Don't send MQTT throttle emails more than once per day.

app/models/device.rb

@@ -201,8 +201,13 @@ class Device < ApplicationRecord
       "see https://developer.farm.bot/docs/connectivity-issues"
   def self.connection_warning(username)
     device_id = username.split("_").last.to_i || 0
-    self
-      .find(device_id)
-      .tell(TOO_MANY_CONNECTIONS, ["fatal_email"]) if self.exists?(device_id)
+    device = self.find_by(id: device_id)
+    return unless device
+
+    last_sent_at = device.mqtt_rate_limit_email_sent_at || 4.years.ago
+    if last_sent_at < 1.day.ago
+      device.update_attributes!(mqtt_rate_limit_email_sent_at: Time.now)
+      device.tell(TOO_MANY_CONNECTIONS, ["fatal_email"])
+    end
   end
 end

db/migrate/20190715214412_add_mqtt_throttle_email_sent_at_to_device.rb

@@ -0,0 +1,7 @@
+class AddMqttThrottleEmailSentAtToDevice < ActiveRecord::Migration[5.2]
+  def change
+    add_column :devices,
+               :mqtt_rate_limit_email_sent_at,
+               :datetime
+  end
+end

db/structure.sql

@@ -206,7 +206,8 @@ CREATE TABLE public.devices (
     mounted_tool_id bigint,
     created_at timestamp without time zone,
     updated_at timestamp without time zone,
-    serial_number character varying(32)
+    serial_number character varying(32),
+    mqtt_rate_limit_email_sent_at timestamp without time zone
 );
 
 
@@ -3019,6 +3020,7 @@ INSERT INTO "schema_migrations" (version) VALUES
 ('20190621160042'),
 ('20190621202204'),
 ('20190701155706'),
-('20190709194037');
+('20190709194037'),
+('20190715214412');
 
 

spec/models/device_spec.rb

@@ -102,4 +102,11 @@ describe Device do
     expect(results).to_not include(🚑)
     expect(results).to_not include(🍞)
   end
+
+  it "throttled emails about MQTT rate limiting" do
+    device.update_attributes!(mqtt_rate_limit_email_sent_at: 2.days.ago)
+    Device.connection_warning("device_#{device.id.to_s}")
+    time = device.reload.mqtt_rate_limit_email_sent_at
+    expect(time).to be > 1.minute.ago
+  end
 end