api: give specific message on json calls missing content-type header (#29856)

tests/test_api.py

@@ -565,6 +565,9 @@ def test_formdef_submit(pub, local_user):
     assert data_class.get(resp.json['data']['id']).user_id == str(local_user.id)
     assert data_class.get(resp.json['data']['id']).tracking_code is None
 
+    resp = get_app(pub).post(url(), json.dumps({'data': {}}), status=400)  # missing Content-Type: application/json header
+    assert resp.json['err_desc'] == 'expected JSON but missing appropriate content-type'
+
     formdef.disabled = True
     formdef.store()
     resp = get_app(pub).post_json(url(), {'data': {}}, status=403)

wcs/qommon/http_request.py

@@ -125,7 +125,7 @@ class HTTPRequest(quixote.http_request.HTTPRequest):
             length = int(self.environ.get('CONTENT_LENGTH') or '0')
             payload = self.django_request.read(length)
             try:
-                self.json = json_loads(payload)
+                self._json = json_loads(payload)
             except ValueError, e:
                 raise RequestError('invalid json payload (%s)' % str(e))
         # Make sure request.form doesn't contain unicode strings, converting
@@ -135,6 +135,12 @@ class HTTPRequest(quixote.http_request.HTTPRequest):
                 for k, v in self.form.items())
         self.parsed = True
 
+    @property
+    def json(self):
+        if not hasattr(self, '_json'):
+            raise RequestError('expected JSON but missing appropriate content-type')
+        return self._json
+
     def is_json(self):
         if self.is_json_marker:
             return True