mongoose/tutorials/device-dashboard/mongoose_dashboard.c

// SPDX-FileCopyrightText: 2026 Cesanta Software Limited
// SPDX-License-Identifier: GPL-2.0-only or commercial

#include "mongoose.h"

#if MG_ARCH == MG_ARCH_UNIX || MG_ARCH == MG_ARCH_WIN32
#define HTTP_ADDR "http://0.0.0.0:8000"
#else
#define HTTP_ADDR "http://0.0.0.0:80"
#endif

// Control panel
static bool s_led1, s_led2, s_led3;

static struct mg_field fields_leds[] = {
    {"led1", MG_VAL_BOOL, &s_led1, sizeof(s_led1)},
    {"led2", MG_VAL_BOOL, &s_led2, sizeof(s_led2)},
    {"led3", MG_VAL_BOOL, &s_led3, sizeof(s_led3)},
    {NULL, 0, NULL, 0},
};

static void sync_leds(bool is_write) {
  if (is_write) {
    // gpio_write(LED1_PIN, s_led1);
    // gpio_write(LED2_PIN, s_led2);
    // gpio_write(LED3_PIN, s_led3);
  } else {
    // s_led1 = gpio_read(LED1_PIN);
    // s_led2 = gpio_read(LED2_PIN);
    // s_led3 = gpio_read(LED3_PIN);
  }
}

// Read-only device Metrics
static int s_ram = 32, s_cpu = 7, s_humidity = 59;
static double s_temperature = 24.8;

static struct mg_field fields_metrics[] = {
    {"ram", MG_VAL_INT, &s_ram, sizeof(s_ram)},
    {"cpu", MG_VAL_INT, &s_cpu, sizeof(s_cpu)},
    {"humidity", MG_VAL_INT, &s_humidity, sizeof(s_humidity)},
    {"temperature", MG_VAL_DBL, &s_temperature, sizeof(s_temperature)},
    {NULL, 0, NULL, 0},
};

static void sync_metrics(bool is_write) {
  if (is_write) return;
  s_ram = 25 + (rand() % 16);  // Sumulate metric change
  s_cpu = 7 + (rand() % 21);
  s_temperature = 14.8 + ((double) rand() / RAND_MAX) * 20.0;
}

// Read-write device settings
static double s_volume = 17.2;
static int s_log_level = MG_LL_DEBUG;
static char s_name[20] = "Dublin";

static struct mg_field fields_settings[] = {
    {"volume", MG_VAL_DBL, &s_volume, sizeof(s_volume)},
    {"name", MG_VAL_STR, &s_name, sizeof(s_name)},
    {"log_level", MG_VAL_INT, &s_log_level, sizeof(s_log_level)},
    {NULL, 0, NULL, 0},
};

static void sync_settings(bool is_write) {
  if (is_write) {
    mg_log_level = s_log_level;
  } else {
    s_log_level = mg_log_level;
  }
}

#define NUM_POINTS 7  // How many data points to send

struct point {
  uint16_t x;   // X coordinate of the data point, usually this is time
  uint16_t y1;  // We can plot multiple values per graph,
  uint16_t y2;  // let's plot 2 values: y1 and y2.
};

// Serialise chart data into a string: [[x,y1,y2],[x,y1,y2],...]
// One uint16_t takes 5 character max, so one entry is 19 bytes max.
// We could be more efficient by storing hex or base64-encoded data, but
// let's keep it simple. However if we do, update data parsing logic in
// the web_root/main.js
#define POINT_SIZE 19
static char s_chart1_data[NUM_POINTS * POINT_SIZE + 2 + 1];

static struct mg_field fields_chart1[] = {
    {"data", MG_VAL_STR, s_chart1_data, sizeof(s_chart1_data)},
    {NULL, 0, NULL, 0},
};

// Randomly generate graph points and serialise them into a string
void sync_chart1(bool is_write) {
  size_t i, len = 0;
  if (is_write) return;
  len += mg_snprintf(s_chart1_data + len, sizeof(s_chart1_data) - len, "[");
  for (i = 0; i < NUM_POINTS; i++) {
    struct point p;
    p.x = (uint16_t) i;
    p.y1 = 85 - (uint16_t) ((49 * i) / NUM_POINTS) + (rand() % 9);
    p.y2 = 20 + (uint16_t) ((69 * i) / NUM_POINTS) + (rand() % 5);
    len += mg_snprintf(s_chart1_data + len, sizeof(s_chart1_data) - len,
                       "%s[%hu,%hu,%hu]", i > 0 ? "," : "", p.x, p.y1, p.y2);
  }
  len += mg_snprintf(s_chart1_data + len, sizeof(s_chart1_data) - len, "]");
}

static int s_num_log_files = 0;
static int s_log_file_index = 0;
static char s_log_file_name[100];
static struct mg_field fields_log_files[] = {
    {"size", MG_VAL_INT, &s_num_log_files, sizeof(s_num_log_files)},
    {"index", MG_VAL_INT, &s_log_file_index, sizeof(s_log_file_index)},
    {"name", MG_VAL_STR, &s_log_file_name, sizeof(s_log_file_name)},
    {NULL, 0, NULL, 0},
};
static void sync_log_files(bool is_write) {
  if (is_write) return;
  mg_log_level = s_log_level;
  s_log_level = mg_log_level;
}

static struct mg_field_set field_sets[] = {
    {"leds", fields_leds, sync_leds, 0, 0},
    {"metrics", fields_metrics, sync_metrics, 0, 0},
    {"settings", fields_settings, sync_settings, 0, 0},
    {"chart1", fields_chart1, sync_chart1, 0, 0},
    {"log_files", fields_log_files, sync_log_files, 0, 0},
    {0, 0, 0, 0, 0},
};
static struct mg_dash s_dashboard = {field_sets, NULL};

static void log_ev_handler(struct mg_connection *c, int ev, void *ev_data) {
  if (ev == MG_EV_HTTP_MSG) {
    mg_http_serve_file(c, ev_data, "Makefile", NULL);
  }
}

void mg_dash_init(struct mg_mgr *mgr) {
  MG_DASH_REGISTER_CUSTOM_HANDLER(&s_dashboard, "/logs/#", log_ev_handler);
  mg_http_listen(mgr, HTTP_ADDR, mg_dash_ev_handler, &s_dashboard);
}

void mg_dash_poll(struct mg_mgr *mgr) {
  // Send metrics change periodically
  static uint64_t timer = 0;
  if (mg_timer_expired(&timer, 30000, mg_now())) {
    mg_dash_send_change(mgr, &s_dashboard, "metrics");
  }
}