I have a micro-benchmark that simulates a gRPC call. Instead of calling the underlying SocketsHttpHandler, a mock handler returns a manually created HttpResponseMessage.

A lot of the allocations in this scenario are related to HTTP headers (obviously they would be less significant in a real world HTTP call).

A request/response has many header collections, and most of the time these header collections are going to be small.

• HttpRequestMessage.Headers
• HttpRequestMessage.Content.Headers
• HttpResponseMessage.Headers
• HttpResponseMessage.Trailers
• HttpResponseMessage.Content.Headers

At the moment an internal dictionary is used in each. This seems unnecessary given their typically small size. Can the internal storage of headers be optimized?