Avoid buffering the content before streaming to the response body

[gfoidl]

Addressed the point outlined in #2408 (comment) and contributes to #2791 (but does not fix that issue¹)

For array streaming the whole content was buffered in a memory stream, then copied to the ASP.NET Core's response stream.
This has some downsides:

• the content-length isn't needed, ASP.NET Core will produce a chunked output, which can be read by any client
• it needs copying to the memory stream to the response -- which can be resource intensive for large data
• for large data it's possible that the memory stream gets bigger than 85.000 bytes, so it's above the large object heap (LOH) threshold of the GC, thus that object will live until a Gen-2 collection happens

These points can be avoided by writing to the response stream directly.

Footnotes

1. I'll try to address the pooling, etc. point later, as that's not so straight forward. ↩

[oskardudycz]

Thanks, that's a nice improvement!