Content-Type: text/plain is added to header if Content-Type header is not present

[PeterFalken]

This was reported previously as issue #4761
In this case FireFox can't render the webpage that was sent and only displays the HTML code instead of rendering the page.
This affects the newest release 2.2.2

./traefik version
Version: 2.2.2
Codename: chevrotin
Go version: go1.14.4
Built: 2020-07-08T15:30:29Z
OS/Arch: linux/amd64

Original headers:

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
X-Powered-By: Servlet 2.4; JBoss-4.0.5.GA (build: CVSTag=Branch_4_0 date=200610162339)/Tomcat-5.5
Transfer-Encoding: chunked
Date: Wed, 08 Jul 2020 19:48:50 GMT

Header server after Traefik:

HTTP/1.1 200 OK
Date: Wed, 08 Jul 2020 19:50:33 GMT
Server: Apache-Coyote/1.1
X-Content-Type-Options: nosniff
X-Powered-By: Servlet 2.4; JBoss-4.0.5.GA (build: CVSTag=Branch_4_0 date=200610162339)/Tomcat-5.5
Content-Type: text/plain; charset=utf-8
Transfer-Encoding: chunked

In order to reproduce - use any other proxy or nginx to strip the Content-Type header and feed the request to Traefik - inspecting the Response Headers after being sent by Traefik, you can see that the Content-Type header is now:
"Content-Type: text/plain;"

[ldez]

Hello,

the problem is already fixed:

• content-type: text is added to header if content-type is not present #4761 (comment)
• Remove Content-Type auto-detection #6097
• https://docs.traefik.io/middlewares/contenttype/

[PeterFalken]

Thank you for pointing me in the right direction, Ludovic.

[PeterFalken]

@ldez , would it be possible to add a similar option for the Compress middleware?
So that the MIME auto-detection can be skipped for responses where Content-Type header is not defined.