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：

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：

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！！