Update time_bucketed.py

ratelimit/time_bucketed.py

@@ -1,12 +1,22 @@
+import time
+import random
 from datetime import timedelta
 from redis import Redis
 
 
 def request_is_limited(r: Redis, key: str, limit: int, period: timedelta):
-    if r.setnx(key, limit):
-        r.expire(key, int(period.total_seconds()))
-    bucket_val = r.get(key)
-    if bucket_val and int(bucket_val) > 0:
-        r.decrby(key, 1)
-        return False
+    #TTL returns -2 if the key does not exist and -1 if the key has no TTL.
+    #Reference: https://redis.io/commands/ttl
+    if int(r.ttl(key)) < 0:
+        #Creates a key and adds an expire atomically.
+        r.setex(key, int(period.total_seconds()), limit)
+    if r.exists(key):
+        #DECR creates a key with the value -1 if the key does not yet exist.
+        #Checks if this happend because there is a race condition.
+        #Reference: https://redis.io/commands/decr
+        if int(r.decr(key)) >= 0:
+            return False
+    #Prevents an unnecessarily high number of database accesses while the
+    #request is limited.
+    time.sleep(random.random()/limit)
     return True