`Content-Encoding: identity` is not a valid value per RFC

[lvivski]

Is there an existing issue for this?

• [x] I have searched the existing issues

Describe the bug

Content-Encoding: identity is not a valid value

RFC references:

RFC 2616, Section 3.5:

identity The default (identity) encoding; the use of no transformation whatsoever. This content-coding is used only in the Accept- Encoding header, and SHOULD NOT be used in the Content-Encoding header.

Newer RFC 7131 mentions it as valid in Accept-Encoding but not in Content-Encoding

RFC 7231 Section 5.3.4:

Accept-Encoding = #( codings [ weight ] ) codings = content-coding / "identity" / "*"

RFC 7231 Section 3.1.2.2:

Content-Encoding = 1#content-coding

Expected Behavior

If no compression is applied, then Content-Encoding header is not necessary

Steps To Reproduce

https://github.com/dotnet/aspnetcore/blob/73ce13e67ec6dbf004b0f85508ae9920e30e0cb6/src/SignalR/common/Http.Connections/src/Internal/Transports/ServerSentEventsServerTransport.cs#L41

Exceptions (if any)

No response

.NET Version

No response

Anything else?

No response

[BrennanConroy]

This is done because IIS compresses text/* by default unless a content-encoding header is present. That breaks streaming SSE as it buffers in order to compress the response.

[lvivski]

Is there any other way to bypass compression without manually specifying a content-encoding header?

[MackinnonBuck]

Thanks for reaching out, @lvivski. Is there any issue you're observing other than the behavior not being compliant with RFC 7131?

You could always add a callback via HttpResponse.OnStarting() to override the header to something else.

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