Remove SynapseRequest.get_user_agent (#9069)

SynapseRequest is in danger of becoming a bit of a dumping-ground for "useful stuff relating to Requests",
which isn't really its intention (its purpose is to override render, finished and connectionLost to set up the 
LoggingContext and write the right entries to the request log).

Putting utility functions inside SynapseRequest means that lots of our code ends up requiring a
SynapseRequest when there is nothing synapse-specific about the Request at all, and any old
twisted.web.iweb.IRequest will do. This increases code coupling and makes testing more difficult.

In short: move get_user_agent out to a utility function.

2 files changed, 6 insertions, 5 deletions

diff --git a/synapse/handlers/auth.py b/synapse/handlers/auth.py
index f4434673dc..5b86ee85c7 100644
--- a/synapse/handlers/auth.py
+++ b/synapse/handlers/auth.py
@@ -49,8 +49,10 @@ from synapse.api.errors import (
     UserDeactivatedError,
 )
 from synapse.api.ratelimiting import Ratelimiter
+from synapse.handlers._base import BaseHandler
 from synapse.handlers.ui_auth import INTERACTIVE_AUTH_CHECKERS
 from synapse.handlers.ui_auth.checkers import UserInteractiveAuthChecker
+from synapse.http import get_request_user_agent
 from synapse.http.server import finish_request, respond_with_html
 from synapse.http.site import SynapseRequest
 from synapse.logging.context import defer_to_thread
@@ -62,8 +64,6 @@ from synapse.util.async_helpers import maybe_awaitable
 from synapse.util.msisdn import phone_number_to_msisdn
 from synapse.util.threepids import canonicalise_email
 
-from ._base import BaseHandler
-
 if TYPE_CHECKING:
     from synapse.app.homeserver import HomeServer
 
@@ -539,7 +539,7 @@ class AuthHandler(BaseHandler):
             # authentication flow.
             await self.store.set_ui_auth_clientdict(sid, clientdict)
 
-        user_agent = request.get_user_agent("")
+        user_agent = get_request_user_agent(request)
 
         await self.store.add_user_agent_ip_to_ui_auth_session(
             session.session_id, user_agent, clientip
diff --git a/synapse/handlers/sso.py b/synapse/handlers/sso.py
index 2da1ea2223..740df7e4a0 100644
--- a/synapse/handlers/sso.py
+++ b/synapse/handlers/sso.py
@@ -23,6 +23,7 @@ from typing_extensions import NoReturn, Protocol
 from twisted.web.http import Request
 
 from synapse.api.errors import Codes, RedirectException, SynapseError
+from synapse.http import get_request_user_agent
 from synapse.http.server import respond_with_html
 from synapse.http.site import SynapseRequest
 from synapse.types import JsonDict, UserID, contains_invalid_mxid_characters
@@ -362,7 +363,7 @@ class SsoHandler:
                     attributes,
                     auth_provider_id,
                     remote_user_id,
-                    request.get_user_agent(""),
+                    get_request_user_agent(request),
                     request.getClientIP(),
                 )
 
@@ -628,7 +629,7 @@ class SsoHandler:
             attributes,
             session.auth_provider_id,
             session.remote_user_id,
-            request.get_user_agent(""),
+            get_request_user_agent(request),
             request.getClientIP(),
         )