Allow custom response body streaming of HTTP Responses without Transfer-Encoding or Content-Length set

[Danielku15]

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Is your feature request related to a problem? Please describe the problem.

I am trying to do a plain HTTP response streaming without chunked HTTP encoding but using an own framing logic. Unfortunately Kestrel automatically switches to chunked encoding based on whether a custom Transfer-Encoding or Content-Length is set.

aspnetcore/src/Servers/Kestrel/Core/src/Internal/Http/HttpProtocol.cs

Lines 1198 to 1228 in 6359c76

	else if (!hasTransferEncoding && !responseHeaders.ContentLength.HasValue)
	{
	if ((appCompleted || !_canWriteResponseBody) && !_hasAdvanced) // Avoid setting contentLength of 0 if we wrote data before calling CreateResponseHeaders
	{
	if (CanAutoSetContentLengthZeroResponseHeader())
	{
	// Since the app has completed writing or cannot write to the response, we can safely set the Content-Length to 0.
	responseHeaders.ContentLength = 0;
	}
	}
	// Note for future reference: never change this to set _autoChunk to true on HTTP/1.0
	// connections, even if we were to infer the client supports it because an HTTP/1.0 request
	// was received that used chunked encoding. Sending a chunked response to an HTTP/1.0
	// client would break compliance with RFC 7230 (section 3.3.1):
	//
	// A server MUST NOT send a response containing Transfer-Encoding unless the corresponding
	// request indicates HTTP/1.1 (or later).
	//
	// This also covers HTTP/2, which forbids chunked encoding in RFC 7540 (section 8.1:
	//
	// The chunked transfer encoding defined in Section 4.1 of [RFC7230] MUST NOT be used in HTTP/2.
	else if (_httpVersion == Http.HttpVersion.Http11)
	{
	_autoChunk = true;
	responseHeaders.SetRawTransferEncoding("chunked", _bytesTransferEncodingChunked);
	}
	else
	{
	DisableKeepAlive(ConnectionEndReason.ResponseNoKeepAlive);
	}
	}

Setting the Transfer-Encoding to something custom (e.g. the outdated identity) breaks compatibliity with reverse proxies like Traeffik. Hence I want to be able to "stream" an endless (no Content-Length known) raw byte response without setting a Transfer-Encoding header.

Describe the solution you'd like

Kestrel should give some control on whether the automatic switch to chunked encoding is done or not allowing me to disable it. This could happen either via a new IFeature or as extension to an existing feature.

Additional context

While this automatic switching might be OK for most standard browser use-cases, it breaks any usecases where HTTP is used as foundation for alternative communication systems. The HTTP/1.1 spec mentions that Transfer-Encodings need to be registered in the HTTP Transfer Coding Registry
so it is better to not send anything than an wrong/unsupported value.

My main real-world usecase is:

• Networked Transport of RTCM via Internet Protocol (NTRIP)