Use Pydantic to systematically validate a first batch of endpoints in…

… `synapse.rest.client.account`. (#13188)

changelog.d/13188.feature

@@ -0,0 +1 @@
+Improve validation of request bodies for the following client-server API endpoints: [`/account/password`](https://spec.matrix.org/v1.3/client-server-api/#post_matrixclientv3accountpassword), [`/account/password/email/requestToken`](https://spec.matrix.org/v1.3/client-server-api/#post_matrixclientv3accountpasswordemailrequesttoken), [`/account/deactivate`](https://spec.matrix.org/v1.3/client-server-api/#post_matrixclientv3accountdeactivate) and [`/account/3pid/email/requestToken`](https://spec.matrix.org/v1.3/client-server-api/#post_matrixclientv3account3pidemailrequesttoken).

mypy.ini

@@ -1,6 +1,6 @@
 [mypy]
 namespace_packages = True
-plugins = mypy_zope:plugin, scripts-dev/mypy_synapse_plugin.py
+plugins = pydantic.mypy, mypy_zope:plugin, scripts-dev/mypy_synapse_plugin.py
 follow_imports = normal
 check_untyped_defs = True
 show_error_codes = True

pyproject.toml

@@ -158,6 +158,9 @@ packaging = ">=16.1"
 # At the time of writing, we only use functions from the version `importlib.metadata`
 # which shipped in Python 3.8. This corresponds to version 1.4 of the backport.
 importlib_metadata = { version = ">=1.4", python = "<3.8" }
+# This is the most recent version of Pydantic with available on common distros.
+pydantic = ">=1.7.4"
+
 
 
 # Optional Dependencies

synapse/http/servlet.py

@@ -23,9 +23,12 @@
     Optional,
     Sequence,
     Tuple,
+    Type,
+    TypeVar,
     overload,
 )
 
+from pydantic import BaseModel, ValidationError
 from typing_extensions import Literal
 
 from twisted.web.server import Request
@@ -694,6 +697,28 @@ def parse_json_object_from_request(
     return content
 
 
+Model = TypeVar("Model", bound=BaseModel)
+
+
+def parse_and_validate_json_object_from_request(
+    request: Request, model_type: Type[Model]
+) -> Model:
+    """Parse a JSON object from the body of a twisted HTTP request, then deserialise and
+    validate using the given pydantic model.
+
+    Raises:
+        SynapseError if the request body couldn't be decoded as JSON or
+            if it wasn't a JSON object.
+    """
+    content = parse_json_object_from_request(request, allow_empty_body=False)
+    try:
+        instance = model_type.parse_obj(content)
+    except ValidationError as e:
+        raise SynapseError(HTTPStatus.BAD_REQUEST, str(e), errcode=Codes.BAD_JSON)
+
+    return instance
+
+
 def assert_params_in_dict(body: JsonDict, required: Iterable[str]) -> None:
     absent = []
     for k in required: