufferedPacketList early_arrived_packets) {
+  QUIC_CODE_COUNT(quic_reject_buffered_packets_expired);
+  StatelesslyTerminateConnection(
+      connection_id,
+      early_arrived_packets.ietf_quic ? IETF_QUIC_LONG_HEADER_PACKET
+                                      : GOOGLE_QUIC_PACKET,
+      early_arrived_packets.version, QUIC_HANDSHAKE_FAILED,
+      "Packets buffered for too long",
+      quic::QuicTimeWaitListManager::SEND_STATELESS_RESET);
+}
+
+void QuicDispatcher::ProcessBufferedChlos(size_t max_connections_to_create) {
+  // Reset the counter before starting creating connections.
+  new_sessions_allowed_per_event_loop_ = max_connections_to_create;
+  for (; new_sessions_allowed_per_event_loop_ > 0;
+       --new_sessions_allowed_per_event_loop_) {
+    QuicConnectionId connection_id;
+    BufferedPacketList packet_list =
+        buffered_packets_.DeliverPacketsForNextConnection(&connection_id);
+    const std::list<BufferedPacket>& packets = packet_list.buffered_packets;
+    if (packets.empty()) {
+      return;
+    }
+    QuicSession* session =
+        CreateQuicSession(connection_id, packets.front().peer_address,
+                          packet_list.alpn, packet_list.version);
+    QUIC_DLOG(INFO) << "Created new session for " << connection_id;
+    session_map_.insert(std::make_pair(connection_id, QuicWrapUnique(session)));
+    DeliverPacketsToSession(packets, session);
+  }
+}
+
+bool QuicDispatcher::HasChlosBuffered() const {
+  return buffered_packets_.HasChlosBuffered();
+}
+
+bool QuicDispatcher::ShouldCreateOrBufferPacketForConnection(
+    QuicConnectionId connection_id,
+    bool ietf_quic) {
+  VLOG(1) << "Received packet from new connection " << connection_id;
+  return true;
+}
+
+// Return true if there is any packet buffered in the store.
+bool QuicDispatcher::HasBufferedPackets(QuicConnectionId connection_id) {
+  return buffered_packets_.HasBufferedPackets(connection_id);
+}
+
+void QuicDispatcher::OnBufferPacketFailure(EnqueuePacketResult result,
+                                           QuicConnectionId connection_id) {
+  QUIC_DLOG(INFO) << "Fail to buffer packet on connection " << connection_id
+                  << " because of " << result;
+}
+
+void QuicDispatcher::OnConnectionRejectedStatelessly() {}
+
+void QuicDispatcher::OnConnectionClosedStatelessly(QuicErrorCode error) {}
+
+bool QuicDispatcher::ShouldAttemptCheapStatelessRejection() {
+  return true;
+}
+
+QuicTimeWaitListManager* QuicDispatcher::CreateQuicTimeWaitListManager() {
+  return new QuicTimeWaitListManager(writer_.get(), this, helper_->GetClock(),
+                                     alarm_factory_.get());
+}
+
+void QuicDispatcher::BufferEarlyPacket(QuicConnectionId connection_id,
+                                       bool ietf_quic,
+                                       ParsedQuicVersion version) {
+  bool is_new_connection = !buffered_packets_.HasBufferedPackets(connection_id);
+  if (is_new_connection &&
+      !ShouldCreateOrBufferPacketForConnection(connection_id, ietf_quic)) {
+    return;
+  }
+
+  EnqueuePacketResult rs = buffered_packets_.EnqueuePacket(
+      connection_id, ietf_quic, *current_packet_, current_self_address_,
+      current_peer_address_, /*is_chlo=*/false,
+      /*alpn=*/"", version);
+  if (rs != EnqueuePacketResult::SUCCESS) {
+    OnBufferPacketFailure(rs, connection_id);
+  }
+}
+
+void QuicDispatcher::ProcessChlo(PacketHeaderFormat form,
+                                 ParsedQuicVersion version) {
+  if (!accept_new_connections_) {
+    // Don't any create new connection.
+    QUIC_CODE_COUNT(quic_reject_stop_accepting_new_connections);
+    StatelesslyTerminateConnection(
+        current_connection_id(), form, version, QUIC_HANDSHAKE_FAILED,
+        "Stop accepting new connections",
+        quic::QuicTimeWaitListManager::SEND_STATELESS_RESET);
+    // Time wait list will reject the packet correspondingly.
+    time_wait_list_manager()->ProcessPacket(
+        current_self_address(), current_peer_address(), current_connection_id(),
+        form, GetPerPacketContext());
+    return;
+  }
+  if (!buffered_packets_.HasBufferedPackets(current_connection_id_) &&
+      !ShouldCreateOrBufferPacketForConnection(current_connection_id_,
+                                               form != GOOGLE_QUIC_PACKET)) {
+    return;
+  }
+  if (FLAGS_quic_allow_chlo_buffering &&
+      new_sessions_allowed_per_event_loop_ <= 0) {
+    // Can't create new session any more. Wait till next event loop.
+    QUIC_BUG_IF(buffered_packets_.HasChloForConnection(current_connection_id_));
+    EnqueuePacketResult rs = buffered_packets_.EnqueuePacket(
+        current_connection_id_, form != GOOGLE_QUIC_PACKET, *current_packet_,
+        current_self_address_, current_peer_address_,
+        /*is_chlo=*/true, current_alpn_, framer_.version());
+    if (rs != EnqueuePacketResult::SUCCESS) {
+      OnBufferPacketFailure(rs, current_connection_id_);
+    }
+    return;
+  }
+  // Creates a new session and process all buffered packets for this connection.
+  QuicSession* session =
+      CreateQuicSession(current_connection_id_, current_peer_address_,
+                        current_alpn_, framer_.version());
+  QUIC_DLOG(INFO) << "Created new session for " << current_connection_id_;
+  session_map_.insert(
+      std::make_pair(current_connection_id_, QuicWrapUnique(session)));
+  std::list<BufferedPacket> packets =
+      buffered_packets_.DeliverPackets(current_connection_id_).buffered_packets;
+  // Process CHLO at first.
+  session->ProcessUdpPacket(current_self_address_, current_peer_address_,
+                            *current_packet_);
+  // Deliver queued-up packets in the same order as they arrived.
+  // Do this even when flag is off because there might be still some packets
+  // buffered in the store before flag is turned off.
+  DeliverPacketsToSession(packets, session);
+  --new_sessions_allowed_per_event_loop_;
+}
+
+const QuicSocketAddress QuicDispatcher::GetClientAddress() const {
+  return current_peer_address_;
+}
+
+bool QuicDispatcher::ShouldDestroySessionAsynchronously() {
+  return true;
+}
+
+void QuicDispatcher::SetLastError(QuicErrorCode error) {
+  last_error_ = error;
+}
+
+bool QuicDispatcher::OnUnauthenticatedUnknownPublicHeader(
+    const QuicPacketHeader& header) {
+  return true;
+}
+
+class StatelessRejectorProcessDoneCallback
+    : public StatelessRejector::ProcessDoneCallback {
+ public:
+  StatelessRejectorProcessDoneCallback(QuicDispatcher* dispatcher,
+                                       ParsedQuicVersion first_version,
+                                       PacketHeaderFormat form)
+      : dispatcher_(dispatcher),
+        current_client_address_(dispatcher->current_client_address_),
+        current_peer_address_(dispatcher->current_peer_address_),
+        current_self_address_(dispatcher->current_self_address_),
+        additional_context_(dispatcher->GetPerPacketContext()),
+        current_packet_(
+            dispatcher->current_packet_->Clone()),  // Note: copies the packet
+        first_version_(first_version),
+        current_packet_format_(form) {}
+
+  void Run(std::unique_ptr<StatelessRejector> rejector) override {
+    if (additional_context_ != nullptr) {
+      dispatcher_->RestorePerPacketContext(std::move(additional_context_));
+    }
+    dispatcher_->OnStatelessRejectorProcessDone(
+        std::move(rejector), current_client_address_, current_peer_address_,
+        current_self_address_, std::move(current_packet_), first_version_,
+        current_packet_format_);
+  }
+
+ private:
+  QuicDispatcher* dispatcher_;
+  QuicSocketAddress current_client_address_;
+  QuicSocketAddress current_peer_address_;
+  QuicSocketAddress current_self_address_;
+  // TODO(wub): Wrap all current_* variables into PerPacketContext. And rename
+  // |additional_context_| to |context_|.
+  std::unique_ptr<QuicPerPacketContext> additional_context_;
+  std::unique_ptr<QuicReceivedPacket> current_packet_;
+  ParsedQuicVersion first_version_;
+  const PacketHeaderFormat current_packet_format_;
+};
+
+void QuicDispatcher::MaybeRejectStatelessly(QuicConnectionId connection_id,
+
+                                            PacketHeaderFormat form,
+                                            ParsedQuicVersion version) {
+  if (version.handshake_protocol == PROTOCOL_TLS1_3) {
+    ProcessUnauthenticatedHeaderFate(kFateProcess, connection_id, form,
+                                     version);
+    return;
+    // TODO(nharper): Support buffering non-ClientHello packets when using TLS.
+  }
+  // TODO(rch): This logic should probably live completely inside the rejector.
+  if (!FLAGS_quic_allow_chlo_buffering ||
+      !GetQuicReloadableFlag(quic_use_cheap_stateless_rejects) ||
+      !GetQuicReloadableFlag(enable_quic_stateless_reject_support) ||
+      !ShouldAttemptCheapStatelessRejection()) {
+    // Not use cheap stateless reject.
+    ChloAlpnExtractor alpn_extractor;
+    if (FLAGS_quic_allow_chlo_buffering &&
+        !ChloExtractor::Extract(*current_packet_, GetSupportedVersions(),
+                                config_->create_session_tag_indicators(),
+                                &alpn_extractor, connection_id.length())) {
+      // Buffer non-CHLO packets.
+      ProcessUnauthenticatedHeaderFate(kFateBuffer, connection_id, form,
+                                       version);
+      return;
+    }
+    current_alpn_ = alpn_extractor.ConsumeAlpn();
+    ProcessUnauthenticatedHeaderFate(kFateProcess, connection_id, form,
+                                     version);
+    return;
+  }
+
+  std::unique_ptr<StatelessRejector> rejector(new StatelessRejector(
+      version, GetSupportedVersions(), crypto_config_, &compressed_certs_cache_,
+      helper()->GetClock(), helper()->GetRandomGenerator(),
+      current_packet_->length(), current_client_address_,
+      current_self_address_));
+  ChloValidator validator(session_helper_.get(), current_client_address_,
+                          current_peer_address_, current_self_address_,
+                          rejector.get());
+  if (!ChloExtractor::Extract(*current_packet_, GetSupportedVersions(),
+                              config_->create_session_tag_indicators(),
+                              &validator, connection_id.length())) {
+    ProcessUnauthenticatedHeaderFate(kFateBuffer, connection_id, form, version);
+    return;
+  }
+  current_alpn_ = validator.ConsumeAlpn();
+
+  if (!validator.can_accept()) {
+    // This CHLO is prohibited by policy.
+    QUIC_CODE_COUNT(quic_reject_cant_accept_chlo);
+    StatelessConnectionTerminator terminator(connection_id, &framer_, helper(),
+                                             time_wait_list_manager_.get());
+    terminator.CloseConnection(QUIC_HANDSHAKE_FAILED, validator.error_details(),
+                               form != GOOGLE_QUIC_PACKET);
+    OnConnectionClosedStatelessly(QUIC_HANDSHAKE_FAILED);
+    ProcessUnauthenticatedHeaderFate(kFateTimeWait, connection_id, form,
+                                     version);
+    return;
+  }
+
+  // If we were able to make a decision about this CHLO based purely on the
+  // information available in OnChlo, just invoke the done callback immediately.
+  if (rejector->state() != StatelessRejector::UNKNOWN) {
+    ProcessStatelessRejectorState(std::move(rejector),
+                                  version.transport_version, form);
+    return;
+  }
+
+  // Insert into set of connection IDs to buffer
+  const bool ok =
+      temporarily_buffered_connections_.insert(connection_id).second;
+  QUIC_BUG_IF(!ok)
+      << "Processing multiple stateless rejections for connection ID "
+      << connection_id;
+
+  // Continue stateless rejector processing
+  std::unique_ptr<StatelessRejectorProcessDoneCallback> cb(
+      new StatelessRejectorProcessDoneCallback(this, version, form));
+  StatelessRejector::Process(std::move(rejector), std::move(cb));
+}
+
+void QuicDispatcher::OnStatelessRejectorProcessDone(
+    std::unique_ptr<StatelessRejector> rejector,
+    const QuicSocketAddress& current_client_address,
+    const QuicSocketAddress& current_peer_address,
+    const QuicSocketAddress& current_self_address,
+    std::unique_ptr<QuicReceivedPacket> current_packet,
+    ParsedQuicVersion first_version,
+    PacketHeaderFormat current_packet_format) {
+  // Reset current_* to correspond to the packet which initiated the stateless
+  // reject logic.
+  current_client_address_ = current_client_address;
+  current_peer_address_ = current_peer_address;
+  current_self_address_ = current_self_address;
+  current_packet_ = current_packet.get();
+  current_connection_id_ = rejector->connection_id();
+  framer_.set_version(first_version);
+
+  // Stop buffering packets on this connection
+  const auto num_erased =
+      temporarily_buffered_connections_.erase(rejector->connection_id());
+  QUIC_BUG_IF(num_erased != 1) << "Completing stateless rejection logic for "
+                                  "non-buffered connection ID "
+                               << rejector->connection_id();
+
+  // If this connection has gone into time-wait during the async processing,
+  // don't proceed.
+  if (time_wait_list_manager_->IsConnectionIdInTimeWait(
+          rejector->connection_id())) {
+    time_wait_list_manager_->ProcessPacket(
+        current_self_address, current_peer_address, rejector->connection_id(),
+        current_packet_format, GetPerPacketContext());
+    return;
+  }
+
+  ProcessStatelessRejectorState(std::move(rejector),
+                                first_version.transport_version,
+                                current_packet_format);
+}
+
+void QuicDispatcher::ProcessStatelessRejectorState(
+    std::unique_ptr<StatelessRejector> rejector,
+    QuicTransportVersion first_version,
+    PacketHeaderFormat form) {
+  QuicPacketFate fate;
+  switch (rejector->state()) {
+    case StatelessRejector::FAILED: {
+      // There was an error processing the client hello.
+      QUIC_CODE_COUNT(quic_reject_error_processing_chlo);
+      StatelessConnectionTerminator terminator(rejector->connection_id(),
+                                               &framer_, helper(),
+                                               time_wait_list_manager_.get());
+      terminator.CloseConnection(rejector->error(), rejector->error_details(),
+                                 form != GOOGLE_QUIC_PACKET);
+      fate = kFateTimeWait;
+      break;
+    }
+
+    case StatelessRejector::UNSUPPORTED:
+      // Cheap stateless rejects are not supported so process the packet.
+      fate = kFateProcess;
+      break;
+
+    case StatelessRejector::ACCEPTED:
+      // Contains a valid CHLO, so process the packet and create a connection.
+      fate = kFateProcess;
+      break;
+
+    case StatelessRejector::REJECTED: {
+      QUIC_BUG_IF(first_version != framer_.transport_version())
+          << "SREJ: Client's version: " << QuicVersionToString(first_version)
+          << " is different from current dispatcher framer's version: "
+          << QuicVersionToString(framer_.transport_version());
+      StatelessConnectionTerminator terminator(rejector->connection_id(),
+                                               &framer_, helper(),
+                                               time_wait_list_manager_.get());
+      terminator.RejectConnection(
+          rejector->reply().GetSerialized().AsStringPiece(),
+          form != GOOGLE_QUIC_PACKET);
+      OnConnectionRejectedStatelessly();
+      fate = kFateTimeWait;
+      break;
+    }
+
+    default:
+      QUIC_BUG << "Rejector has invalid state " << rejector->state();
+      fate = kFateDrop;
+      break;
+  }
+  ProcessUnauthenticatedHeaderFate(fate, rejector->connection_id(), form,
+                                   rejector->version());
+}
+
+const QuicTransportVersionVector&
+QuicDispatcher::GetSupportedTransportVersions() {
+  return version_manager_->GetSupportedTransportVersions();
+}
+
+const ParsedQuicVersionVector& QuicDispatcher::GetSupportedVersions() {
+  return version_manager_->GetSupportedVersions();
+}
+
+void QuicDispatcher::DeliverPacketsToSession(
+    const std::list<BufferedPacket>& packets,
+    QuicSession* session) {
+  for (const BufferedPacket& packet : packets) {
+    session->ProcessUdpPacket(packet.self_address, packet.peer_address,
+                              *(packet.packet));
+  }
+}
+
+void QuicDispatcher::DisableFlagValidation() {
+  framer_.set_validate_flags(false);
+}
+
+}  // namespace quic