Linux網路編程：socket實現client/server通信

一、問題引入

閱讀UNIX網路編程 捲1：套接字聯網API 第3版的前4個章節，覺得有必要對書籍上的源碼案例進行復現，並推敲TCP的C/S通信過程。

二、解決過程

2-1 server

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

#define PORT 8887
#define QUEUE 20
#define BUFFER_SIZE 1024

int main()
{
    // 定義sockfd, AF_INET:IPv4協議，SOCK_STREAM：位元組流套接字
    int server_sockfd = socket(AF_INET, SOCK_STREAM, 0);

    // 定義sockaddr_in
    struct sockaddr_in server_sockaddr;
    server_sockaddr.sin_family = AF_INET;
    server_sockaddr.sin_port = htons(PORT);
    server_sockaddr.sin_addr.s_addr = htonl(INADDR_ANY);

    // bind，成功返回0，出錯返回-1
    if (bind(server_sockfd, (struct sockaddr *)&server_sockaddr, sizeof(server_sockaddr)) == -1)
    {
        perror("bind failure");
        exit(1);
    }

    // listen，成功返回0，出錯返回-1
    if (listen(server_sockfd, QUEUE) == -1)
    {
        perror("listen failure");
        exit(1);
    }

    // 客戶端套接字
    char buffer[BUFFER_SIZE];
    struct sockaddr_in client_addr;
    socklen_t length = sizeof(client_addr);

    // 成功返回非負描述字，出錯返回-1
    // accept()被阻塞，等待客戶端連接，一旦客戶端和伺服器完成TCP三次握手，accept()返回一個已連接描述值
    int conn = accept(server_sockfd, (struct sockaddr *)&client_addr, &length);
    if (conn < 0)
    {
        perror("connect failure");
        exit(1);
    }

    printf("**************************\n");
    printf("accept successful !!!\n");
    char ipbuf[64] = {0};
    printf("client || ip: %s, port: %d\n",
           inet_ntop(AF_INET, &client_addr.sin_addr.s_addr, ipbuf, sizeof(ipbuf)),
           ntohs(client_addr.sin_port));
    printf("**************************\n");
    while (1)
    {
        memset(buffer, 0, sizeof(buffer));
        // 接收
        int len = recv(conn, buffer, sizeof(buffer), 0);
        if (strcmp(buffer, "exit") == 0 || strcmp(buffer, "q") == 0)
            break;
        if(len > 0)
        {
            printf("Recv:%s (%d Byte)\n", buffer, strlen(buffer));
        }
    }
    close(conn);
    close(server_sockfd);
    return 0;
}

2-2 client

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

#define PORT 8887
#define BUFFER_SIZE 1024

int main()
{
    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
    struct sockaddr_in servaddr;
    memset(&servaddr, 0, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(PORT);
    servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");
    /// 連接伺服器，成功返回0，錯誤返回-1
    if (connect(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0)
    {
        perror("connect");
        exit(1);
    }
    printf("**************************\n");
    printf("connect successful !!!\n");
    char ipbuf[64] = {0};
    printf("server || ip: %s, port: %d\n",
           inet_ntop(AF_INET, &servaddr.sin_addr.s_addr, ipbuf, sizeof(ipbuf)),
           ntohs(servaddr.sin_port));
    printf("now you can send message to server\n");
    printf("**************************\n");
    char sendbuf[BUFFER_SIZE];
    while (fgets(sendbuf, sizeof(sendbuf), stdin) != NULL)
    {
        if(sendbuf[strlen(sendbuf)-1] == '\n')
            sendbuf[strlen(sendbuf)-1] = '\0';
        // 發送
        send(sockfd, sendbuf, strlen(sendbuf), 0);
        if (strcmp(sendbuf, "exit") == 0 || strcmp(sendbuf, "q") == 0)
            break;
        memset(sendbuf, 0, sizeof(sendbuf));
    }
    close(sockfd);
    return 0;
}

2-3 編譯和運行測試