Rate limiting

app.rb

@@ -28,6 +28,7 @@
 class TreeStats < Sinatra::Base
   configure :production do
     use Sentry::Rack::CaptureExceptions
+    use RateLimiter, limit: 100, seconds: 60
   end
 
   set :root, File.dirname(__FILE__)

lib/rate_limiter.rb

@@ -0,0 +1,37 @@
+require "redis"
+
+class RateLimiter
+  def initialize(app, options = {})
+    @app = app
+    @limit = options[:limit] || 100
+    @seconds = options[:seconds] || 60
+    @redis = Redis.new
+  end
+
+  def call(env)
+    ip = env['REMOTE_ADDR']
+    key = build_key(ip)
+
+    count = increment(key)
+
+    if count > @limit
+      [429, { 'Content-Type' => 'text/plain' }, ['Rate limit exceeded']]
+    else
+      @app.call(env)
+    end
+  end
+
+  private
+
+  def build_key(ip)
+    "rate_limiter:#{ip}:#{Time.now.to_i / @seconds}"
+  end
+
+  def increment(key)
+    count = @redis.incr(key)
+
+    @redis.expire(key, @seconds) if count == 1
+
+    count
+  end
+end