[ETCM-266]-replaced-rate-limiter-built-on-twitter

Author: Dmitry Voronov

src/main/scala/io/iohk/ethereum/db/cache/SimpleLRU.scala

@@ -0,0 +1,36 @@
+package io.iohk.ethereum.db.cache
+
+import java.util
+
+/**
+  * Simplest-possible implementation of insert-time based LRU
+  *
+  * @param maxElements - capacity of the inner map, between 0 and this value.
+  * @param ttlMillis   - entry invalidation interval
+  * @tparam K - stands for the type of the keys
+  */
+class SimpleLRU[K](maxElements: Int, ttlMillis: Long) {
+
+  private[this] val inner = new util.LinkedHashMap[K, Long](maxElements, 0.75f, false) {
+    override def removeEldestEntry(old: util.Map.Entry[K, Long]): Boolean = {
+      size() > maxElements || tooOld(old.getValue)
+    }
+  }
+
+  /**
+    * @param key - will be searching and added
+    * @return
+    *   true  - if there was such entry already
+    *   false - if not
+    */
+  def checkAndRefreshEntry(key: K): Boolean = inner.synchronized {
+    val existing = Option(inner.put(key, currentTime))
+    existing.exists(!tooOld(_))
+  }
+
+  // Override this to test
+  protected def currentTime: Long = System.currentTimeMillis()
+
+  private[this] def tooOld(time: Long) = time + ttlMillis < currentTime
+
+}

src/main/scala/io/iohk/ethereum/jsonrpc/server/http/JsonRpcHttpServer.scala

@@ -54,7 +54,7 @@ trait JsonRpcHttpServer extends Json4sSupport with Logger {
       }
       .result()
 
-  protected val rateLimit = new RateLimit(config.rateLimit)
+  val rateLimit = new RateLimit(config.rateLimit)
 
   val route: Route = cors(corsSettings) {
     (path("healthcheck") & pathEndOrSingleSlash & get) {
@@ -66,12 +66,11 @@ trait JsonRpcHttpServer extends Json4sSupport with Logger {
       entity(as[JsonRpcRequest]) {
         case statusReq if statusReq.method == FaucetJsonRpcController.Status =>
           handleRequest(statusReq)
-        case jsonReq =>
-          rateLimit {
-            handleRequest(jsonReq)
-          }
-        // TODO: separate paths for single and multiple requests
-        // TODO: to prevent repeated body and json parsing
+        case jsonReq => rateLimit {
+          handleRequest(jsonReq)
+        }
+      // TODO: separate paths for single and multiple requests
+      // TODO: to prevent repeated body and json parsing
       } ~ entity(as[Seq[JsonRpcRequest]]) {
         case _ if config.rateLimit.enabled =>
           complete(StatusCodes.MethodNotAllowed, JsonRpcError.MethodNotFound)

src/test/scala/io/iohk/ethereum/db/cache/SimpleLRUSpec.scala

@@ -0,0 +1,53 @@
+package io.iohk.ethereum.db.cache
+
+import org.scalatest.wordspec.AnyWordSpec
+
+class SimpleLRUSpec extends AnyWordSpec {
+
+  var time = 0L
+
+  private object MockedLRU extends SimpleLRU[Int](10, 100) {
+    override protected def currentTime: Long = SimpleLRUSpec.this.time
+  }
+
+  "It" should {
+
+    "Respond false with all missing entries and preserve length" in {
+      val results = (0 until 100).map { i => MockedLRU.checkAndRefreshEntry(i) }
+      assert( results.forall( _ == false ) )
+    }
+
+    "Drop the records according to maxElements" in {
+      val existing = (90 until 100).map { i => MockedLRU.checkAndRefreshEntry(i) }
+      assert( existing.forall( _ == true ) )
+
+      // maxElements guaranteed that we have no space for those
+      val absent = (0 until 10).map { i => MockedLRU.checkAndRefreshEntry(i) }
+      assert( absent.forall( _ == false ) )
+    }
+
+    "Obsolete the records according to ttlMillis" in {
+      this.time = 0L
+      var results = (0 until 5).map { i => MockedLRU.checkAndRefreshEntry(i) }
+      assert( results.forall( _ == true ) )
+
+      this.time = 50L
+      results = (5 until 10).map { i => MockedLRU.checkAndRefreshEntry(i) }
+      assert( results.forall( _ == true ) )
+
+      this.time = 150L
+      results = (0 until 5).map { i => MockedLRU.checkAndRefreshEntry(i) }
+      assert( results.forall( _ == false ) )
+
+      // those were added at 50ms and still valid
+      results = (5 until 10).map { i => MockedLRU.checkAndRefreshEntry(i) }
+      assert( results.forall( _ == true ) )
+
+      this.time = 300L
+      results = (0 until 10).map { i => MockedLRU.checkAndRefreshEntry(i) }
+      assert( results.forall( _ == false ) )
+    }
+
+  }
+
+}