Add rate limiting code

implementations/java/rate_limiting/FixedWindowCounter.java

@@ -0,0 +1,33 @@
+package implementations.java.rate_limiting;
+
+import java.time.Instant;
+
+public class FixedWindowCounter {
+    private final long windowSizeInSeconds;  // Size of each window in seconds
+    private final long maxRequestsPerWindow; // Maximum number of requests allowed per window
+    private long currentWindowStart;         // Start time of the current window
+    private long requestCount;               // Number of requests in the current window
+
+    public FixedWindowCounter(long windowSizeInSeconds, long maxRequestsPerWindow) {
+        this.windowSizeInSeconds = windowSizeInSeconds;
+        this.maxRequestsPerWindow = maxRequestsPerWindow;
+        this.currentWindowStart = Instant.now().getEpochSecond();
+        this.requestCount = 0;
+    }
+
+    public synchronized boolean allowRequest() {
+        long now = Instant.now().getEpochSecond();
+        
+        // Check if we've moved to a new window
+        if (now - currentWindowStart >= windowSizeInSeconds) {
+            currentWindowStart = now;  // Start a new window
+            requestCount = 0;          // Reset the count for the new window
+        }
+
+        if (requestCount < maxRequestsPerWindow) {
+            requestCount++;  // Increment the count for this window
+            return true;     // Allow the request
+        }
+        return false;  // We've exceeded the limit for this window, deny the request
+    }    
+}

implementations/java/rate_limiting/LeakyBucket.java

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+package implementations.java.rate_limiting;
+
+import java.time.Instant;
+import java.util.LinkedList;
+import java.util.Queue;
+
+public class LeakyBucket {
+    private final long capacity;        // Maximum number of requests the bucket can hold
+    private final double leakRate;      // Rate at which requests leak out of the bucket (requests per second)
+    private final Queue<Instant> bucket; // Queue to hold timestamps of requests
+    private Instant lastLeakTimestamp;   // Last time we leaked from the bucket
+
+    public LeakyBucket(long capacity, double leakRate) {
+        this.capacity = capacity;
+        this.leakRate = leakRate;
+        this.bucket = new LinkedList<>();
+        this.lastLeakTimestamp = Instant.now();
+    }
+
+    public synchronized boolean allowRequest() {
+        leak();  // First, leak out any requests based on elapsed time
+
+        if (bucket.size() < capacity) {
+            bucket.offer(Instant.now());  // Add the new request to the bucket
+            return true;  // Allow the request
+        }
+        return false;  // Bucket is full, deny the request
+    }
+
+    private void leak() {
+        Instant now = Instant.now();
+        long elapsedMillis = now.toEpochMilli() - lastLeakTimestamp.toEpochMilli();
+        int leakedItems = (int) (elapsedMillis * leakRate / 1000.0);  // Calculate how many items should have leaked
+
+        // Remove the leaked items from the bucket
+        for (int i = 0; i < leakedItems && !bucket.isEmpty(); i++) {
+            bucket.poll();
+        }
+
+        lastLeakTimestamp = now;
+    }
+}

implementations/java/rate_limiting/SlidingWindowCounter.java

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+package implementations.java.rate_limiting;
+
+import java.time.Instant;
+
+public class SlidingWindowCounter {
+    private final long windowSizeInSeconds;   // Size of the sliding window in seconds
+    private final long maxRequestsPerWindow;  // Maximum number of requests allowed in the window
+    private long currentWindowStart;          // Start time of the current window
+    private long previousWindowCount;         // Number of requests in the previous window
+    private long currentWindowCount;          // Number of requests in the current window
+
+    public SlidingWindowCounter(long windowSizeInSeconds, long maxRequestsPerWindow) {
+        this.windowSizeInSeconds = windowSizeInSeconds;
+        this.maxRequestsPerWindow = maxRequestsPerWindow;
+        this.currentWindowStart = Instant.now().getEpochSecond();
+        this.previousWindowCount = 0;
+        this.currentWindowCount = 0;
+    }
+
+    public synchronized boolean allowRequest() {
+        long now = Instant.now().getEpochSecond();
+        long timePassedInWindow = now - currentWindowStart;
+
+        // Check if we've moved to a new window
+        if (timePassedInWindow >= windowSizeInSeconds) {
+            previousWindowCount = currentWindowCount;
+            currentWindowCount = 0;
+            currentWindowStart = now;
+            timePassedInWindow = 0;
+        }
+
+        // Calculate the weighted count of requests
+        double weightedCount = previousWindowCount * ((windowSizeInSeconds - timePassedInWindow) / (double) windowSizeInSeconds)
+                + currentWindowCount;
+
+        if (weightedCount < maxRequestsPerWindow) {
+            currentWindowCount++;  // Increment the count for this window
+            return true;           // Allow the request
+        }
+        return false;  // We've exceeded the limit, deny the request
+    }    
+}

implementations/java/rate_limiting/SlidingWindowLog.java

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+package implementations.java.rate_limiting;
+
+import java.time.Instant;
+import java.util.LinkedList;
+import java.util.Queue;
+
+public class SlidingWindowLog {
+    private final long windowSizeInSeconds;   // Size of the sliding window in seconds
+    private final long maxRequestsPerWindow;  // Maximum number of requests allowed in the window
+    private final Queue<Long> requestLog;     // Log of request timestamps
+
+    public SlidingWindowLog(long windowSizeInSeconds, long maxRequestsPerWindow) {
+        this.windowSizeInSeconds = windowSizeInSeconds;
+        this.maxRequestsPerWindow = maxRequestsPerWindow;
+        this.requestLog = new LinkedList<>();
+    }
+
+    public synchronized boolean allowRequest() {
+        long now = Instant.now().getEpochSecond();
+        long windowStart = now - windowSizeInSeconds;
+
+        // Remove timestamps that are outside of the current window
+        while (!requestLog.isEmpty() && requestLog.peek() <= windowStart) {
+            requestLog.poll();
+        }
+
+        if (requestLog.size() < maxRequestsPerWindow) {
+            requestLog.offer(now);  // Log this request
+            return true;            // Allow the request
+        }
+        return false;  // We've exceeded the limit for this window, deny the request
+    }    
+}

implementations/java/rate_limiting/TokenBucket.java

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+package implementations.java.rate_limiting;
+
+import java.time.Instant;
+
+public class TokenBucket {
+    private final long capacity;        // Maximum number of tokens the bucket can hold
+    private final double fillRate;      // Rate at which tokens are added to the bucket (tokens per second)
+    private double tokens;              // Current number of tokens in the bucket
+    private Instant lastRefillTimestamp; // Last time we refilled the bucket
+
+    public TokenBucket(long capacity, double fillRate) {
+        this.capacity = capacity;
+        this.fillRate = fillRate;
+        this.tokens = capacity;  // Start with a full bucket
+        this.lastRefillTimestamp = Instant.now();
+    }
+
+    public synchronized boolean allowRequest(int tokens) {
+        refill();  // First, add any new tokens based on elapsed time
+
+        if (this.tokens < tokens) {
+            return false;  // Not enough tokens, deny the request
+        }
+
+        this.tokens -= tokens;  // Consume the tokens
+        return true;  // Allow the request
+    }
+
+    private void refill() {
+        Instant now = Instant.now();
+        // Calculate how many tokens to add based on the time elapsed
+        double tokensToAdd = (now.toEpochMilli() - lastRefillTimestamp.toEpochMilli()) * fillRate / 1000.0;
+        this.tokens = Math.min(capacity, this.tokens + tokensToAdd);  // Add tokens, but don't exceed capacity
+        this.lastRefillTimestamp = now;
+    }
+}