带有超时的udp客户端

#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <string.h>
#include <signal.h>
#include <unistd.h>
static int sig_alrm(int);
const int maxline=4096;
int readable_timeo(int fd, int sec) 
{
    fd_set rset;
    struct timeval tv;
    FD_ZERO(&rset);
    FD_SET(fd, &rset);
    tv.tv_sec=sec;
    tv.tv_usec=0;
    return select(fd+1, &rset, NULL, NULL, &tv);
}
void dg_cli(FILE *fp, int sockfd, const struct sockaddr * pservaddr, socklen_t servlen) 
{
    int n;
    char sendline[maxline], recvline[maxline+1];
    char errbuff[maxline];
    while(fgets(sendline, maxline, fp) != NULL) 
    {
        if(sendto(sockfd, sendline, strlen(sendline), 0, pservaddr, servlen)<0) 
        {
            strerror_r(errno, errbuff, maxline);
            fprintf(stderr, "sendto error: %sn", errbuff);
            exit(-1);
        }
        if((n=recvfrom(sockfd, recvline, maxline, 0, NULL, NULL))<0) {
            strerror_r(errno, errbuff, maxline);
            fprintf(stderr, "recvfrom error: %sn", errbuff);
            exit(-1);
        }
        recvline[n]=0;
        fputs(recvline, stdout);
    }
}
void dg_cli_so(FILE *fp, int sockfd, const struct sockaddr * pservaddr, socklen_t servlen) {
    int n;
    char sendline[maxline], recvline[maxline+1];
    char errbuff[maxline];
    struct timeval tv;
    tv.tv_sec=5;
    tv.tv_usec=0;
    if(setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv))==-1) {
        strerror_r(errno, errbuff, maxline);
        fprintf(stderr, "setsockopt error: %sn", errbuff);
        exit(-1);
    }
    while(fgets(sendline, maxline, fp) != NULL) {
        if(sendto(sockfd, sendline, strlen(sendline), 0, pservaddr, servlen)<0) {
            strerror_r(errno, errbuff, maxline);
            fprintf(stderr, "sendto error: %sn", errbuff);
            exit(-1);
        }
        n=recvfrom(sockfd, recvline, maxline, 0, NULL, NULL);
        if(n<0) {
            if(errno==EWOULDBLOCK) {
                fprintf(stderr, "socket timeoutn");
                continue;
            } else {
                strerror_r(errno, errbuff, maxline);
                fprintf(stderr, "recvfrom error: %sn", errbuff);
                exit(-1);
            }
        }
        recvline[n]=0;
        fputs(recvline, stdout);
    }
}
void dg_cli_select(FILE *fp, int sockfd, const struct sockaddr * pservaddr, socklen_t servlen) {
    int n;
    char sendline[maxline], recvline[maxline+1];
    char errbuff[maxline];
    while(fgets(sendline, maxline, fp) != NULL) {
        if(sendto(sockfd, sendline, strlen(sendline), 0, pservaddr, servlen)<0) {
            strerror_r(errno, errbuff, maxline);
            fprintf(stderr, "sendto error: %sn", errbuff);
            exit(-1);
        }
        if(readable_timeo(sockfd, 5)==0) {
            fprintf(stderr, "socket timeoutn");
        } else {
            if((n=recvfrom(sockfd, recvline, maxline, 0, NULL, NULL))<0) {
                strerror_r(errno, errbuff, maxline);
                fprintf(stderr, "recvfrom error: %sn", errbuff);
                exit(-1);
            }
            recvline[n]=0;
            fputs(recvline, stdout);
        }
    }
}
void dg_cli_alrm(FILE *fp, int sockfd, const struct sockaddr * pservaddr, socklen_t servlen) {
    int n;
    char sendline[maxline], recvline[maxline+1];
    char errbuff[maxline];
    if(signal(SIGALRM, sig_alrm)<0) {
        strerror_r(errno, errbuff, maxline);
        fprintf(stderr, "signal error: %sn", errbuff);
        exit(-1);
    }
    while(fgets(sendline, maxline, fp) != NULL) {
        if(sendto(sockfd, sendline, strlen(sendline), 0, pservaddr, servlen)<0) {
            strerror_r(errno, errbuff, maxline);
            fprintf(stderr, "sendto error: %sn", errbuff);
            exit(-1);
        }
        alarm(5);
        if((n=recvfrom(sockfd, recvline, maxline, 0, NULL, NULL))<0) {
            if(errno==EINTR) {
                fprintf(stderr, "socket timeoutn");
            } else {
                strerror_r(errno, errbuff, maxline);
                fprintf(stderr, "recvfrom error: %sn", errbuff);
                exit(-1);
            }
        } else {
            alarm(0);
            recvline[n]=0;
            fputs(recvline, stdout);
        }
    }
}
int main(int argc, char **argv) {
    int sockfd, n;
    char recvline[maxline+1], errbuff[maxline];
    struct sockaddr_in servaddr;
    if(argc != 2) {
        fprintf(stderr, "usage: a.out <IPaddress>n");
        exit(-1);
    }
    if((sockfd=socket(AF_INET, SOCK_DGRAM, 0))<0) {
        strerror_r(errno, errbuff, maxline);
        fprintf(stderr, "socket error: %sn", errbuff);
        exit(-1);
    }
    memset(&servaddr, 0, sizeof(servaddr));
    servaddr.sin_family=AF_INET;
    servaddr.sin_port=htons(9999);
    if(inet_pton(AF_INET, argv[1], &servaddr.sin_addr)<=0) {
        fprintf(stderr, "inet_pton error for %s", argv[1]);
        exit(-1);
    }
    dg_cli_so(stdin, sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr));
    return 0;
}
static int sig_alrm(int signo) {
    printf("signal alarmn");
    exit -1;
}