Fixed #13222 -- Repeated iteration of HttpResponse

Thanks teepark for the report and grahamd for his insights.

django/http/response.py

@@ -260,9 +260,9 @@ class HttpResponse(HttpResponseBase):
         else:
             self._container = [value]
             self._base_content_is_iter = False
+        self._iterator = iter(self._container)
 
     def __iter__(self):
-        self._iterator = iter(self._container)
         return self
 
     def __next__(self):
@@ -284,7 +284,7 @@ class HttpResponse(HttpResponseBase):
     def tell(self):
         if self._base_content_is_iter:
             raise Exception("This %s instance cannot tell its position" % self.__class__.__name__)
-        return sum([len(chunk) for chunk in self])
+        return len(self.content)
 
 
 class StreamingHttpResponse(HttpResponseBase):

tests/regressiontests/httpwrappers/tests.py

@@ -330,6 +330,13 @@ class HttpResponseTests(unittest.TestCase):
         self.assertRaises(UnicodeEncodeError,
                           getattr, r, 'content')
 
+    def test_iterator_isnt_rewound(self):
+        # Regression test for #13222
+        r = HttpResponse('abc')
+        i = iter(r)
+        self.assertEqual(list(i), [b'abc'])
+        self.assertEqual(list(i), [])
+
     def test_file_interface(self):
         r = HttpResponse()
         r.write(b"hello")