1 files changed, 12 insertions, 8 deletions
diff --git a/synapse/http/site.py b/synapse/http/site.py
index 6e79b47828..ddb1770b09 100644
--- a/synapse/http/site.py
+++ b/synapse/http/site.py
@@ -109,8 +109,14 @@ class SynapseRequest(Request):
             method = self.method.decode("ascii")
         return method
 
-    def get_user_agent(self):
-        return self.requestHeaders.getRawHeaders(b"User-Agent", [None])[-1]
+    def get_user_agent(self, default: str) -> str:
+        """Return the last User-Agent header, or the given default.
+        """
+        user_agent = self.requestHeaders.getRawHeaders(b"User-Agent", [None])[-1]
+        if user_agent is None:
+            return default
+
+        return user_agent.decode("ascii", "replace")
 
     def render(self, resrc):
         # this is called once a Resource has been found to serve the request; in our
@@ -161,7 +167,9 @@ class SynapseRequest(Request):
             yield
         except Exception:
             # this should already have been caught, and sent back to the client as a 500.
-            logger.exception("Asynchronous messge handler raised an uncaught exception")
+            logger.exception(
+                "Asynchronous message handler raised an uncaught exception"
+            )
         finally:
             # the request handler has finished its work and either sent the whole response
             # back, or handed over responsibility to a Producer.
@@ -274,11 +282,7 @@ class SynapseRequest(Request):
         # with maximum recursion trying to log errors about
         # the charset problem.
         # c.f. https://github.com/matrix-org/synapse/issues/3471
-        user_agent = self.get_user_agent()
-        if user_agent is not None:
-            user_agent = user_agent.decode("utf-8", "replace")
-        else:
-            user_agent = "-"
+        user_agent = self.get_user_agent("-")
 
         code = str(self.code)
         if not self.finished: