MqttAgent: Ignore a retained message previously received.

This should fix the problem where MqttAgent creates an event from the
same last message every time it runs if it is retained by the server.

app/models/agents/mqtt_agent.rb

@@ -115,15 +115,26 @@ module Agents
 
 
     def check
+      last_message = memory['last_message']
+
       mqtt_client.connect do |c|
         begin
           Timeout.timeout((interpolated['max_read_time'].presence || 15).to_i) {
-            c.get(interpolated['topic']) do |topic, message|
+            c.get_packet(interpolated['topic']) do |packet|
+              topic, payload = message = [packet.topic, packet.payload]
 
-              # A lot of services generate JSON. Try that first
-              payload = JSON.parse(message) rescue message
+              # Ignore a message if it is previously received
+              next if (packet.retain || packet.duplicate) && message == last_message
 
-              create_event :payload => {
+              last_message = message
+
+              # A lot of services generate JSON, so try that.
+              begin
+                payload = JSON.parse(payload)
+              rescue
+              end
+
+              create_event payload: {
                 'topic' => topic,
                 'message' => payload,
                 'time' => Time.now.to_i
@@ -133,6 +144,10 @@ module Agents
         rescue Timeout::Error
         end
       end
+
+      # Remember the last original (non-retain, non-duplicate) message
+      self.memory['last_message'] = last_message
+      save!
     end
 
   end

spec/models/agents/mqtt_agent_spec.rb

@@ -8,7 +8,6 @@ describe Agents::MqttAgent do
     @error_log = StringIO.new
 
     @server = MQTT::FakeServer.new(41234, '127.0.0.1')
-    @server.just_one = true
     @server.logger = Logger.new(@error_log)
     @server.logger.level = Logger::DEBUG
     @server.start
@@ -34,7 +33,14 @@ describe Agents::MqttAgent do
   end
 
   describe "#check" do
-    it "should check that initial run creates an event" do
+    it "should create events in the initial run" do
+      expect { @checker.check }.to change { Event.count }.by(2)
+    end
+
+    it "should ignore retained messages that are previously received" do
+      expect { @checker.check }.to change { Event.count }.by(2)
+      expect { @checker.check }.to change { Event.count }.by(1)
+      expect { @checker.check }.to change { Event.count }.by(1)
       expect { @checker.check }.to change { Event.count }.by(2)
     end
   end

spec/support/fake_mqtt_server.rb

@@ -52,7 +52,9 @@ class MQTT::FakeServer
     @port = @socket.addr[1]
     @thread ||= Thread.new do
       logger.info "Started a fake MQTT server on #{@address}:#{@port}"
+      @times = 0
       loop do
+        @times += 1
         # Wait for a client to connect
         client = @socket.accept
         @pings_received = 0
@@ -103,16 +105,33 @@ class MQTT::FakeServer
             :granted_qos => 0
           )
           topic = packet.topics[0][0]
-          client.write MQTT::Packet::Publish.new(
-            :topic => topic,
-            :payload => "hello #{topic}",
-            :retain => true
-          )
-          client.write MQTT::Packet::Publish.new(
-            :topic => topic,
-            :payload => "did you know about #{topic}",
-            :retain => true
-          )
+          case @times
+          when 1, ->x { x >= 3 }
+            # Deliver retained messages
+            client.write MQTT::Packet::Publish.new(
+              :topic => topic,
+              :payload => "did you know about #{topic}",
+              :retain => true
+            )
+            client.write MQTT::Packet::Publish.new(
+              :topic => topic,
+              :payload => "hello #{topic}",
+              :retain => true
+            )
+          when 2
+            # Deliver a still retained message
+            client.write MQTT::Packet::Publish.new(
+              :topic => topic,
+              :payload => "hello #{topic}",
+              :retain => true
+            )
+            # Deliver a fresh message
+            client.write MQTT::Packet::Publish.new(
+              :topic => topic,
+              :payload => "did you know about #{topic}",
+              :retain => false
+            )
+          end
 
         when MQTT::Packet::Pingreq
           client.write MQTT::Packet::Pingresp.new
@@ -134,4 +153,4 @@ if __FILE__ == $0
   server = MQTT::FakeServer.new(MQTT::DEFAULT_PORT)
   server.logger.level = Logger::DEBUG
   server.run
-end
+end