Enchanted Objects Design Challenge - Hans meets "Injector"

7 May 2015

Hans was struggling with installing requests[security] the compile issues seemed to keep coming back like a hydra regrowing its heads.

To take a break he went to visit his friend Albert. Albert invited Hans in and disappeared into the kitchen to make some tea. "Make yourself at home" called Albert from the other room. Hans sat down on the sofa next to a grey cat. It looked friendly so Hans went to pet it. As soon as he moved the cat stretched out its paw and out shot the claws. Hans recoiled narrowly avoiding a serious injury. "Ah, I see you've met, Injector" said Albert as he came back in with a tray of tea and biscuits. Albert grabbed a throw from the back of the sofa and deftly wrapped the cat in it. The cat peered up at Albert and purred contently.

Photo Credit: "Sam cat" by Alan Barnet

When he returned home, Hans decided to work on the python code and roughed out the following high level design.

Steps
Get Location
Generate URL
Check URL
Parse Response
Map Weather Codes

He had considered using the users IP address to identify location but as his Google search page kept sending him to Google.pl and Microsoft thought his office was in the USA he was not so sure on this approach. Rather, he decided to read the value from a file and hopefully would later have some time to change the UI to allow the user to enter the location. If the users were supplying the location he'd need to ensure his code was protected from parameter injection by correctly wrapping and encoding the provided parameters.

This is the resulting python code.

import requests, json, sys, urllib, urlparse


def get_location():
  with open('/etc/WeatherAPI.conf', 'r') as f:
  location_name = f.readline()
  f.close()
  return location_name


def build_url(location):
  url = "https://query.yahooapis.com/v1/public/yql"
  q = "select item.condition from weather.forecast where woeid in (select woeid from geo.places(1) where text = '" + urllib.quote(location) + "') and u='c'"
  params = {'q': q, 'format': 'json', 'env': 'store://datatables.org/alltableswithkeys'}

  url_parts = list(urlparse.urlparse(url))
  query = dict(urlparse.parse_qsl(url_parts[4]))
  query.update(params)

  url_parts[4] = urllib.urlencode(query)

  return urlparse.urlunparse(url_parts)


def call_api(url):
  r = requests.get(url, timeout=(10, 60)) # Connection timeout and read timeout
  if r.status_code != 200:
  raise RuntimeError('API Call Failed(%s)' % r.status_code)
  return r


def map_code(code):
  # Map condition codes to expected precipitation
  # https://developer.yahoo.com/weather/documentation.html
  # 1 = very sunny, 3 = changeable, 5 = very rainy
  codes = {'0': {'n': 'tornado', 'p': '3'},
  '1': {'n': 'tropical storm', 'p': '5'},
  '2': {'n': 'hurricane', 'p': '5'},
  '3': {'n': 'severe thunderstorms', 'p': '5'},
  '4': {'n': 'thunderstorms', 'p': '5'},
  '5': {'n': 'mixed rain and snow', 'p': '5'},
  '6': {'n': 'mixed rain and sleet', 'p': '5'},
  '7': {'n': 'mixed snow and sleet', 'p': '5'},
  '8': {'n': 'freezing drizzle', 'p': '5'},
  '9': {'n': 'drizzle', 'p': '4'},
  '10': {'n': 'freezing rain', 'p': '5'},
  '11': {'n': 'showers', 'p': '4'},
  '12': {'n': 'showers', 'p': '4'},
  '13': {'n': 'snow flurries', 'p': '4'},
  '14': {'n': 'light snow showers', 'p': '4'},
  '15': {'n': 'blowing snow', 'p': '3'},
  '16': {'n': 'snow', 'p': '4'},
  '17': {'n': 'hail', 'p': '4'},
  '18': {'n': 'sleet', 'p': '4'},
  '19': {'n': 'dust', 'p': '3'},
  '20': {'n': 'foggy', 'p': '4'},
  '21': {'n': 'haze', 'p': '3'},
  '22': {'n': 'smoky', 'p': '3'},
  '23': {'n': 'blustery', 'p': '3'},
  '24': {'n': 'windy', 'p': '3'},
  '25': {'n': 'cold', 'p': '3'},
  '26': {'n': 'cloudy', 'p': '3'},
  '27': {'n': 'mostly cloudy (night)', 'p': '3'},
  '28': {'n': 'mostly cloudy (day)', 'p': '3'},
  '29': {'n': 'partly cloudy (night)', 'p': '3'},
  '30': {'n': 'partly cloudy (day)', 'p': '3'},
  '31': {'n': 'clear (night)', 'p': '1'},
  '32': {'n': 'sunny', 'p': '1'},
  '33': {'n': 'fair (night)', 'p': '2'},
  '34': {'n': 'fair (day)', 'p': '2'},
  '35': {'n': 'mixed rain and hail', 'p': '4'},
  '36': {'n': 'hot', 'p': '1'},
  '37': {'n': 'isolated thunderstorms', 'p': '4'},
  '38': {'n': 'scattered thunderstorms', 'p': '4'},
  '39': {'n': 'scattered thunderstorms', 'p': '4'},
  '40': {'n': 'scattered showers', 'p': '4'},
  '41': {'n': 'heavy snow', 'p': '5'},
  '42': {'n': 'scattered snow showers', 'p': '4'},
  '43': {'n': 'heavy snow', 'p': '5'},
  '44': {'n': 'partly cloudy', 'p': '2'},
  '45': {'n': 'thundershowers', 'p': '5'},
  '46': {'n': 'snow showers', 'p': '5'},
  '47': {'n': 'isolated thundershowers', 'p': '4'}}
  state = codes.get(code)
  if not state:
  raise RuntimeError('Unknown weather code returned')
  return state['p']


def parse_weather(json):
  text = json['query']['results']['channel']['item']['condition']['text']
  code = map_code(json['query']['results']['channel']['item']['condition']['code'])
  temp = json['query']['results']['channel']['item']['condition']['temp']
  return {'text': text, 'code': code, 'temp': float(temp)}


def main():
  try:
  loc = get_location()
  weather_url = build_url(loc)
  r = call_api(weather_url)
  j = json.loads(r.content)
  weather = parse_weather(j)

  print 'OK!,%s,%s,%4.2f' % (weather['text'], weather['code'], weather['temp'])

  return 0

  except Exception, err:
  print 'Err,%s,0,0.0' % str(err).replace(",", " ")
  return 1


if __name__ == '__main__':
  sys.exit(main())

For the test location of Chicago,IL the report came out as

OK!,Fair,2,16.00

Changing the URL to one with a known invalid security certificate returns the following:

Err,[Errno bad handshake] [('SSL routines'  'ssl3_get_server_certificate'  'certificate verify failed')],0,0.0

Back into Arduino

So the next job on the coding is on the microcontroller side to parse this string returned from the API and move the servo and light the lights accordingly. The issue with the requests[security] install will also need to be resolved some how.

Next: Enchanted Objects Design Challenge - Farmer Hogg and the Lockity Gowan