Trim whitespace when setting display names

changelog.d/16031.bugfix

@@ -0,0 +1 @@
+Trim any white space when setting display names.

synapse/handlers/profile.py

@@ -163,7 +163,7 @@ async def set_displayname(
                 400, "Displayname is too long (max %i)" % (MAX_DISPLAYNAME_LEN,)
             )
 
-        displayname_to_set: Optional[str] = new_displayname
+        displayname_to_set: Optional[str] = new_displayname.strip()
         if new_displayname == "":
             displayname_to_set = None
 

tests/rest/client/test_profile.py

@@ -68,6 +68,18 @@ def test_set_displayname(self) -> None:
         res = self._get_displayname()
         self.assertEqual(res, "test")
 
+    def test_set_displayname_with_extra_spaces(self) -> None:
+        channel = self.make_request(
+            "PUT",
+            "/profile/%s/displayname" % (self.owner,),
+            content={"displayname": "  test  "},
+            access_token=self.owner_tok,
+        )
+        self.assertEqual(channel.code, 200, channel.result)
+
+        res = self._get_displayname()
+        self.assertEqual(res, "test")
+
     def test_set_displayname_noauth(self) -> None:
         channel = self.make_request(
             "PUT",