add option to not report 4xx as errors for Grape

lib/ddtrace/contrib/grape/configuration/settings.rb

@@ -20,6 +20,7 @@ class Settings < Contrib::Configuration::Settings
 
           option :enabled, default: true
           option :service_name, default: Ext::SERVICE_NAME
+          option :error_for_4xx, default: true
         end
       end
     end

lib/ddtrace/contrib/grape/endpoint.rb

@@ -86,7 +86,9 @@ def endpoint_run(name, start, finish, id, payload)
               end
 
               # catch thrown exceptions
-              span.set_error(payload[:exception_object]) unless payload[:exception_object].nil?
+              if exception_is_error?(payload[:exception_object])
+                span.set_error(payload[:exception_object])
+              end
 
               # override the current span with this notification values
               span.set_tag(Ext::TAG_ROUTE_ENDPOINT, api_view) unless api_view.nil?
@@ -177,6 +179,10 @@ def service_name
             datadog_configuration[:service_name]
           end
 
+          def error_for_4xx?
+            datadog_configuration[:error_for_4xx]
+          end
+
           def analytics_enabled?
             Contrib::Analytics.enabled?(datadog_configuration[:analytics_enabled])
           end
@@ -192,6 +198,16 @@ def enabled?
           def datadog_configuration
             Datadog.configuration[:grape]
           end
+
+          def exception_is_error?(exception)
+            return false unless exception
+
+            if !error_for_4xx? && defined?(::Grape::Exceptions::Base) && exception.class < ::Grape::Exceptions::Base
+              status = exception.status
+            end
+
+            status.nil? || status > 499
+          end
         end
       end
     end

test/contrib/grape/request_test.rb

@@ -60,6 +60,29 @@ def test_traced_api_exception
     assert_nil(run.parent)
   end
 
+  def test_traced_api_4xx_exception_report_no_error
+    Datadog.configure do |c|
+      c.use :grape, error_for_4xx: false
+    end
+    post '/base/hard_failure'
+
+    spans = @tracer.writer.spans()
+    render = spans[0]
+    assert_equal(render.status, 0)
+
+    Datadog.configure do |c|
+      c.use :grape, error_for_4xx: true
+    end
+  end
+
+  def test_mine_4xx_exception_report_error
+    post '/base/hard_failure'
+
+    spans = @tracer.writer.spans()
+    render = spans[0]
+    assert_equal(render.status, 1)
+  end
+
   def test_traced_api_before_after_filters
     # it should trace the endpoint body and all before/after filters
     get '/filtered/before_after'