feat: exp back-off for detached device polling

Author: zfields

src/ArduinoIoTCloudNotecard.cpp

@@ -42,9 +42,11 @@
  * CONSTANTS
  ******************************************************************************/
 
+static size_t const BACKOFF_BASE_MS = 60000;           // 1 minute
+static uint32_t const BACKOFF_MAX_MS = 3600000;        // 1 hour
 static size_t const CBOR_NOTE_MSG_MAX_SIZE = 255;
-static size_t const DEFAULT_READ_INTERVAL_MS = 1000;
-static size_t const FAILSAFE_READ_INTERVAL_MS = 10000;
+static size_t const DEFAULT_READ_INTERVAL_MS = 1000;   // 1 second
+static size_t const FAILSAFE_READ_INTERVAL_MS = 10000; // 10 seconds
 
 /******************************************************************************
  * LOCAL MODULE FUNCTIONS
@@ -71,6 +73,8 @@ ArduinoIoTCloudNotecard::ArduinoIoTCloudNotecard()
   ,_message_stream(std::bind(&ArduinoIoTCloudNotecard::sendMessage, this, std::placeholders::_1))
   ,_thing(&_message_stream)
   ,_device(&_message_stream)
+  ,_backoff_multiplier{1}
+  ,_last_failed_attach_request_ms{0}
   ,_notecard_last_read_ms{static_cast<uint32_t>(-DEFAULT_READ_INTERVAL_MS)}
   ,_notecard_read_interval_ms{DEFAULT_READ_INTERVAL_MS}
   ,_interrupt_pin{-1}
@@ -231,6 +235,18 @@ ArduinoIoTCloudNotecard::State ArduinoIoTCloudNotecard::handle_Connected()
   /* Poll Notecard for new messages */
   pollNotecard();
 
+  /* Respect back-off */
+  if (_last_failed_attach_request_ms) {
+    const uint32_t backoff_ms = (BACKOFF_BASE_MS * _backoff_multiplier);
+    if ((::millis() - _last_failed_attach_request_ms) < backoff_ms) {
+      return State::Connected;
+    } else {
+      DEBUG_DEBUG("ArduinoIoTCloudNotecard::%s back-off expired.", __FUNCTION__);
+      _backoff_multiplier <<= (BACKOFF_MAX_MS > backoff_ms);
+      _last_failed_attach_request_ms = 0;
+    }
+  }
+
   /* Call CloudDevice process to get configuration */
   _device.update();
 
@@ -397,16 +413,26 @@ void ArduinoIoTCloudNotecard::processCommand(const uint8_t *buf, size_t len)
         String new_thing_id = String(command.thingUpdateCmd.params.thing_id);
 
         if (!new_thing_id.length()) {
-          /* Send message to device state machine to inform we have received a null thing-id */
+          _last_failed_attach_request_ms = ::millis();
+          DEBUG_DEBUG("ArduinoIoTCloudNotecard::%s received null Thing ID (current back-off: %u minute%s).", __FUNCTION__, _backoff_multiplier, ((_backoff_multiplier == 1) ? "" : "s"));
           _thing_id = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx";
+
+          /* Send message to device state machine to inform we have received a null thing-id */
           Message message;
           message = { DeviceRegisteredCmdId };
           _device.handleMessage(&message);
         } else {
+          DEBUG_VERBOSE("ArduinoIoTCloudNotecard::%s resetting back-off variables", __FUNCTION__);
+          /* Reset back-off variables */
+          _backoff_multiplier = 1;
+          _last_failed_attach_request_ms = 0;
+
           if (_device.isAttached() && _thing_id != new_thing_id) {
+            DEBUG_DEBUG("ArduinoIoTCloudNotecard::%s detaching Thing ID: %s", __FUNCTION__, _thing_id.c_str());
             detachThing();
           }
           if (!_device.isAttached()) {
+            DEBUG_DEBUG("ArduinoIoTCloudNotecard::%s attaching Thing ID: %s", __FUNCTION__, new_thing_id.c_str());
             attachThing(new_thing_id);
           }
         }
@@ -441,10 +467,11 @@ void ArduinoIoTCloudNotecard::processCommand(const uint8_t *buf, size_t len)
         execCloudEventCallback(ArduinoIoTCloudEvent::SYNC);
 
         /*
-          * NOTE: in this current version properties are not properly integrated with the new paradigm of
-          * modeling the messages with C structs. The current CBOR library allocates an array in the heap
-          * thus we need to delete it after decoding it with the old CBORDecoder
-          */
+         * NOTE: In this current version properties are not properly integrated
+         * with the new paradigm of modeling the messages with C structs. The
+         * current CBOR library allocates an array in the heap thus we need to
+         * delete it after decoding it with the old CBORDecoder
+         */
         free(command.lastValuesUpdateCmd.params.last_values);
       }
       break;

src/ArduinoIoTCloudNotecard.h

@@ -86,6 +86,8 @@ class ArduinoIoTCloudNotecard : public ArduinoIoTCloudClass
     ArduinoCloudDevice _device;
 
     // Notecard member variables
+    uint32_t _backoff_multiplier;
+    uint32_t _last_failed_attach_request_ms;
     uint32_t _notecard_last_read_ms;
     uint32_t _notecard_read_interval_ms;
     int _interrupt_pin;