src/connectivity/bluetooth/core/bt-host/l2cap/enhanced_retransmission_mode_engines_unittest.cc

// Copyright 2020 The Fuchsia 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 "enhanced_retransmission_mode_engines.h"

#include <gtest/gtest.h>

#include "lib/gtest/test_loop_fixture.h"
#include "src/connectivity/bluetooth/core/bt-host/common/test_helpers.h"
#include "src/connectivity/bluetooth/core/bt-host/l2cap/fragmenter.h"

namespace bt {
namespace l2cap {
namespace internal {
namespace {

class L2CAP_EnhancedRetransmissionModeEnginesTest : public ::gtest::TestLoopFixture {};

constexpr size_t kMaxTransmissions = 2;
constexpr size_t kTxWindow = 63;

constexpr hci::ConnectionHandle kTestHandle = 0x0001;
constexpr ChannelId kTestChannelId = 0x0001;
constexpr uint8_t kExtendedControlFBitMask = 0b1000'0000;

void NoOpTxCallback(ByteBufferPtr){};
void NoOpFailureCallback(){};

TEST_F(L2CAP_EnhancedRetransmissionModeEnginesTest, MakeLinkedERTMEngines) {
  auto [rx_engine, tx_engine] =
      MakeLinkedEnhancedRetransmissionModeEngines(kTestChannelId, kDefaultMTU, kMaxTransmissions,
                                                  kTxWindow, NoOpTxCallback, NoOpFailureCallback);
  EXPECT_TRUE(rx_engine);
  EXPECT_TRUE(tx_engine);
}

// This test that TxEngine sends I-Frames whose acknowledgement sequence numbers match the receive
// sequence number in RxEngine. This also tests that peer acknowledgement restarts our outbound data
// that was paused by hitting TxWindow. This mirrors the L2CAP Test Specification L2CAP/ERM/BV-06-C.
TEST_F(L2CAP_EnhancedRetransmissionModeEnginesTest,
       OutboundInformationFramesAcknowledgeReceivedInformationFrames) {
  int tx_count = 0;
  auto tx_callback = [&tx_count](ByteBufferPtr pdu) {
    ASSERT_TRUE(pdu);
    // Unlike the Test Spec's sequence diagram, we respond to the peer's I-Frame with a Receiver
    // Ready (which is always allowed), so our subsequent I-Frame is actually the third outbound.
    if (tx_count == 0) {
      ASSERT_LE(sizeof(SimpleInformationFrameHeader), pdu->size());
      ASSERT_TRUE(pdu->As<EnhancedControlField>().designates_information_frame());
      const auto& header = pdu->As<SimpleInformationFrameHeader>();
      EXPECT_EQ(0, header.tx_seq());
      EXPECT_EQ(0, header.receive_seq_num());
    } else if (tx_count == 2) {
      ASSERT_LE(sizeof(SimpleInformationFrameHeader), pdu->size());
      ASSERT_TRUE(pdu->As<EnhancedControlField>().designates_information_frame());
      const auto& header = pdu->As<SimpleInformationFrameHeader>();
      EXPECT_EQ(1, header.tx_seq());

      // Acknowledges the I-Frame from the peer.
      EXPECT_EQ(1, header.receive_seq_num());
    }
    tx_count++;
  };
  auto [rx_engine, tx_engine] = MakeLinkedEnhancedRetransmissionModeEngines(
      kTestChannelId, kDefaultMTU, kMaxTransmissions, /*n_frames_in_tx_window=*/1, tx_callback,
      NoOpFailureCallback);
  ASSERT_TRUE(rx_engine);
  ASSERT_TRUE(tx_engine);

  tx_engine->QueueSdu(std::make_unique<DynamicByteBuffer>(StaticByteBuffer{'p', 'i', 'n', 'g'}));
  RunLoopUntilIdle();
  EXPECT_EQ(1, tx_count);

  // Receive an I-frame containing an acknowledgment including the frame that we transmitted.
  // See Core Spec, v5, Vol 3, Part A, Section 3.3.2, I-Frame Enhanced Control Field.
  auto info_frame = StaticByteBuffer(0, 1, 'p', 'o', 'n', 'g');
  EXPECT_TRUE(rx_engine->ProcessPdu(
      Fragmenter(kTestHandle)
          .BuildFrame(kTestChannelId, info_frame, FrameCheckSequenceOption::kIncludeFcs)));
  RunLoopUntilIdle();
  EXPECT_EQ(2, tx_count);

  tx_engine->QueueSdu(std::make_unique<DynamicByteBuffer>(StaticByteBuffer{'b', 'y', 'e', 'e'}));
  RunLoopUntilIdle();
  EXPECT_EQ(3, tx_count);
}

// This tests the integration of receiving an acknowledgment sequence with triggering retransmission
// of unacknowledged I-Frames. This mirrors the L2CAP Test Specification L2CAP/ERM/BV-18-C.
TEST_F(L2CAP_EnhancedRetransmissionModeEnginesTest,
       RetransmitAfterPollResponseDoesNotAcknowledgeSentFrames) {
  DynamicByteBuffer info_frame;
  int tx_count = 0;
  auto tx_callback = [&info_frame, &tx_count](ByteBufferPtr pdu) {
    // The first packet is the I-Frame containing the data that we sent.
    // The second packet is the S-Frame polling for the peer after the Retransmission Timer expires.
    // It is not checked to keep the tests less fragile, as the first two packets are already
    // covered by L2CAP_EnhancedRetransmissionModeTxEngineTest.
    if (tx_count == 0) {
      info_frame = DynamicByteBuffer(*pdu);
    } else if (tx_count == 2) {
      EXPECT_TRUE(ContainersEqual(info_frame, *pdu));
    }
    tx_count++;
  };
  auto [rx_engine, tx_engine] = MakeLinkedEnhancedRetransmissionModeEngines(
      kTestChannelId, kDefaultMTU, kMaxTransmissions, kTxWindow, tx_callback, NoOpFailureCallback);
  ASSERT_TRUE(rx_engine);
  ASSERT_TRUE(tx_engine);

  tx_engine->QueueSdu(std::make_unique<DynamicByteBuffer>(StaticByteBuffer{'a'}));
  RunLoopUntilIdle();
  EXPECT_EQ(1, tx_count);

  ASSERT_TRUE(RunLoopFor(kErtmReceiverReadyPollTimerDuration));
  EXPECT_EQ(2, tx_count);

  // Receive an S-frame containing an acknowledgment not including the frame that we transmitted. F
  // is set. See Core Spec, v5, Vol 3, Part A, Section 3.3.2, S-Frame Enhanced Control Field.
  auto receiver_ready = StaticByteBuffer(0b1 | kExtendedControlFBitMask, 0);
  rx_engine->ProcessPdu(
      Fragmenter(kTestHandle)
          .BuildFrame(kTestChannelId, receiver_ready, FrameCheckSequenceOption::kIncludeFcs));
  RunLoopUntilIdle();

  // Check that this caused a retransmission of the initial I-Frame.
  EXPECT_EQ(3, tx_count);
}

}  // namespace
}  // namespace internal
}  // namespace l2cap
}  // namespace bt