ASP.NET Core and 102 status code implementation

Using HTTP 102 requires that the server send two responses for one request. ASP.NET (Core or not) does not support sending a response to the client without completely ending the request. Any attempt to send two responses will end up in throwing an exception and just not working. (I tried a couple different ways)

There's a good discussion here about how it's not actually in the HTTP spec, so implementing it isn't really required.

There are a couple alternatives I can think of:

1. Use web sockets (a persistent connection that allows data to be sent back and forth), like with SignalR, for example.
2. If your request takes a long time because it's getting data from elsewhere, you can try pulling in that data via a stream and send it to the client via a stream. That will send the data as it's coming in, rather than loading it all into memory first before sending it. Here's an example of streaming data from a database to the response: https://stackoverflow.com/a/45682190/1202807