HTTP/2 and HTTP/3: Response trailers collection not reset

[JamesNK]

HTTP/2 and HTTP/3 will cache and reuse streams.

If the trailers collection is set via IHttpResponseTrailersFeature.Trailer = newValue then that collections contents will be reset but the collection itself will still be the user collection.

More info: #34360 (comment)

[ladeak]

I am considering picking this up.

My understanding that Http2Stream's OnReset() or Initialize() method should just set null for the _userTrailers fields.

Would you agree to such approach?