Linux是目前最流行的开源操作系统，网络功能在linux下占有核心的地位，Linux网络编程指的是socket套接字编程。本博文主要介绍socket套接字API的使用及一般客户/服务器模型的编程，并用C语言具体代码实现。

实现简单的功能如下：
1、服务器端显示客户端的IP地址和端口，接收客户端发送过来的信息，并原样发送给该客户端。
2、客户端从标准输入中读取数据，发送给服务器端，然后从服务器端读取发送过来的数据并显示在屏幕上。

一、服务器端源代码

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

#define MAX_BUFFER_LENGTH 4096
#define LISTENQ 5
#define PORT 8000

int main(void)
{
        int serv_fd, cli_fd;
        socklen_t serv_len, cli_len;
        struct sockaddr_in serv_addr, cli_addr;
        char buf[MAX_BUFFER_LENGTH];

        if((serv_fd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
                printf("socket error\n");
                return 1;
        }

        serv_len = sizeof(serv_addr);
        memset(&serv_addr, 0, serv_len);
        serv_addr.sin_family = AF_INET;
        serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
        serv_addr.sin_port = htons(PORT);

        if((bind(serv_fd, (struct sockaddr *)&serv_addr, serv_len)) < 0) {
                printf("bind error\n");
                return 1;
        }

        if((listen(serv_fd, LISTENQ)) < 0) {
                printf("listen error\n");
                return 1;
        }

        for(;;) {
                cli_len = sizeof(cli_addr);
                if((cli_fd = accept(serv_fd, (struct sockaddr *)&cli_addr, &cli_len)) < 0) {
                        printf("accept error\n");
                        return 1;
                }

                printf("client:\t%s : %d\n",
                        inet_ntop(AF_INET, &cli_addr.sin_addr, buf, MAX_BUFFER_LENGTH),
                        ntohs(cli_addr.sin_port));

                int nbytes;
                while((nbytes = read(cli_fd, buf, MAX_BUFFER_LENGTH)) > 0) {
                        buf[nbytes] = '\0';
                        printf("%s", buf);
                        if(write(cli_fd, buf, nbytes) != nbytes) {
                                printf("write error\n");
                                return 1;
                        }
                }

                if(nbytes < 0) {
                        printf("read error\n");
                        return 1;
                }
                close(cli_fd);
        }
        return 0;
}

二、客户端源代码

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

#define MAX_BUFFER_LENGTH 4096
#define PORT 8000

int main(void)
{
        int sockfd, nbytes;
        struct sockaddr_in serv_addr;
        char buf[MAX_BUFFER_LENGTH + 1];
        char *host_ip = "127.0.0.1";

        if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
                printf("socket error\n");
                return 1;
        }

        memset(&serv_addr, 0, sizeof(serv_addr));
        serv_addr.sin_family = AF_INET;
        if(inet_pton(AF_INET, host_ip, &serv_addr.sin_addr) <= 0) {
                printf("inet_pton error\n");
                return 1;
        }
        serv_addr.sin_port = htons(PORT);

        if(connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
                printf("connect error\n");
                return 1;
        }

        while(fgets(buf, MAX_BUFFER_LENGTH, stdin) != NULL) {
                if(write(sockfd, buf, strlen(buf)) != strlen(buf)) {
                        printf("write error\n");
                        return 1;
                }
                if((nbytes = read(sockfd, buf, MAX_BUFFER_LENGTH)) > 0) {
                        buf[nbytes] = '\0';
                        printf("%s", buf);
                }

                if(nbytes < 0) {
                        printf("read error\n");
                        return 1;
                }
        }
        close(sockfd);
        return 0;
}

三、运行结果

[root@localhost workspace]# ./simple_tcp_server
client: 127.0.0.1 : 58013
hello world
www.xieyincai.com
beijing
shanghai
client: 127.0.0.1 : 58089
C LANGUAGE
linux

[root@localhost workspace]# ./simple_tcp_client
hello world
hello world
www.xieyincai.com
www.xieyincai.com
beijing
beijing
shanghai
shanghai
[root@localhost workspace]# ./simple_tcp_client
C LANGUAGE
C LANGUAGE
linux
linux
[root@localhost workspace]#