Docstrings for BaseFederationServlet

... to save me reverse-engineering this stuff again.

synapse/federation/transport/server.py

@@ -190,6 +190,41 @@ def _parse_auth_header(header_bytes):
 
 
 class BaseFederationServlet(object):
+    """Abstract base class for federation servlet classes.
+
+    The servlet object should have a PATH attribute which takes the form of a regexp to
+    match against the request path (excluding the /federation/v1 prefix).
+
+    The servlet should also implement one or more of on_GET, on_POST, on_PUT, to match
+    the appropriate HTTP method. These methods have the signature:
+
+        on_<METHOD>(self, origin, content, query, **kwargs)
+
+        With arguments:
+
+            origin (unicode|None): The authenticated server_name of the calling server,
+                unless REQUIRE_AUTH is set to False and authentication failed.
+
+            content (unicode|None): decoded json body of the request. None if the
+                request was a GET.
+
+            query (dict[bytes, list[bytes]]): Query params from the request. url-decoded
+                (ie, '+' and '%xx' are decoded) but note that it is *not* utf8-decoded
+                yet.
+
+            **kwargs (dict[unicode, unicode]): the dict mapping keys to path
+                components as specified in the path match regexp.
+
+        Returns:
+            Deferred[(int, object)|None]: either (response code, response object) to
+                 return a JSON response, or None if the request has already been handled.
+
+        Raises:
+            SynapseError: to return an error code
+
+            Exception: other exceptions will be caught, logged, and a 500 will be
+                returned.
+    """
     REQUIRE_AUTH = True
 
     def __init__(self, handler, authenticator, ratelimiter, server_name):
@@ -204,6 +239,18 @@ class BaseFederationServlet(object):
         @defer.inlineCallbacks
         @functools.wraps(func)
         def new_func(request, *args, **kwargs):
+            """ A callback which can be passed to HttpServer.RegisterPaths
+
+            Args:
+                request (twisted.web.http.Request):
+                *args: unused?
+                **kwargs (dict[unicode, unicode]): the dict mapping keys to path
+                    components as specified in the path match regexp.
+
+            Returns:
+                Deferred[(int, object)|None]: (response code, response object) as returned
+                    by the callback method. None if the request has already been handled.
+            """
             content = None
             if request.method in ["PUT", "POST"]:
                 # TODO: Handle other method types? other content types?