Merge pull request #184 from DataDog/pedro/ensure-clean-context

Fix trace leak across multiple requests

lib/ddtrace/contrib/rack/middlewares.rb

@@ -40,7 +40,7 @@ def initialize(app, options = {})
 
         def configure
           # ensure that the configuration is executed only once
-          return if @tracer && @service
+          return clean_context if @tracer && @service
 
           # retrieve the current tracer and service
           @tracer = @options.fetch(:tracer)
@@ -135,6 +135,15 @@ def call(env)
 
           [status, headers, response]
         end
+
+        private
+
+        # TODO: Remove this once we change how context propagation works. This
+        # ensures we clean thread-local variables on each HTTP request avoiding
+        # memory leaks.
+        def clean_context
+          @tracer.provider.context = Datadog::Context.new
+        end
       end
     end
   end

test/contrib/rack/helpers.rb

@@ -14,6 +14,7 @@ class RackBaseTest < Minitest::Test
   def app
     tracer = @tracer
 
+    # rubocop:disable Metrics/BlockLength
     Rack::Builder.new do
       use Datadog::Contrib::Rack::TraceMiddleware, tracer: tracer
 
@@ -73,6 +74,18 @@ def app
           [500, { 'Content-Type' => 'text/html' }, 'OK']
         end)
       end
+
+      map '/leak/' do
+        handler = proc do
+          tracer.trace('leaky-span-1')
+          tracer.trace('leaky-span-2')
+          tracer.trace('leaky-span-3')
+
+          [200, { 'Content-Type' => 'text/html' }, 'OK']
+        end
+
+        run(handler)
+      end
     end.to_app
   end
 

test/contrib/rack/middleware_test.rb

@@ -239,6 +239,14 @@ def test_request_middleware_non_standard_error
     assert_equal(1, span.status)
     assert_nil(span.parent)
   end
+
+  def test_middleware_context_cleaning
+    get '/leak'
+    get '/success'
+
+    assert_equal(0, @tracer.provider.context.trace.length)
+    assert_equal(1, @tracer.writer.spans.length)
+  end
 end
 
 class CustomTracerTest < RackBaseTest