#include<stdio.h> //fprintf, printf, perror
#include<unistd.h> //exit, close, read
#include<sys/socket.h> //socket, bind, listen, accept, send
#include<sys/types.h> //bind, accept, send
#include<arpa/inet.h> //htons
#include<string.h> //strncpy
#include<sys/select.h>
#include<stdlib.h> //exit
#include<netinet/tcp.h>
#include<netinet/in.h>
#include<fcntl.h>




int main(int argc,char**argv){
	fd_set deskriptor_set,orig_set;
	int s,connection_socket;
	struct sockaddr_in server_address,client_address;
	socklen_t client_sa_len=sizeof(client_address);
	char buffer[80];
	
	if(argc!=2){
		fprintf(stderr,"\nUsage: %s <port>",argv[0]);
		exit(1);
	}
	if((s=socket(PF_INET,SOCK_STREAM,0))<0){
		perror("socket");
		exit(1);
	}
	
	
	FD_ZERO(&deskriptor_set);
	FD_SET(s,&deskriptor_set);
	FD_SET(0,&deskriptor_set);
//	if(FD_ISSET(s,&deskriptor_set)){
//	}
	
	server_address.sin_family=PF_INET;
	server_address.sin_port=htons(atoi(argv[1]));
	server_address.sin_addr=inet_makeaddr(INADDR_ANY,INADDR_ANY);
	if(bind(s,(struct sockaddr*)&server_address,sizeof(server_address))<0){
		perror("bind");
		close(s);
		exit(1);
	}
	
	if(listen(s,2)<0){
		perror("listen");
		close(s);
		exit(1);
	}
	
	orig_set=deskriptor_set;
	while(1){
		if((connection_socket=accept(s,(struct sockaddr*)&client_address,(socklen_t*)&client_sa_len))<0){
			perror("accept");
			close(s);
			exit(1);
		}
		printf("Verbindung von %s:%d\n",inet_ntoa(client_address.sin_addr),ntohs(client_address.sin_port));
		int anzahl=read(connection_socket,buffer,sizeof(buffer)/sizeof(unsigned char));
		if(anzahl<=0){
			perror("read");
		}else{
			buffer[anzahl]=0;
			printf("\nempfangen: %s\n",buffer);
		}
		strncpy(buffer,"hallo, wie gehts?",sizeof(buffer)/sizeof(char));
		send(connection_socket,buffer,strlen(buffer),0);
		close(connection_socket);
	}
	exit(0);
}