Improved HTTP propagator: Also support HTTP_ style headers

Author: pglombardo

instana/http_propagator.py

@@ -3,27 +3,39 @@
 from basictracer.context import SpanContext
 from instana import util, log
 
-prefix_tracer_state = 'X-Instana-'
-field_name_trace_id = prefix_tracer_state + 'T'
-field_name_span_id = prefix_tracer_state + 'S'
-field_count = 2
+
+# The carrier can be a dict or a list.
+# Using the trace header as an example, it can be in the following forms
+# for extraction:
+#   X-Instana-T
+#   HTTP_X_INSTANA_T
+#
+# The second form above is found in places like Django middleware for
+# incoming requests.
+#
+# For injection, we only support the standard format:
+#   X-Instana-T
 
 
 class HTTPPropagator():
     """A Propagator for Format.HTTP_HEADERS. """
 
+    HEADER_KEY_T = 'X-Instana-T'
+    HEADER_KEY_S = 'X-Instana-S'
+    ALT_HEADER_KEY_T = 'HTTP_X_INSTANA_T'
+    ALT_HEADER_KEY_S = 'HTTP_X_INSTANA_S'
+
     def inject(self, span_context, carrier):
         try:
             trace_id = util.id_to_header(span_context.trace_id)
             span_id = util.id_to_header(span_context.span_id)
+
             if type(carrier) is dict or hasattr(carrier, "__dict__"):
-                carrier[field_name_trace_id] = trace_id
-                carrier[field_name_span_id] = span_id
+                carrier[self.HEADER_KEY_T] = trace_id
+                carrier[self.HEADER_KEY_S] = span_id
             elif type(carrier) is list:
-                trace_header = (field_name_trace_id, trace_id)
-                carrier.append(trace_header)
-                span_header = (field_name_span_id, span_id)
-                carrier.append(span_header)
+                carrier.append((self.HEADER_KEY_T, trace_id))
+                carrier.append((self.HEADER_KEY_S, span_id))
             else:
                 raise Exception("Unsupported carrier type", type(carrier))
 
@@ -39,9 +51,15 @@ def extract(self, carrier):  # noqa
             else:
                 raise ot.SpanContextCorruptedException()
 
-            if field_name_trace_id in dc and field_name_span_id in dc:
-                trace_id = util.header_to_id(dc[field_name_trace_id])
-                span_id = util.header_to_id(dc[field_name_span_id])
+            # Look for standard X-Instana-T/S format
+            if self.HEADER_KEY_T in dc and self.header_key_s in dc:
+                trace_id = util.header_to_id(dc[self.HEADER_KEY_T])
+                span_id = util.header_to_id(dc[self.header_key_s])
+
+            # Alternatively check for HTTP_X_INSTANA_T/S style
+            elif self.ALT_HEADER_KEY_T in dc and self.ALT_HEADER_KEY_S in dc:
+                trace_id = util.header_to_id(dc[self.ALT_HEADER_KEY_T])
+                span_id = util.header_to_id(dc[self.ALT_HEADER_KEY_S])
 
             return SpanContext(span_id=span_id,
                                trace_id=trace_id,