初识TCP/IP及使用套接字进行网络编程

通过对于TCP/IP协议以及套接字的学习，编写了最简单的客户端/服务器端程序：

1.单进程版本的服务器：

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

int startup(char* ip,int port)
{
    int sock = socket(AF_INET,SOCK_STREAM,0);
    if(sock < 0)
    {
        perror("socket");
        exit(2);
    }
    struct sockaddr_in local;
    local.sin_family = AF_INET;
    local.sin_port = htons(port); //host to net
    local.sin_addr.s_addr = inet_addr(ip);   //
    if(bind(sock,(struct sockaddr*)&local,sizeof(local))<0)
    {
        perror("bind");
        exit(3);
    }
    if(listen(sock,5)<0)
    {
        perror("listen");
        exit(4);
    }
    return sock;
}
void Usage(char* proc)
{
    printf("Usage:%s,[local ip],[ip_port]\n",proc);
}
int main(int argc,char* argv[])
{
    if(argc != 3)
    {
        Usage(argv[0]);
        exit(1);
    }

    int listen_sock = startup(argv[1],atoi(argv[2]));
    printf("fd:%d\n",listen_sock);
    while(1)
    {
        struct sockaddr_in client;
        socklen_t len = sizeof(client);
        int new_sock = accept(listen_sock,(struct sockaddr*)&client,&len);
        if(new_sock < 0)
        {
            perror("accept");
            continue;
        }

        printf("get a client:[%s][%d]\n",inet_ntoa(client.sin_addr),ntohs(client.sin_port));

           char buf[1024];
           while(1)
           {
               ssize_t s = read(new_sock,buf,sizeof(buf)-1);
               if(s > 0)
               {
                   buf[s] = 0;
                   printf("the client#: %s\n",buf);
                   write(new_sock,buf,sizeof(buf)-1);
               }
               else
               {
                   if(s == 0)
                   {
                          printf("the client is quit\n");
                       break;
                   }
                   else
                   {
                         perror("read");
                       break;
                   }
               }
          }
        close(new_sock);
    }
    close(listen_sock);
    return 0;
}

2.多线程版本的server.c

#include<stdio.h>
#include<sys/socket.h>
#include<sys/types.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<unistd.h>
#include<string.h>
#include<stdlib.h>
#include<pthread.h>
void* handler_request(void* arg)
{
        int new_sock = (int)arg;
        char buf[1024];
        while(1)
        {
            ssize_t s = read(new_sock,buf,sizeof(buf)-1);
            if(s > 0)
            {
                buf[s] = 0;
                printf("the client#: %s\n",buf);
                write(new_sock,buf,sizeof(buf)-1);
            }
            else
            {
                if(s == 0)
                {
                       printf("the client is quit\n");
                    break;
                }
                else
                {
                      perror("read");
                    break;
                }
            }
        }
        close(new_sock);
}
int startup(char* ip,int port)
{
    int sock = socket(AF_INET,SOCK_STREAM,0);
    if(sock < 0)
    {
        perror("socket");
        exit(2);
    }
    struct sockaddr_in local;
    local.sin_family = AF_INET;
    local.sin_port = htons(port); //host to net
    local.sin_addr.s_addr = inet_addr(ip);   //
    if(bind(sock,(struct sockaddr*)&local,sizeof(local))<0)
    {
        perror("bind");
        exit(3);
    }
    if(listen(sock,5)<0)
    {
        perror("listen");
        exit(4);
    }
    return sock;
}
void Usage(char* proc)
{
    printf("Usage:%s,[local ip],[ip_port]\n",proc);
}
int main(int argc,char* argv[])
{
    if(argc != 3)
    {
        Usage(argv[0]);
        exit(1);
    }

    int listen_sock = startup(argv[1],atoi(argv[2]));
    printf("fd:%d\n",listen_sock);
    while(1)
    {
        struct sockaddr_in client;
        socklen_t len = sizeof(client);
        int new_sock = accept(listen_sock,(struct sockaddr*)&client,&len);
        if(new_sock < 0)
        {
            perror("accept");
            continue;
        }

        printf("get a client:[%s][%d]\n",inet_ntoa(client.sin_addr),ntohs(client.sin_port));

        pthread_t tid;
        pthread_create(&tid,NULL,handler_request,(void*)new_sock);
        pthread_detach(tid);

    }
    close(listen_sock);
    return 0;
}

3.client.c

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

int main(int argc,char* argv[])
{

int sock = socket(AF_INET,SOCK_STREAM,0);
if(sock<0)
{
perror("socket");
return 2;
}

struct sockaddr_in server;
server.sin_family = AF_INET;
server.sin_port = htons(atoi(argv[2]));
server.sin_addr.s_addr = inet_addr(argv[1]);

if(connect(sock,(struct sockaddr*)&server,sizeof(server)) < 0)
{
perror("connect");
return 3;
}

while(1)
{
printf("Please Enter:");
fflush(stdout);
char buf[1024];
ssize_t s = read(0,buf,sizeof(buf)-1);
if(s>0)
{
buf[s-1] = 0;
write(sock,buf,sizeof(buf)-1);
ssize_t s = read(sock,buf,sizeof(buf)-1);
printf("server# %s\n",buf);
}
else
{
perror("read");
break;
}
}

close(sock);
return 0;
}

4.多线程版本的运行结果：

初识TCP/IP及使用套接字进行网络编程

5.当服务器先于客户端断开时：需要及时启动服务器时，会发生server bind错误，启不起来：

初识TCP/IP及使用套接字进行网络编程

原因：

原因：TCP协议规定,主动关闭连接的一方要处于TIME_WAIT状态,等待两个MSL(maximum segment lifetime)的时间后才能回到CLOSED状态,因为我们先Ctrl-C终止了server,所以server是主动关闭连接的一方,在TIME_WAIT期间仍然不能再次监听同样的server端口。MSL在RFC1122中规定为两分钟,但是各操作系统的实现不同,在Linux上一般经过半分钟后就可以再次启动server了。

注：由于作者水平有限，若有问题，请留言，谢谢！！

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初识TCP/IP及使用套接字进行网络编程

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