Is there an existing issue for this?

• I have searched the existing issues

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

Today we support several built in types as result types (along with async versions), string, IResult, any other object (JSON). The idea is to extend support for Stream and PipeReader (along with the async versions). This provides symmetry with automatic binding of Stream and PipeReader in the input and as the built in version of #39383.

Describe the solution you'd like

This is an extension of #39383 to natively understand Stream, Task<Stream>, ValueTask<Stream>, PipeReader, Task<PipeReader>, and ValueTask<PipeReader> as a return type from handler methods. The default behavior would be:

• Set the content type to "application/octet-stream" (if it's not already set)
• We always copy the entire stream to the response body
• Does not support range requests
• Does not support download file names

Additional context

app.MapGet("/blob/download1", () =>
{
    return File.OpenRead("../something.txt");
});