Disable br compression when no Accept-Encoding header is present

[robin-moser]

What does this PR do?

Fixes #9734

To ensure compatibility, it is recommended not to compress a request when there is no Accept-Encoding header present, even though RFC9110 (accept-encoding) would allow any compression.

Motivation

Stops traefik from breaking multiple applications that don't send a Accept-Encoding header and at the same time don't have any support for encoded http responses. Two breaking examples are yum/dnf and Zenarmor on Opnsense.

More

• Added/updated tests
• Added/updated documentation

[rjsocha]

The wording in RFC 2616, specifically in https://datatracker.ietf.org/doc/html/rfc2616#section-14.3 is similar to this

" If no Accept-Encoding field is present in a request, the server MAY
assume that the client will accept any content coding. In this case,
if "identity" is one of the available content-codings, then the
server SHOULD use the "identity" content-coding, unless it has
additional information that a different content-coding is meaningful
to the client.
"

In any case, I believe this option should be configurable. For example:

  label:
  ...
  - traefik.http.middlewares.test4compress.compress.disableCompressionOnMissingAcceptEncoding=true
  - traefik.http.middlewares.test4compress.compress.disableOnMissingAcceptEncoding=true
  - traefik.http.middlewares.test4compress.compress.noAcceptEncodingCompression=true

It should, by default, be disabled, following the semantics of RFC 9110.

[rtribotte]

The wording in RFC 2616, specifically in https://datatracker.ietf.org/doc/html/rfc2616#section-14.3 is similar to this

" If no Accept-Encoding field is present in a request, the server MAY assume that the client will accept any content coding. In this case, if "identity" is one of the available content-codings, then the server SHOULD use the "identity" content-coding, unless it has additional information that a different content-coding is meaningful to the client. "

In any case, I believe this option should be configurable. For example:

  label:
  ...
  - traefik.http.middlewares.test4compress.compress.disableCompressionOnMissingAcceptEncoding=true
  - traefik.http.middlewares.test4compress.compress.disableOnMissingAcceptEncoding=true
  - traefik.http.middlewares.test4compress.compress.noAcceptEncodingCompression=true

It should, by default, be disabled, following the semantics of RFC 9110.

Hello @rjsocha,

Thanks for this feedback. It seems to me that the need to introduce an option to control this behavior should be discussed in a dedicated issue first.

[rtribotte]

Hello @robin-moser,

I have enabled the checks, and as you can see, the TestShouldCompressWhenNoAcceptEncodingHeader test should be adapted as well.

[robin-moser]

Sorry, I missed that one!
I updated the unit tests, locally they are passing now.

[rtribotte]

Thanks 👍

[nmengin]

Hey @robin-moser ,

We'd like to bring your feature in Traefik v3.0.
Do you need some help on it?

[robin-moser]

Hi @nmengin,
sorry for the late reaction. I just committed the suggested documentation changes.

[kevinpollet]

Thanks 👍

[lbenguigui]

LGTM