text: // Copyright (c) 2015 Cesanta Software Limited
  // All rights reserved
  
  #include "mongoose.h"
  
  struct device_settings {
    char setting1[100];
    char setting2[100];
  };
  
  static const char *s_http_port = "8000";
  static struct mg_serve_http_opts s_http_server_opts;
  static struct device_settings s_settings = { "value1", "value2" };
  
  static void handle_save(struct mg_connection *nc, struct http_message *hm) {
    // Get form variables and store settings values
    mg_get_http_var(&hm->body, "setting1", s_settings.setting1,
                    sizeof(s_settings.setting1));
    mg_get_http_var(&hm->body, "setting2", s_settings.setting2,
                    sizeof(s_settings.setting2));
  
    // Send response
    mg_printf(nc, "%s", "HTTP/1.1 302 OK\r\nLocation: /\r\n\r\n");
  }
  
  static void handle_get_cpu_usage(struct mg_connection *nc) {
    // Generate random value, as an example of changing CPU usage
    // Getting real CPU usage depends on the OS.
    int cpu_usage = (double) rand() / RAND_MAX * 100.0;
  
    // Use chunked encoding in order to avoid calculating Content-Length
    mg_printf(nc, "%s", "HTTP/1.1 200 OK\r\nTransfer-Encoding: chunked\r\n\r\n");
  
    // Output JSON object which holds CPU usage data
    mg_printf_http_chunk(nc, "{ \"result\": %d }", cpu_usage);
  
    // Send empty chunk, the end of response
    mg_send_http_chunk(nc, "", 0);
  }
  
  static void handle_ssi_call(struct mg_connection *nc, const char *param) {
    if (strcmp(param, "setting1") == 0) {
      mg_printf_html_escape(nc, "%s", s_settings.setting1);
    } else if (strcmp(param, "setting2") == 0) {
      mg_printf_html_escape(nc, "%s", s_settings.setting2);
    }
  }
  
  static void ev_handler(struct mg_connection *nc, int ev, void *ev_data) {
    struct http_message *hm = (struct http_message *) ev_data;
  
    switch (ev) {
      case MG_EV_HTTP_REQUEST:
        if (mg_vcmp(&hm->uri, "/save") == 0) {
          handle_save(nc, hm);
        } else if (mg_vcmp(&hm->uri, "/get_cpu_usage") == 0) {
          handle_get_cpu_usage(nc);
        } else {
          mg_serve_http(nc, hm, s_http_server_opts);  // Serve static content
        }
        break;
      case MG_EV_SSI_CALL:
        handle_ssi_call(nc, ev_data);
        break;
      default:
        break;
    }
  }
  
  static void push_data_to_all_websocket_connections(struct mg_mgr *m) {
    struct mg_connection *c;
    int memory_usage = (double) rand() / RAND_MAX * 100.0;
  
    for (c = mg_next(m, NULL); c != NULL; c = mg_next(m, c)) {
      if (c->flags & MG_F_IS_WEBSOCKET) {
        mg_printf_websocket_frame(c, WEBSOCKET_OP_TEXT, "%d", memory_usage);
      }
    }
  }
  
  int main(void) {
    struct mg_mgr mgr;
    struct mg_connection *nc;
    cs_stat_t st;
  
    mg_mgr_init(&mgr, NULL);
    nc = mg_bind(&mgr, s_http_port, ev_handler);
    if (nc == NULL) {
      fprintf(stderr, "Cannot bind to %s\n", s_http_port);
      exit(1);
    }
  
    // Set up HTTP server parameters
    mg_set_protocol_http_websocket(nc);
    s_http_server_opts.document_root = "web_root";  // Set up web root directory
  
    if (mg_stat(s_http_server_opts.document_root, &st) != 0) {
      fprintf(stderr, "%s", "Cannot find web_root directory, exiting\n");
      exit(1);
    }
  
    printf("Starting web server on port %s\n", s_http_port);
    for (;;) {
      static time_t last_time;
      time_t now = time(NULL);
      mg_mgr_poll(&mgr, 1000);
      if (now - last_time > 0) {
        push_data_to_all_websocket_connections(&mgr);
        last_time = now;
      }
    }
    mg_mgr_free(&mgr);
  
    return 0;
  }
  