Carrier inject and extraction for Twisted Headers

synapse/util/tracerutils.py

@@ -0,0 +1,47 @@
+from opentracing.propagation import Format
+import opentracing
+
+from .logcontext import LoggingContext
+
+def extract_span_context(headers):
+    """
+    Extracts a span context from Twisted Headers.
+    args:
+        headers (twisted.web.http_headers.Headers)
+    returns:
+        span_context (opentracing.span.SpanContext)
+    """
+    # Twisted encodes the values as lists whereas opentracing doesn't.
+    # So, we take the first item in the list.
+    # Also, twisted uses byte arrays while opentracing expects strings. 
+    header_dict = {k.decode(): v[0].decode() for k, v in headers.getAllRawHeaders()}
+    return opentracing.tracer.extract(Format.HTTP_HEADERS, header_dict)
+    
+
+def inject_span_context(headers, span):
+    """
+    Injects a span context into twisted headers inplace
+    args:
+        headers (twisted.web.http_headers.Headers)
+        span (opentracing.Span)
+
+    note:
+        The headers set by the tracer are custom to the tracer implementation which
+        should be unique enough that they don't interfere with any headers set by
+        synapse or twisted. If we're still using jaeger these headers would be those
+        here: 
+        https://github.com/jaegertracing/jaeger-client-python/blob/master/jaeger_client/constants.py
+    """
+    carrier = {}
+    carrier = opentracing.tracer.inject(span, Format.HTTP_HEADERS, {})
+    
+    for key, value in carrier:
+        headers.addRawHeaders(key, value)
+
+# TODO: Implement whitelisting
+def request_from_whitelisted_homeserver(request):
+    pass
+
+# TODO: Implement whitelisting
+def user_whitelisted(request):
+    pass