[core] Guard against when there is no current call context

Fixes #851

ddtrace/helpers.py

@@ -32,6 +32,6 @@ def get_correlation_ids(tracer=None):
         return None, None
 
     span = tracer.current_span()
-    if span is None:
+    if not span:
         return None, None
     return span.trace_id, span.span_id

ddtrace/tracer.py

@@ -300,14 +300,20 @@ def current_root_span(self):
             # set the host just once on the root span
             root_span.set_tag('host', '127.0.0.1')
         """
-        return self.get_call_context().get_current_root_span()
+        ctx = self.get_call_context()
+        if ctx:
+            return ctx.get_current_root_span()
+        return None
 
     def current_span(self):
         """
         Return the active span for the current call context or ``None``
         if no spans are available.
         """
-        return self.get_call_context().get_current_span()
+        ctx = self.get_call_context()
+        if ctx:
+            return ctx.get_current_span()
+        return None
 
     def record(self, context):
         """

tests/test_helpers.py

@@ -1,6 +1,6 @@
-from ddtrace import helpers
+import mock
 
-from nose.tools import eq_, ok_
+from ddtrace import helpers
 
 from .base import BaseTracerTestCase
 from .util import override_global_tracer
@@ -16,16 +16,16 @@ def test_correlation_identifiers(self):
             active_trace_id, active_span_id = span.trace_id, span.span_id
             trace_id, span_id = helpers.get_correlation_ids()
 
-        eq_(trace_id, active_trace_id)
-        eq_(span_id, active_span_id)
+        self.assertEqual(trace_id, active_trace_id)
+        self.assertEqual(span_id, active_span_id)
 
     def test_correlation_identifiers_without_trace(self):
         # ensures `None` is returned if no Traces are active
         with override_global_tracer(self.tracer):
             trace_id, span_id = helpers.get_correlation_ids()
 
-        ok_(trace_id is None)
-        ok_(span_id is None)
+        self.assertIsNone(trace_id)
+        self.assertIsNone(span_id)
 
     def test_correlation_identifiers_with_disabled_trace(self):
         # ensures `None` is returned if tracer is disabled
@@ -34,5 +34,15 @@ def test_correlation_identifiers_with_disabled_trace(self):
             self.tracer.trace('MockSpan')
             trace_id, span_id = helpers.get_correlation_ids()
 
-        ok_(trace_id is None)
-        ok_(span_id is None)
+        self.assertIsNone(trace_id)
+        self.assertIsNone(span_id)
+
+    def test_correlation_identifiers_missing_context(self):
+        # ensures we return `None` if there is no current context
+        self.tracer.get_call_context = mock.MagicMock(return_value=None)
+
+        with override_global_tracer(self.tracer):
+            trace_id, span_id = helpers.get_correlation_ids()
+
+        self.assertIsNone(trace_id)
+        self.assertIsNone(span_id)

tests/test_tracer.py

@@ -329,6 +329,12 @@ def test_tracer_current_span(self):
         span = self.trace('fake_span')
         self.assertEqual(self.tracer.current_span(), span)
 
+    def test_tracer_current_span_missing_context(self):
+        self.assertIsNone(self.tracer.current_span())
+
+    def test_tracer_current_root_span_missing_context(self):
+        self.assertIsNone(self.tracer.current_root_span())
+
     def test_default_provider_get(self):
         # Tracer Context Provider must return a Context object
         # even if empty