使用select函数

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#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;
}   