/*
 * Copyright (c) 2016 MariaDB Corporation Ab
 *
 * Use of this software is governed by the Business Source License included
 * in the LICENSE.TXT file and at www.mariadb.com/bsl.
 *
 * Change Date: 2019-07-01
 *
 * On the date above, in accordance with the Business Source License, use
 * of this software will be governed by version 2 or later of the General
 * Public License.
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <maxscale/alloc.h>
#include <dcb.h>
#include <buffer.h>
#include <service.h>
#include <session.h>
#include <gw_protocol.h>
#include <sys/ioctl.h>
#include <errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <router.h>
#include <maxscale/poll.h>
#include <atomic.h>
#include <gw.h>
#include <telnetd.h>
#include <adminusers.h>
#include <skygw_utils.h>
#include <log_manager.h>
#include <modinfo.h>

/* @see function load_module in load_utils.c for explanation of the following
 * lint directives.
 */
/*lint -e14 */
MODULE_INFO info =
{
    MODULE_API_PROTOCOL,
    MODULE_GA,
    GWPROTOCOL_VERSION,
    "A telnet deamon protocol for simple administration interface"
};
/*lint +e14 */

/**
 * @file telnetd.c - telnet daemon protocol module
 *
 * The telnetd protocol module is intended as a mechanism to allow connections
 * into the gateway for the purpsoe of accessing debugging information within
 * the gateway rather than a protocol to be used to send queries to backend
 * databases.
 *
 * In the first instance it is intended to allow a debug connection to access
 * internal data structures, however it may also be used to manage the
 * configuration of the gateway.
 *
 * @verbatim
 * Revision History
 * Date         Who                     Description
 * 17/06/2013   Mark Riddoch            Initial version
 * 17/07/2013   Mark Riddoch            Addition of login phase
 * 07/07/2015   Martin Brampton         Call unified dcb_close on error
 *
 * @endverbatim
 */

static char *version_str = "V1.1.1";

static int telnetd_read_event(DCB* dcb);
static int telnetd_write_event(DCB *dcb);
static int telnetd_write(DCB *dcb, GWBUF *queue);
static int telnetd_error(DCB *dcb);
static int telnetd_hangup(DCB *dcb);
static int telnetd_accept(DCB *dcb);
static int telnetd_close(DCB *dcb);
static int telnetd_listen(DCB *dcb, char *config);
static char *telnetd_default_auth();

/**
 * The "module object" for the telnetd protocol module.
 */
static GWPROTOCOL MyObject =
{
    telnetd_read_event,             /**< Read - EPOLLIN handler        */
    telnetd_write,                  /**< Write - data from gateway     */
    telnetd_write_event,            /**< WriteReady - EPOLLOUT handler */
    telnetd_error,                  /**< Error - EPOLLERR handler      */
    telnetd_hangup,                 /**< HangUp - EPOLLHUP handler     */
    telnetd_accept,                 /**< Accept                        */
    NULL,                           /**< Connect                       */
    telnetd_close,                  /**< Close                         */
    telnetd_listen,                 /**< Create a listener             */
    NULL,                           /**< Authentication                */
    NULL,                           /**< Session                       */
    telnetd_default_auth,           /**< Default authenticator         */
    NULL                            /**< Connection limit reached      */
};

static void telnetd_command(DCB *, unsigned char *cmd);
static void telnetd_echo(DCB *dcb, int enable);

/**
 * Implementation of the mandatory version entry point
 *
 * @return version string of the module
 *
 * @see function load_module in load_utils.c for explanation of the following
 * lint directives.
 */
/*lint -e14 */
char* version()
{
    return version_str;
}

/**
 * The module initialisation routine, called when the module
 * is first loaded.
 */
void ModuleInit()
{
    MXS_INFO("Initialise Telnetd Protocol module.");
}

/**
 * The module entry point routine. It is this routine that
 * must populate the structure that is referred to as the
 * "module object", this is a structure with the set of
 * external entry points for this module.
 *
 * @return The module object
 */
GWPROTOCOL* GetModuleObject()
{
    return &MyObject;
}
/*lint +e14 */

/**
 * The default authenticator name for this protocol
 *
 * @return name of authenticator
 */
static char *telnetd_default_auth()
{
    return "NullAuthAllow";
}

/**
 * Read event for EPOLLIN on the telnetd protocol module.
 *
 * @param dcb   The descriptor control block
 * @return
 */
static int telnetd_read_event(DCB* dcb)
{
    int n;
    GWBUF *head = NULL;
    SESSION *session = dcb->session;
    TELNETD *telnetd = (TELNETD *)dcb->protocol;
    char *password, *t;

    if ((n = dcb_read(dcb, &head, 0)) != -1)
    {
        if (head)
        {
            unsigned char *ptr = GWBUF_DATA(head);
            ptr = GWBUF_DATA(head);
            while (GWBUF_LENGTH(head) && *ptr == TELNET_IAC)
            {
                telnetd_command(dcb, ptr + 1);
                GWBUF_CONSUME(head, 3);
                ptr = GWBUF_DATA(head);
            }
            if (GWBUF_LENGTH(head))
            {
                switch (telnetd->state)
                {
                case TELNETD_STATE_LOGIN:
                    telnetd->username = strndup(GWBUF_DATA(head), GWBUF_LENGTH(head));
                    /* Strip the cr/lf from the username */
                    t = strstr(telnetd->username, "\r\n");
                    if (t)
                    {
                        *t = 0;
                    }
                    telnetd->state = TELNETD_STATE_PASSWD;
                    dcb_printf(dcb, "Password: ");
                    telnetd_echo(dcb, 0);
                    gwbuf_consume(head, GWBUF_LENGTH(head));
                    break;
                case TELNETD_STATE_PASSWD:
                    password = strndup(GWBUF_DATA(head), GWBUF_LENGTH(head));
                    /* Strip the cr/lf from the username */
                    t = strstr(password, "\r\n");
                    if (t)
                    {
                        *t = 0;
                    }
                    if (admin_verify(telnetd->username, password))
                    {
                        telnetd_echo(dcb, 1);
                        telnetd->state = TELNETD_STATE_DATA;
                        dcb_printf(dcb, "\n\nMaxScale> ");
                    }
                    else
                    {
                        dcb_printf(dcb, "\n\rLogin incorrect\n\rLogin: ");
                        telnetd_echo(dcb, 1);
                        telnetd->state = TELNETD_STATE_LOGIN;
                        MXS_FREE(telnetd->username);
                    }
                    gwbuf_consume(head, GWBUF_LENGTH(head));
                    MXS_FREE(password);
                    break;
                case TELNETD_STATE_DATA:
                    SESSION_ROUTE_QUERY(session, head);
                    break;
                }
            }
            else
            {
                // Force the free of the buffer header
                gwbuf_consume(head, 0);
            }
        }
    }
    return n;
}

/**
 * EPOLLOUT handler for the telnetd protocol module.
 *
 * @param dcb   The descriptor control block
 * @return
 */
static int telnetd_write_event(DCB *dcb)
{
    return dcb_drain_writeq(dcb);
}

/**
 * Write routine for the telnetd protocol module.
 *
 * Writes the content of the buffer queue to the socket
 * observing the non-blocking principles of the gateway.
 *
 * @param dcb   Descriptor Control Block for the socket
 * @param queue Linked list of buffes to write
 */
static int telnetd_write(DCB *dcb, GWBUF *queue)
{
    int rc;
    rc = dcb_write(dcb, queue);
    return rc;
}

/**
 * Handler for the EPOLLERR event.
 *
 * @param dcb   The descriptor control block
 */
static int telnetd_error(DCB *dcb)
{
    return 0;
}

/**
 * Handler for the EPOLLHUP event.
 *
 * @param dcb   The descriptor control block
 */
static int telnetd_hangup(DCB *dcb)
{
    return 0;
}

/**
 * Handler for the EPOLLIN event when the DCB refers to the listening
 * socket for the protocol.
 *
 * @param listener   The descriptor control block
 * @return The number of new connections created
 */
static int telnetd_accept(DCB *listener)
{
    int n_connect = 0;
    DCB *client_dcb;

    while ((client_dcb = dcb_accept(listener, &MyObject)) != NULL)
    {
        TELNETD* telnetd_protocol = NULL;

        if ((telnetd_protocol = (TELNETD *)MXS_CALLOC(1, sizeof(TELNETD))) == NULL)
        {
            dcb_close(client_dcb);
            continue;
        }
        telnetd_protocol->state = TELNETD_STATE_LOGIN;
        telnetd_protocol->username = NULL;
        client_dcb->protocol = (void *)telnetd_protocol;

        client_dcb->session = session_alloc(listener->session->service, client_dcb);
        if (NULL == client_dcb->session || poll_add_dcb(client_dcb))
        {
            dcb_close(client_dcb);
            continue;
        }

        ssl_authenticate_client(client_dcb, client_dcb->authfunc.connectssl(client_dcb));

        n_connect++;
        dcb_printf(client_dcb, "MaxScale login: ");
    }
    return n_connect;
}

/**
 * The close handler for the descriptor. Called by the gateway to
 * explicitly close a connection.
 *
 * @param dcb   The descriptor control block
 */

static int telnetd_close(DCB *dcb)
{
    TELNETD *telnetd = dcb->protocol;

    if (telnetd && telnetd->username)
    {
        MXS_FREE(telnetd->username);
    }

    return 0;
}

/**
 * Telnet daemon listener entry point
 *
 * @param       listener        The Listener DCB
 * @param       config          Configuration (ip:port)
 */
static int telnetd_listen(DCB *listener, char *config)
{
    return (dcb_listen(listener, config, "telnet") < 0) ? 0 : 1;
}

/**
 * Telnet command implementation
 *
 * Called for each command in the telnet stream.
 *
 * Currently we do no command execution
 *
 * @param       dcb     The client DCB
 * @param       cmd     The command stream
 */
static void telnetd_command(DCB *dcb, unsigned char *cmd)
{
}

/**
 * Enable or disable telnet protocol echo
 *
 * @param dcb           DCB of the telnet connection
 * @param enable        Enable or disable echo functionality
 */
static void telnetd_echo(DCB *dcb, int enable)
{
    GWBUF *gwbuf;
    unsigned char *buf;

    if ((gwbuf = gwbuf_alloc(3)) == NULL)
    {
        return;
    }
    buf = GWBUF_DATA(gwbuf);
    buf[0] = TELNET_IAC;
    buf[1] = enable ? TELNET_WONT : TELNET_WILL;
    buf[2] = TELNET_ECHO;
    dcb_write(dcb, gwbuf);
}