CloseErrors should cause fRPC to Close the underlying connection

[ShivanshVij]

Currently, returning an error from an fRPC handler does not close the underlying connection. This default behaviour is fine.

However, users should be able to return a special CloseError type - which will close the underlying connection once the error has been written.

An example implementation the CloseError

type CloseError struct {
	err error
}

func NewCloseError(err error) CloseError {
	return CloseError{err: err}
}

func (e CloseError) Error() string {
	return e.err.Error()
}

And in the generated fRPC Code, an example check:

table[10] = func(ctx context.Context, incoming *packet.Packet) (outgoing *packet.Packet, action frisbee.Action) {
		req := NewProxyRequest()
		err := req.Decode((*incoming.Content)[:incoming.Metadata.ContentLength])
		if err == nil {
			if req.ignore {
				controller.Proxy(ctx, req)
			} else {
				var res *ProxyResponse
				outgoing = incoming
				outgoing.Content.Reset()
				res, err = controller.Proxy(ctx, req)
				if err != nil {
					if _, ok := err.(CloseError); ok {
						action = frisbee.CLOSE
					}
					res.Error(outgoing.Content, err)
				} else {
					res.Encode(outgoing.Content)
				}
				outgoing.Metadata.ContentLength = uint32(len(*outgoing.Content))
			}
		}
		return
	}