[ETCM-448] json rpc - status code (#836)

* fix status code

* change strategy from status code

* remove redundancy

* change style

* test improvement

Author: biandratti

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

@@ -36,6 +36,9 @@ trait JsonRpcHttpServer extends Json4sSupport with RateLimit with Logger {
 
   def corsAllowedOrigins: HttpOriginMatcher
 
+  lazy val jsonRpcErrorCodes: List[Int] =
+    List(JsonRpcError.InvalidRequest.code, JsonRpcError.ParseError.code, JsonRpcError.InvalidParams().code)
+
   val corsSettings = CorsSettings.defaultSettings
     .withAllowGenericHttpRequests(true)
     .withAllowedOrigins(corsAllowedOrigins)
@@ -70,12 +73,12 @@ trait JsonRpcHttpServer extends Json4sSupport with RateLimit with Logger {
     // As a temporary solution, it is being excluded from the Rate Limit.
     if (config.rateLimit.enabled && request.method != FaucetJsonRpcController.Status) {
       handleRateLimitedRequest(clientAddress, request)
-    } else complete(jsonRpcController.handleRequest(request).runToFuture)
+    } else complete(handleResponse(jsonRpcController.handleRequest(request)).runToFuture)
   }
 
   def handleRateLimitedRequest(clientAddress: RemoteAddress, request: JsonRpcRequest): StandardRoute = {
     if (isBelowRateLimit(clientAddress))
-      complete(jsonRpcController.handleRequest(request).runToFuture)
+      complete(handleResponse(jsonRpcController.handleRequest(request)).runToFuture)
     else {
       log.warn(s"Request limit exceeded for ip ${clientAddress.toIP.getOrElse("unknown")}")
       complete(
@@ -84,6 +87,14 @@ trait JsonRpcHttpServer extends Json4sSupport with RateLimit with Logger {
     }
   }
 
+  private def handleResponse(f: Task[JsonRpcResponse]): Task[(StatusCode, JsonRpcResponse)] = f map { jsonRpcResponse =>
+    jsonRpcResponse.error match {
+      case Some(JsonRpcError(error, _, _)) if jsonRpcErrorCodes.contains(error) =>
+        (StatusCodes.BadRequest, jsonRpcResponse)
+      case _ => (StatusCodes.OK, jsonRpcResponse)
+    }
+  }
+
   /**
     * Try to start JSON RPC server
     */