1.  使用read函数返回长度0的情景：对端关闭连接，服务端调用了Close函数。

//intro/daytimetcpcli.c
while ((n = read(sockfd, recvline,  MAXLINE)) > 0){
    recvline[n] = 0;
    if (fputs(recvline, stdout) == EOF)
        err_sys("fputs error");
}
if (n < 0)
    err_sys("read error");

/*-------------------------------------------------------------*/
//intro/daytimetcpsrv.c
for ( ; ; ) {
    connfd = Accept(listenfd, (SA *) NULL, NULL);

    ticks = time(NULL);
    snprintf(buff, sizeof(buff), "%.24s\r\n", ctime(&ticks));
    Write(connfd, buff, strlen(buff));

    Close(connfd);
}