（一）简单的TcpServer

1. TcpServer.h

#ifndef TCP_SERVER_H
#define TCP_SERVER_H

#include <thread>

class TcpServer
{
public:
    TcpServer(const int port);
    ~TcpServer();
    int Initialize();
    int Start();

private:
    void Process();

private:
    int m_fd;
    int m_port;
    std::thread *t;
};

#endif  // TCP_SERVER_H

2. TcpServer.cpp

#include "TcpServer.h"

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#include <string>

#include <thread>

TcpServer::TcpServer(const int port):
    m_fd(-1),
    m_port(port)
    {
    }

TcpServer::~TcpServer()
{
    if(t->joinable())
    {
        t->join();
        t = nullptr;
    }
    close(m_fd);
}

int TcpServer::Initialize()
{
    m_fd = ::socket(AF_INET, SOCK_STREAM, 0);
    if( m_fd == -1 )
        return -1;

    struct sockaddr_in sin;
    sin.sin_family = AF_INET;
    sin.sin_addr.s_addr = 0;
    sin.sin_port = htons(m_port);

    int flag = 1;
    socklen_t len = sizeof(flag);
    if(::setsockopt(m_fd, SOL_SOCKET, SO_REUSEADDR, &flag, len) < 0)
    {
        return -4;
    }

    if( ::bind(m_fd, (struct sockaddr *)&sin, sizeof(sin)) < 0 )
    {
        return -2;
    }

    if( ::listen(m_fd, 10) < 0)
    {
        return -3;
    }

    return 0;
}

int TcpServer::Start()
{
    // thread accept
    t = new std::thread(&TcpServer::Process,this);
    return 0;
}

void TcpServer::Process()
{
    printf("process...
");

    while(true)
    {
        struct sockaddr_in client;
        socklen_t len = sizeof(client);

        int sockfd = ::accept(m_fd, (struct sockaddr*)&client, &len );
        if(sockfd < 0){
            return;
        }
        
        /* 提取客户端IP地址 */
        char  szIP[64]  = { 0 };   // 客户端IP地址
        std::string strIP = inet_ntop(AF_INET, &client.sin_addr, szIP, sizeof(szIP));
        printf("connect from client: %s
", strIP.c_str());

        char msg[4096];  
        int length = read(sockfd, msg, sizeof(msg) - 1);
        if( length <= 0 )
        {
            printf("some error happen when read
");
            return ;
        }
        printf("%s",msg);

        if(strcmp(msg,"get stats") != 0)
        {
            // return;
        }

        // {'stat':'1', 'version':'${project.name}-V${project.version}-B${SVN.revision}' }
        char reply_msg[4096] = "{'stat':'1', 'version':'middleware-V1.0.0-B12965'}";
        write(sockfd, reply_msg, strlen(reply_msg) );

        close(sockfd);
        printf("close
");
    }
}

3. main.cpp

#include "TcpServer.h"

#include <unistd.h>
#include <memory>
#include <iostream>
using namespace std;

int main()
{
    shared_ptr<TcpServer> spServer = make_shared<TcpServer>(7773);
    int ret = 0;
    ret = spServer->Initialize();
    if (ret != 0){
    	std::cout<<"initialize failed "<<ret<<std::endl;
    }
    spServer->Start();

    // while(true)
    // {
    //  sleep(1);
    // }
    return 0;
}

4. telnet

[root@thor ~]# telnet 127.0.0.1 7773
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
get stats
{'stat':'1', 'version':'middleware-V1.0.0-B12965'}Connection closed by foreign host.