Fix exceptions on requests for non-ascii urls (#6682)

* commit 'feee81997':
  Fix exceptions on requests for non-ascii urls (#6682)
  comment for run_in_background

changelog.d/6682.bugfix

@@ -0,0 +1,2 @@
+Fix "CRITICAL" errors being logged when a request is received for a uri containing non-ascii characters.
+

synapse/http/site.py

@@ -88,7 +88,7 @@ class SynapseRequest(Request):
     def get_redacted_uri(self):
         uri = self.uri
         if isinstance(uri, bytes):
-            uri = self.uri.decode("ascii")
+            uri = self.uri.decode("ascii", errors="replace")
         return redact_uri(uri)
 
     def get_method(self):

synapse/logging/context.py

@@ -571,6 +571,9 @@ def run_in_background(f, *args, **kwargs):
     yield or await on (for instance because you want to pass it to
     deferred.gatherResults()).
 
+    If f returns a Coroutine object, it will be wrapped into a Deferred (which will have
+    the side effect of executing the coroutine).
+
     Note that if you completely discard the result, you should make sure that
     `f` doesn't raise any deferred exceptions, otherwise a scary-looking
     CRITICAL error about an unhandled error will be logged without much