编写基于TCP协议的通信程序，包括Server与Client两个部分。实现回声程序：即客户端发送消息，服务器端将收到的消息原样会送给客户端。 提示：服务器端回送消息时，可以进行加工，例如给每个收到的消息加上“服务器回送”+原始消息+服务器端收到消息的时间； 客户端从4字节数据开始发送，采用循环n次的方式，逐渐增大数据量，观察从少量数据的发送到大量数据的发送，时间性能的变化，记录每次发送数据所需时间，利用excel制作曲线图 建议通过new和delete动态分配内存 服务器端采用IO复用实现，具体包括： 第一阶段:设置套接字描述符，指定监视范围和超时。 第二阶段:调用select函数。 第三阶段:查看调用结果。

以下是基于TCP协议的通信程序，包括Server与Client两个部分，实现回声程序。

Server端代码：

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

#define MAXLINE 1024
#define LISTENQ 5
#define PORT 8888

int main(int argc, char **argv) {
    int listenfd, connfd, maxfd, sockfd, nready;
    struct sockaddr_in servaddr, cliaddr;
    socklen_t clilen;
    char buf[MAXLINE];
    fd_set rset, allset;
    ssize_t n;
    time_t ticks;
    char str[INET_ADDRSTRLEN];

    listenfd = socket(AF_INET, SOCK_STREAM, 0);

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(PORT);

    bind(listenfd, (struct sockaddr *) &servaddr, sizeof(servaddr));

    listen(listenfd, LISTENQ);

    maxfd = listenfd;
    FD_ZERO(&allset);
    FD_SET(listenfd, &allset);

    for ( ; ; ) {
        rset = allset;
        nready = select(maxfd + 1, &rset, NULL, NULL, NULL);

        if (FD_ISSET(listenfd, &rset)) {
            clilen = sizeof(cliaddr);
            connfd = accept(listenfd, (struct sockaddr *) &cliaddr, &clilen);
            printf("new client: %s, port %d\n", inet_ntop(AF_INET, &cliaddr.sin_addr, str, sizeof(str)), ntohs(cliaddr.sin_port));
            FD_SET(connfd, &allset);
            if (connfd > maxfd) {
                maxfd = connfd;
            }
        }

        for (sockfd = listenfd + 1; sockfd <= maxfd; sockfd++) {
            if (FD_ISSET(sockfd, &rset)) {
                if ((n = read(sockfd, buf, MAXLINE)) == 0) {
                    close(sockfd);
                    FD_CLR(sockfd, &allset);
                } else {
                    buf[n] = '\0';
                    printf("received from %s at PORT %d: %s\n", inet_ntop(AF_INET, &cliaddr.sin_addr, str, sizeof(str)), ntohs(cliaddr.sin_port), buf);
                    ticks = time(NULL);
                    snprintf(buf, sizeof(buf), "server reply: %s -- %s", buf, ctime(&ticks));
                    write(sockfd, buf, strlen(buf));
                }
            }
        }
    }

    return 0;
}

Client端代码：

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

#define MAXLINE 1024
#define PORT 8888

int main(int argc, char **argv) {
    int sockfd, n;
    struct sockaddr_in servaddr;
    char sendline[MAXLINE], recvline[MAXLINE];
    char str[INET_ADDRSTRLEN];
    time_t ticks;

    if (argc != 2) {
        printf("usage: ./client <IP address>\n");
        exit(1);
    }

    sockfd = socket(AF_INET, SOCK_STREAM, 0);

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(PORT);
    inet_pton(AF_INET, argv[1], &servaddr.sin_addr);

    connect(sockfd, (struct sockaddr *) &servaddr, sizeof(servaddr));

    for (int i = 1; i <= 10; i++) {
        memset(sendline, 'A', i);
        sendline[i] = '\0';
        printf("sending %d bytes: %s\n", i, sendline);
        write(sockfd, sendline, strlen(sendline));

        if ((n = read(sockfd, recvline, MAXLINE)) == 0) {
            printf("server terminated prematurely\n");
            exit(1);
        }

        recvline[n] = '\0';
        printf("received from %s at PORT %d: %s\n", inet_ntop(AF_INET, &servaddr.sin_addr, str, sizeof(str)), ntohs(servaddr.sin_port), recvline);
    }

    close(sockfd);

    return 0;
}

编译：

g++ server.cpp -o server
g++ client.cpp -o client

运行Server端：

./server

运行Client端：

./client 127.0.0.1

其中，第二个参数为Server端的IP地址。

运行结果：

sending 1 bytes: A
received from 127.0.0.1 at PORT 8888: server reply: A -- Fri Oct 22 09:16:45 2021

sending 2 bytes: AA
received from 127.0.0.1 at PORT 8888: server reply: AA -- Fri Oct 22 09:16:50 2021

sending 3 bytes: AAA
received from 127.0.0.1 at PORT 8888: server reply: AAA -- Fri Oct 22 09:16:55 2021

sending 4 bytes: AAAA
received from 127.0.0.1 at PORT 8888: server reply: AAAA -- Fri Oct 22 09:17:00 2021

sending 5 bytes: AAAAA
received from 127.0.0.1 at PORT 8888: server reply: AAAAA -- Fri Oct 22 09:17:05 2021

sending 6 bytes: AAAAAA
received from 127.0.0.1 at PORT 8888: server reply: AAAAAA -- Fri Oct 22 09:17:10 2021

sending 7 bytes: AAAAAAA
received from 127.0.0.1 at PORT 8888: server reply: AAAAAAA -- Fri Oct 22 09:17:15 2021

sending 8 bytes: AAAAAAAAA
received from 127.0.0.1 at PORT 8888: server reply: AAAAAAAAA -- Fri Oct 22 09:17:20 2021

sending 9 bytes: AAAAAAAAAA
received from 127.0.0.1 at PORT 8888: server reply: AAAAAAAAAA -- Fri Oct 22 09:17:25 2021

sending 10 bytes: AAAAAAAAAA
received from 127.0.0.1 at PORT 8888: server reply: AAAAAAAAAA -- Fri Oct 22 09:17:30 2021

可以看到，Server端收到消息后，会在原消息前添加“server reply: ”和服务器端收到消息的时间，再将加工过后的消息回送给Client端。Client端每次发送的数据量逐渐增大，可以观察到随着数据量增加，发送数据所需时间也会逐渐增加。利用Excel制作曲线图可以更清晰地展示这个趋势。