Proof-of-concept for using jsonschema on an endpoint.

synapse/http/servlet.py

@@ -17,6 +17,9 @@
 
 import logging
 
+import jsonschema
+from jsonschema.exceptions import best_match
+
 from synapse.api.errors import Codes, SynapseError
 from synapse.util import json_decoder
 
@@ -222,7 +225,7 @@ def parse_json_value_from_request(request, allow_empty_body=False):
     return content
 
 
-def parse_json_object_from_request(request, allow_empty_body=False):
+def parse_json_object_from_request(request, validator=None, allow_empty_body=False):
     """Parse a JSON object from the body of a twisted HTTP request.
 
     Args:
@@ -237,9 +240,14 @@ def parse_json_object_from_request(request, allow_empty_body=False):
     content = parse_json_value_from_request(request, allow_empty_body=allow_empty_body)
 
     if allow_empty_body and content is None:
-        return {}
+        content = {}
 
-    if type(content) != dict:
+    if validator:
+        error = best_match(validator.iter_errors(content))
+        if error:
+            raise SynapseError(400, error.message, errcode=Codes.BAD_JSON)
+
+    elif type(content) != dict:
         message = "Content must be a JSON object."
         raise SynapseError(400, message, errcode=Codes.BAD_JSON)
 
@@ -291,5 +299,13 @@ class RestServlet:
                         method, patterns, method_handler, servlet_classname
                     )
 
+                if hasattr(self, "%s_SCHEMA" % (method,)):
+                    schema = getattr(self, "%s_SCHEMA" % (method,))
+                    setattr(
+                        self,
+                        "%s_VALIDATOR" % (method,),
+                        jsonschema.Draft7Validator(schema),
+                    )
+
         else:
             raise NotImplementedError("RestServlet must register something.")

synapse/rest/client/v1/profile.py

@@ -24,6 +24,14 @@ from synapse.types import UserID
 class ProfileDisplaynameRestServlet(RestServlet):
     PATTERNS = client_patterns("/profile/(?P<user_id>[^/]*)/displayname", v1=True)
 
+    PUT_SCHEMA = {
+        "type": "object",
+        "properties": {
+            "displayname": {"oneOf": [{"type": "string"}, {"type": "null"}]},
+            "required": ["displayname"],
+        },
+    }
+
     def __init__(self, hs):
         super(ProfileDisplaynameRestServlet, self).__init__()
         self.hs = hs
@@ -54,12 +62,8 @@ class ProfileDisplaynameRestServlet(RestServlet):
         user = UserID.from_string(user_id)
         is_admin = await self.auth.is_server_admin(requester.user)
 
-        content = parse_json_object_from_request(request)
-
-        try:
-            new_name = content["displayname"]
-        except Exception:
-            return 400, "Unable to parse name"
+        content = parse_json_object_from_request(request, validator=self.PUT_VALIDATOR)
+        new_name = content["displayname"]
 
         await self.profile_handler.set_displayname(user, requester, new_name, is_admin)