Default w3c sampled flag to 01 (#152)

Receiving OTEL instrumentation ignores spans coming with the 00 sampled flag.

This is a stop-gap measure to ensure w3c parser hooks work with an OTEL receiver. Ideally, we would like to set the sampled flag based on an actual sampler, but that requires further investigation.

Author: vreynolds

beeline/propagation/test_w3c.py

@@ -4,6 +4,7 @@
 import beeline.propagation.w3c as w3c
 
 _TEST_TRACEPARENT_HEADER = "00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-00"
+_TEST_TRACEPARENT_HEADER_DEFAULT_TRACEFLAGS = "00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01"
 _TEST_TRACESTATE_HEADER = "foo=bar,bar=baz"
 
 _TEST_HEADERS = {
@@ -73,3 +74,12 @@ def test_generates_correct_headers(self):
                          _TEST_TRACEPARENT_HEADER)
         self.assertEqual(headers['tracestate'],
                          _TEST_TRACESTATE_HEADER)
+
+    def test_defaults_trace_flags_to_sampled(self):
+        pc = PropagationContext(
+            _TEST_TRACE_ID, _TEST_PARENT_ID
+        )
+        headers = w3c.http_trace_propagation_hook(pc)
+        self.assertIn('traceparent', headers)
+        self.assertEqual(headers['traceparent'],
+                         _TEST_TRACEPARENT_HEADER_DEFAULT_TRACEFLAGS)

beeline/propagation/w3c.py

@@ -70,7 +70,7 @@ def marshal_traceparent(propagation_context):
 
     trace_flags = propagation_context.trace_fields.get('traceflags')
     if not trace_flags:
-        trace_flags = "00"
+        trace_flags = "01"
 
     traceparent_header = "00-{}-{}-{}".format(
         propagation_context.trace_id,