Fix handling of missing ParentSpanId for B3 codec (#182)

Signed-off-by: Gabriel Gravel <ggravel@appnexus.com>

jaeger_client/codecs.py

@@ -254,6 +254,7 @@ def header_to_hex(header):
 class B3Codec(Codec):
     """
     Support B3 header properties
+    https://github.com/openzipkin/b3-propagation
 
     """
     def __init__(self):
@@ -277,7 +278,9 @@ def extract(self, carrier):
             raise InvalidCarrierException('carrier not a dictionary')
         trace_id = header_to_hex(carrier.get(self.trace_header.lower()))
         span_id = header_to_hex(carrier.get(self.span_header.lower()))
-        parent_id = header_to_hex(carrier.get(self.parent_span_header.lower()))
+        parent_id = carrier.get(self.parent_span_header.lower(), None)
+        if parent_id:
+            parent_id = header_to_hex(parent_id)
         flags = 0x00
         sampled = carrier.get(self.sampled_header.lower())
         if sampled == '1':

tests/test_codecs.py

@@ -337,6 +337,11 @@ def test_b3_extract(self):
         assert span_context.parent_id == int('0020000000000001', 16)
         assert span_context.flags == 0x02
 
+        # validate that missing parentspanid does not cause an error
+        carrier.pop('x-b3-parentspanid')
+        span_context = codec.extract(carrier)
+        assert span_context.parent_id is None
+
         carrier.update({'x-b3-sampled': '1'})
 
         span_context = codec.extract(carrier)