Abort streamed request

[LostKobrakai]

Say I'm using Finch to proxy some request to an upstream http server I might want to stop the stream if the caller closed the connection:

Finch.stream(request, Pour.HTTP, conn, fn
  {:status, status}, conn -> 
    send_chunked(conn, status)
    
  {:headers, _}, conn -> 
    conn
    
  {:data, _}, conn -> 
    case Plug.Conn.chunk(conn, chunk) do
      {:ok, conn} -> conn
      {:error, :closed} -> # how to abort here
    end
end)

[thbar]

This can also be useful when e.g. you'd want to halt the processing based on headers or status. For instance, if one wants to use streaming to compute a checksum of the data, but only compute it if the status is 200, and ignore otherwise (or follow a redirect header etc).

[ericmj]

You cannot abort HTTP/1 requests, the only thing you can do is close the connection. If you want to make a choice based on the headers you should use Expect: 100-continue.

With HTTP/2 you can abort requests, Mint exposes that through Mint.HTTP2.cancel_request/2.

[thbar]

Thanks! To simulate the abortion, is there a recommended way to close an HTTP/1 connection inside a Finch.stream stream function?

[chargreezy]

Sorry to bump this issue, but I was also curious if there is recommended way to close a connection inside a Finch.stream?

[chargreezy]

To expand on this, when streaming in finch we pass a reducing function for status, headers and data. This underlying mint connection is not available inside these calls, would adding the mint connection to the call make the functionality possible?

Before:

      {:status, value}, {_, headers, body} ->
        {value, headers, body}
      {:headers, value}, {status, headers, body} ->
        {status, headers ++ value, body}
      {:data, value}, {status, headers, body} ->
        {status, headers, [value | body]}

After:

      {:status, value, mint}, {_, headers, body} ->
        {value, headers, body}
      {:headers, value, mint}, {status, headers, body} ->
        {status, headers ++ value, body}
      {:data, value, mint}, {status, headers, body} ->
        // Maybe close the connection with Mint.HTTP.close(mint)

[ericmj]

If you throw inside the streaming function the connection will be closed (for HTTP/1.1) and the request will be cancelled: https://github.com/sneako/finch/blob/main/test/finch/http1/integration_test.exs#L83

[sneako]

Thanks @ericmj, that is a great point! If you throw in your stream function HTTP/1 will close the connection here and HTTP/2 will cancel the request here. I think that should be sufficient but if anyone can describe a situation where it would not be please share.

[chargreezy]

Thanks for the response! I saw the integration test but it's great to get a confirmation this is expected.