Allow per blueprint json encoder decoder

re #1710

tests/test_helpers.py

@@ -90,12 +90,12 @@ class TestJSON(object):
         app = flask.Flask(__name__)
 
         app.config['JSON_AS_ASCII'] = True
-        with app.app_context():
+        with app.test_request_context():
             rv = flask.json.dumps(u'\N{SNOWMAN}')
             assert rv == '"\\u2603"'
 
         app.config['JSON_AS_ASCII'] = False
-        with app.app_context():
+        with app.test_request_context():
             rv = flask.json.dumps(u'\N{SNOWMAN}')
             assert rv == u'"\u2603"'
 
@@ -234,6 +234,41 @@ class TestJSON(object):
         }), content_type='application/json')
         assert rv.data == b'"<42>"'
 
+    def test_blueprint_json_customization(self):
+        class X(object):
+            def __init__(self, val):
+                self.val = val
+        class MyEncoder(flask.json.JSONEncoder):
+            def default(self, o):
+                if isinstance(o, X):
+                    return '<%d>' % o.val
+                return flask.json.JSONEncoder.default(self, o)
+        class MyDecoder(flask.json.JSONDecoder):
+            def __init__(self, *args, **kwargs):
+                kwargs.setdefault('object_hook', self.object_hook)
+                flask.json.JSONDecoder.__init__(self, *args, **kwargs)
+            def object_hook(self, obj):
+                if len(obj) == 1 and '_foo' in obj:
+                    return X(obj['_foo'])
+                return obj
+
+        blue = flask.Blueprint('blue', __name__)
+        blue.json_encoder = MyEncoder
+        blue.json_decoder = MyDecoder
+        @blue.route('/bp', methods=['POST'])
+        def index():
+            return flask.json.dumps(flask.request.get_json()['x'])
+
+        app = flask.Flask(__name__)
+        app.testing = True
+        app.register_blueprint(blue)
+
+        c = app.test_client()
+        rv = c.post('/bp', data=flask.json.dumps({
+            'x': {'_foo': 42}
+        }), content_type='application/json')
+        assert rv.data == b'"<42>"'
+
     def test_modified_url_encoding(self):
         class ModifiedRequest(flask.Request):
             url_charset = 'euc-kr'