Add a helper from decoding bytes, then json.

synapse/api/errors.py

@@ -20,10 +20,10 @@
 from http import HTTPStatus
 from typing import Dict, List
 
-from canonicaljson import json
-
 from twisted.web import http
 
+from synapse.util.json import load_bytes
+
 logger = logging.getLogger(__name__)
 
 
@@ -572,15 +572,8 @@ def to_synapse_error(self):
         """
         # try to parse the body as json, to get better errcode/msg, but
         # default to M_UNKNOWN with the HTTP status as the error text
-
-        # Decode to Unicode since json on Python 3.5 requires str, not bytes.
-        try:
-            response_unicode = self.response.decode("utf8")
-        except UnicodeDecodeError:
-            response_unicode = "{}"
-
         try:
-            j = json.loads(response_unicode)
+            j = load_bytes(self.response)
         except ValueError:
             j = {}
 

synapse/http/servlet.py

@@ -17,9 +17,8 @@
 
 import logging
 
-from canonicaljson import json
-
 from synapse.api.errors import Codes, SynapseError
+from synapse.util.json import load_bytes
 
 logger = logging.getLogger(__name__)
 
@@ -214,15 +213,8 @@ def parse_json_value_from_request(request, allow_empty_body=False):
     if not content_bytes and allow_empty_body:
         return None
 
-    # Decode to Unicode since json on Python 3.5 requires str, not bytes.
-    try:
-        content_unicode = content_bytes.decode("utf8")
-    except UnicodeDecodeError:
-        logger.warning("Unable to decode UTF-8")
-        raise SynapseError(400, "Content not JSON.", errcode=Codes.NOT_JSON)
-
     try:
-        content = json.loads(content_unicode)
+        content = load_bytes(content_bytes)
     except Exception as e:
         logger.warning("Unable to parse JSON: %s", e)
         raise SynapseError(400, "Content not JSON.", errcode=Codes.NOT_JSON)

synapse/util/json.py

@@ -0,0 +1,40 @@
+#  Copyright 2020 The Matrix.org Foundation C.I.C.
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+import json
+import logging
+import typing
+
+# Guard against an import loop from synapse.types -> synapse.api.errors -> here.
+if typing.TYPE_CHECKING:
+    from synapse.types import JsonDict
+
+logger = logging.getLogger(__name__)
+
+
+def load_bytes(s: bytes) -> "JsonDict":
+    """
+    Deserialize a bytes containing a JSON document to a Python object.
+
+    This is a compatibility shim since Python 3.5 does NOT support deserializing
+    bytes.
+
+    Note that this does not do error handling.
+
+    Raises:
+        UnicodeDecodeError if the bytes cannot be converted to UTF-8.
+        JSONDecodeError if the data is not a valid JSON document.
+    """
+    # Decode to Unicode since json on Python 3.5 requires str, not bytes.
+    s_str = s.decode("utf8")
+    return json.loads(s_str)