前言

在上一篇中Socket网络通信基础（一）：简易TCP服务端和客户端
server使用while循环来持续accept新的client连接
但是client连接上server后，在recv接收到server消息后，就退出了

本篇优化方向
1、让client可以发送自定义的消息，并在收到server消息后继续循环等待新的指令
2、server和client使用结构化的网络消息数据交互

一、优化内容

1、新增结构化消息DataPackage

struct DataPackage
{
	int age;
	char name[32];
};

2、server的while优化

根据收到的client命令向client发送不同的消息

while (true)
	{
		int nLen = recv(sock_client, recvBuf, 128, 0);
		if (nLen <= 0)
		{
			printf("客户端已退出，任务结束。\n");
			break;
		}
		printf("收到命令：%s \n", recvBuf);
		if (0 == strcmp(recvBuf, "getInfo"))
		{
			DataPackage dp = { 80,"张三" };
			send(sock_client, (const char*)&dp, sizeof(DataPackage), 0);
		}
		else
		{
			char msgBuf[] = "???.";
			send(sock_client, msgBuf, strlen(msgBuf) + 1, 0);
		}
	}

3、client持续send逻辑

使用scanf来接收用户的命令输入
根据用户输入的指令分别执行退出、发送消息
根据server返回的消息内容转换成DataPackage结构体指针并打印输出

	while (true)
	{
		char cmdBuf[128] = {};
		scanf("%s", cmdBuf);
		if (0 == strcmp(cmdBuf, "exit"))
		{
			printf("收到exit命令，任务结束。\n");
			break;
		}
		else
		{
			send(sock_client, cmdBuf, strlen(cmdBuf) + 1, 0);
		}
		char recvBuf[128] = {};
		int nLen = recv(sock_client, recvBuf, 128, 0);
		if (nLen > 0)
		{
			DataPackage* dp = (DataPackage*)recvBuf;
			printf("接收到数据：年龄=%d，姓名=%s \n", dp->age, dp->name);
		}
	}

二、测试结果

这里我们还发现个问题
当消息内容getInfo正确的时候，是可以正常解析的
但是当内容错误的话，client依然会收到server返回的消息
这时候再解析成DataPackage就出问题
这个后续我们再解决

三、server是如何知道client退出的

首先TCP协议的连接是经过三次握手，断开是经过四次握手（更具体大家可以查资料）
我们可以在client的closesocket处断点，然后在client中输入命令exit
这时候可以看到当client的closesocket执行后，server就已经收到recv的nLen=0
客户端退出

在这里插入图片描述

四、完整源码

1、server.cpp

#define WIN32_LEAN_AND_MEAN
#define _WINSOCK_DEPRECATED_NO_WARNINGS

#include <Windows.h>
#include <WinSock2.h>
#include<stdio.h>

#pragma comment(lib,"ws2_32.lib")

struct DataPackage
{
	int age;
	char name[32];
};

int main()
{
	WORD ver = MAKEWORD(2, 2);
	WSADATA dat;
	WSAStartup(ver, &dat);

	SOCKET sock_server = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
	if (INVALID_SOCKET == sock_server)
	{
		printf("socket 创建失败\n");
		WSACleanup();
		return -1;
	}

	sockaddr_in _sin = {};
	_sin.sin_family = AF_INET;
	_sin.sin_port = htons(4567);
	_sin.sin_addr.S_un.S_addr = INADDR_ANY;// INADDR_ANY：这个代表本机的地址都可以访问，如IPV4,IPV6
	//_sin.sin_addr.s_addr = inet_addr("127.0.0.1");// 指定地址的绑定

	if (SOCKET_ERROR == bind(sock_server, (sockaddr*)&_sin, sizeof(_sin)))
	{
		printf("ERROR，绑定网络端口失败...\n");
		closesocket(sock_server);
		WSACleanup();
		return -1;
	}
	else
	{
		printf("绑定网络端口成功...\n");
	}
	if (SOCKET_ERROR == listen(sock_server, 5))
	{
		printf("ERROR，监听网络端口失败...\n");
		closesocket(sock_server);
		WSACleanup();
		return -1;
	}
	else
	{
		printf("监听网络端口成功...\n");
	}

	sockaddr_in clientAddr = {};
	int nAddrLen = sizeof(clientAddr);
	SOCKET sock_client = INVALID_SOCKET;

	sock_client = accept(sock_server, (sockaddr*)&clientAddr, &nAddrLen);
	if (INVALID_SOCKET == sock_client)
	{
		printf("错误，接受到无效客户端SOCKET...\n");
		closesocket(sock_server);
		WSACleanup();
		return -1;
	}
	printf("新客户端加入：IP = %s \n", inet_ntoa(clientAddr.sin_addr));

	char recvBuf[128] = {};
	while (true)
	{
		int nLen = recv(sock_client, recvBuf, 128, 0);
		if (nLen <= 0)
		{
			printf("<nLen=%d>，客户端已退出，任务结束。\n", nLen);
			break;
		}
		printf("收到命令：%s \n", recvBuf);

		if (0 == strcmp(recvBuf, "getInfo"))
		{
			DataPackage dp = { 80,"张三" };
			send(sock_client, (const char*)&dp, sizeof(DataPackage), 0);
		}
		else
		{
			char msgBuf[] = "???.";
			send(sock_client, msgBuf, strlen(msgBuf) + 1, 0);
		}
	}

	closesocket(sock_server);
	WSACleanup();
	printf("已退出，任务结束。\n");
	getchar();
	return 0;
}

2、client.cpp

#define _CRT_SECURE_NO_WARNINGS
#define WIN32_LEAN_AND_MEAN
#define _WINSOCK_DEPRECATED_NO_WARNINGS

#include <Windows.h>
#include <WinSock2.h>
#include<stdio.h>

#pragma comment(lib,"ws2_32.lib")

struct DataPackage
{
	int age;
	char name[32];
};

int main()
{
	WORD ver = MAKEWORD(2, 2);
	WSADATA dat;
	WSAStartup(ver, &dat);

	SOCKET sock_client = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
	if (INVALID_SOCKET == sock_client)
	{
		printf("socket 创建失败\n");
		WSACleanup();
		return -1;
	}

	sockaddr_in _sin = {};
	_sin.sin_family = AF_INET;
	_sin.sin_port = htons(4567);
	_sin.sin_addr.s_addr = inet_addr("127.0.0.1");

	int ret = connect(sock_client, (sockaddr*)&_sin, sizeof(_sin));
	if (SOCKET_ERROR == ret)
	{
		printf("错误，连接服务器失败...\n");
		closesocket(sock_client);
		WSACleanup();
		return -1;
	}
	else
	{
		printf("连接服务器成功...\n");
	}

	while (true)
	{
		char cmdBuf[128] = {};
		scanf("%s", cmdBuf);
		if (0 == strcmp(cmdBuf, "exit"))
		{
			printf("收到exit命令，任务结束。\n");
			break;
		}
		else
		{
			send(sock_client, cmdBuf, strlen(cmdBuf) + 1, 0);
		}
		char recvBuf[128] = {};
		int nLen = recv(sock_client, recvBuf, 128, 0);
		if (nLen > 0)
		{
			DataPackage* dp = (DataPackage*)recvBuf;
			printf("接收到数据：年龄=%d，姓名=%s \n", dp->age, dp->name);
		}
	}

	closesocket(sock_client);
	WSACleanup();
	printf("已退出，任务结束。\n");
	getchar();
	return 0;
}