页次： 1
quic协议最早是google提出来的，所以狗家的源码肯定是最“正宗”的！google把quic协议的源码放在了chromium里面，所以要看quic的源码原则上需要下载chromium源码！但是这份源码体积很大，并且还需要FQ，所以多年前就有好心人把quic源码剥离出来单独放github了，在文章末尾的参考2处；
1、quic相比tcp实现的tls，前面省略了3~4个RTT，根因就是发起连接请求时就发送自己的公钥给对方，让对方利用自己的公钥计算后续对称加密的key，这就是所谓的handshake；在libquic-master\src\net\quic\core\quic_crypto_client_stream.cc中有具体实现握手的代码，先看DoHandshakeLoop函数：
void QuicCryptoClientStream::DoHandshakeLoop(const CryptoHandshakeMessage* in) {
QuicCryptoClientConfig::CachedState* cached =
crypto_config_->LookupOrCreate(server_id_);
QuicAsyncStatus rv = QUIC_SUCCESS;
do {
CHECK_NE(STATE_NONE, next_state_);
const State state = next_state_;
next_state_ = STATE_IDLE;
rv = QUIC_SUCCESS;
switch (state) {
case STATE_INITIALIZE:
DoInitialize(cached);
break;
case STATE_SEND_CHLO:
DoSendCHLO(cached);
return; // return waiting to hear from server.
case STATE_RECV_REJ:
DoReceiveREJ(in, cached);
break;
case STATE_VERIFY_PROOF:
rv = DoVerifyProof(cached);
break;
case STATE_VERIFY_PROOF_COMPLETE:
DoVerifyProofComplete(cached);
break;
case STATE_GET_CHANNEL_ID:
rv = DoGetChannelID(cached);
break;
case STATE_GET_CHANNEL_ID_COMPLETE:
DoGetChannelIDComplete();
break;
case STATE_RECV_SHLO:
DoReceiveSHLO(in, cached);
break;
case STATE_IDLE:
// This means that the peer sent us a message that we weren't expecting.
CloseConnectionWithDetails(QUIC_INVALID_CRYPTO_MESSAGE_TYPE,
"Handshake in idle state");
return;
case STATE_INITIALIZE_SCUP:
DoInitializeServerConfigUpdate(cached);
break;
case STATE_NONE:
NOTREACHED();
return; // We are done.
}
} while (rv != QUIC_PENDING && next_state_ != STATE_NONE);
}只要quic的状态不是pending，并且下一个状态不是NONE，就根据不同的状态调用不同的处理函数！具体发送handshake小的函数是DoSendCHLO，代码如下：
/*发送client hello消息*/
void QuicCryptoClientStream::DoSendCHLO(
QuicCryptoClientConfig::CachedState* cached) {
if (stateless_reject_received_) {//如果收到了server拒绝的消息
// If we've gotten to this point, we've sent at least one hello
// and received a stateless reject in response. We cannot
// continue to send hellos because the server has abandoned state
// for this connection. Abandon further handshakes.
next_state_ = STATE_NONE;
if (session()->connection()->connected()) {
session()->connection()->CloseConnection(//关闭连接
QUIC_CRYPTO_HANDSHAKE_STATELESS_REJECT, "stateless reject received",
ConnectionCloseBehavior::SILENT_CLOSE);
}
return;
}
// Send the client hello in plaintext.
//注意：这是client hello消息，没必要加密
session()->connection()->SetDefaultEncryptionLevel(ENCRYPTION_NONE);
encryption_established_ = false;
if (num_client_hellos_ > kMaxClientHellos) {//握手消息已经发送了很多，不能再发了
CloseConnectionWithDetails(
QUIC_CRYPTO_TOO_MANY_REJECTS,
base::StringPrintf("More than %u rejects", kMaxClientHellos).c_str());
return;
}
num_client_hellos_++;
//开始构造握手消息了
CryptoHandshakeMessage out;
DCHECK(session() != nullptr);
DCHECK(session()->config() != nullptr);
// Send all the options, regardless of whether we're sending an
// inchoate or subsequent hello.
/*填充握手消息的各个字段*/
session()->config()->ToHandshakeMessage(&out);
// Send a local timestamp to the server.
out.SetValue(kCTIM,
session()->connection()->clock()->WallNow().ToUNIXSeconds());
if (!cached->IsComplete(session()->connection()->clock()->WallNow())) {
crypto_config_->FillInchoateClientHello(
server_id_, session()->connection()->supported_versions().front(),
cached, session()->connection()->random_generator(),
/* demand_x509_proof= */ true, &crypto_negotiated_params_, &out);
// Pad the inchoate client hello to fill up a packet.
const QuicByteCount kFramingOverhead = 50; // A rough estimate.
const QuicByteCount max_packet_size =
session()->connection()->max_packet_length();
if (max_packet_size <= kFramingOverhead) {
DLOG(DFATAL) << "max_packet_length (" << max_packet_size
<< ") has no room for framing overhead.";
CloseConnectionWithDetails(QUIC_INTERNAL_ERROR,
"max_packet_size too smalll");
return;
}
if (kClientHelloMinimumSize > max_packet_size - kFramingOverhead) {
DLOG(DFATAL) << "Client hello won't fit in a single packet.";
CloseConnectionWithDetails(QUIC_INTERNAL_ERROR, "CHLO too large");
return;
}
// TODO(rch): Remove this when we remove:
// FLAGS_quic_use_chlo_packet_size
out.set_minimum_size(
static_cast<size_t>(max_packet_size - kFramingOverhead));
next_state_ = STATE_RECV_REJ;
/*做hash签名，接收方会根据hash验证消息是否完整*/
CryptoUtils::HashHandshakeMessage(out, &chlo_hash_);
//发送消息
SendHandshakeMessage(out);
return;
}
// If the server nonce is empty, copy over the server nonce from a previous
// SREJ, if there is one.
if (FLAGS_enable_quic_stateless_reject_support &&
crypto_negotiated_params_.server_nonce.empty() &&
cached->has_server_nonce()) {
crypto_negotiated_params_.server_nonce = cached->GetNextServerNonce();
DCHECK(!crypto_negotiated_params_.server_nonce.empty());
}
string error_details;
/*继续填充client hello消息*/
QuicErrorCode error = crypto_config_->FillClientHello(
server_id_, session()->connection()->connection_id(),
session()->connection()->version(),
session()->connection()->supported_versions().front(), cached,
session()->connection()->clock()->WallNow(),
//这个随机数会被server用来计算生成对称加密的key
session()->connection()->random_generator(),
channel_id_key_.get(),
//保存了nonce、key、token相关信息；后续对称加密的方法是CTR，需要NONCE值
&crypto_negotiated_params_,
&out, &error_details);
if (error != QUIC_NO_ERROR) {
// Flush the cached config so that, if it's bad, the server has a
// chance to send us another in the future.
cached->InvalidateServerConfig();
CloseConnectionWithDetails(error, error_details);
return;
}
/*继续对消息做hash，便于server验证收到的消息是否完整*/
CryptoUtils::HashHandshakeMessage(out, &chlo_hash_);
channel_id_sent_ = (channel_id_key_.get() != nullptr);
if (cached->proof_verify_details()) {
proof_handler_->OnProofVerifyDetailsAvailable(
*cached->proof_verify_details());
}
next_state_ = STATE_RECV_SHLO;
SendHandshakeMessage(out);
// Be prepared to decrypt with the new server write key.
session()->connection()->SetAlternativeDecrypter(
ENCRYPTION_INITIAL,
crypto_negotiated_params_.initial_crypters.decrypter.release(),
true /* latch once used */);
// Send subsequent packets under encryption on the assumption that the
// server will accept the handshake.
session()->connection()->SetEncrypter(
ENCRYPTION_INITIAL,
crypto_negotiated_params_.initial_crypters.encrypter.release());
session()->connection()->SetDefaultEncryptionLevel(ENCRYPTION_INITIAL);
// TODO(ianswett): Merge ENCRYPTION_REESTABLISHED and
// ENCRYPTION_FIRST_ESTABLSIHED
encryption_established_ = true;
session()->OnCryptoHandshakeEvent(QuicSession::ENCRYPTION_REESTABLISHED);
}个人觉得最核心的代码就是FillClientHello函数了，这里会生成随机数，后续server会利用这个随机数生成对称加密的key！部分通信的参数也会通过这个函数的执行保存在crypto_negotiated_params_对象中！client发送了hello包，接下来该server处理这个包了，代码在libquic-master\src\net\quic\core\quic_crypto_server_stream.cc和quic_crypto_server_config.cc中，代码如下：核心功能是生成自己的公钥，还有后续对称加密的key！
QuicErrorCode QuicCryptoServerConfig::ProcessClientHello(
const ValidateClientHelloResultCallback::Result& validate_chlo_result,
bool reject_only,
QuicConnectionId connection_id,
const IPAddress& server_ip,
const IPEndPoint& client_address,
QuicVersion version,
const QuicVersionVector& supported_versions,
bool use_stateless_rejects,
QuicConnectionId server_designated_connection_id,
const QuicClock* clock,
QuicRandom* rand,//发送给client用于计算对称key
QuicCompressedCertsCache* compressed_certs_cache,
QuicCryptoNegotiatedParameters* params,
QuicCryptoProof* crypto_proof,
QuicByteCount total_framing_overhead,
QuicByteCount chlo_packet_size,
CryptoHandshakeMessage* out,
DiversificationNonce* out_diversification_nonce,
string* error_details) const {
DCHECK(error_details);
const CryptoHandshakeMessage& client_hello =
validate_chlo_result.client_hello;
const ClientHelloInfo& info = validate_chlo_result.info;
QuicErrorCode valid = CryptoUtils::ValidateClientHello(
client_hello, version, supported_versions, error_details);
if (valid != QUIC_NO_ERROR)
return valid;
StringPiece requested_scid;
client_hello.GetStringPiece(kSCID, &requested_scid);
const QuicWallTime now(clock->WallNow());
scoped_refptr<Config> requested_config;
scoped_refptr<Config> primary_config;
{
base::AutoLock locked(configs_lock_);
if (!primary_config_.get()) {
*error_details = "No configurations loaded";
return QUIC_CRYPTO_INTERNAL_ERROR;
}
if (!next_config_promotion_time_.IsZero() &&
next_config_promotion_time_.IsAfter(now)) {
SelectNewPrimaryConfig(now);
DCHECK(primary_config_.get());
DCHECK_EQ(configs_.find(primary_config_->id)->second, primary_config_);
}
// Use the config that the client requested in order to do key-agreement.
// Otherwise give it a copy of |primary_config_| to use.
primary_config = crypto_proof->config;
requested_config = GetConfigWithScid(requested_scid);
}
if (validate_chlo_result.error_code != QUIC_NO_ERROR) {
*error_details = validate_chlo_result.error_details;
return validate_chlo_result.error_code;
}
out->Clear();
if (!ClientDemandsX509Proof(client_hello)) {
*error_details = "Missing or invalid PDMD";
return QUIC_UNSUPPORTED_PROOF_DEMAND;
}
DCHECK(proof_source_.get());
string chlo_hash;
CryptoUtils::HashHandshakeMessage(client_hello, &chlo_hash);
// No need to get a new proof if one was already generated.
if (!crypto_proof->chain &&
!proof_source_->GetProof(server_ip, info.sni.as_string(),
primary_config->serialized, version, chlo_hash,
&crypto_proof->chain, &crypto_proof->signature,
&crypto_proof->cert_sct)) {
return QUIC_HANDSHAKE_FAILED;
}
StringPiece cert_sct;
if (client_hello.GetStringPiece(kCertificateSCTTag, &cert_sct) &&
cert_sct.empty()) {
params->sct_supported_by_client = true;
}
if (!info.reject_reasons.empty() || !requested_config.get()) {
BuildRejection(version, clock->WallNow(), *primary_config, client_hello,
info, validate_chlo_result.cached_network_params,
use_stateless_rejects, server_designated_connection_id, rand,
compressed_certs_cache, params, *crypto_proof,
total_framing_overhead, chlo_packet_size, out);
return QUIC_NO_ERROR;
}
if (reject_only) {
return QUIC_NO_ERROR;
}
const QuicTag* their_aeads;
const QuicTag* their_key_exchanges;
size_t num_their_aeads, num_their_key_exchanges;
if (client_hello.GetTaglist(kAEAD, &their_aeads, &num_their_aeads) !=
QUIC_NO_ERROR ||
client_hello.GetTaglist(kKEXS, &their_key_exchanges,
&num_their_key_exchanges) != QUIC_NO_ERROR ||
num_their_aeads != 1 || num_their_key_exchanges != 1) {
*error_details = "Missing or invalid AEAD or KEXS";
return QUIC_INVALID_CRYPTO_MESSAGE_PARAMETER;
}
size_t key_exchange_index;
if (!QuicUtils::FindMutualTag(requested_config->aead, their_aeads,
num_their_aeads, QuicUtils::LOCAL_PRIORITY,
¶ms->aead, nullptr) ||
!QuicUtils::FindMutualTag(requested_config->kexs, their_key_exchanges,
num_their_key_exchanges,
QuicUtils::LOCAL_PRIORITY,
¶ms->key_exchange, &key_exchange_index)) {
*error_details = "Unsupported AEAD or KEXS";
return QUIC_CRYPTO_NO_SUPPORT;
}
if (!requested_config->tb_key_params.empty()) {
const QuicTag* their_tbkps;
size_t num_their_tbkps;
switch (client_hello.GetTaglist(kTBKP, &their_tbkps, &num_their_tbkps)) {
case QUIC_CRYPTO_MESSAGE_PARAMETER_NOT_FOUND:
break;
case QUIC_NO_ERROR:
if (QuicUtils::FindMutualTag(
requested_config->tb_key_params, their_tbkps, num_their_tbkps,
QuicUtils::LOCAL_PRIORITY, ¶ms->token_binding_key_param,
nullptr)) {
break;
}
default:
*error_details = "Invalid Token Binding key parameter";
return QUIC_INVALID_CRYPTO_MESSAGE_PARAMETER;
}
}
StringPiece public_value;
/*提取client hello数据包发送的公钥，server要用来生成对称加密的key*/
if (!client_hello.GetStringPiece(kPUBS, &public_value)) {
*error_details = "Missing public value";
return QUIC_INVALID_CRYPTO_MESSAGE_PARAMETER;
}
const KeyExchange* key_exchange =
requested_config->key_exchanges[key_exchange_index];
if (!key_exchange->CalculateSharedKey(public_value,
¶ms->initial_premaster_secret)) {
*error_details = "Invalid public value";
return QUIC_INVALID_CRYPTO_MESSAGE_PARAMETER;
}
if (!info.sni.empty()) {
std::unique_ptr<char[]> sni_tmp(new char[info.sni.length() + 1]);
memcpy(sni_tmp.get(), info.sni.data(), info.sni.length());
sni_tmp[info.sni.length()] = 0;
params->sni = CryptoUtils::NormalizeHostname(sni_tmp.get());
}
string hkdf_suffix;
//client hello消息序列化，便于提取？
const QuicData& client_hello_serialized = client_hello.GetSerialized();
/*根据一个原始密钥材料，用hkdf算法推导出指定长度的密钥；
这里明显是要根据client hello的数据生成对称加密的密钥了
*/
hkdf_suffix.reserve(sizeof(connection_id) + client_hello_serialized.length() +
requested_config->serialized.size());
hkdf_suffix.append(reinterpret_cast<char*>(&connection_id),
sizeof(connection_id));
hkdf_suffix.append(client_hello_serialized.data(),
client_hello_serialized.length());
hkdf_suffix.append(requested_config->serialized);
DCHECK(proof_source_.get());
if (crypto_proof->chain->certs.empty()) {
*error_details = "Failed to get certs";
return QUIC_CRYPTO_INTERNAL_ERROR;
}
hkdf_suffix.append(crypto_proof->chain->certs.at(0));
StringPiece cetv_ciphertext;
if (requested_config->channel_id_enabled &&
client_hello.GetStringPiece(kCETV, &cetv_ciphertext)) {
CryptoHandshakeMessage client_hello_copy(client_hello);
client_hello_copy.Erase(kCETV);
client_hello_copy.Erase(kPAD);
const QuicData& client_hello_copy_serialized =
client_hello_copy.GetSerialized();
string hkdf_input;
hkdf_input.append(QuicCryptoConfig::kCETVLabel,
strlen(QuicCryptoConfig::kCETVLabel) + 1);
hkdf_input.append(reinterpret_cast<char*>(&connection_id),
sizeof(connection_id));
hkdf_input.append(client_hello_copy_serialized.data(),
client_hello_copy_serialized.length());
hkdf_input.append(requested_config->serialized);
CrypterPair crypters;
if (!CryptoUtils::DeriveKeys(params->initial_premaster_secret, params->aead,
info.client_nonce, info.server_nonce,
hkdf_input, Perspective::IS_SERVER,
CryptoUtils::Diversification::Never(),
&crypters, nullptr /* subkey secret */)) {
*error_details = "Symmetric key setup failed";
return QUIC_CRYPTO_SYMMETRIC_KEY_SETUP_FAILED;
}
char plaintext[kMaxPacketSize];
size_t plaintext_length = 0;
const bool success = crypters.decrypter->DecryptPacket(
kDefaultPathId, 0 /* packet number */,
StringPiece() /* associated data */, cetv_ciphertext, plaintext,
&plaintext_length, kMaxPacketSize);
if (!success) {
*error_details = "CETV decryption failure";
return QUIC_INVALID_CRYPTO_MESSAGE_PARAMETER;
}
std::unique_ptr<CryptoHandshakeMessage> cetv(
CryptoFramer::ParseMessage(StringPiece(plaintext, plaintext_length)));
if (!cetv.get()) {
*error_details = "CETV parse error";
return QUIC_INVALID_CRYPTO_MESSAGE_PARAMETER;
}
StringPiece key, signature;
if (cetv->GetStringPiece(kCIDK, &key) &&
cetv->GetStringPiece(kCIDS, &signature)) {
if (!ChannelIDVerifier::Verify(key, hkdf_input, signature)) {
*error_details = "ChannelID signature failure";
return QUIC_INVALID_CRYPTO_MESSAGE_PARAMETER;
}
params->channel_id = key.as_string();
}
}
string hkdf_input;
size_t label_len = strlen(QuicCryptoConfig::kInitialLabel) + 1;
hkdf_input.reserve(label_len + hkdf_suffix.size());
hkdf_input.append(QuicCryptoConfig::kInitialLabel, label_len);
hkdf_input.append(hkdf_suffix);
string* subkey_secret = ¶ms->initial_subkey_secret;
CryptoUtils::Diversification diversification =
CryptoUtils::Diversification::Never();
if (version > QUIC_VERSION_32) {
rand->RandBytes(out_diversification_nonce->data(),
out_diversification_nonce->size());
diversification =
CryptoUtils::Diversification::Now(out_diversification_nonce);
}
if (!CryptoUtils::DeriveKeys(params->initial_premaster_secret, params->aead,
info.client_nonce, info.server_nonce, hkdf_input,
Perspective::IS_SERVER, diversification,
¶ms->initial_crypters, subkey_secret)) {
*error_details = "Symmetric key setup failed";
return QUIC_CRYPTO_SYMMETRIC_KEY_SETUP_FAILED;
}
string forward_secure_public_value;
if (ephemeral_key_source_.get()) {
params->forward_secure_premaster_secret =
ephemeral_key_source_->CalculateForwardSecureKey(
key_exchange, rand, clock->ApproximateNow(), public_value,
&forward_secure_public_value);
} else {
std::unique_ptr<KeyExchange> forward_secure_key_exchange(
key_exchange->NewKeyPair(rand));
forward_secure_public_value =
forward_secure_key_exchange->public_value().as_string();
/*生成共享密钥*/
if (!forward_secure_key_exchange->CalculateSharedKey(
public_value, ¶ms->forward_secure_premaster_secret)) {
*error_details = "Invalid public value";
return QUIC_INVALID_CRYPTO_MESSAGE_PARAMETER;
}
}
string forward_secure_hkdf_input;
label_len = strlen(QuicCryptoConfig::kForwardSecureLabel) + 1;
forward_secure_hkdf_input.reserve(label_len + hkdf_suffix.size());
forward_secure_hkdf_input.append(QuicCryptoConfig::kForwardSecureLabel,
label_len);
forward_secure_hkdf_input.append(hkdf_suffix);
string shlo_nonce;
shlo_nonce = NewServerNonce(rand, info.now);
out->SetStringPiece(kServerNonceTag, shlo_nonce);
/*生成密钥*/
if (!CryptoUtils::DeriveKeys(
params->forward_secure_premaster_secret, params->aead,
info.client_nonce,
shlo_nonce.empty() ? info.server_nonce : shlo_nonce,
forward_secure_hkdf_input, Perspective::IS_SERVER,
CryptoUtils::Diversification::Never(),
¶ms->forward_secure_crypters, ¶ms->subkey_secret)) {
*error_details = "Symmetric key setup failed";
return QUIC_CRYPTO_SYMMETRIC_KEY_SETUP_FAILED;
}
out->set_tag(kSHLO);
QuicTagVector supported_version_tags;
for (size_t i = 0; i < supported_versions.size(); ++i) {
supported_version_tags.push_back(
QuicVersionToQuicTag(supported_versions[i]));
}
out->SetVector(kVER, supported_version_tags);
out->SetStringPiece(
kSourceAddressTokenTag,
NewSourceAddressToken(*requested_config.get(), info.source_address_tokens,
client_address.address(), rand, info.now, nullptr));
QuicSocketAddressCoder address_coder(client_address);
out->SetStringPiece(kCADR, address_coder.Encode());
/*server hello包中设置server的公钥，后续client会利用这个生成对称加密的key*/
out->SetStringPiece(kPUBS, forward_secure_public_value);
return QUIC_NO_ERROR;
}这里用了不同的方法来生成对称加密的key。这里以椭圆曲线为例，计算对称加密key的代码如下：这是直接调用了openssl/curve25519.h的接口计算出来的。一旦双方都生成了对称密钥，后续就可以通过对称加密通信了！
bool Curve25519KeyExchange::CalculateSharedKey(StringPiece peer_public_value,
string* out_result) const {
if (peer_public_value.size() != crypto::curve25519::kBytes) {
return false;
}
uint8_t result[crypto::curve25519::kBytes];
if (!crypto::curve25519::ScalarMult(
private_key_,
reinterpret_cast<const uint8_t*>(peer_public_value.data()), result)) {
return false;
}
out_result->assign(reinterpret_cast<char*>(result), sizeof(result));
return true;
}
bool ScalarMult(const uint8_t* private_key,
const uint8_t* peer_public_key,
uint8_t* shared_key) {
return !!X25519(shared_key, private_key, peer_public_key);
}通信时给packet加密的方法：
bool AeadBaseEncrypter::EncryptPacket(QuicPathId path_id,
QuicPacketNumber packet_number,
StringPiece associated_data,
StringPiece plaintext,
char* output,
size_t* output_length,
size_t max_output_length) {
size_t ciphertext_size = GetCiphertextSize(plaintext.length());
if (max_output_length < ciphertext_size) {
return false;
}
// TODO(ianswett): Introduce a check to ensure that we don't encrypt with the
// same packet number twice.
const size_t nonce_size = nonce_prefix_size_ + sizeof(packet_number);
ALIGNAS(4) char nonce_buffer[kMaxNonceSize];
memcpy(nonce_buffer, nonce_prefix_, nonce_prefix_size_);
uint64_t path_id_packet_number =
QuicUtils::PackPathIdAndPacketNumber(path_id, packet_number);
memcpy(nonce_buffer + nonce_prefix_size_, &path_id_packet_number,
sizeof(path_id_packet_number));
/*这里用nonce给明文加密*/
if (!Encrypt(StringPiece(nonce_buffer, nonce_size), associated_data,
plaintext, reinterpret_cast<unsigned char*>(output))) {
return false;
}
*output_length = ciphertext_size;
return true;
}最后，server hello消息是从这里发出去的，并且在某些情况下server hello已经用server新生成的key加密了，如下：
void QuicCryptoServerStream::FinishProcessingHandshakeMessage(
const ValidateClientHelloResultCallback::Result& result,
std::unique_ptr<ProofSource::Details> details) {
const CryptoHandshakeMessage& message = result.client_hello;
// Clear the callback that got us here.
DCHECK(validate_client_hello_cb_ != nullptr);
validate_client_hello_cb_ = nullptr;
if (use_stateless_rejects_if_peer_supported_) {
peer_supports_stateless_rejects_ = DoesPeerSupportStatelessRejects(message);
}
CryptoHandshakeMessage reply;
DiversificationNonce diversification_nonce;
string error_details;
QuicErrorCode error =
/*server处理client的hello消息：重点是生成对称加密key、自己的公钥和nonce
同时生成给client回复的消息*/
ProcessClientHello(result, std::move(details), &reply,
&diversification_nonce, &error_details);
if (error != QUIC_NO_ERROR) {
CloseConnectionWithDetails(error, error_details);
return;
}
if (reply.tag() != kSHLO) {
if (reply.tag() == kSREJ) {
DCHECK(use_stateless_rejects_if_peer_supported_);
DCHECK(peer_supports_stateless_rejects_);
// Before sending the SREJ, cause the connection to save crypto packets
// so that they can be added to the time wait list manager and
// retransmitted.
session()->connection()->EnableSavingCryptoPackets();
}
SendHandshakeMessage(reply);//给client发server hello
if (reply.tag() == kSREJ) {
DCHECK(use_stateless_rejects_if_peer_supported_);
DCHECK(peer_supports_stateless_rejects_);
DCHECK(!handshake_confirmed());
DVLOG(1) << "Closing connection "
<< session()->connection()->connection_id()
<< " because of a stateless reject.";
session()->connection()->CloseConnection(
QUIC_CRYPTO_HANDSHAKE_STATELESS_REJECT, "stateless reject",
ConnectionCloseBehavior::SILENT_CLOSE);
}
return;
}
// If we are returning a SHLO then we accepted the handshake. Now
// process the negotiated configuration options as part of the
// session config.
//代码到这里已经给client发送了client hello，表示server已经准备好接受数据了
//这里保存一些双方协商好的通信配置
QuicConfig* config = session()->config();
OverrideQuicConfigDefaults(config);
error = config->ProcessPeerHello(message, CLIENT, &error_details);
if (error != QUIC_NO_ERROR) {
CloseConnectionWithDetails(error, error_details);
return;
}
session()->OnConfigNegotiated();
config->ToHandshakeMessage(&reply);
// Receiving a full CHLO implies the client is prepared to decrypt with
// the new server write key. We can start to encrypt with the new server
// write key. 可以开始用服务端新生成的key解密数据了
//
// NOTE: the SHLO will be encrypted with the new server write key.
/*既然在server已经生成了对称加密的key，这里可以用这个key加密server hello消息*/
session()->connection()->SetEncrypter(
ENCRYPTION_INITIAL,
crypto_negotiated_params_.initial_crypters.encrypter.release());
session()->connection()->SetDefaultEncryptionLevel(ENCRYPTION_INITIAL);
// Set the decrypter immediately so that we no longer accept unencrypted
// packets.
session()->connection()->SetDecrypter(
ENCRYPTION_INITIAL,
crypto_negotiated_params_.initial_crypters.decrypter.release());
if (version() > QUIC_VERSION_32) {
session()->connection()->SetDiversificationNonce(diversification_nonce);
}
SendHandshakeMessage(reply);//发送server hello
session()->connection()->SetEncrypter(
ENCRYPTION_FORWARD_SECURE,
crypto_negotiated_params_.forward_secure_crypters.encrypter.release());
session()->connection()->SetDefaultEncryptionLevel(ENCRYPTION_FORWARD_SECURE);
session()->connection()->SetAlternativeDecrypter(
ENCRYPTION_FORWARD_SECURE,
crypto_negotiated_params_.forward_secure_crypters.decrypter.release(),
false /* don't latch */);
encryption_established_ = true;
handshake_confirmed_ = true;
session()->OnCryptoHandshakeEvent(QuicSession::HANDSHAKE_CONFIRMED);
}（2）为了防止tcp的队头阻塞，quic在前面丢包的情况下任然继续发包，丢的包用新的packet number重新发，怎么区别这个新包是以往丢包的重发了？核心是每个包都有stream id和stream offset字段，根据这两个字段定位包的位置，而不是packet number。整个包结构定义的类在这里：
struct NET_EXPORT_PRIVATE QuicStreamFrame {
QuicStreamFrame();
QuicStreamFrame(QuicStreamId stream_id,
bool fin,
QuicStreamOffset offset,
base::StringPiece data);
QuicStreamFrame(QuicStreamId stream_id,
bool fin,
QuicStreamOffset offset,
QuicPacketLength data_length,
UniqueStreamBuffer buffer);
~QuicStreamFrame();
NET_EXPORT_PRIVATE friend std::ostream& operator<<(std::ostream& os,
const QuicStreamFrame& s);
QuicStreamId stream_id;
bool fin;
QuicPacketLength data_length;
const char* data_buffer;
QuicStreamOffset offset; // Location of this data in the stream.
// nullptr when the QuicStreamFrame is received, and non-null when sent.
UniqueStreamBuffer buffer;
private:
QuicStreamFrame(QuicStreamId stream_id,
bool fin,
QuicStreamOffset offset,
const char* data_buffer,
QuicPacketLength data_length,
UniqueStreamBuffer buffer);
DISALLOW_COPY_AND_ASSIGN(QuicStreamFrame);
};收到后自然要把payload取出来拼接成完整的数据，stream id和stream offset必不可少，拼接和处理的逻辑在这里：里面涉及到很多duplicate冗余去重的动作，都是依据offset来判断的！
QuicErrorCode QuicStreamSequencerBuffer::OnStreamData(
QuicStreamOffset starting_offset,
base::StringPiece data,
QuicTime timestamp,
size_t* const bytes_buffered,
std::string* error_details) {
*bytes_buffered = 0;
QuicStreamOffset offset = starting_offset;
size_t size = data.size();
if (size == 0) {
*error_details = "Received empty stream frame without FIN.";
return QUIC_EMPTY_STREAM_FRAME_NO_FIN;
}
// Find the first gap not ending before |offset|. This gap maybe the gap to
// fill if the arriving frame doesn't overlaps with previous ones.
std::list<Gap>::iterator current_gap = gaps_.begin();
while (current_gap != gaps_.end() && current_gap->end_offset <= offset) {
++current_gap;
}
DCHECK(current_gap != gaps_.end());
// "duplication": might duplicate with data alread filled,but also might
// overlap across different base::StringPiece objects already written.
// In both cases, don't write the data,
// and allow the caller of this method to handle the result.
if (offset < current_gap->begin_offset &&
offset + size <= current_gap->begin_offset) {
DVLOG(1) << "Duplicated data at offset: " << offset << " length: " << size;
return QUIC_NO_ERROR;
}
if (offset < current_gap->begin_offset &&
offset + size > current_gap->begin_offset) {
// Beginning of new data overlaps data before current gap.
*error_details =
string("Beginning of received data overlaps with buffered data.\n") +
"New frame range " + RangeDebugString(offset, offset + size) +
" with first 128 bytes: " +
string(data.data(), data.length() < 128 ? data.length() : 128) +
"\nCurrently received frames: " + ReceivedFramesDebugString() +
"\nCurrent gaps: " + GapsDebugString();
return QUIC_OVERLAPPING_STREAM_DATA;
}
if (offset + size > current_gap->end_offset) {
// End of new data overlaps with data after current gap.
*error_details =
string("End of received data overlaps with buffered data.\n") +
"New frame range " + RangeDebugString(offset, offset + size) +
" with first 128 bytes: " +
string(data.data(), data.length() < 128 ? data.length() : 128) +
"\nCurrently received frames: " + ReceivedFramesDebugString() +
"\nCurrent gaps: " + GapsDebugString();
return QUIC_OVERLAPPING_STREAM_DATA;
}
// Write beyond the current range this buffer is covering.
if (offset + size > total_bytes_read_ + max_buffer_capacity_bytes_) {
*error_details = "Received data beyond available range.";
return QUIC_INTERNAL_ERROR;
}
if (current_gap->begin_offset != starting_offset &&
current_gap->end_offset != starting_offset + data.length() &&
gaps_.size() >= kMaxNumGapsAllowed) {
// This frame is going to create one more gap which exceeds max number of
// gaps allowed. Stop processing.
*error_details = "Too many gaps created for this stream.";
return QUIC_TOO_MANY_FRAME_GAPS;
}
size_t total_written = 0;
size_t source_remaining = size;
const char* source = data.data();
// Write data block by block. If corresponding block has not created yet,
// create it first.
// Stop when all data are written or reaches the logical end of the buffer.
while (source_remaining > 0) {
const size_t write_block_num = GetBlockIndex(offset);
const size_t write_block_offset = GetInBlockOffset(offset);
DCHECK_GT(blocks_count_, write_block_num);
size_t block_capacity = GetBlockCapacity(write_block_num);
size_t bytes_avail = block_capacity - write_block_offset;
// If this write meets the upper boundary of the buffer,
// reduce the available free bytes.
if (offset + bytes_avail > total_bytes_read_ + max_buffer_capacity_bytes_) {
bytes_avail = total_bytes_read_ + max_buffer_capacity_bytes_ - offset;
}
if (reduce_sequencer_buffer_memory_life_time_ && blocks_ == nullptr) {
blocks_.reset(new BufferBlock*[blocks_count_]());
for (size_t i = 0; i < blocks_count_; ++i) {
blocks_[i] = nullptr;
}
}
if (blocks_[write_block_num] == nullptr) {
// TODO(danzh): Investigate if using a freelist would improve performance.
// Same as RetireBlock().
blocks_[write_block_num] = new BufferBlock();
}
const size_t bytes_to_copy = min<size_t>(bytes_avail, source_remaining);
char* dest = blocks_[write_block_num]->buffer + write_block_offset;
DVLOG(1) << "Write at offset: " << offset << " length: " << bytes_to_copy;
memcpy(dest, source, bytes_to_copy);
source += bytes_to_copy;
source_remaining -= bytes_to_copy;
offset += bytes_to_copy;
total_written += bytes_to_copy;
}
DCHECK_GT(total_written, 0u);
*bytes_buffered = total_written;
UpdateGapList(current_gap, starting_offset, total_written);
frame_arrival_time_map_.insert(
std::make_pair(starting_offset, FrameInfo(size, timestamp)));
num_bytes_buffered_ += total_written;
return QUIC_NO_ERROR;
}（3）为了精准测量RTT，quic协议的数据包编号都是单调递增的，哪怕是重发的包的编号都是增加的，这部分的控制代码在WritePacket函数里面：函数开头就判断数据包编号。一旦发现编号比最后一次发送包的编号还小，说明出错了，这时就关闭连接退出函数！
bool QuicConnection::WritePacket(SerializedPacket* packet) {
/*如果数据包号比最后一个发送包的号还小，说明顺序错了，直接关闭连接*/
if (packet->packet_number <
sent_packet_manager_->GetLargestSentPacket(packet->path_id)) {
QUIC_BUG << "Attempt to write packet:" << packet->packet_number << " after:"
<< sent_packet_manager_->GetLargestSentPacket(packet->path_id);
CloseConnection(QUIC_INTERNAL_ERROR, "Packet written out of order.",
ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
return true;
}
/*没有连接、没有加密的包是不能发的*/
if (ShouldDiscardPacket(*packet)) {
++stats_.packets_discarded;
return true;
}
.........................
}（4）为啥quic协议要基于udp了？应用层现成的协议很复杂，改造的难度大！传输层只有tcp和udp两种协议；tcp的缺点不再赘述，udp的优点就是简单，只提供最原始的发包功能，完全不管对方有没有收到，quic就是利用了udp这种最基础的send package发包能力，在此之上完成了tls（保证数据安全）、拥塞控制（保证链路被塞满）、多路复用（保证数据不丢失）等应用层的功能！
参考：
1、https://www.cnblogs.com/dream397/p/14605040.html quic实现代码分析
2、https://github.com/devsisters/libquic libquic源码
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