Always use flask.json to serialize

flask_smorest/etag.py

@@ -2,13 +2,12 @@
 
 from functools import wraps
 from copy import deepcopy
-import json
 import http
 import warnings
 
 import hashlib
 
-from flask import request
+from flask import request, json
 
 from .exceptions import PreconditionRequired, PreconditionFailed, NotModified
 from .utils import deepupdate, resolve_schema_instance, get_appcontext
@@ -98,11 +97,13 @@ def wrapper(*args, **kwargs):
     def _generate_etag(etag_data, extra_data=None):
         """Generate an ETag from data
 
-        etag_data: Data to use to compute ETag (must be json serializable)
+        etag_data: Data to use to compute ETag
         extra_data: Extra data to add before hashing
 
         Typically, extra_data is used to add pagination metadata to the hash.
         It is not dumped through the Schema.
+
+        Data is JSON serialized before hashing using the Flask app JSON serializer.
         """
         if extra_data:
             etag_data = (etag_data, extra_data)

flask_smorest/spec/__init__.py

@@ -1,6 +1,4 @@
 """API specification using OpenAPI"""
-
-import json
 import http
 
 import flask
@@ -126,10 +124,9 @@ def _register_rapidoc_rule(self, blueprint):
 
     def _openapi_json(self):
         """Serve JSON spec file"""
-        # We don't use Flask.jsonify here as it would sort the keys
-        # alphabetically while we want to preserve the order.
         return current_app.response_class(
-            json.dumps(self.spec.to_dict(), indent=2), mimetype="application/json"
+            flask.json.dumps(self.spec.to_dict(), indent=2, sort_keys=False),
+            mimetype="application/json",
         )
 
     def _openapi_redoc(self):
@@ -396,7 +393,9 @@ def print_openapi_doc(format, config_prefix):
     """Print OpenAPI JSON document."""
     config_prefix = normalize_config_prefix(config_prefix)
     if format == "json":
-        click.echo(json.dumps(_get_spec_dict(config_prefix), indent=2))
+        click.echo(
+            flask.json.dumps(_get_spec_dict(config_prefix), indent=2, sort_keys=False)
+        )
     else:  # format == "yaml"
         if HAS_PYYAML:
             click.echo(yaml.dump(_get_spec_dict(config_prefix)))
@@ -415,7 +414,7 @@ def write_openapi_doc(format, output_file, config_prefix):
     config_prefix = normalize_config_prefix(config_prefix)
     if format == "json":
         click.echo(
-            json.dumps(_get_spec_dict(config_prefix), indent=2),
+            flask.json.dumps(_get_spec_dict(config_prefix), indent=2, sort_keys=False),
             file=output_file,
         )
     else:  # format == "yaml"

tests/test_api.py

@@ -1,8 +1,10 @@
 """Test Api class"""
+import json
 
 import pytest
 from flask import jsonify
 from flask.views import MethodView
+from flask.json.provider import DefaultJSONProvider
 from werkzeug.routing import BaseConverter
 import marshmallow as ma
 import apispec
@@ -522,3 +524,45 @@ def test_api_config_proxying_flask_config(self, app):
             "API_V2_OPENAPI_VERSION",
         }
         assert len(api_v2.config) == 3
+
+    @pytest.mark.parametrize("openapi_version", ["2.0", "3.0.2"])
+    def test_api_serializes_doc_with_flask_json(self, app, openapi_version):
+        """Check that app.json, not standard json, is used to serialize API doc"""
+
+        class CustomType:
+            """Custom type"""
+
+        class CustomJSONEncoder(json.JSONEncoder):
+            def default(self, object):
+                if isinstance(object, CustomType):
+                    return 42
+                return super().default(object)
+
+        class CustomJsonProvider(DefaultJSONProvider):
+            def dumps(self, obj, **kwargs):
+                return json.dumps(obj, **kwargs, cls=CustomJSONEncoder)
+
+        class CustomSchema(ma.Schema):
+            custom_field = ma.fields.Field(load_default=CustomType())
+
+        app.config["OPENAPI_VERSION"] = openapi_version
+        app.json = CustomJsonProvider(app)
+        api = Api(app)
+        blp = Blueprint("test", "test", url_prefix="/test")
+
+        @blp.route("/")
+        @blp.arguments(CustomSchema)
+        def test(args):
+            pass
+
+        api.register_blueprint(blp)
+
+        with app.app_context():
+            spec_dict = api._openapi_json().json
+
+        if openapi_version == "2.0":
+            schema = spec_dict["definitions"]["Custom"]
+        else:
+            schema = spec_dict["components"]["schemas"]["Custom"]
+
+        assert schema["properties"]["custom_field"]["default"] == 42