wifidog源码分析 - 用户连接过程

引言

　　之前的文章已经描述wifidog大概的一个工作流程，这里我们具体说说wifidog是怎么把一个新用户重定向到认证服务器中的，它又是怎么对一个已认证的用户实行放行操作的。我们已经知道wifidog在启动时会删除iptables中mangle、nat、filter表中的所有规则，并在这三个表中添加wifidog自己的规则，其规则简单来说就是将网关80端口重定向到指定端口（默认为2060），禁止非认证用户连接外网（除认证服务器外）。当有新用户连接路由器上网时，wifidog会通过监听2060端口获取新用户的http报文，通过报文即可知道报文是否携带token进行认证，如果没有token，wifidog会返回一个重定向的http报文给新用户，用户则会跳转到认证服务器进行认证，当认证成功后，认真服务器又会对用户重定向到网关，并在重定向报文中添加关键路径"/wifidog/auth"和token，wifidog重新获取到用户的http报文，检测到包含关键路径"/wifidog/auth"后，会通过认证服务器验证token是否有效，有效则修改iptables放行此客户端。

main_loop

　　此函数几乎相当于我们写程序的main函数，主要功能都是在这里面实现的，函数主要实现了主循环，并启动了三个线程，这三个线程的功能具体见wifidog源码分析 - wifidog原理，在此函数最后主循环中会等待用户连接，新用户只要通过浏览器打开非认证服务器网页时主循环就会监听到，监听到后会启动一个处理线程。其流程为

• 设置程序启动时间
• 获取网关信息
• 绑定http端口（80重定向到了2060）
• 设置关键路径和404错误的回调函数
• 重新建立iptables规则
• 启动客户端检测线程 （稍后文章分析）
• 启动wdctrl交互线程 （稍后文章分析）
• 认证服务器心跳检测线程 （稍后文章分析）
• 循环等待用户http请求，为每个请求启动一个处理线程。（代码片段1.2 代码片段1.3 代码片段1.4）

　　代码片段1.1

 static void
 main_loop(void)
 {
     int result;
     pthread_t    tid;
     s_config *config = config_get_config();
     request *r;
     void **params;

     /* 设置启动时间 */
     if (!started_time) {
         debug(LOG_INFO, "Setting started_time");
         started_time = time(NULL);
     }
     else if (started_time < MINIMUM_STARTED_TIME) {
         debug(LOG_WARNING, "Detected possible clock skew - re-setting started_time");
         started_time = time(NULL);
     }

     /* 获取网关IP，失败退出程序 */
     if (!config->gw_address) {
         debug(LOG_DEBUG, "Finding IP address of %s", config->gw_interface);
         if ((config->gw_address = get_iface_ip(config->gw_interface)) == NULL) {
             debug(LOG_ERR, "Could not get IP address information of %s, exiting...", config->gw_interface);
             exit();
         }
         debug(LOG_DEBUG, "%s = %s", config->gw_interface, config->gw_address);
     }

     /* 获取网关ID，失败退出程序 */
     if (!config->gw_id) {
         debug(LOG_DEBUG, "Finding MAC address of %s", config->gw_interface);
         if ((config->gw_id = get_iface_mac(config->gw_interface)) == NULL) {
             debug(LOG_ERR, "Could not get MAC address information of %s, exiting...", config->gw_interface);
             exit();
         }
         debug(LOG_DEBUG, "%s = %s", config->gw_interface, config->gw_id);
     }

     /* 初始化监听网关2060端口的socket */
     debug(LOG_NOTICE, "Creating web server on %s:%d", config->gw_address, config->gw_port);

     if ((webserver = httpdCreate(config->gw_address, config->gw_port)) == NULL) {
         debug(LOG_ERR, "Could not create web server: %s", strerror(errno));
         exit();
     }

     debug(LOG_DEBUG, "Assigning callbacks to web server");
     /* 设置关键路径及其回调函数，在代码片段1.2中会使用到 */
     httpdAddCContent(webserver, "/", "wifidog", , NULL, http_callback_wifidog);
     httpdAddCContent(webserver, "/wifidog", "", , NULL, http_callback_wifidog);
     httpdAddCContent(webserver, "/wifidog", "about", , NULL, http_callback_about);
     httpdAddCContent(webserver, "/wifidog", "status", , NULL, http_callback_status);
     httpdAddCContent(webserver, "/wifidog", "auth", , NULL, http_callback_auth);
     /* 设置404错误回调函数，在里面实现了重定向至认证服务器 */
     httpdAddC404Content(webserver, http_callback_404);

     /* 清除iptables规则 */
     fw_destroy();
     /* 重新设置iptables规则 */
     if (!fw_init()) {
         debug(LOG_ERR, "FATAL: Failed to initialize firewall");
         exit();
     }

     /* 客户端检测线程 */
     result = pthread_create(&tid_fw_counter, NULL, (void *)thread_client_timeout_check, NULL);
     if (result != ) {
         debug(LOG_ERR, "FATAL: Failed to create a new thread (fw_counter) - exiting");
         termination_handler();
     }
     pthread_detach(tid_fw_counter);

     /* wdctrl交互线程 */
     result = pthread_create(&tid, NULL, (void *)thread_wdctl, (void *)safe_strdup(config->wdctl_sock));
     if (result != ) {
         debug(LOG_ERR, "FATAL: Failed to create a new thread (wdctl) - exiting");
         termination_handler();
     }
     pthread_detach(tid);

     /* 认证服务器心跳检测线程 */
     result = pthread_create(&tid_ping, NULL, (void *)thread_ping, NULL);
     if (result != ) {
         debug(LOG_ERR, "FATAL: Failed to create a new thread (ping) - exiting");
         termination_handler();
     }
     pthread_detach(tid_ping);

     debug(LOG_NOTICE, "Waiting for connections");
     while() {
         /* 监听2060端口等待用户http请求 */
         r = httpdGetConnection(webserver, NULL);

         /* 错误处理 */
         if (webserver->lastError == -) {
             /* Interrupted system call */
             continue; /* restart loop */
         }
         else if (webserver->lastError < -) {
             debug(LOG_ERR, "FATAL: httpdGetConnection returned unexpected value %d, exiting.", webserver->lastError);
             termination_handler();
         }
         else if (r != NULL) {
             /* 用户http请求接收成功 */
             debug(LOG_INFO, "Received connection from %s, spawning worker thread", r->clientAddr);
             params = safe_malloc( * sizeof(void *));
             *params = webserver;
             *(params + ) = r;

             /* 开启http请求处理线程 */
             result = pthread_create(&tid, NULL, (void *)thread_httpd, (void *)params);
             if (result != ) {
                 debug(LOG_ERR, "FATAL: Failed to create a new thread (httpd) - exiting");
                 termination_handler();
             }
             pthread_detach(tid);
         }
         else {
             ;
         }
     }

     /* never reached */
 }        

用户连接启动线程（void thread_httpd(void * args)）

代码片段1.2

此段代码是当有新用户（未认证的用户 代码片段1.3，已在认证服务器上认证但没有在wifidog认证的用户 代码片段1.4）连接时创建的线程，其主要功能为

• 获取用户浏览器发送过来的http报头
• 分析http报头，分析是否包含关键路径
• 不包含关键路径则调用404回调函数
• 包含关键路径则执行关键路径回调函数（这里主要讲解"/wifidog/auth"路径）

 void
 thread_httpd(void *args)
 {
     void    **params;
     httpd    *webserver;
     request    *r;

     params = (void **)args;
     webserver = *params;
     r = *(params + );
     free(params);

     /* 获取http报文 */
     if (httpdReadRequest(webserver, r) == ) {
         debug(LOG_DEBUG, "Processing request from %s", r->clientAddr);
         debug(LOG_DEBUG, "Calling httpdProcessRequest() for %s", r->clientAddr);
         /* 分析http报文 */
         httpdProcessRequest(webserver, r);
         debug(LOG_DEBUG, "Returned from httpdProcessRequest() for %s", r->clientAddr);
     }
     else {
         debug(LOG_DEBUG, "No valid request received from %s", r->clientAddr);
     }
     debug(LOG_DEBUG, "Closing connection with %s", r->clientAddr);
     httpdEndRequest(r);
 }

 /* 被thread_httpd调用 */
 void httpdProcessRequest(httpd *server, request *r)
 {
     char    dirName[HTTP_MAX_URL],
         entryName[HTTP_MAX_URL],
         *cp;
     httpDir    *dir;
     httpContent *entry;

     r->response.responseLength = ;
     strncpy(dirName, httpdRequestPath(r), HTTP_MAX_URL);
     dirName[HTTP_MAX_URL-]=;
     cp = rindex(dirName, '/');
     if (cp == NULL)
     {
         printf("Invalid request path '%s'\n",dirName);
         return;
     }
     strncpy(entryName, cp + , HTTP_MAX_URL);
     entryName[HTTP_MAX_URL-]=;
     if (cp != dirName)
         *cp = ;
     else
         *(cp+) = ;

      /* 获取http报文中的关键路径，在main_loop中已经设置 */
     dir = _httpd_findContentDir(server, dirName, HTTP_FALSE);
     if (dir == NULL)
     {
         /* http报文中未包含关键路径，执行404回调函数（在404回调函数中新用户被重定向到认证服务器），见代码片段1.3 */
         _httpd_send404(server, r);
         _httpd_writeAccessLog(server, r);
         return;
     }
     /* 获取关键路径内容描述符 */
     entry = _httpd_findContentEntry(r, dir, entryName);
     if (entry == NULL)
     {
         _httpd_send404(server, r);
         _httpd_writeAccessLog(server, r);
         return;
     }
     if (entry->preload)
     {
         if ((entry->preload)(server) < )
         {
             _httpd_writeAccessLog(server, r);
             return;
         }
     }
     switch(entry->type)
     {
         case HTTP_C_FUNCT:
         case HTTP_C_WILDCARD:
             /* 如果是被认证服务器重定向到网关的用户，此处的关键路径为"/wifidog/auth"，并执行回调函数 */
             (entry->function)(server, r);
             break;

         case HTTP_STATIC:
             _httpd_sendStatic(server, r, entry->data);
             break;

         case HTTP_FILE:
             _httpd_sendFile(server, r, entry->path);
             break;

         case HTTP_WILDCARD:
             if (_httpd_sendDirectoryEntry(server, r, entry,
                         entryName)<)
             {
                 _httpd_send404(server, r);
             }
             break;
     }
     _httpd_writeAccessLog(server, r);
 }

代码片段1.3

此段代码表示wifidog是如何通过http 404回调函数实现客户端重定向了，实际上就是在404回调函数中封装了一个307状态的http报头，http的307状态在http协议中就是用于重定向的，封装完成后通过已经与客户端连接的socket返回给客户端。步骤流程为

• 判断本机是否处于离线状态
• 判断认证服务器是否在线
• 封装http 307报文
• 发送于目标客户端

 void
 http_callback_404(httpd *webserver, request *r)
 {
     char        tmp_url[MAX_BUF],
             *url;
     s_config    *config = config_get_config();
     t_auth_serv    *auth_server = get_auth_server();

     memset(tmp_url, , sizeof(tmp_url));

         snprintf(tmp_url, (sizeof(tmp_url) - ), "http://%s%s%s%s",
                         r->request.host,
                         r->request.path,
                         r->request.query[] ? "?" : "",
                         r->request.query);
     url = httpdUrlEncode(tmp_url);

     if (!is_online()) {
         /* 本机处于离线状态，此函数调用结果由认证服务器检测线程设置 */
         char * buf;
         safe_asprintf(&buf,
             "<p>We apologize, but it seems that the internet connection that powers this hotspot is temporarily unavailable.</p>"
             "<p>If at all possible, please notify the owners of this hotspot that the internet connection is out of service.</p>"
             "<p>The maintainers of this network are aware of this disruption.  We hope that this situation will be resolved soon.</p>"
             "<p>In a while please <a href='%s'>click here</a> to try your request again.</p>", tmp_url);

                 send_http_page(r, "Uh oh! Internet access unavailable!", buf);
         free(buf);
         debug(LOG_INFO, "Sent %s an apology since I am not online - no point sending them to auth server", r->clientAddr);
     }
     else if (!is_auth_online()) {
         /* 认证服务器处于离线状态 */
         char * buf;
         safe_asprintf(&buf,
             "<p>We apologize, but it seems that we are currently unable to re-direct you to the login screen.</p>"
             "<p>The maintainers of this network are aware of this disruption.  We hope that this situation will be resolved soon.</p>"
             "<p>In a couple of minutes please <a href='%s'>click here</a> to try your request again.</p>", tmp_url);

                 send_http_page(r, "Uh oh! Login screen unavailable!", buf);
         free(buf);
         debug(LOG_INFO, "Sent %s an apology since auth server not online - no point sending them to auth server", r->clientAddr);
     }
     else {
         /* 本机与认证服务器都在线，返回重定向包于客户端 */
         char *urlFragment;
         safe_asprintf(&urlFragment, "%sgw_address=%s&gw_port=%d&gw_id=%s&url=%s",
             auth_server->authserv_login_script_path_fragment,
             config->gw_address,
             config->gw_port,
             config->gw_id,
             url);
         debug(LOG_INFO, "Captured %s requesting [%s] and re-directing them to login page", r->clientAddr, url);
         http_send_redirect_to_auth(r, urlFragment, "Redirect to login page");  /* 实际上此函数中通过socket返回一个307状态的http报头给客户端，里面包含有认证服务器地址 */
         free(urlFragment);
     }
     free(url);
 }

代码片段1.4

此段表明当客户端已经在认证服务器确认登陆，认证服务器将客户端重新重定向回网关，并在重定向包中包含关键路径"/wifidog/auth"和token，认证服务器所执行的操作。

 void
 http_callback_auth(httpd *webserver, request *r)
 {
     t_client    *client;
     httpVar * token;
     char    *mac;
     /* 判断http报文是否包含登出logout */
     httpVar *logout = httpdGetVariableByName(r, "logout");
     if ((token = httpdGetVariableByName(r, "token"))) {
         /* 获取http报文中的token */
         if (!(mac = arp_get(r->clientAddr))) {
             /* 获取客户端mac地址失败 */
             debug(LOG_ERR, "Failed to retrieve MAC address for ip %s", r->clientAddr);
             send_http_page(r, "WiFiDog Error", "Failed to retrieve your MAC address");
         } else {
             LOCK_CLIENT_LIST();
             /* 判断客户端是否存在于列表中 */
             if ((client = client_list_find(r->clientAddr, mac)) == NULL) {
                 debug(LOG_DEBUG, "New client for %s", r->clientAddr);
                 /* 将此客户端添加到客户端列表 */
                 client_list_append(r->clientAddr, mac, token->value);
             } else if (logout) {
                 /* http报文为登出 */
                 t_authresponse  authresponse;
                 s_config *config = config_get_config();
                 unsigned long long incoming = client->counters.incoming;
                 unsigned long long outgoing = client->counters.outgoing;
                 char *ip = safe_strdup(client->ip);
                 char *urlFragment = NULL;
                 t_auth_serv    *auth_server = get_auth_server();
                 /* 修改iptables禁止客户端访问外网 */
                 fw_deny(client->ip, client->mac, client->fw_connection_state);
                 /* 从客户端列表中删除此客户端 */
                 client_list_delete(client);
                 debug(LOG_DEBUG, "Got logout from %s", client->ip);

                 if (config->auth_servers != NULL) {
                     UNLOCK_CLIENT_LIST();
                     /* 发送登出认证包给认证服务器 */
                     auth_server_request(&authresponse, REQUEST_TYPE_LOGOUT, ip, mac, token->value,
                                         incoming, outgoing);
                     LOCK_CLIENT_LIST();

                     /* 将客户端重定向到认证服务器 */
                     debug(LOG_INFO, "Got manual logout from client ip %s, mac %s, token %s"
                     "- redirecting them to logout message", client->ip, client->mac, client->token);
                     safe_asprintf(&urlFragment, "%smessage=%s",
                         auth_server->authserv_msg_script_path_fragment,
                         GATEWAY_MESSAGE_ACCOUNT_LOGGED_OUT
                     );
                     http_send_redirect_to_auth(r, urlFragment, "Redirect to logout message");
                     free(urlFragment);
                 }
                 free(ip);
              }
              else {
                 debug(LOG_DEBUG, "Client for %s is already in the client list", client->ip);
             }
             UNLOCK_CLIENT_LIST();
             if (!logout) {
                 /* 通过认证服务器认证此客户端token */
                 authenticate_client(r);
             }
             free(mac);
         }
     } else {
         send_http_page(r, "WiFiDog error", "Invalid token");
     }
 }

 /* 此函数用于提交token到认证服务器进行认证 */
 void
 authenticate_client(request *r)
 {
     t_client    *client;
     t_authresponse    auth_response;
     char    *mac,
         *token;
     char *urlFragment = NULL;
     s_config    *config = NULL;
     t_auth_serv    *auth_server = NULL;

     LOCK_CLIENT_LIST();

     client = client_list_find_by_ip(r->clientAddr);
     /* 判断此客户端是否在列表中 */
     if (client == NULL) {
         debug(LOG_ERR, "Could not find client for %s", r->clientAddr);
         UNLOCK_CLIENT_LIST();
         return;
     }

     mac = safe_strdup(client->mac);
     token = safe_strdup(client->token);

     UNLOCK_CLIENT_LIST();

     /* 提交token、客户端ip、客户端mac至认证服务器 */
     auth_server_request(&auth_response, REQUEST_TYPE_LOGIN, r->clientAddr, mac, token, , );

     LOCK_CLIENT_LIST();

     /*再次判断客户端是否存在于列表中，保险起见，因为有可能在于认证服务器认证过程中，客户端检测线程把此客户端下线 */
     client = client_list_find(r->clientAddr, mac);

     if (client == NULL) {
         debug(LOG_ERR, "Could not find client node for %s (%s)", r->clientAddr, mac);
         UNLOCK_CLIENT_LIST();
         free(token);
         free(mac);
         return;
     }

     free(token);
     free(mac);

     config = config_get_config();
     auth_server = get_auth_server();

         /* 判断认证服务器认证结果 */
     switch(auth_response.authcode) {

     case AUTH_ERROR:
         /* 认证错误 */
         debug(LOG_ERR, "Got %d from central server authenticating token %s from %s at %s", auth_response, client->token, client->ip, client->mac);
         send_http_page(r, "Error!", "Error: We did not get a valid answer from the central server");
         break;

     case AUTH_DENIED:
         /* 认证服务器拒绝此客户端 */
         debug(LOG_INFO, "Got DENIED from central server authenticating token %s from %s at %s - redirecting them to denied message", client->token, client->ip, client->mac);
         safe_asprintf(&urlFragment, "%smessage=%s",
             auth_server->authserv_msg_script_path_fragment,
             GATEWAY_MESSAGE_DENIED
         );
         http_send_redirect_to_auth(r, urlFragment, "Redirect to denied message");
         free(urlFragment);
         break;

     case AUTH_VALIDATION:
         /* 认证服务器处于等待此客户端电子邮件确认回执状态 */
         debug(LOG_INFO, "Got VALIDATION from central server authenticating token %s from %s at %s"
                 "- adding to firewall and redirecting them to activate message", client->token,
                 client->ip, client->mac);
         client->fw_connection_state = FW_MARK_PROBATION;
         fw_allow(client->ip, client->mac, FW_MARK_PROBATION);
         safe_asprintf(&urlFragment, "%smessage=%s",
             auth_server->authserv_msg_script_path_fragment,
             GATEWAY_MESSAGE_ACTIVATE_ACCOUNT
         );
         http_send_redirect_to_auth(r, urlFragment, "Redirect to activate message");
         free(urlFragment);
         break;

     case AUTH_ALLOWED:
         /* 认证通过 */
         debug(LOG_INFO, "Got ALLOWED from central server authenticating token %s from %s at %s - "
                 "adding to firewall and redirecting them to portal", client->token, client->ip, client->mac);
         client->fw_connection_state = FW_MARK_KNOWN;
         fw_allow(client->ip, client->mac, FW_MARK_KNOWN);
         served_this_session++;
         safe_asprintf(&urlFragment, "%sgw_id=%s",
             auth_server->authserv_portal_script_path_fragment,
             config->gw_id
         );
         http_send_redirect_to_auth(r, urlFragment, "Redirect to portal");
         free(urlFragment);
         break;

     case AUTH_VALIDATION_FAILED:
          /* 电子邮件确认回执超时 */
         debug(LOG_INFO, "Got VALIDATION_FAILED from central server authenticating token %s from %s at %s "
                 "- redirecting them to failed_validation message", client->token, client->ip, client->mac);
         safe_asprintf(&urlFragment, "%smessage=%s",
             auth_server->authserv_msg_script_path_fragment,
             GATEWAY_MESSAGE_ACCOUNT_VALIDATION_FAILED
         );
         http_send_redirect_to_auth(r, urlFragment, "Redirect to failed validation message");
         free(urlFragment);
         break;

     default:
         debug(LOG_WARNING, "I don't know what the validation code %d means for token %s from %s at %s - sending error message", auth_response.authcode, client->token, client->ip, client->mac);
         send_http_page(r, "Internal Error", "We can not validate your request at this time");
         break;

     }

     UNLOCK_CLIENT_LIST();
     return;
 }