本文详细介绍了evpp网络库的使用方法，包括TCP服务器的创建、初始化、启动流程，以及如何设置连接和消息回调函数。同时，展示了如何利用C++11特性提高代码的可读性和效率。
1
安装方法，源码包有说明：https://github.com/Qihoo360/evpp
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2
tcp回声服务器（官方示例）
#include <evpp/tcp_server.h>
#include <evpp/buffer.h>
#include <evpp/tcp_conn.h>
#ifdef _WIN32
#include "../../winmain-inl.h"
#endif
void OnMessage(const evpp::TCPConnPtr& conn,
evpp::Buffer* msg) {
std::string s = msg->NextAllString();
LOG_INFO << "Received a message [" << s << "]";
conn->Send(s);
if (s == "quit" || s == "exit") {
conn->Close();
}
}
void OnConnection(const evpp::TCPConnPtr& conn) {
if (conn->IsConnected()) {
LOG_INFO << "Accept a new connection from " << conn->remote_addr();
} else {
LOG_INFO << "Disconnected from " << conn->remote_addr();
}
}
int main(int argc, char* argv[]) {
std::string port = "9099";
if (argc == 2) {
port = argv[1];
}
std::string addr = std::string("0.0.0.0:") + port;
evpp::EventLoop loop;
evpp::TCPServer server(&loop, addr, "TCPEcho", 0);
server.SetMessageCallback(&OnMessage);
server.SetConnectionCallback(&OnConnection);
server.Init();
server.Start();
loop.Run();
return 0;
}----------------------------------------------------------------------------------------------------------------
3
evpp::TCPServer类（主要）
#include <evpp/tcp_server.h>
#pragma once
#include "evpp/inner_pre.h"
#include "evpp/event_loop.h"
#include "evpp/event_loop_thread_pool.h"
#include "evpp/tcp_callbacks.h"
#include "evpp/thread_dispatch_policy.h"
#include "evpp/server_status.h"
#include <map>
namespace evpp {
class Listener;
// We can use this class to create a TCP server.
// The typical usage is :
// 1. Create a TCPServer object
// 2. Set the message callback and connection callback
// 3. Call TCPServer::Init()
// 4. Call TCPServer::Start()
// 5. Process TCP client connections and messages in callbacks
// 6. At last call Server::Stop() to stop the whole server
//
// The examples code is as bellow:
// <code>
// std::string addr = "0.0.0.0:9099";
// int thread_num = 4;
// evpp::EventLoop loop;
// evpp::TCPServer server(&loop, addr, "TCPEchoServer", thread_num);
// server.SetMessageCallback([](const evpp::TCPConnPtr& conn,
// evpp::Buffer* msg) {
// // Do something with the received message
// conn->Send(msg); // At here, we just send the received message back.
// });
// server.SetConnectionCallback([](const evpp::TCPConnPtr& conn) {
// if (conn->IsConnected()) {
// LOG_INFO << "A new connection from " << conn->remote_addr();
// } else {
// LOG_INFO << "Lost the connection from " << conn->remote_addr();
// }
// });
// server.Init();
// server.Start();
// loop.Run();
// </code>
//
class EVPP_EXPORT TCPServer : public ThreadDispatchPolicy, public ServerStatus {
public:
typedef std::function<void()> DoneCallback;
// @brief The constructor of a TCPServer.
// @param loop -
// @param listen_addr - The listening address with "ip:port" format
// @param name - The name of this object
// @param thread_num - The working thread count
TCPServer(EventLoop* loop,
const std::string& listen_addr/*ip:port*/,
const std::string& name,
uint32_t thread_num);
~TCPServer();
// @brief Do the initialization works here.
// It will create a nonblocking TCP socket, and bind with the give address
// then listen on it. If there is anything wrong it will return false.
// @return bool - True if anything goes well
bool Init();
// @brief Start the TCP server and we can accept new connections now.
// @return bool - True if anything goes well
bool Start();
// @brief Stop the TCP server
// @param cb - the callback cb will be invoked when
// the TCP server is totally stopped
void Stop(DoneCallback cb = DoneCallback());
// @brief Reinitialize some data fields after a fork
void AfterFork();
public:
// Set a connection event relative callback when the TCPServer
// receives a new connection or an exist connection breaks down.
// When these two events happened, the value of the parameter in the callback is:
// 1. Received a new connection : TCPConn::IsConnected() == true
// 2. An exist connection broken down : TCPConn::IsDisconnecting() == true
void SetConnectionCallback(const ConnectionCallback& cb) {
conn_fn_ = cb;
}
// Set the message callback to handle the messages from remote client
void SetMessageCallback(MessageCallback cb) {
msg_fn_ = cb;
}
public:
const std::string& listen_addr() const {
return listen_addr_;
}
private:
void StopThreadPool();
void StopInLoop(DoneCallback on_stopped_cb);
void RemoveConnection(const TCPConnPtr& conn);
void HandleNewConn(evpp_socket_t sockfd, const std::string& remote_addr/*ip:port*/, const struct sockaddr_in* raddr);
EventLoop* GetNextLoop(const struct sockaddr_in* raddr);
private:
EventLoop* loop_; // the listening loop
const std::string listen_addr_; // ip:port
const std::string name_;
std::unique_ptr<Listener> listener_;
std::shared_ptr<EventLoopThreadPool> tpool_;
ConnectionCallback conn_fn_;
MessageCallback msg_fn_;
DoneCallback stopped_cb_;
// always in the listening loop thread
uint64_t next_conn_id_ = 0;
typedef std::map<uint64_t/*the id of the connection*/, TCPConnPtr> ConnectionMap;
ConnectionMap connections_;
};
}----------------------------------------------------------------------------------------------------------------
4
std::function回调类型
part3中的两个evpp::TCPServer类的成员函数（设置回调函数）
void SetConnectionCallback(const ConnectionCallback& cb)
void SetMessageCallback(MessageCallback cb)
其回调类型在源码 #include "evpp/tcp_callbacks.h"
#pragma once
#include "evpp/inner_pre.h"
namespace evpp {
class Buffer;
class TCPConn;
typedef std::shared_ptr<TCPConn> TCPConnPtr;
typedef std::function<void()> TimerCallback;
// When a connection established, broken down, connecting failed, this callback will be called
// This is called from a work-thread this is not the listening thread probably
typedef std::function<void(const TCPConnPtr&)> ConnectionCallback;
typedef std::function<void(const TCPConnPtr&)> CloseCallback;
typedef std::function<void(const TCPConnPtr&)> WriteCompleteCallback;
typedef std::function<void(const TCPConnPtr&, size_t)> HighWaterMarkCallback;
typedef std::function<void(const TCPConnPtr&, Buffer*)> MessageCallback;
namespace internal {
inline void DefaultConnectionCallback(const TCPConnPtr&) {}
inline void DefaultMessageCallback(const TCPConnPtr&, Buffer*) {}
}
}----------------------------------------------------------------------------------------------------------------
5
evpp::EventLoop类
evpp::EventLoop类是IO事件的驱动内核。这个类是event_base类的包装器，但不仅仅是一个包装器。它通过简单的方式，运行IO事件驱动循环。一个线程一个循环。
在evpp::TCPServer对象设置完回调函数及调用Init()、Start()之后，必须执行IO事件线程Run()，如part2示例。
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6
以上是evpp tcp网络库的大致用法。udp、http用法参照源码。
evpp语法采用C++11的特性，大量使用std::string，而不是char*独占天；使用std::stringstream，而不是sprintf；易读的Lambda,而不是函数指针等等。满满的C++11诚意。http库更是可以弥补C++开发http服务器效率低的问题。膜拜360大佬们！
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