Add custom loads function (#2445)

Co-authored-by: Zhiwei <chihwei.public@outlook.com>
Co-authored-by: Adam Hopkins <adam@amhopkins.com>

tests/test_json_decoding.py

@@ -0,0 +1,52 @@
+from json import loads as sloads
+
+import pytest
+
+
+try:
+    from ujson import loads as uloads
+
+    NO_UJSON = False
+    DEFAULT_LOADS = uloads
+except ModuleNotFoundError:
+    NO_UJSON = True
+    DEFAULT_LOADS = sloads
+
+from sanic import Request, Sanic, json
+
+
+@pytest.fixture(autouse=True)
+def default_back_to_ujson():
+    yield
+    Request._loads = DEFAULT_LOADS
+
+
+def test_change_decoder():
+    Sanic("Test", loads=sloads)
+    assert Request._loads == sloads
+
+
+def test_change_decoder_to_some_custom():
+    def my_custom_decoder(some_str: str):
+        dict = sloads(some_str)
+        dict["some_key"] = "new_value"
+        return dict
+
+    app = Sanic("Test", loads=my_custom_decoder)
+    assert Request._loads == my_custom_decoder
+
+    req_body = {"some_key": "some_value"}
+
+    @app.post("/test")
+    def handler(request):
+        new_json = request.json
+        return json(new_json)
+
+    req, res = app.test_client.post("/test", json=req_body)
+    assert sloads(res.body) == {"some_key": "new_value"}
+
+
+@pytest.mark.skipif(NO_UJSON is True, reason="ujson not installed")
+def test_default_decoder():
+    Sanic("Test")
+    assert Request._loads == uloads