1、前言
- 本文通过学习google quic默认客户端的网络IO事件读取实现，来学习在google quic中数据的发送和接收的处理/分发机制
- 同时通过本节学习默认IO读写实现和其他模块的关系，为后续深入分析google quic源码做铺垫
2、QuicClientDefaultNetworkHelper定义
-
在google quic中，默认实现QuicClientDefaultNetworkHelper模块用于往socket中写入数据，以及从socket中读取数据
-
其中QuicClientDefaultNetworkHelper的派生关系如下：
quic_client_socket_read_write_01.png
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QuicClientDefaultNetworkHelper模块分别由QuicClientBase::NetWorkHelper、QuicSocketEventListener、ProcessPacketInterface接口派生,其中1）QuicClientBase::NetWorkHelper用于创建socket，往QuicEventLoop注册和注销IO读写事件；2）QuicSocketEventListener用于接收处理socket IO事件如可读和可写事件的处理；3）ProcessPacketInterface接口提供ProcessPacket()函数完成对QuicReceivedPacket报文传递到QuicClientDefaultNetworkHelper模块
-
同时QuicClientDefaultNetworkHelper由三大成员变量QuicEventLoop、QuicPacketReader、QuicClientBase组成，1）成员event_loop_指针由其他模块传入用于关联socket io框架监听socket 读写事件；2）packet_reader成员用于读取Udp报文，并将udp包转成QuicReceivedPacket包，并最终通过ProcessPacketInterface接口将QuicReceivedPacket报文回调到QuicClientDefaultNetworkHelper模块，然后再将该报文交给成员client_进行处理
3、QuicClientBase::NetworkHelper接口的定义及实现
class QuicClientBase : public QuicSession::Visitor {
public:
// An interface to various network events that the QuicClient will need to
// interact with.
class NetworkHelper {
public:
virtual ~NetworkHelper();
// Runs one iteration of the event loop.
// 用于socket io 循环loop
virtual void RunEventLoop() = 0;
// Used during initialization: creates the UDP socket FD, sets socket
// options, and binds the socket to our address.
// 创建一个udp socket,并将socket fd 向事件循环注册，通过IO监听该socket
virtual bool CreateUDPSocketAndBind(QuicSocketAddress server_address,
QuicIpAddress bind_to_address,
int bind_to_port) = 0;
// Unregister and close all open UDP sockets.
// 关闭一个socket,并将socket从io 事件循环中注销
virtual void CleanUpAllUDPSockets() = 0;
// If the client has at least one UDP socket, return address of the latest
// created one. Otherwise, return an empty socket address.
virtual QuicSocketAddress GetLatestClientAddress() const = 0;
// Creates a packet writer to be used for the next connection.
// 创建一个socket writer，用于往socket写入数据
virtual QuicPacketWriter* CreateQuicPacketWriter() = 0;
};
....
}
- RunEventLoop函数的视线如下
void QuicClientDefaultNetworkHelper::RunEventLoop() {
quiche::QuicheRunSystemEventLoopIteration();
event_loop_->RunEventLoopOnce(QuicTime::Delta::FromMilliseconds(50));
}
- 该函数实现较为简单,就是直接调用```QuicEventLoop::RunEventLoopOnce()``，对IO时间循环就行迭代,并且在50ms后假设无其他时间触发，将退出IO迭代
bool QuicClientDefaultNetworkHelper::CreateUDPSocketAndBind(
QuicSocketAddress server_address, QuicIpAddress bind_to_address,
int bind_to_port) {
SocketFd fd = CreateUDPSocket(server_address, &overflow_supported_);
if (fd == kInvalidSocketFd) {
return false;
}
auto closer = absl::MakeCleanup([fd] { (void)socket_api::Close(fd); });
......
if (event_loop_->RegisterSocket(
fd, kSocketEventReadable | kSocketEventWritable, this)) {
fd_address_map_[fd] = client_address;
std::move(closer).Cancel();
return true;
}
return false;
}
- CreateUDPSocketAndBind函数的核心作用是根据一个server_address创建一个udp端口，并将该fd往时间循环中注册读写事件
- 在QuicClientBase::Initialize()函数中有使用该函数创建socket句柄
void QuicClientDefaultNetworkHelper::CleanUpAllUDPSockets() {
for (std::pair<int, QuicSocketAddress> fd_address : fd_address_map_) {
CleanUpUDPSocketImpl(fd_address.first);
}
fd_address_map_.clear();
}
void QuicClientDefaultNetworkHelper::CleanUpUDPSocketImpl(SocketFd fd) {
if (fd != kInvalidSocketFd) {
bool success = event_loop_->UnregisterSocket(fd);
QUICHE_DCHECK(success || fds_unregistered_externally_);
absl::Status rc = socket_api::Close(fd);
QUICHE_DCHECK(rc.ok()) << rc;
}
}
- 以上为关闭socket fd的实现,同时注销事件循环
QuicPacketWriter* QuicClientDefaultNetworkHelper::CreateQuicPacketWriter() {
if (event_loop_->SupportsEdgeTriggered()) {
return new QuicDefaultPacketWriter(GetLatestFD());
} else {
return new LevelTriggeredPacketWriter(GetLatestFD(), event_loop_);
}
}
- 创建QuicPacketWriter指针，用于往socket fd中写入数据
4、QuicSocketEventListener接口的定义及实现
class QUICHE_NO_EXPORT QuicSocketEventListener {
public:
virtual ~QuicSocketEventListener() = default;
virtual void OnSocketEvent(QuicEventLoop* event_loop, SocketFd fd,
QuicSocketEventMask events) = 0;
};
-
在上节中有提到通过CreateUDPSocketAndBind()函数创建socket fd，并将fd向QuicEventLoop注册读写事件，当IO检测到该fd有可读或者可写事件的时候，就会触发对应的回调，而该回调就是OnSocketEvent(...)函数
-
对应的实现如下：
void QuicClientDefaultNetworkHelper::OnSocketEvent(
QuicEventLoop* /*event_loop*/, QuicUdpSocketFd fd,
QuicSocketEventMask events) {
if (events & kSocketEventReadable) {
QUIC_DVLOG(1) << "Read packets on kSocketEventReadable";
int times_to_read = max_reads_per_event_loop_;
bool more_to_read = true;
QuicPacketCount packets_dropped = 0;
while (client_->connected() && more_to_read && times_to_read > 0) {
// 读取udp包,并将包转换成QuicReceivedPacket包，然后通过ProcessPacketInterface::ProcessPacket
// 对报文进行处理
more_to_read = packet_reader_->ReadAndDispatchPackets(
fd, GetLatestClientAddress().port(), *client_->helper()->GetClock(),
this, overflow_supported_ ? &packets_dropped : nullptr);
--times_to_read;
}
....
}
if (client_->connected() && (events & kSocketEventWritable)) {
client_->writer()->SetWritable();
client_->session()->connection()->OnCanWrite();
}
}
- OnSocketEvent函数为IO事件监听函数，当socket可读的时候，通过QuicPacketReader模块读取Udp包，并将包转换成QuicReceivedPacket同时将QuicReceivedPacket通过ProcessPacketInterface::ProcessPacket()由传递到QuicClientDefaultNetworkHelper模块
- 当socket有可写事件触发的时候,通过成员client_将QuicPacketWriter置成可写，同时也对对应的QuicConnection模块调用**OnCanWrite()处理，后面进行详细分析
5、ProcessPacketInterface接口的定义及实现
// A class to process each incoming packet.
class QUIC_NO_EXPORT ProcessPacketInterface {
public:
virtual ~ProcessPacketInterface() {}
virtual void ProcessPacket(const QuicSocketAddress& self_address,
const QuicSocketAddress& peer_address,
const QuicReceivedPacket& packet) = 0;
};
void QuicClientDefaultNetworkHelper::ProcessPacket(
const QuicSocketAddress& self_address,
const QuicSocketAddress& peer_address, const QuicReceivedPacket& packet) {
client_->session()->ProcessUdpPacket(self_address, peer_address, packet);
}
- 由QuicClientDefaultNetworkHelper::ProcessPacket()函数的视线可以看出，最终对QuicReceivedPacket报文的处理是在QuicSession中进行处理的
- 而QuicSession最终包报文解析工作交给QuicConnection模块
void QuicSession::ProcessUdpPacket(const QuicSocketAddress& self_address,
const QuicSocketAddress& peer_address,
const QuicReceivedPacket& packet) {
QuicConnectionContextSwitcher cs(connection_->context());
connection_->ProcessUdpPacket(self_address, peer_address, packet);
}
- 在google quic应用中无论是服务端还是客户端端，都是以QuicSession为一次会话单位，而每个QuicSession一定会有一个QuicConnection成员，可以称作为连接
- 此处无论是服务端还是客户端对QuicReceivedPacket的解析工作最终都是在*QuicConnection模块中完成
总结
- 通过本文学习google quiche开源项目中客户端socket发送数据和接收数据的基本模型
- 在上文的分析中最终引出了QuicSession、QuicConnection、以及QuicPacketWriter模块，这些模块是google quic中的核心模块
- 通过本文的学习对后续深入研究google quic做一个简单铺垫工作
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