Add TTL to Redis token bucket implementation (#1757)

Author: pilcrowonpaper

pages/rate-limit/token-bucket.md

@@ -73,27 +73,36 @@ local cost                  = tonumber(ARGV[3])
 local now                   = tonumber(ARGV[4]) -- Current unix time in seconds
 
 local fields = redis.call("HGETALL", key)
+
 if #fields == 0 then
-    redis.call("HSET", key, "count", max - cost, "refilled_at", now)
-    return {1}
+	local expiresInSeconds = cost * refillIntervalSeconds
+	redis.call("HSET", key, "count", max - cost, "refilled_at", now)
+	redis.call("EXPIRE", key, expiresInSeconds)
+	return {1}
 end
+
 local count = 0
 local refilledAt = 0
 for i = 1, #fields, 2 do
 	if fields[i] == "count" then
-        count = tonumber(fields[i+1])
-    elseif fields[i] == "refilled_at" then
-        refilledAt = tonumber(fields[i+1])
-    end
+		count = tonumber(fields[i+1])
+	elseif fields[i] == "refilled_at" then
+		refilledAt = tonumber(fields[i+1])
+	end
 end
+
 local refill = math.floor((now - refilledAt) / refillIntervalSeconds)
 count = math.min(count + refill, max)
 refilledAt = refilledAt + refill * refillIntervalSeconds
+
 if count < cost then
-    return {0}
+	return {0}
 end
+
 count = count - cost
+local expiresInSeconds = (max - count) * refillIntervalSeconds
 redis.call("HSET", key, "count", count, "refilled_at", now)
+redis.call("EXPIRE", key, expiresInSeconds)
 return {1}
 ```