wifidog报错: Auth server did NOT say pong!

在wifidog启动过程中，我们可能会经常看到这种log：
Auth server did NOT say pong!

这个debug信息是再告诉我们，wifidog的ping协议没有收到来自auth server 的pong 回应。
首先解释下什么是ping协议。这种协议是路由器用来告诉auth server 路由器当前的状态，协议格式：
http://auth_server/ping/?gw_id=xxx&sys_uptime=xxx&sys_memfree&sys_load=xxx&wifidog_uptime=xxx
gw_id是路由器的标识符，sys_uptime是路由器启动时间，sys_memfree是路由器的内存剩余，sys_load是系统负载,wifidog_uptime是wifidog启动时间，路由器将这些信息发送给auth server，server 回"Pong" 来表示server知道这台路由器还在工作。

下面是出现上述log的代码：

do {   
        FD_ZERO(&readfds);   
        FD_SET(sockfd, &readfds);   
        timeout.tv_sec = 30; /* XXX magic... 30 second */   
        timeout.tv_usec = 0;   
        nfds = sockfd + 1;   

        nfds = select(nfds, &readfds, NULL, NULL, &timeout);   

        if (nfds > 0) {   
            /** We don't have to use FD_ISSET() because there  
             *  was only one fd. */   
            numbytes = read(sockfd, request + totalbytes, MAX_BUF - (totalbytes + 1));   
            if (numbytes < 0) {   
                debug(LOG_ERR, "An error occurred while reading from auth server: %s", strerror(errno));   
                /* FIXME */   
                close(sockfd);   
                return;   
            }   
            else if (numbytes == 0) {   
                done = 1;   
            }   
            else {   
                totalbytes += numbytes;   
                debug(LOG_DEBUG, "Read %d bytes, total now %d", numbytes, totalbytes);   
            }   
        }
else if (nfds == 0) {   
            debug(LOG_ERR, "Timed out reading data via select() from auth server");   
            /* FIXME */   
            close(sockfd);   
            return;   
        }   
        else if (nfds < 0) {   
            debug(LOG_ERR, "Error reading data via select() from auth server: %s", strerror(errno));   
            /* FIXME */   
            close(sockfd);   
            return;   
        }   
    } while (!done);   
    close(sockfd);   

    debug(LOG_DEBUG, "Done reading reply, total %d bytes", totalbytes);   

    request[totalbytes] = '\0';   

    debug(LOG_DEBUG, "HTTP Response from Server: [%s]", request);   

    if (strstr(request, "Pong") == 0) {   
        debug(LOG_WARNING, "Auth server did NOT say pong!");   
        /* FIXME */   
    }   
    else {   
        debug(LOG_DEBUG, "Auth Server Says: Pong");   
    }

这段log 出现在wifidog 在接收server 的响应包里没有出现Pong字符串。

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