gpsd/libgps/libgps_dbus.c

/*
 * This file is Copyright 2010 by the GPSD project
 * SPDX-License-Identifier: BSD-2-clause
 */

#include "../include/gpsd_config.h"   // must be before all includes

#if defined(DBUS_EXPORT_ENABLE)

#include <dbus/dbus.h>
#include <errno.h>
#include <libgen.h>
#include <math.h>
#include <signal.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <time.h>
#include <unistd.h>

#include "../include/gps.h"
#include "../include/libgps.h"
#include "../include/os_compat.h"
#include "../include/timespec.h"


struct privdata_t
{
    void (*handler)(struct gps_data_t *);
};

/*
 * Unpleasant that we have to declare a static context pointer here - means
 * you can't have multiple DBUS sessions open (not that this matters
 * much in practice). The problem is the DBUS API lacks some hook
 * arguments that it ought to have.
 */
static struct gps_data_t *share_gpsdata;
static DBusConnection *connection;

static DBusHandlerResult handle_gps_fix(DBusMessage * message)
{
    DBusError error;
    const char *gpsd_devname = NULL;
    double fix_time;

    dbus_error_init(&error);

    dbus_message_get_args(message,
                          &error,
                          DBUS_TYPE_DOUBLE, &fix_time,
                          DBUS_TYPE_INT32, &share_gpsdata->fix.mode,
                          DBUS_TYPE_DOUBLE, &share_gpsdata->fix.ept,
                          DBUS_TYPE_DOUBLE, &share_gpsdata->fix.latitude,
                          DBUS_TYPE_DOUBLE, &share_gpsdata->fix.longitude,
                          DBUS_TYPE_DOUBLE, &share_gpsdata->fix.eph,
                          /* The dbus doc does not seem to specify
                           * altHAE or altMSL */
                          DBUS_TYPE_DOUBLE, &share_gpsdata->fix.altHAE,
                          DBUS_TYPE_DOUBLE, &share_gpsdata->fix.epv,
                          DBUS_TYPE_DOUBLE, &share_gpsdata->fix.track,
                          DBUS_TYPE_DOUBLE, &share_gpsdata->fix.epd,
                          DBUS_TYPE_DOUBLE, &share_gpsdata->fix.speed,
                          DBUS_TYPE_DOUBLE, &share_gpsdata->fix.eps,
                          DBUS_TYPE_DOUBLE, &share_gpsdata->fix.climb,
                          DBUS_TYPE_DOUBLE, &share_gpsdata->fix.epc,
                          DBUS_TYPE_STRING, &gpsd_devname, DBUS_TYPE_INVALID);

    // convert time as double back to timespec_t, potential loss of precision.
    DTOTS(&share_gpsdata->fix.time, fix_time);

    if (MODE_NO_FIX < share_gpsdata->fix.mode) {
        share_gpsdata->fix.status = STATUS_GPS;
    } else {
        share_gpsdata->fix.status = STATUS_UNK;
    }

    dbus_error_free(&error);

    PRIVATE(share_gpsdata)->handler(share_gpsdata);
    return DBUS_HANDLER_RESULT_HANDLED;
}

/*
 * Message dispatching function
 *
 */
static DBusHandlerResult signal_handler(DBusConnection * connection UNUSED,
                                        DBusMessage * message,
                                        void *user_data UNUSED)
{
    if (dbus_message_is_signal(message, "org.gpsd", "fix"))
        return handle_gps_fix(message);
    /*
     * ignore all other messages
     */

    return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;
}

int gps_dbus_open(struct gps_data_t *gpsdata)
{
    DBusError error;

    gpsdata->privdata = (void *)malloc(sizeof(struct privdata_t));
    if (NULL == gpsdata->privdata) {
        return -1;
    }

    dbus_error_init(&error);
    connection = dbus_bus_get(DBUS_BUS_SYSTEM, &error);
    if (dbus_error_is_set(&error)) {
        syslog(LOG_CRIT, "%s: %s", error.name, error.message);
        dbus_error_free(&error);
        return 3;
    }

    dbus_bus_add_match(connection, "type='signal'", &error);
    if (dbus_error_is_set(&error)) {
        syslog(LOG_CRIT, "unable to add match for signals %s: %s", error.name,
               error.message);
        dbus_error_free(&error);
        return 4;
    }

    if (!dbus_connection_add_filter
        (connection, (DBusHandleMessageFunction) signal_handler, NULL,
         NULL)) {
        syslog(LOG_CRIT, "unable to register filter with the connection");
        return 5;
    }

#ifndef USE_QT
    gpsdata->gps_fd = DBUS_PSEUDO_FD;
#else
    gpsdata->gps_fd = (void *)(intptr_t)DBUS_PSEUDO_FD;
#endif  // USE_QT
    share_gpsdata = gpsdata;
    return 0;
}

/* run a DBUS main loop with a specified handler
 *
 * timeout is in micro seconds
 *
 * Returns: -1 on timeout
 *          -2 on error or disconnect
 * FIXME: read error should return different than timeout
 */
int gps_dbus_mainloop(struct gps_data_t *gpsdata,
                       int timeout,
                       void (*hook)(struct gps_data_t *))
{
    struct timespec ts_from, ts_to;
    double d_timeout;

    d_timeout = (double)timeout / 1000000;  // timeout in seconds
    share_gpsdata = gpsdata;
    PRIVATE(share_gpsdata)->handler = (void (*)(struct gps_data_t *))hook;
    for (;;) {
        bool status;
        double diff;

        if (0 != clock_gettime(CLOCK_REALTIME, &ts_from)) {
            return -2;
        }

        status = dbus_connection_read_write_dispatch(connection,
                                                     (int)(timeout/1000));
        if (FALSE == status) {
            // lost connection
            break;
        }
        if (0 != clock_gettime(CLOCK_REALTIME, &ts_to)) {
            return -2;
        }
        diff = TS_SUB_D(&ts_to, &ts_from);
        if (d_timeout <= diff) {
            // timeout
            return -1;
        }
    }
    return -2;
}

#endif  // defined(DBUS_EXPORT_ENABLE)
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