Created endpoint to get the device pairing code

api/public/endpoints/device_code.py

@@ -0,0 +1,53 @@
+import json
+import hashlib
+import random
+import uuid
+
+from selene.api import SeleneEndpoint
+from selene.util.selene_cache import SeleneCache
+
+
+class DeviceCodeEndpoint(SeleneEndpoint):
+    """Endpoint to get a pairing code"""
+
+    # We need to do that to avoid ambiguous characters, like 0 and O, that is even harder to distinguish
+    # in the display of the mark 1
+    ALLOWED_CHARACTERS = "ACEFHJKLMNPRTUVWXY3479"
+
+    def __init__(self):
+        super(DeviceCodeEndpoint, self).__init__()
+        self.device_pairing_time = 86400
+        self.cache: SeleneCache = self.config.get('SELENE_CACHE')
+        self.sha512 = hashlib.sha512()
+
+    def get(self):
+        # The pairing process happens in two steps, the step where we get the pairing code and
+        # the step to activate the device. The state parameter is used to make sure that the device that is
+        # trying to be activate is the device which started the previous step
+        state = self.request.args['state']
+        return self._create(state)
+
+    def _create(self, state):
+        self.sha512.update(bytes(str(uuid.uuid4()), 'utf-8'))
+        token = self.sha512.hexdigest()
+        code = self._pairing_code()
+        pairing = json.dumps({'code': code,
+                              'state': state,
+                              'token': token,
+                              'expiration': self.device_pairing_time})
+        # This is to deal with the case where we generate a pairing code that already exists in the
+        # cache, meaning another device is trying to pairing using the same code. In this case, we should
+        # call the method again to get another random pairing code
+        if self.cache.set_if_not_exists_with_expiration(self._code_key(code),
+                                                        value=pairing,
+                                                        expiration=self.device_pairing_time):
+            return code
+        else:
+            return self._create(state)
+
+    @staticmethod
+    def _code_key(code):
+        return 'pairing.code:{}'.format(code)
+
+    def _pairing_code(self):
+        return ''.join(random.choice(self.ALLOWED_CHARACTERS) for _ in range(6))

shared/Pipfile

@@ -10,6 +10,7 @@ psycopg2-binary = "*"
 passlib = "*"
 pyhamcrest = "*"
 schematics = "*"
+redis = "*"
 
 [dev-packages]
 

shared/Pipfile.lock

@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "63164ec5172150b56a6a3930e1eb1bfa195837d6dbc019864a1b5475cdfdf590"
+            "sha256": "c0c1a9ec56002f00c9a50fc67aba1b0463d05323813944a244860fd69f49b75c"
         },
         "pipfile-spec": 6,
         "requires": {
@@ -111,6 +111,14 @@
             "index": "pypi",
             "version": "==1.7.1"
         },
+        "redis": {
+            "hashes": [
+                "sha256:724932360d48e5407e8f82e405ab3650a36ed02c7e460d1e6fddf0f038422b54",
+                "sha256:9b19425a38fd074eb5795ff2b0d9a55b46a44f91f5347995f27e3ad257a7d775"
+            ],
+            "index": "pypi",
+            "version": "==3.2.0"
+        },
         "requests": {
             "hashes": [
                 "sha256:502a824f31acdacb3a35b6690b5fbf0bc41d63a24a45c4004352b0242707598e",

shared/selene/util/selene_cache.py

@@ -0,0 +1,16 @@
+import os
+
+from redis import Redis
+
+
+class SeleneCache(object):
+
+    def __init__(self):
+        # should the variables host and port be in the config class?
+        redis_host = os.environ['REDIS_HOST']
+        redis_port = int(os.environ['REDIS_PORT'])
+        self.redis = Redis(host=redis_host, port=redis_port)
+
+    def set_if_not_exists_with_expiration(self, key, value, expiration):
+        """Sets a key only if it doesn't exist and using a given expiration time"""
+        return self.redis.set(name=key, value=value, ex=expiration, nx=True)

shared/setup.py

@@ -16,6 +16,8 @@ setup(
         'pyhamcrest',
         'pyjwt',
         'psycopg2-binary',
-        'schematics'
+        'schematics',
+        'validator-collection',
+        'redis'
     ]
 )