wifidog源码分析 - 初始化阶段

    Wifidog是一个linux下开源的认证网关软件，它主要用于配合认证服务器实现无线路由器的认证放行功能。

wifidog是一个后台的服务程序，可以通过wdctrl命令对wifidog主程序进行控制。

本文解释wifidog在启动阶段所做的初始化主要工作（代码片段1.1）

• 初始化配置（先将配置结构体初始化为默认值，在读取配置文件修改配置结构体）
• 初始化已连接客户端列表（如果是通过wdctrl重启wifidog，将会读取之前wifidog的已连接客户端列表 代码片段1.2 代码片段1.3）
• 如无特殊情况，分离进程，建立守护进程 （代码片段1.1）
• 添加多个http请求回调函数（包括404错误回调函数） （见之后章节）
• 摧毁删除现有的iptables路由表规则 （见之后章节）
• 建立新的iptables路由表规则 （见之后章节）
• 启动多个功能线程 （见之后章节）
• 循环等待客户端连接 （见之后章节）

代码片段1.1

int main(int argc, char **argv) {

    s_config *config = config_get_config(); //就是返回全局变量config结构体的地址
    config_init(); //初始化全局变量config结构体为默认值

    parse_commandline(argc, argv); //根据传入参数执行操作（如果参数有-x则会设置restart_orig_pid为已运行的wifidog的pid）

    /* Initialize the config */
    config_read(config->configfile); //根据配置文件设置全局变量config结构体
    config_validate(); //判断GatewayInterface和AuthServer是否为空，空则无效退出程序。

    /* Initializes the linked list of connected clients */
    client_list_init(); //将已连接客户端链表置空。

    /* Init the signals to catch chld/quit/etc */
    init_signals(); //初始化一些信号

    if (restart_orig_pid) { //用于restart，如果有已运行的wifidog，先会kill它
        /*
         * We were restarted and our parent is waiting for us to talk to it over the socket
         */
        get_clients_from_parent(); //从已运行的wifidog中获取客户端列表，详见 代码片段1.2

        /*
         * At this point the parent will start destroying itself and the firewall. Let it finish it's job before we continue
         */

        while (kill(restart_orig_pid, 0) != -1) { //kill已运行的wifidog
            debug(LOG_INFO, "Waiting for parent PID %d to die before continuing loading", restart_orig_pid);
            sleep(1);
        }

        debug(LOG_INFO, "Parent PID %d seems to be dead. Continuing loading.");
    }

    if (config->daemon) { //创建为守护进程，config->daemon默认值为-1

        debug(LOG_INFO, "Forking into background");

        switch(safe_fork()) {
            case 0: /* child */
                setsid(); //创建新会话，脱离此终端，实现守护进程
                append_x_restartargv();
                main_loop(); //进入主循环（核心代码在此）。
                break;

            default: /* parent */
                exit(0);
                break;
        }
    }
    else {
        append_x_restartargv();
        main_loop();
    }

    return(0); /* never reached */
}

代码片段1.2（获取已启动的wifidog的客户端列表）：

此段代表描述了新启动的wifidog如何从已启动的wifidog程序中获取已连接的客户端列表。发送端见 代码片段1.3

void get_clients_from_parent(void) {
    int sock;
    struct sockaddr_un    sa_un;
    s_config * config = NULL;
    char linebuffer[MAX_BUF];
    int len = 0;
    char *running1 = NULL;
    char *running2 = NULL;
    char *token1 = NULL;
    char *token2 = NULL;
    char onechar;
    char *command = NULL;
    char *key = NULL;
    char *value = NULL;
    t_client * client = NULL;
    t_client * lastclient = NULL;

    config = config_get_config();

    debug(LOG_INFO, "Connecting to parent to download clients");

    /* 连接socket */
    sock = socket(AF_UNIX, SOCK_STREAM, 0);
    memset(&sa_un, 0, sizeof(sa_un));
    sa_un.sun_family = AF_UNIX;
    strncpy(sa_un.sun_path, config->internal_sock, (sizeof(sa_un.sun_path) - 1)); //config->internal_sock的值为"/tmp/wifidog.sock"

    /* 连接已启动的wifidog */
    if (connect(sock, (struct sockaddr *)&sa_un, strlen(sa_un.sun_path) + sizeof(sa_un.sun_family))) {
        debug(LOG_ERR, "Failed to connect to parent (%s) - client list not downloaded", strerror(errno));
        return;
    }

    debug(LOG_INFO, "Connected to parent.  Downloading clients");

    LOCK_CLIENT_LIST();

    command = NULL;
    memset(linebuffer, 0, sizeof(linebuffer));
    len = 0;
    client = NULL;
    /* 接收数据，逐个字符接收 */
    /* 数据包格式为 CLIENT|ip=%s|mac=%s|token=%s|fw_connection_state=%u|fd=%d|counters_incoming=%llu|counters_outgoing=%llu|counters_last_updated=%lu\n */
    while (read(sock, &onechar, 1) == 1) {
        if (onechar == '\n') {
            /* 如果接收到末尾（'\n'），则转为'\0' */
            onechar = '\0';
        }
        linebuffer[len++] = onechar;

        if (!onechar) {
            /* 以下将数据转化为t_client结构体添加到客户端列表 */
            debug(LOG_DEBUG, "Received from parent: [%s]", linebuffer);
            running1 = linebuffer;
            while ((token1 = strsep(&running1, "|")) != NULL) {
                if (!command) {
                    /* The first token is the command */
                    command = token1;
                }
                else {
                /* Token1 has something like "foo=bar" */
                    running2 = token1;
                    key = value = NULL;
                    while ((token2 = strsep(&running2, "=")) != NULL) {
                        if (!key) {
                            key = token2;
                        }
                        else if (!value) {
                            value = token2;
                        }
                    }
                }

                if (strcmp(command, "CLIENT") == 0) {
                    /* This line has info about a client in the client list */
                    if (!client) {
                        /* Create a new client struct */
                        client = safe_malloc(sizeof(t_client));
                        memset(client, 0, sizeof(t_client));
                    }
                }

                if (key && value) {
                    if (strcmp(command, "CLIENT") == 0) {
                        /* Assign the key into the appropriate slot in the connection structure */
                        if (strcmp(key, "ip") == 0) {
                            client->ip = safe_strdup(value);
                        }
                        else if (strcmp(key, "mac") == 0) {
                            client->mac = safe_strdup(value);
                        }
                        else if (strcmp(key, "token") == 0) {
                            client->token = safe_strdup(value);
                        }
                        else if (strcmp(key, "fw_connection_state") == 0) {
                            client->fw_connection_state = atoi(value);
                        }
                        else if (strcmp(key, "fd") == 0) {
                            client->fd = atoi(value);
                        }
                        else if (strcmp(key, "counters_incoming") == 0) {
                            client->counters.incoming_history = atoll(value);
                            client->counters.incoming = client->counters.incoming_history;
                        }
                        else if (strcmp(key, "counters_outgoing") == 0) {
                            client->counters.outgoing_history = atoll(value);
                            client->counters.outgoing = client->counters.outgoing_history;
                        }
                        else if (strcmp(key, "counters_last_updated") == 0) {
                            client->counters.last_updated = atol(value);
                        }
                        else {
                            debug(LOG_NOTICE, "I don't know how to inherit key [%s] value [%s] from parent", key, value);
                        }
                    }
                }
            }

            /* End of parsing this command */
            if (client) {
                /* Add this client to the client list */
                if (!firstclient) {
                    firstclient = client;
                    lastclient = firstclient;
                }
                else {
                    lastclient->next = client;
                    lastclient = client;
                }
            }

            /* Clean up */
            command = NULL;
            memset(linebuffer, 0, sizeof(linebuffer));
            len = 0;
            client = NULL;
        }
    }

    UNLOCK_CLIENT_LIST();
    debug(LOG_INFO, "Client list downloaded successfully from parent");

    close(sock);
}

代码片段1.3（已启动的wifidog发送客户端列表到新启动的wifidog）：

//thread_wdctl_handler(void *arg)函数是wifidog启动后自动创建的控制线程，主要用于与wdctrl进行socket通信，根据wdctrl命令执行不同的操作。这里我们着重讲解的是wdctrl发送restart后wifidog的执行逻辑。
static void *
thread_wdctl_handler(void *arg)
{
    int fd,
        done,
        i;
    char    request[MAX_BUF];
    ssize_t    read_bytes,
        len;

    debug(LOG_DEBUG, "Entering thread_wdctl_handler....");

    fd = (int)arg;

    debug(LOG_DEBUG, "Read bytes and stuff from %d", fd);

    /* 初始化变量 */
    read_bytes = 0;
    done = 0;
    memset(request, 0, sizeof(request));

    /* 读取命令 */
    while (!done && read_bytes < (sizeof(request) - 1)) {
        len = read(fd, request + read_bytes,
                sizeof(request) - read_bytes); //读取wdctrl发送的命令

        /* 判断命令正确性 */
        for (i = read_bytes; i < (read_bytes + len); i++) {
            if (request[i] == '\r' || request[i] == '\n') {
                request[i] = '\0';
                done = 1;
            }
        }

        /* Increment position */
        read_bytes += len;
    }

        //判断命令
    if (strncmp(request, "status", 6) == 0) {
        wdctl_status(fd);
    } else if (strncmp(request, "stop", 4) == 0) {
        wdctl_stop(fd);
    } else if (strncmp(request, "reset", 5) == 0) {
        wdctl_reset(fd, (request + 6));
    } else if (strncmp(request, "restart", 7) == 0) {
        wdctl_restart(fd); //执行wdctl_restart(int afd)函数
    }

    if (!done) {
        debug(LOG_ERR, "Invalid wdctl request.");
                //关闭套接字
        shutdown(fd, 2);
        close(fd);
        pthread_exit(NULL);
    }

    debug(LOG_DEBUG, "Request received: [%s]", request);

        //关闭套接字
    shutdown(fd, 2);
    close(fd);
    debug(LOG_DEBUG, "Exiting thread_wdctl_handler....");

    return NULL;
}


//wdctl_restart(int afd)函数详解
static void
wdctl_restart(int afd)
{
    int sock,
        fd;
    char *sock_name;
    struct     sockaddr_un    sa_un;
    s_config * conf = NULL;
    t_client * client = NULL;
    char * tempstring = NULL;
    pid_t pid;
    ssize_t written;
    socklen_t len;

    conf = config_get_config();

    debug(LOG_NOTICE, "Will restart myself");

    /*
     * 准备内部连接socket
     */
    memset(&sa_un, 0, sizeof(sa_un));
    sock_name = conf->internal_sock; //conf->internal_sock值为"/tmp/wifidog.sock"
    debug(LOG_DEBUG, "Socket name: %s", sock_name);

    if (strlen(sock_name) > (sizeof(sa_un.sun_path) - 1)) {

        debug(LOG_ERR, "INTERNAL socket name too long");
        return;
    }

    debug(LOG_DEBUG, "Creating socket");
    sock = socket(PF_UNIX, SOCK_STREAM, 0); //建立内部socket套接字

    debug(LOG_DEBUG, "Got internal socket %d", sock);

    /* 如果sock_name文件存在，则删除*/
    unlink(sock_name);

    debug(LOG_DEBUG, "Filling sockaddr_un");
    strcpy(sa_un.sun_path, sock_name);
    sa_un.sun_family = AF_UNIX;

    debug(LOG_DEBUG, "Binding socket (%s) (%d)", sa_un.sun_path, strlen(sock_name));


    if (bind(sock, (struct sockaddr *)&sa_un, strlen(sock_name) + sizeof(sa_un.sun_family))) {
        debug(LOG_ERR, "Could not bind internal socket: %s", strerror(errno));
        return;
    }

    if (listen(sock, 5)) {
        debug(LOG_ERR, "Could not listen on internal socket: %s", strerror(errno));
        return;
    }

    /*
     * socket建立完成，创建子进程
     */
    debug(LOG_DEBUG, "Forking in preparation for exec()...");
    pid = safe_fork();
    if (pid > 0) {
        /* 父进程 */

        /* 等待子进程连接此socket :*/
        debug(LOG_DEBUG, "Waiting for child to connect on internal socket");
        len = sizeof(sa_un);
        if ((fd = accept(sock, (struct sockaddr *)&sa_un, &len)) == -1){ //接受连接
            debug(LOG_ERR, "Accept failed on internal socket: %s", strerror(errno));
            close(sock);
            return;
        }

        close(sock);

        debug(LOG_DEBUG, "Received connection from child.  Sending them all existing clients");

        /*子进程已经完成连接，发送客户端列表 */
        LOCK_CLIENT_LIST();
        client = client_get_first_client(); //获取第一个客户端
        while (client) {
            /* Send this client */
            safe_asprintf(&tempstring, "CLIENT|ip=%s|mac=%s|token=%s|fw_connection_state=%u|fd=%d|counters_incoming=%llu|counters_outgoing=%llu|counters_last_updated=%lu\n", client->ip, client->mac, client->token, client->fw_connection_state, client->fd, client->counters.incoming, client->counters.outgoing, client->counters.last_updated);
            debug(LOG_DEBUG, "Sending to child client data: %s", tempstring);
            len = 0;
            while (len != strlen(tempstring)) {
                written = write(fd, (tempstring + len), strlen(tempstring) - len); //发送给子进程
                if (written == -1) {
                    debug(LOG_ERR, "Failed to write client data to child: %s", strerror(errno));
                    free(tempstring);
                    break;
                }
                else {
                    len += written;
                }
            }
            free(tempstring);
            client = client->next;
        }
        UNLOCK_CLIENT_LIST();

        close(fd);

        debug(LOG_INFO, "Sent all existing clients to child.  Committing suicide!");

        shutdown(afd, 2);
        close(afd);


        wdctl_stop(afd);
    }
    else {
        /* 子进程，先关闭资源 */
        close(wdctl_socket_server);
        close(icmp_fd);
        close(sock);
        shutdown(afd, 2);
        close(afd);
        debug(LOG_NOTICE, "Re-executing myself (%s)", restartargv[0]);

        setsid();
        execvp(restartargv[0], restartargv); //执行外部命令，这里重新启动wifidog

        debug(LOG_ERR, "I failed to re-execute myself: %s", strerror(errno));
        debug(LOG_ERR, "Exiting without cleanup");
        exit(1);
    }
}

小结

　　客户端列表只有在restart命令中才会执行，实际上流程就是

• 父wifidog准备socket
• 父wifidog启动子wifidog
• 子wifidog连接父wifidog
• 客户端列表传递
• 子wifidog终止父wifidog