Added: distributed_tracing option to Sinatra.

docs/GettingStarted.md

@@ -107,6 +107,7 @@ Where `options` is an optional `Hash` that accepts the following parameters:
 | --- | --- | --- |
 | ``service_name`` | Service name used for `sinatra` instrumentation | sinatra |
 | ``resource_script_names`` | Prepend resource names with script name | ``false`` |
+| ``distributed_tracing`` | Enables [distributed tracing](#Distributed_Tracing) so that this service trace is connected with a trace of another service if tracing headers are received | `false` |
 | ``tracer`` | A ``Datadog::Tracer`` instance used to instrument the application. Usually you don't need to set that. | ``Datadog.tracer`` |
 
 ### Rack

lib/ddtrace/contrib/sinatra/tracer.rb

@@ -4,6 +4,7 @@
 require 'ddtrace/ext/app_types'
 require 'ddtrace/ext/errors'
 require 'ddtrace/ext/http'
+require 'ddtrace/propagation/http_propagator'
 
 sinatra_vs = Gem::Version.new(Sinatra::VERSION)
 sinatra_min_vs = Gem::Version.new('1.4.0')
@@ -29,8 +30,8 @@ module Tracer
         end
 
         option :tracer, default: Datadog.tracer
-
         option :resource_script_names, default: false
+        option :distributed_tracing, default: false
 
         def route(verb, action, *)
           # Keep track of the route name when the app is instantiated for an
@@ -83,6 +84,11 @@ def render(engine, data, *)
 
             tracer = Datadog.configuration[:sinatra][:tracer]
 
+            if Datadog.configuration[:sinatra][:distributed_tracing]
+              context = HTTPPropagator.extract(request.env)
+              tracer.provider.context = context if context.trace_id
+            end
+
             span = tracer.trace('sinatra.request',
                                 service: Datadog.configuration[:sinatra][:service_name],
                                 span_type: Datadog::Ext::HTTP::TYPE)

test/contrib/sinatra/tracer_test.rb

@@ -79,6 +79,32 @@ def test_request
     assert_nil(span.parent)
   end
 
+  def test_distributed_request
+    # Enable distributed tracing
+    Datadog.configuration.use(:sinatra, distributed_tracing: true)
+
+    response = get '/request', {}, {
+      'HTTP_X_DATADOG_TRACE_ID' => '1',
+      'HTTP_X_DATADOG_PARENT_ID' => '2',
+      'HTTP_X_DATADOG_SAMPLING_PRIORITY' => Datadog::Ext::Priority::USER_KEEP.to_s
+    }
+
+    assert_equal(200, response.status)
+
+    # Check spans
+    spans = @writer.spans
+    assert_equal(1, spans.length)
+
+    # Check span
+    span = spans[0]
+    assert_equal(1, span.trace_id)
+    assert_equal(2, span.parent_id)
+    assert_equal(2.0, span.get_metric('_sampling_priority_v1'))
+  ensure
+    # Disable distributed tracing
+    Datadog.configuration.use(:sinatra, distributed_tracing: false)
+  end
+
   def test_bad_request
     get '/bad-request'
     assert_equal(400, last_response.status)