Fixed #13222 -- Made HttpResponse iterable once

response.content can be accessed many times as desired, and always
returns the same result.

iter(response) works only once and consumes the iterator.

django/http/response.py

@@ -283,7 +283,8 @@ class HttpResponse(HttpResponseBase):
                 'deprecated. Use `StreamingHttpResponse` instead '
                 'if you need the streaming behavior.',
                 PendingDeprecationWarning, stacklevel=2)
-        self._iterator = iter(self._container)
+        if not hasattr(self, '_iterator'):
+            self._iterator = iter(self._container)
         return self
 
     def __next__(self):
@@ -303,7 +304,7 @@ class HttpResponse(HttpResponseBase):
 
     def tell(self):
         self._consume_content()
-        return sum(len(chunk) for chunk in self)
+        return len(self.content)
 
 
 class StreamingHttpResponse(HttpResponseBase):

django/test/testcases.py

@@ -596,7 +596,11 @@ class TransactionTestCase(SimpleTestCase):
             msg_prefix + "Couldn't retrieve content: Response code was %d"
             " (expected %d)" % (response.status_code, status_code))
         text = force_text(text, encoding=response._charset)
-        content = b''.join(response).decode(response._charset)
+        if response.streaming:
+            content = b''.join(response.streaming_content)
+        else:
+            content = response.content
+        content = content.decode(response._charset)
         # Avoid ResourceWarning about unclosed files.
         response.close()
         if html: