/*
 *  Copyright 2011 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 <algorithm>
#include <memory>
#include <set>

#include "p2p/base/dtlstransport.h"
#include "p2p/base/fakeicetransport.h"
#include "p2p/base/packettransportinternal.h"
#include "rtc_base/checks.h"
#include "rtc_base/dscp.h"
#include "rtc_base/gunit.h"
#include "rtc_base/helpers.h"
#include "rtc_base/ssladapter.h"
#include "rtc_base/sslidentity.h"
#include "rtc_base/sslstreamadapter.h"
#include "rtc_base/stringutils.h"

#define MAYBE_SKIP_TEST(feature)                                  \
  if (!(rtc::SSLStreamAdapter::feature())) {                      \
    RTC_LOG(LS_INFO) << #feature " feature disabled... skipping"; \
    return;                                                       \
  }

namespace cricket {

static const size_t kPacketNumOffset = 8;
static const size_t kPacketHeaderLen = 12;
static const int kFakePacketId = 0x1234;
static const int kTimeout = 10000;

static bool IsRtpLeadByte(uint8_t b) {
  return ((b & 0xC0) == 0x80);
}

// |modify_digest| is used to set modified fingerprints that are meant to fail
// validation.
void SetRemoteFingerprintFromCert(
    DtlsTransport* transport,
    const rtc::scoped_refptr<rtc::RTCCertificate>& cert,
    bool modify_digest = false) {
  rtc::SSLFingerprint* fingerprint =
      rtc::SSLFingerprint::CreateFromCertificate(cert);
  if (modify_digest) {
    ++fingerprint->digest[0];
  }
  // Even if digest is verified to be incorrect, should fail asynchrnously.
  EXPECT_TRUE(transport->SetRemoteFingerprint(
      fingerprint->algorithm,
      reinterpret_cast<const uint8_t*>(fingerprint->digest.data()),
      fingerprint->digest.size()));
  delete fingerprint;
}

class DtlsTestClient : public sigslot::has_slots<> {
 public:
  explicit DtlsTestClient(const std::string& name) : name_(name) {}
  void CreateCertificate(rtc::KeyType key_type) {
    certificate_ =
        rtc::RTCCertificate::Create(std::unique_ptr<rtc::SSLIdentity>(
            rtc::SSLIdentity::Generate(name_, key_type)));
  }
  const rtc::scoped_refptr<rtc::RTCCertificate>& certificate() {
    return certificate_;
  }
  void SetupMaxProtocolVersion(rtc::SSLProtocolVersion version) {
    ssl_max_version_ = version;
  }
  // Set up fake ICE transport and real DTLS transport under test.
  void SetupTransports(IceRole role, int async_delay_ms = 0) {
    fake_ice_transport_.reset(new FakeIceTransport("fake", 0));
    fake_ice_transport_->SetAsync(true);
    fake_ice_transport_->SetAsyncDelay(async_delay_ms);
    fake_ice_transport_->SetIceRole(role);
    fake_ice_transport_->SetIceTiebreaker((role == ICEROLE_CONTROLLING) ? 1
                                                                        : 2);
    // Hook the raw packets so that we can verify they are encrypted.
    fake_ice_transport_->SignalReadPacket.connect(
        this, &DtlsTestClient::OnFakeIceTransportReadPacket);

    dtls_transport_.reset(
        new DtlsTransport(fake_ice_transport_.get(), rtc::CryptoOptions()));
    dtls_transport_->SetSslMaxProtocolVersion(ssl_max_version_);
    // Note: Certificate may be null here if testing passthrough.
    dtls_transport_->SetLocalCertificate(certificate_);
    dtls_transport_->SignalWritableState.connect(
        this, &DtlsTestClient::OnTransportWritableState);
    dtls_transport_->SignalReadPacket.connect(
        this, &DtlsTestClient::OnTransportReadPacket);
    dtls_transport_->SignalSentPacket.connect(
        this, &DtlsTestClient::OnTransportSentPacket);
  }

  FakeIceTransport* fake_ice_transport() { return fake_ice_transport_.get(); }

  DtlsTransport* dtls_transport() { return dtls_transport_.get(); }

  // Simulate fake ICE transports connecting.
  bool Connect(DtlsTestClient* peer, bool asymmetric) {
    fake_ice_transport_->SetDestination(peer->fake_ice_transport(), asymmetric);
    return true;
  }

  int received_dtls_client_hellos() const {
    return received_dtls_client_hellos_;
  }

  int received_dtls_server_hellos() const {
    return received_dtls_server_hellos_;
  }

  void CheckRole(rtc::SSLRole role) {
    if (role == rtc::SSL_CLIENT) {
      ASSERT_EQ(0, received_dtls_client_hellos_);
      ASSERT_GT(received_dtls_server_hellos_, 0);
    } else {
      ASSERT_GT(received_dtls_client_hellos_, 0);
      ASSERT_EQ(0, received_dtls_server_hellos_);
    }
  }

  void CheckSrtp(int expected_crypto_suite) {
    int crypto_suite;
    bool rv = dtls_transport_->GetSrtpCryptoSuite(&crypto_suite);
    if (dtls_transport_->IsDtlsActive() && expected_crypto_suite) {
      ASSERT_TRUE(rv);
      ASSERT_EQ(crypto_suite, expected_crypto_suite);
    } else {
      ASSERT_FALSE(rv);
    }
  }

  void CheckSsl() {
    int cipher;
    bool rv = dtls_transport_->GetSslCipherSuite(&cipher);
    if (dtls_transport_->IsDtlsActive()) {
      ASSERT_TRUE(rv);
      EXPECT_TRUE(
          rtc::SSLStreamAdapter::IsAcceptableCipher(cipher, rtc::KT_DEFAULT));
    } else {
      ASSERT_FALSE(rv);
    }
  }

  void SendPackets(size_t size, size_t count, bool srtp) {
    std::unique_ptr<char[]> packet(new char[size]);
    size_t sent = 0;
    do {
      // Fill the packet with a known value and a sequence number to check
      // against, and make sure that it doesn't look like DTLS.
      memset(packet.get(), sent & 0xff, size);
      packet[0] = (srtp) ? 0x80 : 0x00;
      rtc::SetBE32(packet.get() + kPacketNumOffset,
                   static_cast<uint32_t>(sent));

      // Only set the bypass flag if we've activated DTLS.
      int flags = (certificate_ && srtp) ? PF_SRTP_BYPASS : 0;
      rtc::PacketOptions packet_options;
      packet_options.packet_id = kFakePacketId;
      int rv = dtls_transport_->SendPacket(packet.get(), size, packet_options,
                                           flags);
      ASSERT_GT(rv, 0);
      ASSERT_EQ(size, static_cast<size_t>(rv));
      ++sent;
    } while (sent < count);
  }

  int SendInvalidSrtpPacket(size_t size) {
    std::unique_ptr<char[]> packet(new char[size]);
    // Fill the packet with 0 to form an invalid SRTP packet.
    memset(packet.get(), 0, size);

    rtc::PacketOptions packet_options;
    return dtls_transport_->SendPacket(packet.get(), size, packet_options,
                                       PF_SRTP_BYPASS);
  }

  void ExpectPackets(size_t size) {
    packet_size_ = size;
    received_.clear();
  }

  size_t NumPacketsReceived() { return received_.size(); }

  // Inverse of SendPackets.
  bool VerifyPacket(const char* data, size_t size, uint32_t* out_num) {
    if (size != packet_size_ ||
        (data[0] != 0 && static_cast<uint8_t>(data[0]) != 0x80)) {
      return false;
    }
    uint32_t packet_num = rtc::GetBE32(data + kPacketNumOffset);
    for (size_t i = kPacketHeaderLen; i < size; ++i) {
      if (static_cast<uint8_t>(data[i]) != (packet_num & 0xff)) {
        return false;
      }
    }
    if (out_num) {
      *out_num = packet_num;
    }
    return true;
  }
  bool VerifyEncryptedPacket(const char* data, size_t size) {
    // This is an encrypted data packet; let's make sure it's mostly random;
    // less than 10% of the bytes should be equal to the cleartext packet.
    if (size <= packet_size_) {
      return false;
    }
    uint32_t packet_num = rtc::GetBE32(data + kPacketNumOffset);
    int num_matches = 0;
    for (size_t i = kPacketNumOffset; i < size; ++i) {
      if (static_cast<uint8_t>(data[i]) == (packet_num & 0xff)) {
        ++num_matches;
      }
    }
    return (num_matches < ((static_cast<int>(size) - 5) / 10));
  }

  // Transport callbacks
  void OnTransportWritableState(rtc::PacketTransportInternal* transport) {
    RTC_LOG(LS_INFO) << name_ << ": Transport '" << transport->transport_name()
                     << "' is writable";
  }

  void OnTransportReadPacket(rtc::PacketTransportInternal* transport,
                             const char* data,
                             size_t size,
                             const rtc::PacketTime& packet_time,
                             int flags) {
    uint32_t packet_num = 0;
    ASSERT_TRUE(VerifyPacket(data, size, &packet_num));
    received_.insert(packet_num);
    // Only DTLS-SRTP packets should have the bypass flag set.
    int expected_flags =
        (certificate_ && IsRtpLeadByte(data[0])) ? PF_SRTP_BYPASS : 0;
    ASSERT_EQ(expected_flags, flags);
  }

  void OnTransportSentPacket(rtc::PacketTransportInternal* transport,
                             const rtc::SentPacket& sent_packet) {
    sent_packet_ = sent_packet;
  }

  rtc::SentPacket sent_packet() const { return sent_packet_; }

  // Hook into the raw packet stream to make sure DTLS packets are encrypted.
  void OnFakeIceTransportReadPacket(rtc::PacketTransportInternal* transport,
                                    const char* data,
                                    size_t size,
                                    const rtc::PacketTime& time,
                                    int flags) {
    // Flags shouldn't be set on the underlying Transport packets.
    ASSERT_EQ(0, flags);

    // Look at the handshake packets to see what role we played.
    // Check that non-handshake packets are DTLS data or SRTP bypass.
    if (data[0] == 22 && size > 17) {
      if (data[13] == 1) {
        ++received_dtls_client_hellos_;
      } else if (data[13] == 2) {
        ++received_dtls_server_hellos_;
      }
    } else if (dtls_transport_->IsDtlsActive() &&
               !(data[0] >= 20 && data[0] <= 22)) {
      ASSERT_TRUE(data[0] == 23 || IsRtpLeadByte(data[0]));
      if (data[0] == 23) {
        ASSERT_TRUE(VerifyEncryptedPacket(data, size));
      } else if (IsRtpLeadByte(data[0])) {
        ASSERT_TRUE(VerifyPacket(data, size, NULL));
      }
    }
  }

 private:
  std::string name_;
  rtc::scoped_refptr<rtc::RTCCertificate> certificate_;
  std::unique_ptr<FakeIceTransport> fake_ice_transport_;
  std::unique_ptr<DtlsTransport> dtls_transport_;
  size_t packet_size_ = 0u;
  std::set<int> received_;
  rtc::SSLProtocolVersion ssl_max_version_ = rtc::SSL_PROTOCOL_DTLS_12;
  int received_dtls_client_hellos_ = 0;
  int received_dtls_server_hellos_ = 0;
  rtc::SentPacket sent_packet_;
};

// Base class for DtlsTransportTest and DtlsEventOrderingTest, which
// inherit from different variants of testing::Test.
//
// Note that this test always uses a FakeClock, due to the |fake_clock_| member
// variable.
class DtlsTransportTestBase {
 public:
  DtlsTransportTestBase() : client1_("P1"), client2_("P2"), use_dtls_(false) {}

  void SetMaxProtocolVersions(rtc::SSLProtocolVersion c1,
                              rtc::SSLProtocolVersion c2) {
    client1_.SetupMaxProtocolVersion(c1);
    client2_.SetupMaxProtocolVersion(c2);
  }
  // If not called, DtlsTransport will be used in SRTP bypass mode.
  void PrepareDtls(rtc::KeyType key_type) {
    client1_.CreateCertificate(key_type);
    client2_.CreateCertificate(key_type);
    use_dtls_ = true;
  }

  // This test negotiates DTLS parameters before the underlying transports are
  // writable. DtlsEventOrderingTest is responsible for exercising differerent
  // orderings.
  bool Connect(bool client1_server = true) {
    Negotiate(client1_server);
    EXPECT_TRUE(client1_.Connect(&client2_, false));

    EXPECT_TRUE_SIMULATED_WAIT(client1_.dtls_transport()->writable() &&
                                   client2_.dtls_transport()->writable(),
                               kTimeout, fake_clock_);
    if (!client1_.dtls_transport()->writable() ||
        !client2_.dtls_transport()->writable())
      return false;

    // Check that we used the right roles.
    if (use_dtls_) {
      client1_.CheckRole(client1_server ? rtc::SSL_SERVER : rtc::SSL_CLIENT);
      client2_.CheckRole(client1_server ? rtc::SSL_CLIENT : rtc::SSL_SERVER);
    }

    if (use_dtls_) {
      // Check that we negotiated the right ciphers. Since GCM ciphers are not
      // negotiated by default, we should end up with SRTP_AES128_CM_SHA1_32.
      client1_.CheckSrtp(rtc::SRTP_AES128_CM_SHA1_32);
      client2_.CheckSrtp(rtc::SRTP_AES128_CM_SHA1_32);
    } else {
      // If DTLS isn't actually being used, GetSrtpCryptoSuite should return
      // false.
      client1_.CheckSrtp(rtc::SRTP_INVALID_CRYPTO_SUITE);
      client2_.CheckSrtp(rtc::SRTP_INVALID_CRYPTO_SUITE);
    }

    client1_.CheckSsl();
    client2_.CheckSsl();

    return true;
  }

  void Negotiate(bool client1_server = true) {
    client1_.SetupTransports(ICEROLE_CONTROLLING);
    client2_.SetupTransports(ICEROLE_CONTROLLED);
    client1_.dtls_transport()->SetSslRole(client1_server ? rtc::SSL_SERVER
                                                         : rtc::SSL_CLIENT);
    client2_.dtls_transport()->SetSslRole(client1_server ? rtc::SSL_CLIENT
                                                         : rtc::SSL_SERVER);
    if (client2_.certificate()) {
      SetRemoteFingerprintFromCert(client1_.dtls_transport(),
                                   client2_.certificate());
    }
    if (client1_.certificate()) {
      SetRemoteFingerprintFromCert(client2_.dtls_transport(),
                                   client1_.certificate());
    }
  }

  void TestTransfer(size_t size, size_t count, bool srtp) {
    RTC_LOG(LS_INFO) << "Expect packets, size=" << size;
    client2_.ExpectPackets(size);
    client1_.SendPackets(size, count, srtp);
    EXPECT_EQ_SIMULATED_WAIT(count, client2_.NumPacketsReceived(), kTimeout,
                             fake_clock_);
  }

 protected:
  rtc::ScopedFakeClock fake_clock_;
  DtlsTestClient client1_;
  DtlsTestClient client2_;
  bool use_dtls_;
  rtc::SSLProtocolVersion ssl_expected_version_;
};

class DtlsTransportTest : public DtlsTransportTestBase,
                          public ::testing::Test {};

// Connect without DTLS, and transfer RTP data.
TEST_F(DtlsTransportTest, TestTransferRtp) {
  ASSERT_TRUE(Connect());
  TestTransfer(1000, 100, /*srtp=*/false);
}

// Test that the SignalSentPacket signal is wired up.
TEST_F(DtlsTransportTest, TestSignalSentPacket) {
  ASSERT_TRUE(Connect());
  // Sanity check default value (-1).
  ASSERT_EQ(client1_.sent_packet().send_time_ms, -1);
  TestTransfer(1000, 100, false);
  // Check that we get the expected fake packet ID, and a time of 0 from the
  // fake clock.
  EXPECT_EQ(kFakePacketId, client1_.sent_packet().packet_id);
  EXPECT_GE(client1_.sent_packet().send_time_ms, 0);
}

// Connect without DTLS, and transfer SRTP data.
TEST_F(DtlsTransportTest, TestTransferSrtp) {
  ASSERT_TRUE(Connect());
  TestTransfer(1000, 100, /*srtp=*/true);
}

// Connect with DTLS, and transfer data over DTLS.
TEST_F(DtlsTransportTest, TestTransferDtls) {
  PrepareDtls(rtc::KT_DEFAULT);
  ASSERT_TRUE(Connect());
  TestTransfer(1000, 100, /*srtp=*/false);
}

// Connect with DTLS, combine multiple DTLS records into one packet.
// Our DTLS implementation doesn't do this, but other implementations may;
// see https://tools.ietf.org/html/rfc6347#section-4.1.1.
// This has caused interoperability problems with ORTCLib in the past.
TEST_F(DtlsTransportTest, TestTransferDtlsCombineRecords) {
  PrepareDtls(rtc::KT_DEFAULT);
  ASSERT_TRUE(Connect());
  // Our DTLS implementation always sends one record per packet, so to simulate
  // an endpoint that sends multiple records per packet, we configure the fake
  // ICE transport to combine every two consecutive packets into a single
  // packet.
  FakeIceTransport* transport = client1_.fake_ice_transport();
  transport->combine_outgoing_packets(true);
  TestTransfer(500, 100, /*srtp=*/false);
}

class DtlsTransportVersionTest
    : public DtlsTransportTestBase,
      public ::testing::TestWithParam<
          ::testing::tuple<rtc::SSLProtocolVersion, rtc::SSLProtocolVersion>> {
};

// Test that an acceptable cipher suite is negotiated when different versions
// of DTLS are supported. Note that it's IsAcceptableCipher that does the actual
// work.
TEST_P(DtlsTransportVersionTest, TestCipherSuiteNegotiation) {
  PrepareDtls(rtc::KT_DEFAULT);
  SetMaxProtocolVersions(::testing::get<0>(GetParam()),
                         ::testing::get<1>(GetParam()));
  ASSERT_TRUE(Connect());
}

// Will test every combination of 1.0/1.2 on the client and server.
INSTANTIATE_TEST_CASE_P(
    TestCipherSuiteNegotiation,
    DtlsTransportVersionTest,
    ::testing::Combine(::testing::Values(rtc::SSL_PROTOCOL_DTLS_10,
                                         rtc::SSL_PROTOCOL_DTLS_12),
                       ::testing::Values(rtc::SSL_PROTOCOL_DTLS_10,
                                         rtc::SSL_PROTOCOL_DTLS_12)));

// Connect with DTLS, negotiating DTLS-SRTP, and transfer SRTP using bypass.
TEST_F(DtlsTransportTest, TestTransferDtlsSrtp) {
  PrepareDtls(rtc::KT_DEFAULT);
  ASSERT_TRUE(Connect());
  TestTransfer(1000, 100, /*srtp=*/true);
}

// Connect with DTLS-SRTP, transfer an invalid SRTP packet, and expects -1
// returned.
TEST_F(DtlsTransportTest, TestTransferDtlsInvalidSrtpPacket) {
  PrepareDtls(rtc::KT_DEFAULT);
  ASSERT_TRUE(Connect());
  EXPECT_EQ(-1, client1_.SendInvalidSrtpPacket(100));
}

// Create a single transport with DTLS, and send normal data and SRTP data on
// it.
TEST_F(DtlsTransportTest, TestTransferDtlsSrtpDemux) {
  PrepareDtls(rtc::KT_DEFAULT);
  ASSERT_TRUE(Connect());
  TestTransfer(1000, 100, /*srtp=*/false);
  TestTransfer(1000, 100, /*srtp=*/true);
}

// Test transferring when the "answerer" has the server role.
TEST_F(DtlsTransportTest, TestTransferDtlsSrtpAnswererIsPassive) {
  PrepareDtls(rtc::KT_DEFAULT);
  ASSERT_TRUE(Connect(/*client1_server=*/false));
  TestTransfer(1000, 100, /*srtp=*/true);
}

// Test that renegotiation (setting same role and fingerprint again) can be
// started before the clients become connected in the first negotiation.
TEST_F(DtlsTransportTest, TestRenegotiateBeforeConnect) {
  PrepareDtls(rtc::KT_DEFAULT);
  // Note: This is doing the same thing Connect normally does, minus some
  // additional checks not relevant for this test.
  Negotiate();
  Negotiate();
  EXPECT_TRUE(client1_.Connect(&client2_, false));
  EXPECT_TRUE_SIMULATED_WAIT(client1_.dtls_transport()->writable() &&
                                 client2_.dtls_transport()->writable(),
                             kTimeout, fake_clock_);
  TestTransfer(1000, 100, true);
}

// Test Certificates state after negotiation but before connection.
TEST_F(DtlsTransportTest, TestCertificatesBeforeConnect) {
  PrepareDtls(rtc::KT_DEFAULT);
  Negotiate();

  // After negotiation, each side has a distinct local certificate, but still no
  // remote certificate, because connection has not yet occurred.
  auto certificate1 = client1_.dtls_transport()->GetLocalCertificate();
  auto certificate2 = client2_.dtls_transport()->GetLocalCertificate();
  ASSERT_NE(certificate1->ssl_certificate().ToPEMString(),
            certificate2->ssl_certificate().ToPEMString());
  ASSERT_FALSE(client1_.dtls_transport()->GetRemoteSSLCertificate());
  ASSERT_FALSE(client2_.dtls_transport()->GetRemoteSSLCertificate());
}

// Test Certificates state after connection.
TEST_F(DtlsTransportTest, TestCertificatesAfterConnect) {
  PrepareDtls(rtc::KT_DEFAULT);
  ASSERT_TRUE(Connect());

  // After connection, each side has a distinct local certificate.
  auto certificate1 = client1_.dtls_transport()->GetLocalCertificate();
  auto certificate2 = client2_.dtls_transport()->GetLocalCertificate();
  ASSERT_NE(certificate1->ssl_certificate().ToPEMString(),
            certificate2->ssl_certificate().ToPEMString());

  // Each side's remote certificate is the other side's local certificate.
  std::unique_ptr<rtc::SSLCertificate> remote_cert1 =
      client1_.dtls_transport()->GetRemoteSSLCertificate();
  ASSERT_TRUE(remote_cert1);
  ASSERT_EQ(remote_cert1->ToPEMString(),
            certificate2->ssl_certificate().ToPEMString());
  std::unique_ptr<rtc::SSLCertificate> remote_cert2 =
      client2_.dtls_transport()->GetRemoteSSLCertificate();
  ASSERT_TRUE(remote_cert2);
  ASSERT_EQ(remote_cert2->ToPEMString(),
            certificate1->ssl_certificate().ToPEMString());
}

// Test that packets are retransmitted according to the expected schedule.
// Each time a timeout occurs, the retransmission timer should be doubled up to
// 60 seconds. The timer defaults to 1 second, but for WebRTC we should be
// initializing it to 50ms.
TEST_F(DtlsTransportTest, TestRetransmissionSchedule) {
  // We can only change the retransmission schedule with a recently-added
  // BoringSSL API. Skip the test if not built with BoringSSL.
  MAYBE_SKIP_TEST(IsBoringSsl);

  PrepareDtls(rtc::KT_DEFAULT);
  // Exchange fingerprints and set SSL roles.
  Negotiate();

  // Make client2_ writable, but not client1_.
  // This means client1_ will send DTLS client hellos but get no response.
  EXPECT_TRUE(client2_.Connect(&client1_, true));
  EXPECT_TRUE_SIMULATED_WAIT(client2_.fake_ice_transport()->writable(),
                             kTimeout, fake_clock_);

  // Wait for the first client hello to be sent.
  EXPECT_EQ_WAIT(1, client1_.received_dtls_client_hellos(), kTimeout);
  EXPECT_FALSE(client1_.fake_ice_transport()->writable());

  static int timeout_schedule_ms[] = {50,   100,  200,   400,   800,   1600,
                                      3200, 6400, 12800, 25600, 51200, 60000};

  int expected_hellos = 1;
  for (size_t i = 0;
       i < (sizeof(timeout_schedule_ms) / sizeof(timeout_schedule_ms[0]));
       ++i) {
    // For each expected retransmission time, advance the fake clock a
    // millisecond before the expected time and verify that no unexpected
    // retransmissions were sent. Then advance it the final millisecond and
    // verify that the expected retransmission was sent.
    fake_clock_.AdvanceTime(
        rtc::TimeDelta::FromMilliseconds(timeout_schedule_ms[i] - 1));
    EXPECT_EQ(expected_hellos, client1_.received_dtls_client_hellos());
    fake_clock_.AdvanceTime(rtc::TimeDelta::FromMilliseconds(1));
    EXPECT_EQ(++expected_hellos, client1_.received_dtls_client_hellos());
  }
}

// The following events can occur in many different orders:
// 1. Caller receives remote fingerprint.
// 2. Caller is writable.
// 3. Caller receives ClientHello.
// 4. DTLS handshake finishes.
//
// The tests below cover all causally consistent permutations of these events;
// the caller must be writable and receive a ClientHello before the handshake
// finishes, but otherwise any ordering is possible.
//
// For each permutation, the test verifies that a connection is established and
// fingerprint verified without any DTLS packet needing to be retransmitted.
//
// Each permutation is also tested with valid and invalid fingerprints,
// ensuring that the handshake fails with an invalid fingerprint.
enum DtlsTransportEvent {
  CALLER_RECEIVES_FINGERPRINT,
  CALLER_WRITABLE,
  CALLER_RECEIVES_CLIENTHELLO,
  HANDSHAKE_FINISHES
};

class DtlsEventOrderingTest
    : public DtlsTransportTestBase,
      public ::testing::TestWithParam<
          ::testing::tuple<std::vector<DtlsTransportEvent>, bool>> {
 protected:
  // If |valid_fingerprint| is false, the caller will receive a fingerprint
  // that doesn't match the callee's certificate, so the handshake should fail.
  void TestEventOrdering(const std::vector<DtlsTransportEvent>& events,
                         bool valid_fingerprint) {
    // Pre-setup: Set local certificate on both caller and callee, and
    // remote fingerprint on callee, but neither is writable and the caller
    // doesn't have the callee's fingerprint.
    PrepareDtls(rtc::KT_DEFAULT);
    // Simulate packets being sent and arriving asynchronously.
    // Otherwise the entire DTLS handshake would occur in one clock tick, and
    // we couldn't inject method calls in the middle of it.
    int simulated_delay_ms = 10;
    client1_.SetupTransports(ICEROLE_CONTROLLING, simulated_delay_ms);
    client2_.SetupTransports(ICEROLE_CONTROLLED, simulated_delay_ms);
    // Similar to how NegotiateOrdering works.
    client1_.dtls_transport()->SetSslRole(rtc::SSL_SERVER);
    client2_.dtls_transport()->SetSslRole(rtc::SSL_CLIENT);
    SetRemoteFingerprintFromCert(client2_.dtls_transport(),
                                 client1_.certificate());

    for (DtlsTransportEvent e : events) {
      switch (e) {
        case CALLER_RECEIVES_FINGERPRINT:
          if (valid_fingerprint) {
            SetRemoteFingerprintFromCert(client1_.dtls_transport(),
                                         client2_.certificate());
          } else {
            SetRemoteFingerprintFromCert(client1_.dtls_transport(),
                                         client2_.certificate(),
                                         true /*modify_digest*/);
          }
          break;
        case CALLER_WRITABLE:
          EXPECT_TRUE(client1_.Connect(&client2_, true));
          EXPECT_TRUE_SIMULATED_WAIT(client1_.fake_ice_transport()->writable(),
                                     kTimeout, fake_clock_);
          break;
        case CALLER_RECEIVES_CLIENTHELLO:
          // Sanity check that a ClientHello hasn't already been received.
          EXPECT_EQ(0, client1_.received_dtls_client_hellos());
          // Making client2_ writable will cause it to send the ClientHello.
          EXPECT_TRUE(client2_.Connect(&client1_, true));
          EXPECT_TRUE_SIMULATED_WAIT(client2_.fake_ice_transport()->writable(),
                                     kTimeout, fake_clock_);
          EXPECT_EQ_SIMULATED_WAIT(1, client1_.received_dtls_client_hellos(),
                                   kTimeout, fake_clock_);
          break;
        case HANDSHAKE_FINISHES:
          // Sanity check that the handshake hasn't already finished.
          EXPECT_FALSE(client1_.dtls_transport()->IsDtlsConnected() ||
                       client1_.dtls_transport()->dtls_state() ==
                           DTLS_TRANSPORT_FAILED);
          EXPECT_TRUE_SIMULATED_WAIT(
              client1_.dtls_transport()->IsDtlsConnected() ||
                  client1_.dtls_transport()->dtls_state() ==
                      DTLS_TRANSPORT_FAILED,
              kTimeout, fake_clock_);
          break;
      }
    }

    DtlsTransportState expected_final_state =
        valid_fingerprint ? DTLS_TRANSPORT_CONNECTED : DTLS_TRANSPORT_FAILED;
    EXPECT_EQ_SIMULATED_WAIT(expected_final_state,
                             client1_.dtls_transport()->dtls_state(), kTimeout,
                             fake_clock_);
    EXPECT_EQ_SIMULATED_WAIT(expected_final_state,
                             client2_.dtls_transport()->dtls_state(), kTimeout,
                             fake_clock_);

    // Transports should be writable iff there was a valid fingerprint.
    EXPECT_EQ(valid_fingerprint, client1_.dtls_transport()->writable());
    EXPECT_EQ(valid_fingerprint, client2_.dtls_transport()->writable());

    // Check that no hello needed to be retransmitted.
    EXPECT_EQ(1, client1_.received_dtls_client_hellos());
    EXPECT_EQ(1, client2_.received_dtls_server_hellos());

    if (valid_fingerprint) {
      TestTransfer(1000, 100, false);
    }
  }
};

TEST_P(DtlsEventOrderingTest, TestEventOrdering) {
  TestEventOrdering(::testing::get<0>(GetParam()),
                    ::testing::get<1>(GetParam()));
}

INSTANTIATE_TEST_CASE_P(
    TestEventOrdering,
    DtlsEventOrderingTest,
    ::testing::Combine(
        ::testing::Values(
            std::vector<DtlsTransportEvent>{
                CALLER_RECEIVES_FINGERPRINT, CALLER_WRITABLE,
                CALLER_RECEIVES_CLIENTHELLO, HANDSHAKE_FINISHES},
            std::vector<DtlsTransportEvent>{
                CALLER_WRITABLE, CALLER_RECEIVES_FINGERPRINT,
                CALLER_RECEIVES_CLIENTHELLO, HANDSHAKE_FINISHES},
            std::vector<DtlsTransportEvent>{
                CALLER_WRITABLE, CALLER_RECEIVES_CLIENTHELLO,
                CALLER_RECEIVES_FINGERPRINT, HANDSHAKE_FINISHES},
            std::vector<DtlsTransportEvent>{
                CALLER_WRITABLE, CALLER_RECEIVES_CLIENTHELLO,
                HANDSHAKE_FINISHES, CALLER_RECEIVES_FINGERPRINT},
            std::vector<DtlsTransportEvent>{
                CALLER_RECEIVES_FINGERPRINT, CALLER_RECEIVES_CLIENTHELLO,
                CALLER_WRITABLE, HANDSHAKE_FINISHES},
            std::vector<DtlsTransportEvent>{
                CALLER_RECEIVES_CLIENTHELLO, CALLER_RECEIVES_FINGERPRINT,
                CALLER_WRITABLE, HANDSHAKE_FINISHES},
            std::vector<DtlsTransportEvent>{
                CALLER_RECEIVES_CLIENTHELLO, CALLER_WRITABLE,
                CALLER_RECEIVES_FINGERPRINT, HANDSHAKE_FINISHES},
            std::vector<DtlsTransportEvent>{CALLER_RECEIVES_CLIENTHELLO,
                                            CALLER_WRITABLE, HANDSHAKE_FINISHES,
                                            CALLER_RECEIVES_FINGERPRINT}),
        ::testing::Bool()));

}  // namespace cricket