preliminary sliding window log implementation

Author: shalarewicz

src/rateLimiters/slidingWindowLog.ts

@@ -1,5 +1,5 @@
 import Redis from 'ioredis';
-import { RateLimiter, RateLimiterResponse } from '../@types/rateLimit';
+import { RateLimiter, RateLimiterResponse, RedisBucket, RedisLog } from '../@types/rateLimit';
 
 /**
  * The SlidingWindowLog instance of a RateLimiter limits requests based on a unique user ID.
@@ -33,7 +33,40 @@ class SlidingWindowLog implements RateLimiter {
         this.capacity = capacity;
         this.client = client;
         if (windowSize <= 0 || capacity <= 0)
-            throw SyntaxError('SlidingWindowLog windowSize and capacity must be positive');
+            throw SyntaxError('SlidingWindowLog window size and capacity must be positive');
+
+        // TODO: Define lua script for server side computation
+        // while x.timestamp + window_size < timestamp lpop
+        // //https://stackoverflow.com/questions/35677682/filtering-deleting-items-from-a-redis-set
+        this.client.defineCommand('popWindow', {
+            // 2 value timestamp and complexity of this request
+            lua: `
+                local totalComplexity = 0 -- complexity of active requests
+                local expiredMembers = 0 -- number of requests to remove
+                local key = keys[1] -- uuid 
+                local current_time = keys[2]
+
+                for index, value in next, redis.call(key, ????) do
+                    -- string comparisson of timestamps
+                    if .... then
+                    
+                    else
+                        totalComplexity += ????
+                    end
+                end
+
+                redis.call(pop, ???)
+
+                if total_complexity < window_size then
+                    then 
+                end
+                return {
+
+                }
+            `,
+            numberOfKeys: 3, // uuid
+            readOnly: true,
+        });
     }
 
     /**
@@ -50,9 +83,41 @@ class SlidingWindowLog implements RateLimiter {
     ): Promise<RateLimiterResponse> {
         // set the expiry of key-value pairs in the cache to 24 hours
         const keyExpiry = 86400000; // TODO: Make this a global for consistency across each algo.
-        if (tokens > this.capacity) return { success: false, tokens: this.capacity };
+        // if (tokens > this.capacity) return { success: false, tokens: this.capacity };
+
+        // Each user's log is represented by a redis list with a score = request timestamp
+        // and a value equal to the complexity
+        // Drop expired requests from the log. represented by a sorted set in redis
+
+        // Get the log from redis
+        let requestLog: RedisLog = JSON.parse((await this.client.get(uuid)) || '[]');
+
+        // if (requestLog.length === 0) {
+        //     if (tokens > 0) requestLog.push({ timestamp, tokens });
+        //     // return { success: true, tokens: this.capacity - tokens };
+        // }
+        const cutoff = timestamp - this.windowSize;
+        let tokensInLog = 0;
+        requestLog = requestLog.filter((bucket: RedisBucket) => {
+            if (bucket.timestamp > cutoff) {
+                // get complexity sum of active requests
+                tokensInLog += bucket.tokens;
+                return true;
+            }
+            // drop expired requests
+            return false;
+        });
 
-        throw new Error('SlidingWindowLog.processRequest not implemented');
+        // allow/disallow current request
+        if (tokensInLog + tokens <= this.capacity) {
+            // update the log
+            if (tokens > 0) requestLog.push({ timestamp, tokens });
+            await this.client.setex(uuid, keyExpiry, JSON.stringify(requestLog));
+            tokensInLog += tokens;
+            return { success: true, tokens: this.capacity - tokensInLog };
+        }
+        await this.client.setex(uuid, keyExpiry, JSON.stringify(requestLog));
+        return { success: false, tokens: this.capacity - tokensInLog };
     }
 
     /**