Make the trace flags optional when parsing x-cloud-trace-context (#181)

Fixes #167

Author: muncus

opentelemetry-propagator-gcp/src/opentelemetry/propagators/cloud_trace_propagator/__init__.py

@@ -22,7 +22,7 @@
 from opentelemetry.trace.span import SpanContext, TraceFlags, format_trace_id
 
 _TRACE_CONTEXT_HEADER_NAME = "x-cloud-trace-context"
-_TRACE_CONTEXT_HEADER_FORMAT = r"(?P<trace_id>[0-9a-f]{32})\/(?P<span_id>[\d]{1,20});o=(?P<trace_flags>\d+)"
+_TRACE_CONTEXT_HEADER_FORMAT = r"(?P<trace_id>[0-9a-f]{32})\/(?P<span_id>[\d]{1,20})(;o=(?P<trace_flags>\d+))?"
 _TRACE_CONTEXT_HEADER_RE = re.compile(_TRACE_CONTEXT_HEADER_FORMAT)
 _FIELDS = {_TRACE_CONTEXT_HEADER_NAME}
 
@@ -71,7 +71,7 @@ def extract(
 
         trace_id = match.group("trace_id")
         span_id = match.group("span_id")
-        trace_options = match.group("trace_flags")
+        trace_options = match.group("trace_flags") or "0"
 
         if trace_id == "0" * 32 or int(span_id) == 0:
             return context

opentelemetry-propagator-gcp/tests/test_cloud_trace_propagator.py

@@ -115,6 +115,13 @@ def test_valid_header(self):
         self.assertEqual(new_span_context.trace_flags, TraceFlags(0))
         self.assertTrue(new_span_context.is_remote)
 
+        header = "{}/{}".format(format_trace_id(self.valid_trace_id), 345)
+        new_span_context = self._extract_span_context(header)
+        self.assertEqual(new_span_context.trace_id, self.valid_trace_id)
+        self.assertEqual(new_span_context.span_id, 345)
+        self.assertEqual(new_span_context.trace_flags, TraceFlags(0))
+        self.assertTrue(new_span_context.is_remote)
+
     def test_mixed_case_header_key(self):
         header_value = "{}/{};o=1".format(
             format_trace_id(self.valid_trace_id), self.valid_span_id