New JsonResponse checker

to validate common anti-patterns with http responses returning
JSON data

Author: atodorov

pylint_django/checkers/__init__.py

@@ -1,9 +1,11 @@
 """Checkers."""
 from pylint_django.checkers.django_installed import DjangoInstalledChecker
 from pylint_django.checkers.models import ModelChecker
+from pylint_django.checkers.json_response import JsonResponseChecker
 
 
 def register_checkers(linter):
     """Register checkers."""
     linter.register_checker(ModelChecker(linter))
     linter.register_checker(DjangoInstalledChecker(linter))
+    linter.register_checker(JsonResponseChecker(linter))

pylint_django/checkers/json_response.py

@@ -0,0 +1,59 @@
+# Copyright (c) 2018 Alexander Todorov <atodorov@MrSenko.com>
+
+# Licensed under the GPL 2.0: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
+# For details: https://github.com/PyCQA/pylint-django/blob/master/LICENSE
+"""
+Various suggestions about JSON http responses
+"""
+
+import astroid
+
+from pylint import interfaces
+from pylint import checkers
+from pylint.checkers import utils
+from pylint_django.__pkginfo__ import BASE_ID
+
+
+class JsonResponseChecker(checkers.BaseChecker):
+    """
+    Looks for some common patterns when returning http responses containing
+    JSON data!
+    """
+
+    __implements__ = (interfaces.IAstroidChecker,)
+
+    # configuration section name
+    name = 'json-response-checker'
+    msgs = {'R%s01' % BASE_ID: ("Instead of HttpResponse(json.dumps(data)) use JsonResponse(data)",
+                                'http-response-with-json-dumps',
+                                'Used when json.dumps() is used as an argument to HttpResponse().'),
+            'R%s02' % BASE_ID: ("Instead of HttpResponse(content_type='application/json') use JsonResponse()",
+                                'http-response-with-content-type-json',
+                                'Used when HttpResponse() is returning application/json.'),
+            'R%s03' % BASE_ID: ("Redundant content_type parameter for JsonResponse()",
+                                'redundant-content-type-for-json-response',
+                                'Used when JsonResponse() contains content_type parameter. '
+                                'This is either redundant or the content_type is not JSON '
+                                'which is probably an error.')}
+
+    @utils.check_messages('http-response-with-json-dumps',
+                          'http-response-with-content-type-json',
+                          'redundant-content-type-for-json-response')
+    def visit_call(self, node):
+        if (node.func.as_string().endswith('HttpResponse') and node.args
+                and isinstance(node.args[0], astroid.Call)
+                and node.args[0].func.as_string() == 'json.dumps'):
+            self.add_message('http-response-with-json-dumps', node=node)
+
+        if node.func.as_string().endswith('HttpResponse') and node.keywords:
+            for keyword in node.keywords:
+                if (keyword.arg == 'content_type'
+                        and keyword.value.as_string().lower().find('application/json') > -1):
+                    self.add_message('http-response-with-content-type-json', node=node)
+                    break
+
+        if node.func.as_string().endswith('JsonResponse') and node.keywords:
+            for keyword in node.keywords:
+                if keyword.arg == 'content_type':
+                    self.add_message('redundant-content-type-for-json-response', node=node)
+                    break

pylint_django/tests/input/func_json_response.py

@@ -0,0 +1,28 @@
+# pylint: disable=missing-docstring, line-too-long
+
+import json
+from django import http
+from django.http import HttpResponse
+
+
+def say_yes():
+    return HttpResponse(json.dumps({'rc': 0, 'response': 'ok'}))  # [http-response-with-json-dumps]
+
+
+def say_yes2():
+    data = {'rc': 0, 'response': 'ok'}
+    return http.HttpResponse(json.dumps(data))  # [http-response-with-json-dumps]
+
+
+def say_no():
+    return HttpResponse("no")
+
+
+def redundant_content_type():
+    data = {'rc': 0, 'response': 'ok'}
+    return http.JsonResponse(data, content_type='application/json')  # [redundant-content-type-for-json-response]
+
+
+def content_type_json():
+    json_data = "this comes from somewhere"
+    return HttpResponse(json_data, content_type='application/json')  # [http-response-with-content-type-json]

pylint_django/tests/input/func_json_response.txt

@@ -0,0 +1,4 @@
+http-response-with-json-dumps:9:say_yes:Instead of HttpResponse(json.dumps(data)) use JsonResponse(data)
+http-response-with-json-dumps:14:say_yes2:Instead of HttpResponse(json.dumps(data)) use JsonResponse(data)
+redundant-content-type-for-json-response:23:redundant_content_type:Redundant content_type parameter for JsonResponse()
+http-response-with-content-type-json:28:content_type_json:Instead of HttpResponse(content_type='application/json') use JsonResponse()