struct sockaddr_in {
     short            sin_family;     /* 2 字节 ，地址族，e.g. AF_INET, AF_INET6 */
     unsigned short   sin_port;       /* 2 字节 ，16位TCP/UDP 端口号 e.g. htons(3490)， */
     struct in_addr   sin_addr;       /* 4 字节 ，32位IP地址 */
     char             sin_zero[8];    /* 8 字节 ，不使用 */
};

struct in_addr {
     unsigned long s_addr;            /* 32位IPV4地址打印的时候可以调用inet_ntoa()函数将其转换为char *类型*/
}; 

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>

#define BUFFER_SIZE 1024

void error(const char *msg) 
{
    perror(msg);
    exit(EXIT_FAILURE);
}

void run_client(const char *address, int port) {
    int sockfd;
    struct sockaddr_in server_addr;  /* 用于socket通信的地址结构体 */
    char buffer[BUFFER_SIZE];        /* 用于io操作的缓冲区 */
    
    /* 创建套接字 */
    sockfd = socket(AF_INET, SOCK_STREAM, 0);/* AF_INET表示我们使用32位ip地址 */
    if (sockfd < 0) {
        error("Socket creation failed");
    }

    /* 用ipv4协议族，地址，端口等信息 初始化socket*/
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(port);
    if (inet_pton(AF_INET, address, &server_addr.sin_addr) <= 0)   /* 将ip地址转换位点分十进制 */
    {
        error("Invalid address/ Address not supported");
    }

    if (connect(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
        error("Connection failed");
    }

    printf("Connected to %s:%d\n", address, port);
    printf("Type 'exit' to close the connection.\n");

    /*  循环执行io操作 */
    while (1) {
        printf("You: ");
        fgets(buffer, BUFFER_SIZE, stdin);

        /*检查是否接收到 "exit"*/
        if (strncmp(buffer, "exit", 4) == 0) {
            printf("Closing connection...\n");
            break;
        }

        send(sockfd, buffer, strlen(buffer), 0);
	perror("Error TCP send");
        
        int n = recv(sockfd, buffer, BUFFER_SIZE, 0);
        if (n <= 0) {
            printf("Connection closed by server\n");
            break;
        }
        buffer[n] = '\0';
        printf("Server: %s", buffer);
    }

    close(sockfd);
}

void run_server(int port) {
    int sockfd, newsockfd;               /* 单独创建一个监听描述符实现多线程操作 */
    struct sockaddr_in server_addr, client_addr;
    socklen_t client_len;
    char buffer[BUFFER_SIZE];

    /* 创建套接字 */
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) {
        error("Socket creation failed");
    }

    /* 设置服务器地址 */
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = INADDR_ANY;
    server_addr.sin_port = htons(port);

    /* 绑定端口 */
    if (bind(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
        error("Bind failed");
    }

    /*  监听连接 */
    if (listen(sockfd, 5) < 0) {
        error("Listen failed");
    }

    printf("Listening on port %d...\n", port);

     /* 接受客户端连接 */
    client_len = sizeof(client_addr);
    newsockfd = accept(sockfd, (struct sockaddr *)&client_addr, &client_len);
    if (newsockfd < 0) {
        error("Accept failed");
    }

    printf("Connected to client\n");
    printf("Type 'exit' to close the connection.\n");

     /* 数据传输 */
    while (1) {
        int n = recv(newsockfd, buffer, BUFFER_SIZE, 0);
        if (n <= 0) {
            printf("Connection closed by client\n");
            break;
        }
        buffer[n] = '\0';
        printf("Client: %s", buffer);

        /*检查是否接收到 "exit"*/
        if (strncmp(buffer, "exit", 4) == 0) {
            printf("Closing connection...\n");
            break;
        }

        printf("You: ");
        fgets(buffer, BUFFER_SIZE, stdin);

        /*  检查是否输入了 "exit" */
        if (strncmp(buffer, "exit", 4) == 0) {
            printf("Closing connection...\n");
            send(newsockfd, buffer, strlen(buffer), 0);
            break;
        }

        send(newsockfd, buffer, strlen(buffer), 0);
    }

    close(newsockfd);
    close(sockfd);
}

int main(int argc, char *argv[]) {
    /* 检查命令行参数 */
    if (argc < 4) {
        fprintf(stderr, "Usage: %s -l <port> tcp (for server) or %s <address> <port> tcp (for client)\n", argv[0], argv[0]);
        exit(EXIT_FAILURE);
    }
    
    if (strcmp(argv[1], "-l") == 0)/* 检查程序模式 */
    {
        int port = atoi(argv[2]);
        run_server(port);
    } 
    else 
    {
        const char *address = argv[1];
        int port = atoi(argv[2]);
        run_client(address, port);
    }
return 0;
}