In-memory reaper. TtlSet needs tests.

lib/units/device/index.js

@@ -16,6 +16,7 @@ module.exports = function(options) {
       var log = logger.createLogger('device')
       log.info('Preparing device')
       return syrup.serial()
+        .dependency(require('./plugins/heartbeat'))
         .dependency(require('./plugins/solo'))
         .dependency(require('./plugins/screen/stream'))
         .dependency(require('./plugins/screen/capture'))
@@ -38,7 +39,7 @@ module.exports = function(options) {
         .dependency(require('./plugins/ringer'))
         .dependency(require('./plugins/wifi'))
         .dependency(require('./plugins/sd'))
-        .define(function(options, solo) {
+        .define(function(options, heartbeat, solo) {
           if (process.send) {
             // Only if we have a parent process
             process.send('ready')

lib/units/device/plugins/heartbeat.js

@@ -0,0 +1,24 @@
+var syrup = require('stf-syrup')
+
+var lifecycle = require('../../../util/lifecycle')
+var wire = require('../../../wire')
+var wireutil = require('../../../wire/util')
+
+module.exports = syrup.serial()
+  .dependency(require('../support/push'))
+  .define(function(options, push) {
+    function beat() {
+      push.send([
+        wireutil.global
+      , wireutil.envelope(new wire.DeviceHeartbeatMessage(
+          options.serial
+        ))
+      ])
+    }
+
+    var timer = setInterval(beat, options.heartbeatInterval)
+
+    lifecycle.observe(function() {
+      clearInterval(timer)
+    })
+  })