Merge ~troyanov/maas:fix-1990014 into maas:master

[Anton Troyanov]

LP:1990014 fix debug middleware

When response jas no `content` attribute, default value will be
returned.

Default value should be of type `bytes`, not `str`, otherwise it will
fail to decode with an exception:

```
AttributeError: 'str' object has no attribute 'decode'.
```

From Django documentation:
  HttpResponse.content
  A bytestring representing the content, encoded from a string if necessary.

[Christian Grabowski (cgrabowski)]

+1

review: Approve

[Anton Troyanov (troyanov)]

Unfortunately I didn't find a way on how to write a test that would reproduce the failure.

For testing I used steps to reproduce provided by Joao Andre Simioni

1. Add `debug_http: true` to regiond.conf,
2. Restart MAAS, and try to get: http://localhost:5240/MAAS/images-stream/grub-efi-signed/amd64/generic/uefi/20210819.0/grub2-signed.tar.xz
3. You get a 500 Internal Server Error with the body as 'str' object has no attribute 'decode'

[MAAS Lander (maas-lander)]

UNIT TESTS
-b fix-1990014 lp:~troyanov/maas/+git/maas into -b master lp:~maas-committers/maas

STATUS: FAILED
LOG: http://maas-ci.internal:8080/job/maas-tester/651/consoleText
COMMIT: f27283a647ac1775c6f881fd3e8298fab9909875

review: Needs Fixing

[MAAS Lander (maas-lander)]

UNIT TESTS
-b fix-1990014 lp:~troyanov/maas/+git/maas into -b master lp:~maas-committers/maas

STATUS: SUCCESS
COMMIT: a55ae18a9ea56201cebd772e0a140c0a39ec481b

review: Approve

diff --git a/src/maasserver/middleware.py b/src/maasserver/middleware.py
index 0012557..db5872d 100644
--- a/src/maasserver/middleware.py
+++ b/src/maasserver/middleware.py
@@ -331,7 +331,7 @@ class DebuggingLoggerMiddleware:
         response = self.get_response(request)
         if settings.DEBUG_HTTP and logger.isEnabledFor(self.log_level):
             header = " Response dump ".center(79, "#")
-            content = getattr(response, "content", "{no content}")
+            content = getattr(response, "content", b"{no content}")
             try:
                 decoded_content = content.decode("utf-8")
             except UnicodeDecodeError: