#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <sys/socket.h>

#define N 100

int main()
{
	pid_t pid;
	int listenfd;
	int connectfd;
	struct sockaddr_in servaddr;
	struct sockaddr_in cliaddr;
	socklen_t clilen;
	char msg[N];
	int ret;
	int i;
	int n;
	int opt = 1;

	listenfd = socket(AF_INET,SOCK_STREAM,0);
	if(listenfd == -1)
	{
		printf("socket error!\n");
		exit(-1);
	}

	setsockopt(listenfd,SOL_SOCKET,SO_REUSEADDR,&opt,sizeof(opt));

	bzero(&servaddr,sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
	servaddr.sin_port = htons(8000);

	ret = bind(listenfd,(struct sockaddr *)&servaddr,sizeof(servaddr));
	if(ret == -1)
	{
		printf("bind error!\n");
		exit(-1);
	}

	ret = listen(listenfd,1024);
	if(ret == -1)
	{
		printf("listen error!\n");
		exit(-1);
	}

	for(;;)
	{
		clilen = sizeof(cliaddr);

		connectfd = accept(listenfd,(struct sockaddr *)&cliaddr,&clilen);
		if(connectfd == -1)
		{
			printf("accept error!\n");
			exit(-1);
		}
		if((pid = fork()) == 0)
		{
			close(listenfd);
			while(1)
			{
				n = recvfrom(connectfd,msg,N,0,(struct sockaddr *)&cliaddr,&clilen);
				if(n == 0)
				{
					printf("client is closed!\n");
					close(connectfd);
					exit(0);
					//break;
				}
				msg[n] = '\0';
				printf("recv:%s\n",msg);
	
				for(i = 0;i < n; i++)
				{
					if(msg[i] >= 'a' && msg[i] <= 'z')
					{
						msg[i] -= 32;
					}	
				}
				printf("send:%s\n",msg);
				sendto(connectfd,msg,n,0,(struct sockaddr *)&cliaddr,sizeof(cliaddr));
			}

		//	close(connectfd);
		}
	}

	close(listenfd);

    return 0;
}
 

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <string.h>

#define N 100

int main(int argc,char **argv)
{
	int sockfd;
	struct sockaddr_in servaddr;
	char sendbuf[N];
	char recvbuf[N];
	int ret;
	int n;

	if(argc != 2)
	{
		printf("usage:server <ip address>\n");
		exit(-1);
	}

	sockfd = socket(AF_INET,SOCK_STREAM,0);
	if(sockfd == -1)
	{
		printf("socket error!\n");
		exit(-1);
	}

	bzero(&servaddr,sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_addr.s_addr = inet_addr(argv[1]);
	servaddr.sin_port = htons(8000);

	ret = connect(sockfd,(struct sockaddr *)&servaddr,sizeof(servaddr));
	if(ret == -1)
	{
		printf("connect error!\n");
		exit(-1);
	}

	//printf("Please enter info:");

	while(fgets(sendbuf,N,stdin) != 0)
	{
		sendto(sockfd,sendbuf,strlen(sendbuf),0,(struct sockaddr *)&servaddr,sizeof(servaddr));
		n = recvfrom(sockfd,recvbuf,N,0,NULL,NULL);
		recvbuf[n] = '\0';
		printf("recv:%s",recvbuf);
	}

	close(sockfd);

    return 0;
}