一、思维导图

二、给代码添加链表

        【server.c】

#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <fcntl.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>

typedef struct sockaddr_in addr_in_t;
typedef struct sockaddr addr_t;

enum Type{
	TYPE_REGIST,
	TYPE_LOGIN
};

typedef struct Pack{
	int size;
	enum Type type;
	char buf[2048];
	int count;
}pack_t;

/*
typedef struct user_info{
	union Data{
		struct user_info* tail;
		char ui[20];
	}data;
	struct user_info* next;
	struct user_info* prev;
}UserInfo;

UserInfo* create_node(){
	UserInfo* node = malloc(sizeof(UserInfo));
	node->next = NULL;
	node->prev = NULL;
	node->data.tail = node;
	return node;
}
*/

//从pack协议包中解析数据
void read_pack(pack_t* pack)
{
	char* buf = pack->buf;
	//记录buf已经读取的字节个数，方便定位到最靠前的未读取的位置
	int readed_size = 0;
	while(1){
		//将buf中最靠前未读取的2个字节，当作short读取，并赋值给data_size
		short data_size = *(short*)(buf + readed_size);
		if(data_size == 0){
			printf("数据解析完毕\n");
			break;
		}
		//因为已经读取了2个字节，readed_size要自增2字节
		readed_size += 2;
		//准备一个大小为data_size+1的字符数组，用来接收数据
		char temp[data_size + 1];
		//初始化该数组
		memset(temp, 0, data_size+1);
		memcpy(temp, buf + readed_size, data_size);
		readed_size += data_size;

		printf("temp = %s\n", temp);
	}
}

int main(int argc, const char* argv[])
{
	if(argc != 2){
		printf("请输入端口号！\n");
		return 1;
	}
	//将字符串转换成int类型port
	int port = atoi(argv[1]);

	//创建服务器套接字
	int server = socket(AF_INET, SOCK_STREAM, 0);

	//准备网络地址结构体： struct sockaddr_in
	addr_in_t addr = {0};
	addr.sin_family = AF_INET;
	addr.sin_port = htons(port);
	addr.sin_addr.s_addr = inet_addr("0.0.0.0");

	//为套接字绑定ip和port
	if(bind(server, (addr_t*)&addr, sizeof(addr)) == -1){
		perror("bind()");
		return 1;
	}

	//监听
	listen(server, 10);

	//接收客户端的连接
	addr_in_t client_addr = {0};
	int client_addr_len = sizeof(client_addr);
	int client = accept(server, (addr_t*)&client_addr, &client_addr_len);
	if(client != -1){
		printf("=== 客户端连接 ===\n");
	}

	//读取客户端发来的消息
	while(1){
		int pack_size = 0;
		int res = read(client, &pack_size, 4);
		if(res == 0){
			printf("=== 客户端断开连接 === \n");
			return 0;
		}
		//当前的 pack_size = 4(pack.size大小) + 4(pack.type大小) + buf大小
		pack_t pack = {0};
		read(client, (char*)&pack+4, pack_size-4);
		pack.size = pack_size;

		//解析协议包的所有数据
		read_pack(&pack);
	}

	return 0;
}

        【client.c】

#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <fcntl.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>

typedef struct sockaddr_in addr_in_t;
typedef struct sockaddr addr_t;

enum Type{
	TYPE_REGIST,
	TYPE_LOGIN
};

typedef struct Pack{
	int size; //记录整个协议包实际大小(定长部分，占4个字节)
	enum Type type; //定长部分，占4个字节
	char buf[2048]; //变长部分，占count个字节
	int count; //记录指针偏移量，即buf使用了多少个字节
}pack_t;

/*
typedef struct user_info{
	union Data{
		struct user_info* tail;
		char ui[20];
	}data;
	struct user_info* next;
	struct user_info* prev;
}UserInfo;

UserInfo* create_node(){
	UserInfo* node = malloc(sizeof(UserInfo));
	node->next = NULL;
	node->prev = NULL;
	node->data.tail = node;
	return node;
}
*/

void append(pack_t* pack, const char* data)
{
	char* buf = pack->buf;
	int len = strlen(data);
	//将buf的前2个字节当作short来存储数据len
	*(short*)(buf + pack->count) = len;
	pack->count += 2;

	memcpy(buf + pack->count, data, len);
	pack->count += len;

	pack->size = pack->count + 8;
}

int main(int argc, const char* argv[])
{
	if(argc != 2){
		printf("请输入端口号！\n");
		return 1;
	}
	//将字符串转换成int类型port
	int port = atoi(argv[1]);

	int client = socket(AF_INET, SOCK_STREAM, 0);

	addr_in_t addr = {0};
	addr.sin_family = AF_INET;
	addr.sin_port = htons(port);
	addr.sin_addr.s_addr = inet_addr("192.168.126.155");

	if(connect(client, (addr_t*)&addr, sizeof(addr)) == -1){
		perror("connect()");
		return 1;
	}

	while(1){
		pack_t pack = {0};
		pack.type=TYPE_LOGIN;
		char name[20] = "";
		char pwd[20] = "";
		printf("请输入账号：");
		scanf("%20s", name);
		while(getchar() != 10);
		
		printf("请输入密码：");
		scanf("%20s", pwd);
		while(getchar() != 10);
		
		//前2个字节记录数据长度n，紧接着的n个字节记录数据本身
		//将name和pwd存入pack.buf中（即将name和pwd按照既定格式添加进协议包））
		append(&pack, name);
		append(&pack, pwd);

		//协议包总共占据 pack.count + 4 字节
		//pack.count 的长度，根据name和pwd的长度动态决定
		write(client, &pack, pack.size);
	}

	return 0;
}