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应用层：自定义网络协议：序列化和反序列化，如果是TCP传输的：还要关心区分报文边界（在序列化设计的时候设计好）——粘包问题
——两个问题：粘包、序列化反序列化

1、首先想要使用TCP协议传输的网络，服务器和客户端都应该要创建自己的套接字，因为两个都要创建，所以我们把套接字封装为一个类：
封装方法：设计模式：模版方法：先写一个模版类（基类），里面有各种函数，然后再写一个派生类里面有各种方法的实现，创建对象的时候

#pragma once
#include <iostream>
#include <string>
#include <cstring>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>#define Convert(addrptr) ((struct sockaddr *)addrptr)namespace Net_Work
{const static int defaultsockfd = -1;const int backlog = 5;enum{SocketError = 1,BindError,ListenError,};// 封装一个基类，Socket接口类// 设计模式：模版方法类class Socket{public:virtual ~Socket() {}virtual void CreateSocketOrDie() = 0;virtual void BindSocketOrDie(uint16_t port) = 0;virtual void ListenSocketOrDie(int backlog) = 0;virtual Socket *AcceptConnection(std::string *peerip, uint16_t *peerport) = 0;virtual bool ConnectServer(std::string &serverip, uint16_t serverport) = 0;virtual int GetSockFd() = 0;virtual void SetSockFd(int sockfd) = 0;virtual void CloseSocket() = 0;virtual bool Recv(std::string *buffer, int size) = 0;// TODOpublic:// 创建服务器端的套接字，并设置为监听状态监听套接字void BuildListenSocketMethod(uint16_t port, int backlog){CreateSocketOrDie();BindSocketOrDie(port);ListenSocketOrDie(backlog);}// 创建客户端的套接字，并且申请链接bool BuildConnectSocketMethod(std::string &serverip, uint16_t serverport){CreateSocketOrDie();return ConnectServer(serverip, serverport);}void BuildNormalSocketMethod(int sockfd){SetSockFd(sockfd);}};class TcpSocket : public Socket{public:TcpSocket(int sockfd = defaultsockfd) : _sockfd(sockfd){}~TcpSocket(){}void CreateSocketOrDie() override // 创建套接字{_sockfd = ::socket(AF_INET, SOCK_STREAM, 0);if (_sockfd < 0)exit(SocketError);}void BindSocketOrDie(uint16_t port) override // 绑定套接字{struct sockaddr_in local;memset(&local, 0, sizeof(local));local.sin_family = AF_INET;local.sin_addr.s_addr = INADDR_ANY;local.sin_port = htons(port);int n = ::bind(_sockfd, Convert(&local), sizeof(local));if (n < 0)exit(BindError);}void ListenSocketOrDie(int backlog) override // 设置套接字为监听状态{int n = ::listen(_sockfd, backlog);if (n < 0)exit(ListenError);}// 获取链接套接字——服务器Socket *AcceptConnection(std::string *peerip, uint16_t *peerport) override{struct sockaddr_in peer;socklen_t len = sizeof(peer);int newsockfd = ::accept(_sockfd, Convert(&peer), &len);if (newsockfd < 0)return nullptr;*peerport = ntohs(peer.sin_port);*peerip = inet_ntoa(peer.sin_addr);Socket *s = new TcpSocket(newsockfd);return s;}// 申请链接——客户端bool ConnectServer(std::string &serverip, uint16_t serverport) override{struct sockaddr_in server;memset(&server, 0, sizeof(server));server.sin_family = AF_INET;server.sin_addr.s_addr = inet_addr(serverip.c_str());server.sin_port = htons(serverport);int n = ::connect(_sockfd, Convert(&server), sizeof(server));if (n == 0)return true;elsereturn false;}int GetSockFd() override{return _sockfd;}void SetSockFd(int sockfd) override{_sockfd = sockfd;}void CloseSocket() override{if (_sockfd > defaultsockfd)::close(_sockfd);}bool Recv(std::string *buffer, int size)//接收消息到buffer中{char inbuffer[size];ssize_t n = recv(_sockfd, inbuffer, size - 1, 0);if (n > 0){inbuffer[n] = 0;*buffer += inbuffer;return true;}else if (n == 0 || n < 0)return false;}private:int _sockfd;};}

创建服务器：
1、创建套接字
2、把套接字设置为监听状态
3、获取连接，产生新的套接字
4、把新的套接字作为新线程的参数传到新线程执行的代码中，实现收发消息的操作

代码：

#pragma once#include"Socket.hpp"
#include<pthread.h>
#include<functional>using func_t=std::function<void(Net_Work::Socket* sockp)>;//服务器类
class TcpServer;class ThreadData
{public:ThreadData(TcpServer*tcp_this, Net_Work::Socket *sockp): _this(tcp_this), _sockp(sockp){}public:TcpServer *_this;Net_Work::Socket *_sockp;
};class TcpServer
{public:TcpServer(uint16_t port, func_t handler_request):_port(port),_listensocket(new Net_Work::TcpSocket()),_handler_request(handler_request){_listensocket->BuildListenSocketMethod(_port,Net_Work::backlog);}static void *ThreadRun(void *args){pthread_detach(pthread_self());//分离线程ThreadData *td=static_cast<ThreadData*>(args);td->_this->_handler_request(td->_sockp);td->_sockp->CloseSocket();delete td->_sockp;delete td;return nullptr;}void Loop(){while(true){//获取连接std::string peerip;uint16_t peerport;Net_Work::Socket* newsock=_listensocket->AcceptConnection(&peerip,&peerport);if(newsock==nullptr) continue;;std::cout<<"获取了一个新链接,sockfd: "<<newsock->GetSockFd()<<"client info:"<< peerip<<":"<<peerport<<std::endl;//创建线程去完成此次sockfd收发pthread_t tid;ThreadData *td=new ThreadData(this,newsock);pthread_create(&tid,nullptr,ThreadRun,td);}}~TcpServer(){delete _listensocket;}private:int _port;Net_Work::Socket *_listensocket;
public:func_t _handler_request;};

客户端：

2、TCP是向字节流（字符串）

序列化、反序列化

自定义协议就是定义双方都认识的结构化字段，并且协议中有序列化和反序列化的实现
先定义一个协议（结构化字段）——双方都能看到
设计模式：工厂模式：
客户端发送的结构体+序列化函数+反序列化函数

服务器反序列化的接收的结构体+反序列函数+序列化函数

代码：

#pragma once#include <iostream>
#include <memory>namespace Protocol
{const std::string ProtSep = " ";const std::string LineBreakSep = "\n";// 封装为报文——序列化的一部分std::string Encode(const std::string &message) //"x op y"或者"_result _code"{std::string len = std::to_string(message.size());std::string package = len + LineBreakSep + message + LineBreakSep; //"len\n""x op y\n"return package;}// 解报——反序列化的一部分bool Decode(std::string &package, std::string *message) //"len\n""x op y\n"{// 除了解报，我们还要判断是否认正确auto pos = package.find(LineBreakSep);if (pos == std::string::npos)return false;std::string lens = package.substr(0, pos);int messagelen = std::stoi(lens);int total = lens.size() + messagelen + 2 * LineBreakSep.size();if (package.size() < total)return false;// 至少有一个完整报文*message = package.substr(pos + LineBreakSep.size(), messagelen);// 收到的报文可能是"len\n""x op y\n""len\n""x op y\n""len\n""x op y\n"// 所以我解报一个报文后，要删除这个报文，让后面的继续Dcode解报package.erase(0, total);return true;}class Requset{public:Requset() : _data_x(0), _data_y(0), _oper(0){}Requset(int x, int y, int op) : _data_x(x), _data_y(y), _oper(op){}~Requset(){}void Debug(){std::cout << "_data_x:" << _data_x << std::endl;std::cout << "_data_y:" << _data_y << std::endl;std::cout << "_oper:" << _oper << std::endl;}void Inc(){_data_x++;_data_y++;}// 自定义序列化协议：结构体数据->字符串bool Serialize(std::string *out){//"x op y"*out = std::to_string(_data_x) + ProtSep + _oper + ProtSep + std::to_string(_data_y);return true;}// 反序列化   :  字符串->结构体数据bool Deserialize(std::string &in) //"x op y"{auto left = in.find(ProtSep);if (left == std::string::npos)return false;auto right = in.rfind(ProtSep);if (right == std::string::npos)return false;//[)_data_x = std::stoi(in.substr(0, left));_data_y = std::stoi(in.substr(right + ProtSep.size()));std::string oper = in.substr(left + ProtSep.size(), right - (left + ProtSep.size()));if (oper.size() == 1)return false;_oper = oper[0];return true;}int Getx() { return _data_x; }int Gety() { return _data_y; }char GetOper() { return _oper; }//_data_x+_data_y// 报文的自描述//"len\n""x op y\n"private:int _data_x; // 第一个参数int _data_y; // 第二个参数char _oper;  //+ - * / %};class Response{public:Response(): _rseult(0), _code(0){}Response(int result, int code) : _result(result), _code(code){}// 自定义序列化协议：结构体数据->字符串bool Serialize(std::string *out){//"_result  _code"*out = std::to_string(_result) + ProtSep + std::to_string(_code);return true;}// 反序列化：字符串->数据架构数据bool Deserialize(std::string &in) //"_result  _code"{auto pos = in.find(ProtSep);if (pos == std::string::npos)return false;_result = std::stoi(in.substr(0, pos));_code = std::stoi(in.substr(pos + ProtSep.size()));return true;}void SetResult(int res) { _result = res; }void SetCode(int code){ _code=code;}private:int _result; // 运算结果int _code;   // 运算状态};// 简单的工厂模式，建造类设计模式class Factory{public:std::shared_ptr<Requset> BulidRequest(){std::shared_ptr<Requset> req = std::make_shared<Requset>();return req;}std::shared_ptr<Requset> BulidRequest(int x, int y, int op){std::shared_ptr<Requset> req = std::make_shared<Requset>(x, y, op);return req;}std::shared_ptr<Response> BulidResponse(){std::shared_ptr<Response> resp = std::make_shared<Response>();return resp;}std::shared_ptr<Response> BulidResponse(int result, int code){std::shared_ptr<Response> resp = std::make_shared<Response>(result, code);return resp;}};
}

成熟的序列化反序列化：
Json:Value 万能类型

那么我们序列化和反序列化就可以用这样的：

总结：发送的数据为结构体，这个结构体就是我们自定义的协议，他的序列化反序列化 这些都是应用层的协议