引言
但wifidog启动时，会自动启动认证服务器心跳检测线程，此线程默认每隔60s与认证服务器交互一次，会将路由器的信息（系统启动时长，内存使用情况和系统平均负载）告知认证服务器，并通过一个"ping"字符串作为信号，而当认证服务器接收到此数据包后，会返回一个"pong"给路由器，具体我们看看代码。
代码片段1.1
此段代码很简单，就是调用ping函数，然后等待60s：
void
thread_ping(void *arg)
{
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
pthread_mutex_t cond_mutex = PTHREAD_MUTEX_INITIALIZER;
struct timespec timeout;
while (1) {
/* 调用ping，具体代码看 代码片段1.2 */
debug(LOG_DEBUG, "Running ping()");
ping();
/* 睡眠一个checkinterval，默认为60s */
timeout.tv_sec = time(NULL) + config_get_config()->checkinterval;
timeout.tv_nsec = 0;
pthread_mutex_lock(&cond_mutex);
pthread_cond_timedwait(&cond, &cond_mutex, &timeout);
pthread_mutex_unlock(&cond_mutex);
}
代码片段1.2
static void
ping(void)
{
ssize_t numbytes;
size_t totalbytes;
int sockfd, nfds, done;
char request[MAX_BUF];
fd_set readfds;
struct timeval timeout;
FILE * fh;
unsigned long int sys_uptime = 0;
unsigned int sys_memfree = 0;
float sys_load = 0;
t_auth_serv *auth_server = NULL;
auth_server = get_auth_server();
debug(LOG_DEBUG, "Entering ping()");
/* 其实认证服务器就是一个web服务器，路由器跟他做通信行为就是通过发送http请求进行通信，首先先连接认证服务器的http端口，获取其socket */
sockfd = connect_auth_server();
if (sockfd == -1) {
/* 无法连接认证服务器，connect_auth_server分析见 代码片段1.3 */
return;
}
/*
* 从/proc文件系统获取路由器信息
*/
if ((fh = fopen("/proc/uptime", "r"))) {
fscanf(fh, "%lu", &sys_uptime);
fclose(fh);
}
if ((fh = fopen("/proc/meminfo", "r"))) {
while (!feof(fh)) {
if (fscanf(fh, "MemFree: %u", &sys_memfree) == 0) {
while (!feof(fh) && fgetc(fh) != '\n');
}
else {
break;
}
}
fclose(fh);
}
if ((fh = fopen("/proc/loadavg", "r"))) {
fscanf(fh, "%f", &sys_load);
fclose(fh);
}
/*
* 准备http请求包
*/
snprintf(request, sizeof(request) - 1,
"GET %s%sgw_id=%s&sys_uptime=%lu&sys_memfree=%u&sys_load=%.2f&wifidog_uptime=%lu HTTP/1.0\r\n"
"User-Agent: WiFiDog %s\r\n"
"Host: %s\r\n"
"\r\n",
auth_server->authserv_path,
auth_server->authserv_ping_script_path_fragment,
config_get_config()->gw_id,
sys_uptime,
sys_memfree,
sys_load,
(long unsigned int)((long unsigned int)time(NULL) - (long unsigned int)started_time),
VERSION,
auth_server->authserv_hostname);
debug(LOG_DEBUG, "HTTP Request to Server: [%s]", request);
/* 发送 */
send(sockfd, request, strlen(request), 0);
debug(LOG_DEBUG, "Reading response");
numbytes = totalbytes = 0;
done = 0;
do {
FD_ZERO(&readfds);
FD_SET(sockfd, &readfds);
/* 设置超时30s */
timeout.tv_sec = 30;
timeout.tv_usec = 0;
nfds = sockfd + 1;
nfds = select(nfds, &readfds, NULL, NULL, &timeout);
if (nfds > 0) {
/* 多路复用 */
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));
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");
close(sockfd);
return;
}
else if (nfds < 0) {
debug(LOG_ERR, "Error reading data via select() from auth server: %s", strerror(errno));
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);
/* 判断认证服务器返回包中有没有"Pong"字符串 */
if (strstr(request, "Pong") == 0) {
debug(LOG_WARNING, "Auth server did NOT say pong!");
}
else {
debug(LOG_DEBUG, "Auth Server Says: Pong");
}
return;
}
代码片段1.3
connect_auth_server函数用于连接认证服务器并返回socket套接字，其具体实现是通过_connect_auth_server实现的，而在_connect_auth_server中，递归认证服务器列表，每次递归中首先会根据认证服务器域名获取ip，如果失败，会通过公共网站判断是否为DNS问题，再判断是否为认证服务器问题，如果都失败，继续递归，否则返回认证服务器socket。
int connect_auth_server() {
int sockfd;
LOCK_CONFIG();
/* 连接认证服务器 */
sockfd = _connect_auth_server(0);
UNLOCK_CONFIG();
if (sockfd == -1) {
debug(LOG_ERR, "Failed to connect to any of the auth servers");
/* 标记认证服务器离线 */
mark_auth_offline();
}
else {
debug(LOG_DEBUG, "Connected to auth server");
/* 标记认证服务器在线 */
mark_auth_online();
}
return (sockfd);
}
int _connect_auth_server(int level) {
s_config *config = config_get_config();
t_auth_serv *auth_server = NULL;
struct in_addr *h_addr;
int num_servers = 0;
char * hostname = NULL;
/* 公共网站，用于判断DNS问题 */
char * popular_servers[] = {
"www.google.com",
"www.yahoo.com",
NULL
};
char ** popularserver;
char * ip;
struct sockaddr_in their_addr;
int sockfd;
/* 用于递归，因为可能会有多个认证服务器，如果第一个认证服务器无法连接，会递归尝试连接后面的认证服务器，此参数用于递归判断的，当成功连接任意一个认证服务器后停止 */
level++;
/*
* 获取认证服务器数量
*/
for (auth_server = config->auth_servers; auth_server; auth_server = auth_server->next) {
num_servers++;
}
debug(LOG_DEBUG, "Level %d: Calculated %d auth servers in list", level, num_servers);
/* 已经尝试递归连接所有认证服务器，都不能连接 */
if (level > num_servers) {
return (-1);
}
/*
* 获取认证服务器列表中的第一个认证服务器
*/
auth_server = config->auth_servers;
hostname = auth_server->authserv_hostname;
debug(LOG_DEBUG, "Level %d: Resolving auth server [%s]", level, hostname);
h_addr = wd_gethostbyname(hostname);
if (!h_addr) {
/*
* DNS解析错误，尝试解析公共网站判断是否为DNS错误
*/
debug(LOG_DEBUG, "Level %d: Resolving auth server [%s] failed", level, hostname);
for (popularserver = popular_servers; *popularserver; popularserver++) {
debug(LOG_DEBUG, "Level %d: Resolving popular server [%s]", level, *popularserver);
h_addr = wd_gethostbyname(*popularserver);
/* 公共网站DNS解析正确 */
if (h_addr) {
debug(LOG_DEBUG, "Level %d: Resolving popular server [%s] succeeded = [%s]", level, *popularserver, inet_ntoa(*h_addr));
break;
}
else {
debug(LOG_DEBUG, "Level %d: Resolving popular server [%s] failed", level, *popularserver);
}
}
if (h_addr) {
/* DNS正确，尝试递归下一个认证服务器 */
free (h_addr);
debug(LOG_DEBUG, "Level %d: Marking auth server [%s] as bad and trying next if possible", level, hostname);
if (auth_server->last_ip) {
free(auth_server->last_ip);
auth_server->last_ip = NULL;
}
/* 将此认证服务器放入bad_server链表，并将config->auth_server指向认证服务器的下一个节点 */
mark_auth_server_bad(auth_server);
/* 递归 */
return _connect_auth_server(level);
}
else {
/* DNS问题，标记路由器离线 */
mark_offline();
debug(LOG_DEBUG, "Level %d: Failed to resolve auth server and all popular servers. "
"The internet connection is probably down", level);
return(-1);
}
}
else {
/* DNS解析成功 */
ip = safe_strdup(inet_ntoa(*h_addr));
debug(LOG_DEBUG, "Level %d: Resolving auth server [%s] succeeded = [%s]", level, hostname, ip);
if (!auth_server->last_ip || strcmp(auth_server->last_ip, ip) != 0) {
/* DNS解析到的IP与我们上一次连接的IP不同，更新上一次连接的IP */
debug(LOG_DEBUG, "Level %d: Updating last_ip IP of server [%s] to [%s]", level, hostname, ip);
if (auth_server->last_ip) free(auth_server->last_ip);
auth_server->last_ip = ip;
/* 将此新的认证服务器IP添加到iptables中的可访问外网地址中 */
fw_clear_authservers();
fw_set_authservers();
}
else {
/*
* DNS解析到的IP与我们上一次连接的IP相同
*/
free(ip);
}
/*
* 连接
*/
debug(LOG_DEBUG, "Level %d: Connecting to auth server %s:%d", level, hostname, auth_server->authserv_http_port);
their_addr.sin_family = AF_INET;
their_addr.sin_port = htons(auth_server->authserv_http_port);
their_addr.sin_addr = *h_addr;
memset(&(their_addr.sin_zero), '\0', sizeof(their_addr.sin_zero));
free (h_addr);
if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
debug(LOG_ERR, "Level %d: Failed to create a new SOCK_STREAM socket: %s", strerror(errno));
return(-1);
}
if (connect(sockfd, (struct sockaddr *)&their_addr, sizeof(struct sockaddr)) == -1) {
/*
* 连接失败
* 将此认证服务器放入bad_server链表，并将config->auth_server指向认证服务器的下一个节点
*/
debug(LOG_DEBUG, "Level %d: Failed to connect to auth server %s:%d (%s). Marking it as bad and trying next if possible", level, hostname, auth_server->authserv_http_port, strerror(errno));
close(sockfd);
mark_auth_server_bad(auth_server);
return _connect_auth_server(level); /* Yay recursion! */
}
else {
/*
* 连接成功
*/
debug(LOG_DEBUG, "Level %d: Successfully connected to auth server %s:%d", level, hostname, auth_server->authserv_http_port);
return sockfd;
}
}
}
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