Rename json=1 to format=json and respect accept header order

README.rst

@@ -145,7 +145,7 @@ Getting machine readable JSON reports
 
 If you want machine readable status reports you can request the ``/ht/``
 endpoint with the ``Accept`` HTTP header set to ``application/json``
-or pass ``json=1`` as a query parameter.
+or pass ``format=json`` as a query parameter.
 
 The backend will return a JSON response:
 
@@ -168,7 +168,7 @@ The backend will return a JSON response:
 
     $ curl -v -X GET http://www.example.com/ht/?json=1
 
-    > GET /ht/?json=1 HTTP/1.1
+    > GET /ht/?format=json HTTP/1.1
     > Host: www.example.com
     >
     < HTTP/1.1 200 OK

health_check/views.py

@@ -10,6 +10,43 @@
 from health_check.plugins import plugin_dir
 
 
+class MediaType:
+    """
+    Sortable object representing HTTP's accept header.
+
+    .. seealso:: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept
+    """
+
+    def __init__(self, mime_type, weight=1.0):
+        self.mime_type = mime_type
+        self.weight = float(weight)
+
+    @classmethod
+    def from_string(cls, value):
+        """Return single instance parsed from given accept header string."""
+        try:
+            return cls(*value.split(';'))
+        except ValueError:
+            return cls(value)
+
+    @classmethod
+    def parse_header(cls, value='*/*'):
+        """Parse HTTP accept header and return instances sorted by weight."""
+        yield from sorted((cls.from_string(token.strip()) for token in value.split(',')), reverse=True)
+
+    def __str__(self):
+        return "%s;%d" % (self.mime_type, self.weight)
+
+    def __repr__(self):
+        return "%s: %s" % (type(self).__name__, self.__str__())
+
+    def __eq__(self, other):
+        return self.weight == other.weight and self.mime_type == other.mime_type
+
+    def __lt__(self, other):
+        return self.weight.__lt__(other.weight)
+
+
 class MainView(TemplateView):
     template_name = 'health_check/index.html'
 
@@ -43,14 +80,18 @@ def _run(plugin):
 
         status_code = 500 if errors else 200
 
-        accept_format = request.META.get('HTTP_ACCEPT', '')
-        accepts_json = 'application/json' in accept_format
+        format_override = request.GET.get('format')
 
-        if accepts_json or request.GET.get('json', False):
+        if format_override == 'json':
             return self.render_to_response_json(plugins, status_code)
-        else:
-            context = {'plugins': plugins, 'status_code': status_code}
-            return self.render_to_response(context, status=status_code)
+
+        accept_header = request.META.get('HTTP_ACCEPT', '*/*')
+        for media in MediaType.parse_header(accept_header):
+            if media.mime_type in ['text/html', '	application/xhtml+xml', '*/*']:
+                context = {'plugins': plugins, 'status_code': status_code}
+                return self.render_to_response(context, status=status_code)
+            if 'application/json' == media.mime_type:
+                return self.render_to_response_json(plugins, status_code)
 
     def render_to_response_json(self, plugins, status):
         return JsonResponse(

tests/test_views.py

@@ -4,13 +4,48 @@
 from health_check.conf import HEALTH_CHECK
 from health_check.exceptions import ServiceWarning
 from health_check.plugins import plugin_dir
+from health_check.views import MediaType
 
 try:
     from django.urls import reverse
 except ImportError:
     from django.core.urlresolvers import reverse
 
 
+
+class TestMediaType:
+
+    def test_lt(self):
+        assert not MediaType('*/*') < MediaType('*/*')
+        assert not MediaType('*/*') < MediaType('*/*', 0.9)
+        assert MediaType('*/*', 0.9) < MediaType('*/*')
+
+    def test_str(self):
+        assert str(MediaType('*/*')) == "*/*;1"
+
+    def test_repr(self):
+        assert repr(MediaType('*/*')) == "MediaType: */*;1"
+
+    def test_eq(self):
+        assert MediaType('*/*') == MediaType('*/*')
+        assert MediaType('*/*', 0.9) != MediaType('*/*')
+
+    def test_from_string(self):
+        assert MediaType.from_string('*/*') == MediaType('*/*')
+        assert MediaType.from_string('*/*;0.9') == MediaType('*/*', 0.9)
+        assert MediaType.from_string('*/*;0.9') == MediaType('*/*', 0.9)
+
+    def test_parse_header(self):
+        assert list(MediaType.parse_header()) == [
+            MediaType('*/*'),
+        ]
+        assert list(MediaType.parse_header('text/html;0.1,application/xhtml+xml;0.1,application/json')) == [
+            MediaType('application/json'),
+            MediaType('text/html', 0.1),
+            MediaType('application/xhtml+xml', 0.1),
+        ]
+
+
 class TestMainView:
     url = reverse('health_check:health_check_home')
 
@@ -71,10 +106,48 @@ def run_check(self):
         plugin_dir.reset()
         plugin_dir.register(JSONSuccessBackend)
         response = client.get(self.url, HTTP_ACCEPT='application/json')
-        assert response.status_code == 200, response.content.decode('utf-8')
         assert response['content-type'] == 'application/json'
-        assert json.loads(response.content.decode('utf-8')) == \
-            {JSONSuccessBackend().identifier(): JSONSuccessBackend().pretty_status()}
+
+    def test_success_accept_order(self, client):
+        class JSONSuccessBackend(BaseHealthCheckBackend):
+            def run_check(self):
+                pass
+
+        plugin_dir.reset()
+        plugin_dir.register(JSONSuccessBackend)
+        response = client.get(self.url, HTTP_ACCEPT='text/html,application/xhtml+xml,application/json;0.9,*/*;0.1')
+        assert response['content-type'] == 'text/html; charset=utf-8'
+
+    def test_success_accept_order__reverse(self, client):
+        class JSONSuccessBackend(BaseHealthCheckBackend):
+            def run_check(self):
+                pass
+
+        plugin_dir.reset()
+        plugin_dir.register(JSONSuccessBackend)
+        response = client.get(self.url, HTTP_ACCEPT='text/html;0.1,application/xhtml+xml;0.1,application/json')
+        assert response['content-type'] == 'application/json'
+
+    def test_format_override(self, client):
+        class JSONSuccessBackend(BaseHealthCheckBackend):
+            def run_check(self):
+                pass
+
+        plugin_dir.reset()
+        plugin_dir.register(JSONSuccessBackend)
+        response = client.get(self.url + '?format=json', HTTP_ACCEPT='text/html')
+        assert response['content-type'] == 'application/json'
+
+    def test_format_no_accept_header(self, client):
+        class JSONSuccessBackend(BaseHealthCheckBackend):
+            def run_check(self):
+                pass
+
+        plugin_dir.reset()
+        plugin_dir.register(JSONSuccessBackend)
+        response = client.get(self.url)
+        assert response.status_code == 200, response.content.decode('utf-8')
+        assert response['content-type'] == 'text/html; charset=utf-8'
 
     def test_error_accept_json(self, client):
         class JSONErrorBackend(BaseHealthCheckBackend):
@@ -95,7 +168,7 @@ def run_check(self):
 
         plugin_dir.reset()
         plugin_dir.register(JSONSuccessBackend)
-        response = client.get(self.url, {'json': 1})
+        response = client.get(self.url, {'format': 'json'})
         assert response.status_code == 200, response.content.decode('utf-8')
         assert response['content-type'] == 'application/json'
         assert json.loads(response.content.decode('utf-8')) == \
@@ -108,7 +181,7 @@ def run_check(self):
 
         plugin_dir.reset()
         plugin_dir.register(JSONErrorBackend)
-        response = client.get(self.url, {'json': 1})
+        response = client.get(self.url, {'format': 'json'})
         assert response.status_code == 500, response.content.decode('utf-8')
         assert response['content-type'] == 'application/json'
         assert 'JSON Error' in json.loads(response.content.decode('utf-8'))[JSONErrorBackend().identifier()]