Add a new periodic temperature resource.

The temperature sensor is sampled once per second.
If observed, temperature readings are reported on change or every
Max-Age interval (default: 60s).

examples/er-rest-example/resources/res-temperature.c

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+/*
+ * Copyright (c) 2013, Institute for Pervasive Computing, ETH Zurich
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the Institute nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * This file is part of the Contiki operating system.
+ */
+
+/**
+ * \file
+ *      Example of an observable "on-change" temperature resource
+ * \author
+ *      Matthias Kovatsch <kovatsch@inf.ethz.ch>
+ * \author
+ *      Cristiano De Alti <cristiano_dealti@hotmail.com>
+ */
+
+#include "contiki.h"
+
+#if PLATFORM_HAS_TEMPERATURE
+
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include "rest-engine.h"
+#include "dev/temperature-sensor.h"
+
+static void res_get_handler(void *request, void *response, uint8_t *buffer, uint16_t preferred_size, int32_t *offset);
+static void res_periodic_handler(void);
+
+#define MAX_AGE      60
+#define INTERVAL_MIN 5
+#define INTERVAL_MAX (MAX_AGE - 1)
+#define CHANGE       1 
+
+static int32_t interval_counter = INTERVAL_MIN;
+static int temperature_old = INT_MIN;
+
+PERIODIC_RESOURCE(res_temperature,
+         "title=\"Temperature\";rt=\"Temperature\";obs",
+         res_get_handler,
+         NULL,
+         NULL,
+         NULL,
+         CLOCK_SECOND,
+         res_periodic_handler);
+
+static void
+res_get_handler(void *request, void *response, uint8_t *buffer, uint16_t preferred_size, int32_t *offset)
+{
+  /*
+   * For minimal complexity, request query and options should be ignored for GET on observable resources.
+   * Otherwise the requests must be stored with the observer list and passed by REST.notify_subscribers().
+   * This would be a TODO in the corresponding files in contiki/apps/erbium/!
+   */
+
+  int temperature = temperature_sensor.value(0);
+
+  unsigned int accept = -1;
+  REST.get_header_accept(request, &accept);
+
+  if(accept == -1 || accept == REST.type.TEXT_PLAIN) {
+    REST.set_header_content_type(response, REST.type.TEXT_PLAIN);
+    snprintf((char *)buffer, REST_MAX_CHUNK_SIZE, "%d", temperature);
+
+    REST.set_response_payload(response, (uint8_t *)buffer, strlen((char *)buffer));
+  } else if(accept == REST.type.APPLICATION_JSON) {
+    REST.set_header_content_type(response, REST.type.APPLICATION_JSON);
+    snprintf((char *)buffer, REST_MAX_CHUNK_SIZE, "{'temperature':%d}", temperature);
+
+    REST.set_response_payload(response, buffer, strlen((char *)buffer));
+  } else {
+    REST.set_response_status(response, REST.status.NOT_ACCEPTABLE);
+    const char *msg = "Supporting content-types text/plain and application/json";
+    REST.set_response_payload(response, msg, strlen(msg));
+  }
+
+  REST.set_header_max_age(response, MAX_AGE);
+
+  /* The REST.subscription_handler() will be called for observable resources by the REST framework. */
+}
+
+/*
+ * Additionally, a handler function named [resource name]_handler must be implemented for each PERIODIC_RESOURCE.
+ * It will be called by the REST manager process with the defined period.
+ */
+static void
+res_periodic_handler()
+{
+  int temperature = temperature_sensor.value(0);
+
+  ++interval_counter;
+
+  if((abs(temperature - temperature_old) >= CHANGE && interval_counter >= INTERVAL_MIN) || 
+     interval_counter >= INTERVAL_MAX) {
+     interval_counter = 0;
+     temperature_old = temperature;
+    /* Notify the registered observers which will trigger the res_get_handler to create the response. */
+    REST.notify_subscribers(&res_temperature);
+  }
+}
+#endif /* PLATFORM_HAS_TEMPERATURE */