Add endpoint to get device state

CHANGELOG.md

@@ -1,3 +1,4 @@
+* Add endpoint to get device state [Pablo]
 * Check for valid strings or ints in all config values [Pablo]
 * Remove quotes in OS version [Pablo]
 

docs/API.md

@@ -405,3 +405,38 @@ $ curl -X POST --header "Content-Type:application/json" \
 	--data '{"deviceId": <deviceId>, "appId": <appId>}' \
 	"https://api.resin.io/supervisor/v1/regenerate-api-key"
 ```
+
+<hr>
+
+### GET /v1/device
+
+Introduced in supervisor v1.6.
+Returns the current device state, as reported to the Resin API.
+The state is a JSON object that contains some or all of the following:
+* `api_port`: Port on which the supervisor is listening.
+* `ip_address`: Space-separated list of IP addresses of the device.
+* `status`: Status of the device regarding the app, as a string, i.e. "Stopping", "Starting", "Downloading", "Installing", "Idle".
+* `download_progress`: Amount of the application image that has been downloaded, expressed as a percentage.
+* `os_version`: Version of the host OS running on the device.
+* `supervisor_version`: Version of the supervisor running on the device.
+
+Other attributes may be added in the future, and some may be missing or null if they haven't been set yet.
+
+#### Examples:
+From the app on the device:
+```bash
+$ curl -X GET --header "Content-Type:application/json" \
+	"$RESIN_SUPERVISOR_ADDRESS/v1/device?apikey=$RESIN_SUPERVISOR_API_KEY"
+```
+Response:
+```json
+{"api_port":48484,"ip_address":"192.168.0.114 10.42.0.3","status":"Downloading","download_progress":84,"os_version":"Resin OS 1.0.4 (fido)","supervisor_version":"1.6.0"}
+```
+
+Remotely via the API proxy:
+```bash
+$ curl -X POST --header "Content-Type:application/json" \
+	--header "Authorization: Bearer <auth token>" \
+	--data '{"deviceId": <deviceId>, "appId": <appId>, "method": "GET"}' \
+	"https://api.resin.io/supervisor/v1/device"
+```

src/api.coffee

@@ -136,4 +136,7 @@ module.exports = (application) ->
 		.catch (err) ->
 			res.status(503).send(err?.message or err or 'Unknown error')
 
+	api.get '/v1/device', (req, res) ->
+		res.json(device.getState())
+
 	return api

src/device.coffee

@@ -128,12 +128,16 @@ exports.getDeviceType = do ->
 					throw new Error('Device type not specified in config file')
 				return configFromFile.deviceType
 
+targetState = {}
+exports.getState = ->
+	fieldsToOmit = ['api_secret', 'logs_channel', 'provisioning_progress', 'provisioning_state']
+	return _.omit(targetState, fieldsToOmit)
+
 # Calling this function updates the local device state, which is then used to synchronise
 # the remote device state, repeating any failed updates until successfully synchronised.
 # This function will also optimise updates by merging multiple updates and only sending the latest state.
 exports.updateState = do ->
 	applyPromise = Promise.resolve()
-	targetState = {}
 	actualState = {}
 
 	getStateDiff = ->