使用select函数的TCP和UDP回射服务器程序

1，创建一个监听TCP套接字并捆绑服务器的总所周知端口， 设置SO_REUSEADDR套接字选项以防该端口上已有连接存在

2，还创建一个UDP套接字并捆绑与TCP套接字相同的端口，这里无需在调用bind之前设置SO_REUSEADDR套接字选项，因为TCP端口是独立于UDP端口的

3，我们调用select只是为了等待监听TCP套接字的可读条件或UDP套接字的可读条件。既然我们的sig_chld信号处理函数可能中断我们队select的调用，我们于是需要处理EINTR错误

udpservselect.c

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

int main(int argc, char **argv)
{
int	listenfd, connfd, udpfd, nready, maxfdp1;
char	mesg[MAXLINE];
pid_t	clildpid;
fd_set 	rset;
ssize_t	n;
socklen_t	len;
const int on = 1;
struct sockaddr_in cliaddr, servaddr;
void	sig_chld(int);

listenfd = socket(AF_INET, SOCK_STREAM, 0);

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

setsockopt(listenfd, SQL_SOCKET, SO_REUSEADDR, &on, sizeof(on));
bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr));

listen(listenfd, LISTENQ);

udpfd = socket(AF_INET, SOCK_DGRAM, 0);

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

bind(udpfd, (struct sockaddr *)&servaddr, sizeof(servaddr));

signal(SIGCHLD, sig_chld);

FD_SET(&rset);
maxfdp1 = max(listenfd, udpfd) + 1;
for( ; ; )
{
FD_SET(listenfd, &rset);
FD_SET(udpfd, &rset);
if((nready = select(maxfdp1, &rset, NULL, NULL, NULL)) < 0)
{
if(errno == EINTR)
continue;
else
perror("select error");
}

if(FD_ISSET(listenfd, &rset)
{
len = sizeof(cliaddr);
connfd = accept(listenfd, (struct sockaddr *)&cliaddr, &len);

if((childpid = fork()) == 0)
{
close(listenfd);
str_echo(connfd);
exit(0);
}
close(connfd);
}

if(FD_ISSET(udpfd, &rset))
{
len = sizeof(cliaddr);
n = recvfrom(udpfd, mesg, MAXLINE, 0, (struct sockaddr *)&cliaddr, &len);
sendto(udpfd, mesg, n, 0, (struct sockaddr *)&cliaddr, &len);
}
}
}

void sig_chld(int signo)
{
pid_t	pid;
int	stat;

while((pid = waitpid(-1, &stat, WNOHANG)) > 0)
printf("child %d terminated\n", pid);
return;
}