Implement dict-like API on request objects for custom data. (#1666)

* Implement dict-like API on request objects for custom data.
* Updated docs about custom_context.

tests/test_request_data.py

@@ -8,22 +8,72 @@ try:
 except ImportError:
     from json import loads
 
-
-def test_storage(app):
+def test_custom_context(app):
     @app.middleware("request")
     def store(request):
+        request.ctx.user = "sanic"
+        request.ctx.session = None
+
+    @app.route("/")
+    def handler(request):
+        # Accessing non-existant key should fail with AttributeError
+        try:
+            invalid = request.ctx.missing
+        except AttributeError as e:
+            invalid = str(e)
+        return json({
+            "user": request.ctx.user,
+            "session": request.ctx.session,
+            "has_user": hasattr(request.ctx, "user"),
+            "has_session": hasattr(request.ctx, "session"),
+            "has_missing": hasattr(request.ctx, "missing"),
+            "invalid": invalid
+        })
+
+    request, response = app.test_client.get("/")
+    assert response.json == {
+        "user": "sanic",
+        "session": None,
+        "has_user": True,
+        "has_session": True,
+        "has_missing": False,
+        "invalid": "'types.SimpleNamespace' object has no attribute 'missing'",
+    }
+
+
+# Remove this once the deprecated API is abolished.
+def test_custom_context_old(app):
+    @app.middleware("request")
+    def store(request):
+        try:
+            request["foo"]
+        except KeyError:
+            pass
         request["user"] = "sanic"
-        request["sidekick"] = "tails"
+        sidekick = request.get("sidekick", "tails")  # Item missing -> default
+        request["sidekick"] = sidekick
+        request["bar"] = request["sidekick"]
         del request["sidekick"]
 
     @app.route("/")
     def handler(request):
         return json(
-            {"user": request.get("user"), "sidekick": request.get("sidekick")}
+            {
+                "user": request.get("user"),
+                "sidekick": request.get("sidekick"),
+                "has_bar": "bar" in request,
+                "has_sidekick": "sidekick" in request,
+            }
         )
 
     request, response = app.test_client.get("/")
 
+    assert response.json == {
+        "user": "sanic",
+        "sidekick": None,
+        "has_bar": True,
+        "has_sidekick": False,
+    }
     response_json = loads(response.text)
     assert response_json["user"] == "sanic"
     assert response_json.get("sidekick") is None