#36688: GzipMiddleware adds 'Vary: Accept-Encoding' unnecessarily
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Reporter: Adam Johnson | Owner: Adam Johnson
Type: Bug | Status: closed
Component: HTTP handling | Version: dev
Severity: Normal | Resolution: invalid
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by Adam Johnson):
* resolution: => invalid
* status: assigned => closed
Comment:
Okay, I'm wrong. `Vary: Accept-Encoding` should be sent anyway, because
the `Accept-Encoding` header is inspected, regardless of compression
outcome. I checked this with Claude, by asking its opinion and getting it
to test the behaviour of nginx and caddy with incompressible random data.
[https://gist.github.com/adamchainz/17c22f9aa87ce821972186964ce3d310 log
in this GIST]. (Oddly nginx requires `gzip_vary on` to even set the `Vary`
header, which seems wrong.)
But I think something is wrong then that we don't add the `Vary` header
before the *first* early-return clause:
{{{#!python
if not response.streaming and len(response.content) < 200:
return response
}}}
Just because the length was too small doesn't mean we wouldn't compress
the same URL when it sends larger values, as size may be dynamic. But I
think this is minor and I will reserve reporting it as a bug for a future
larger proposal to refactor the whole middleware to support zstd too,
based on [https://github.com/adamchainz/django-http-compression django-
http-compression].
--
Ticket URL: <https://code.djangoproject.com/ticket/36688#comment:2>
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