Weave Packet Receiver

components/proximity_auth/ble/bluetooth_low_energy_weave_packet_receiver.cc

+// Copyright 2016 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 "components/proximity_auth/ble/bluetooth_low_energy_weave_packet_receiver.h"
+
+#include "base/logging.h"
+
+using proximity_auth::BluetoothLowEnergyWeavePacketGenerator;
+
+namespace proximity_auth {
+namespace {

[Kyle Horimoto, 2016/06/09 23:59:46]

The anonymous namespace should be above the proximity_auth one, not nested
inside of it.

[jingxuy, 2016/06/10 23:11:12]

Done.

+typedef BluetoothLowEnergyWeavePacketGenerator::PacketType PacketType;
+typedef BluetoothLowEnergyWeavePacketGenerator::ControlCommand ControlCommand;
+typedef BluetoothLowEnergyWeavePacketGenerator::ReasonForClose ReasonForClose;
+
+const uint8_t kMaxPacketCounter = 8;
+}  // namespace
+
+BluetoothLowEnergyWeavePacketReceiver::Factory*
+    BluetoothLowEnergyWeavePacketReceiver::Factory::factory_instance_ = nullptr;
+
+std::unique_ptr<BluetoothLowEnergyWeavePacketReceiver>
+BluetoothLowEnergyWeavePacketReceiver::Factory::NewInstance() {
+  if (factory_instance_ == nullptr) {
+    factory_instance_ = new Factory();
+  }
+  return std::unique_ptr<BluetoothLowEnergyWeavePacketReceiver>(
+      factory_instance_->BuildInstance());
+}
+
+void BluetoothLowEnergyWeavePacketReceiver::Factory::SetInstanceForTesting(
+    Factory* factory) {
+  factory_instance_ = factory;
+}
+
+BluetoothLowEnergyWeavePacketReceiver*
+BluetoothLowEnergyWeavePacketReceiver::Factory::BuildInstance() {
+  return new BluetoothLowEnergyWeavePacketReceiver();
+}
+
+BluetoothLowEnergyWeavePacketReceiver::BluetoothLowEnergyWeavePacketReceiver()
+    : packet_size_(0),
+      packet_number_(0),
+      state_(State::EXCHANGING_CONTROLS),
+      reason_for_close_(ReasonForClose::CLOSE_WITHOUT_ERROR) {}
+
+BluetoothLowEnergyWeavePacketReceiver::
+    ~BluetoothLowEnergyWeavePacketReceiver() {}
+
+void BluetoothLowEnergyWeavePacketReceiver::ResetReceiver() {
+  packet_size_ = 0;
+  packet_number_ = 0;
+  state_ = State::EXCHANGING_CONTROLS;
+  reason_for_close_ = ReasonForClose::CLOSE_WITHOUT_ERROR;
+}
+
+BluetoothLowEnergyWeavePacketReceiver::State
+BluetoothLowEnergyWeavePacketReceiver::GetState() {
+  return state_;
+}
+
+uint32_t BluetoothLowEnergyWeavePacketReceiver::GetPacketSize() {
+  // packet_size_ is well defined in every state.
+  return packet_size_;
+}
+
+ReasonForClose BluetoothLowEnergyWeavePacketReceiver::GetReasonForClose() {
+  DCHECK(state_ == State::CONNECTION_CLOSED);
+  return reason_for_close_;
+}
+
+std::string BluetoothLowEnergyWeavePacketReceiver::GetDataMessage() {
+  DCHECK(state_ == State::DATA_READY);
+  return std::string(data_message_.begin(), data_message_.end());
+}
+
+BluetoothLowEnergyWeavePacketReceiver::State
+BluetoothLowEnergyWeavePacketReceiver::ReceivePacket(const Packet& packet) {

[Kyle Horimoto, 2016/06/09 23:59:46]

General comment: You don't preserve messages if they aren't immediately
received. For example, say you receive 2 data messages back-to-back that are 2
packets each.

1) Receive packet 1 of message 1. State = RECEIVING_DATA.
2) Receive packet 2 of message 1. State = DATA_READY.
3) No one has called GetDataMessage() yet.
4) Receive packet 1 of message 2. State = RECEIVING DATA.
5) First message is lost and was never read.

You need to make sure that this class keeps track of previous messages which
have not yet been retrieved.

[jingxuy, 2016/06/10 23:11:12]

Acknowledged.

+  VerifyPacketCounter(packet);
+
+  switch (state_) {
+    case State::EXCHANGING_CONTROLS:
+      ReceiveWithEmptyData(packet);
+      break;
+    case State::RECEIVING_DATA:
+      ReceiveWithPartialData(packet);
+      break;
+    case State::DATA_READY:
+      data_message_.clear();
+      ReceiveWithEmptyData(packet);
+      break;
+    default:
+      // Receiving an message in connection close or error state is not valid
+      state_ = State::ERROR;
+      break;
+  }
+  return state_;
+}
+
+void BluetoothLowEnergyWeavePacketReceiver::ReceiveWithEmptyData(
+    const Packet& packet) {
+  // TODO(jingxuy): add dcheck stuff
+  PacketType type = GetPacketType(packet);
+  switch (type) {
+    case PacketType::CONTROL:
+      switch (GetControlCommand(packet)) {
+        case ControlCommand::CONNECTION_REQUEST:
+          ReceiveConnectionRequest(packet);
+          break;
+        case ControlCommand::CONNECTION_RESPONSE:
+          ReceiveConnectionResponse(packet);
+          break;
+        case ControlCommand::CONNECTION_CLOSE:
+          ReceiveConnectionClose(packet);
+          break;
+        default:
+          state_ = State::ERROR;
+          break;
+      }
+      break;
+    case PacketType::DATA:
+      if (!IsFirstDataPacket(packet)) {
+        state_ = State::ERROR;
+      } else {
+        AppendData(packet);

[Kyle Horimoto, 2016/06/09 23:59:46]

You also need to check that it has data at all (packet.size() > 1). Same
everywhere else you call AppendData().

[jingxuy, 2016/06/10 23:11:12]

Acknowledged.

+      }
+      break;
+    default:
+      state_ = State::ERROR;
+      break;
+  }
+}
+
+void BluetoothLowEnergyWeavePacketReceiver::ReceiveWithPartialData(
+    const Packet& packet) {
+  // TODO(jingxuy): add dcheck stuff
+  PacketType type = GetPacketType(packet);
+  switch (type) {
+    case PacketType::CONTROL:

[Kyle Horimoto, 2016/06/09 23:59:46]

If we're receiving partial data, we shouldn't even receive a CONNECTION_CLOSE.
Think about it: say we are in the middle of a data transfer with counters 0, 1,
2, and 3. But, midway through, we get a connection close packet with counter 4.
That packet counter would be out of order, so an error would occur and this code
would never be executed.

[jingxuy, 2016/06/10 23:11:12]

Pending response from Gustavo

+      if (GetControlCommand(packet) == ControlCommand::CONNECTION_CLOSE) {
+        ReceiveConnectionClose(packet);
+      } else {
+        // Shouldn't be receiving request/response in the middle of a data

[Kyle Horimoto, 2016/06/09 23:59:46]

DLOG something here and everywhere else where there's an unexpected error.

+        // transaction.
+        state_ = State::ERROR;
+      }
+      break;
+    case PacketType::DATA:
+      if (IsFirstDataPacket(packet)) {
+        state_ = State::ERROR;
+      } else {
+        AppendData(packet);
+        if (IsLastDataPacket(packet)) {
+          state_ = State::DATA_READY;
+        }
+      }
+      break;
+    default:
+      state_ = State::ERROR;
+      break;
+  }
+}
+
+void BluetoothLowEnergyWeavePacketReceiver::ReceiveConnectionRequest(
+    const Packet& packet) {
+  // TODO(jingxuy): add dcheck stuff
+  uint16_t min_version = GetShortField(packet, 1);
+  uint16_t max_version = GetShortField(packet, 3);
+  if (!(min_version == 1 && max_version == 1)) {
+    state_ = State::ERROR;
+  } else {
+    packet_size_ = GetShortField(packet, 5);
+    // TODO(jingxuy): what do I do with the 13 bytes of data?

[Kyle Horimoto, 2016/06/09 23:59:45]

You should AppendData() and set state to DATA_READY.

Same below.

[jingxuy, 2016/06/10 23:11:12]

Pending response from Gustavo

+  }
+}
+
+void BluetoothLowEnergyWeavePacketReceiver::ReceiveConnectionResponse(
+    const Packet& packet) {
+  // TODO(jingxuy): add dcheck stuff
+  uint16_t selected_version = GetShortField(packet, 1);
+  if (selected_version != 1) {
+    state_ = State::ERROR;
+  } else {
+    packet_size_ = GetShortField(packet, 3);
+    // TODO(jingxuy): what do I do with the 15 bytes of data?
+  }
+}
+
+void BluetoothLowEnergyWeavePacketReceiver::ReceiveConnectionClose(
+    const Packet& packet) {
+  // TODO(jingxuy): add dcheck stuff
+  reason_for_close_ = static_cast<ReasonForClose>(GetShortField(packet, 1));

[Kyle Horimoto, 2016/06/09 23:59:46]

What happens if the value passed isn't a ReasonForClose? Remember that you're
receiving this from another (possibly buggy) client, so you can't assume that
the data you're receiving is always correct.

[jingxuy, 2016/06/10 23:11:12]

Done.

+  state_ = State::CONNECTION_CLOSED;
+}
+
+void BluetoothLowEnergyWeavePacketReceiver::AppendData(const Packet& packet) {
+  // TODO(jingxuy): add dcheck stuff
+  // Append to data_message_ bytes 1 through end of the packet.
+  data_message_.insert(data_message_.end(), packet.begin() + 1, packet.end());
+}
+
+uint16_t BluetoothLowEnergyWeavePacketReceiver::GetShortField(
+    const Packet& packet,
+    uint32_t index) {
+  DCHECK_LT(index, packet.size());
+  DCHECK_LT(index + 1, packet.size());
+
+  // packet[index + 1] is the upper byte and packet[index] is the lower byte.
+  return (packet[index + 1] << 8) | packet[index];
+}
+
+PacketType BluetoothLowEnergyWeavePacketReceiver::GetPacketType(
+    const Packet& packet) {
+  // Packet type is stored in the highest bit of the first byte.
+  return static_cast<PacketType>((packet[0] >> 7) & 1);
+}
+
+ControlCommand BluetoothLowEnergyWeavePacketReceiver::GetControlCommand(
+    const Packet& packet) {
+  // Control command is stored in the lower 4 bits of the first byte.
+  return static_cast<ControlCommand>((packet[0] & 0x0F));
+}
+
+void BluetoothLowEnergyWeavePacketReceiver::VerifyPacketCounter(
+    const Packet& packet) {
+  if (state_ == State::ERROR)
+    return;
+
+  // Packet counter is bits 4, 5, and 6 of the first byte.
+  uint8_t count = (packet[0] >> 4) & 7;
+
+  if (count == (packet_number_ % kMaxPacketCounter)) {
+    packet_number_++;
+  } else {
+    state_ = State::ERROR;
+  }
+}
+
+bool BluetoothLowEnergyWeavePacketReceiver::IsFirstDataPacket(
+    const Packet& packet) {
+  // Bit 3 determines whether the packet is the first packet of the message.
+  return (packet[0] >> 3) & 1;
+}
+
+bool BluetoothLowEnergyWeavePacketReceiver::IsLastDataPacket(
+    const Packet& packet) {
+  // Bit 2 determines whether the packet is the last packet of the message.
+  return (packet[0] >> 2) & 1;
+}
+
+}  // namespace proximity_auth