使用select函数

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

#define max(a,b) ((a)>(b)?(a):(b))

const int maxline = 4096;

size_t writen(int fd, const void *vptr, size_t n) {
        size_t nleft;
        size_t nwritten;
        const char *ptr;

        ptr=vptr;
        nleft=n;
        while(nleft>0) {
                if((nwritten=write(fd, ptr, nleft))<=0) {
                        if(nwritten<0 && errno==EINTR)
                                nwritten=0;
                        else
                                return -1;
                }
                nleft-=nwritten;
                ptr+=nwritten;
        }
        return n;
}

void str_echo(int sockfd) {
	size_t n;
	char buff[maxline];

again:
	while((n=read(sockfd, buff, maxline))>0) {
		if(writen(sockfd, buff, n)!=n) {
			fprintf(stderr, "writen error!\n");
		}
	}
	if(n<0 && errno==EINTR)
		goto again;
	else if(n<0) {
		fprintf(stderr, "read error\n");
		exit(-1);
	}
}

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

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

	if((listenfd=socket(AF_INET, SOCK_STREAM, 0))<0) {
		strerror_r(errno, errbuff, maxline);
		fprintf(stderr, "socket error: %s\n", errbuff);
		exit(-1);
	}
	
	memset(&servaddr, 0, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
	servaddr.sin_port = htons(9999);

	if(setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on))==-1) {
		strerror_r(errno, errbuff, maxline);
		fprintf(stderr, "setsockopt error: %s\n", errbuff);
		exit(-1);
	}

	if(bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr))<0) {
		strerror_r(errno, errbuff, maxline);
		fprintf(stderr, "tcp bind error: %s\n", errbuff);
		exit(-1);
	}

	if(listen(listenfd, 1024)<0) {
		strerror_r(errno, errbuff, maxline);
		fprintf(stderr, "listen error: %s\n", errbuff);
		exit(-1);
	}

	if((udpfd=socket(AF_INET, SOCK_DGRAM, 0))<0) {
		strerror_r(errno, errbuff, maxline);
		fprintf(stderr, "socket error: %s\n", errbuff);
		exit(-1);
	}

	memset(&servaddr, 0, sizeof(servaddr));
	servaddr.sin_family=AF_INET;
	servaddr.sin_port=htons(9999);
	servaddr.sin_addr.s_addr=htonl(INADDR_ANY);

	if(bind(udpfd, (struct sockaddr *)&servaddr, sizeof(servaddr))<0) {
		strerror_r(errno, errbuff, maxline);
		fprintf(stderr, "udp bind error: %s\n", errbuff);
		exit(-1);
	}

	signal(SIGCHLD, sig_chld);
	FD_ZERO(&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 {
				fprintf(stderr, "select error\n");
				exit(-1);
			}
		}

		if(FD_ISSET(listenfd, &rset)) {
			len=sizeof(cliaddr);
			if((connfd=accept(listenfd, (struct sockaddr *)&cliaddr, &len))<0) {
				strerror_r(errno, errbuff, maxline);
				fprintf(stderr, "accept error: %s\n", errbuff);
				exit(-1);
			}
			printf("connection from %s, port %d\n", inet_ntop(AF_INET, &cliaddr.sin_addr, mesg, sizeof(mesg)), ntohs(cliaddr.sin_port));
			if((childpid=fork())<0) {
				strerror_r(errno, errbuff, maxline);
				fprintf(stderr, "fork error: %s\n", errbuff);
				exit(-1);
			} else if(childpid == 0) {
				printf("ppid: %d\n", getppid());
				if(close(listenfd)<0) {
					strerror_r(errno, errbuff, maxline);
					fprintf(stderr, "child pid close listenfd error: %s\n", errbuff);
					exit(-1);
				}
				str_echo(connfd);
				exit(0);
			} else {
				printf("childpid: %d\n", childpid);
				if(close(connfd)<0) {
					strerror_r(errno, errbuff, maxline);
					fprintf(stderr, "parent pid close connfd error: %s\n", errbuff);
					exit(-1);
				}
			}
		}

		if(FD_ISSET(udpfd, &rset)) {
			len=sizeof(cliaddr);
			if((n=recvfrom(udpfd, mesg, maxline, 0, (struct sockaddr*)&cliaddr, &len))<0) {
				strerror_r(errno, errbuff, maxline);
				fprintf(stderr, "recvfrom error: %s\n", errbuff);
				exit(-1);
			}
			printf("client ip: %s, client port: %d\n", inet_ntop(AF_INET, &cliaddr.sin_addr, errbuff, sizeof(errbuff)), ntohs(cliaddr.sin_port));

			if(sendto(udpfd, mesg, n, 0, (struct sockaddr*)&cliaddr, len)<0) {
				strerror_r(errno, errbuff, maxline);
				fprintf(stderr, "sendto error: %s\n", errbuff);
				exit(-1);
			}
		}
	}
	return 0;
}