select() 기반 echo_server

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/select.h>

#define BUF_SIZE 100
void error_handling(char *buf);

int main(int argc, char *argv[]){
int serv_sock, clnt_sock;
struct sockaddr_in serv_adr, clnt_adr;
struct timeval timeout;
fd_set reads, cpy_reads;

socklen_t adr_sz;
int fd_max, str_len, fd_num, i;
char buf[BUF_SIZE];
if(argc!=2){
printf("Usage : %s <port>\n", argv[0]);
exit(1);
}

serv_sock=socket(PF_INET, SOCK_STREAM,0); //socket creative
memset(&serv_adr, 0, sizeof(serv_adr)); //socket setting
serv_adr.sin_family=AF_INET;
serv_adr.sin_addr.s_addr=htonl(INADDR_ANY);
serv_adr.sin_port=htons(atoi(argv[1]));

if(bind(serv_sock, (struct sockaddr*) &serv_adr, sizeof(serv_adr))==-1) //bind
error_handling("bind() error");
if(listen(serv_sock, 5)==-1) //listen
error_handling("listen() error");

FD_ZERO(&reads);
FD_SET(serv_sock, &reads); //serv_sock=file discripter, 0
fd_max=serv_sock;

while(1){
cpy_reads=reads;
timeout.tv_sec=5;
timeout.tv_usec=5000;

if((fd_num=select(fd_max+1, &cpy_reads, 0, 0, &timeout))==-1) //select 실행 결과 -1이 나올경우
break;
if(fd_num==0) // 0일 경우 변화 없음 다시 반복
continue;

for(i=0; i<fd_max+1; i++){ //정상일 경우 루프 수행
if(FD_ISSET(i, &cpy_reads)){ //최대 fd_max 까지 돌면서 cpy_reads의 변화된 부분을 찾음
if(i==serv_sock){ //connection request! 서버파일디스크립터의
//변화 생길시 connect로 간주하여 accept 시도
adr_sz=sizeof(clnt_adr);
clnt_sock=accept(serv_sock,(struct sockaddr*)&clnt_adr, &adr_sz);
FD_SET(clnt_sock, &reads); //새로운 디스크립터(clnt_sock)등록
if(fd_max<clnt_sock) //fd_max가 clnt_sock보다 작으면 max재수정
fd_max=clnt_sock;
printf("connected client : %d \n", clnt_sock);
}
else { //read message!
str_len=read(i, buf, BUF_SIZE);
if(str_len==0){ //close request!
FD_CLR(i, &reads);
close(i);
printf("closed client: %d \n", i);
}
else{
write(i, buf, str_len); //echo!
}
}
}
}
}
close(serv_sock);
return 0;
}

void error_handling(char *buf){
fputs(buf, stderr);
fputc('\n', stderr);
exit(1);
}