fix: Ensure injected headers are str (#325)

The python3.7 runtime cannot serialize byte strings

Author: Wesitos

datadog_lambda/wrapper.py

@@ -236,7 +236,7 @@ def _inject_authorizer_span_headers(self, request_id):
         injected_headers[Headers.Parent_Span_Finish_Time] = finish_time_ns
         if request_id is not None:
             injected_headers[Headers.Authorizing_Request_Id] = request_id
-        datadog_data = base64.b64encode(json.dumps(injected_headers).encode())
+        datadog_data = base64.b64encode(json.dumps(injected_headers).encode()).decode()
         self.response.setdefault("context", {})
         self.response["context"]["_datadog"] = datadog_data
 

tests/test_wrapper.py

@@ -548,7 +548,9 @@ def lambda_handler(event, context):
         lambda_handler.inferred_span = mock_span
         lambda_handler.make_inferred_span = False
         result = lambda_handler(lambda_event, lambda_context)
-        inject_data = json.loads(base64.b64decode(result["context"]["_datadog"]))
+        raw_inject_data = result["context"]["_datadog"]
+        self.assertIsInstance(raw_inject_data, str)
+        inject_data = json.loads(base64.b64decode(raw_inject_data))
         self.assertEquals(inject_data[TraceHeader.PARENT_ID], "123")
         self.assertEquals(inject_data[TraceHeader.TRACE_ID], "456")
         self.assertEquals(inject_data[TraceHeader.SAMPLING_PRIORITY], "1")