API endpoint to return a transfer's estimated fees

[rakanalh]

Abstract

Currently, Raiden requests a route from the PFS when the user decides to send a transfer of an X amount. The mediation fees charged by mediators of this transfer is unknown to the user before hitting the send button or calling the transfer API.

Motivation

To improve UX, Raiden should provide an endpoint that could be integrated in the UI to return the estimated fee value depending on the transfer amount.

Specification

• Make sure there is a decision on whether the PFS will be paid for such a request or not.
• Create an API endpoint which receives the transfer's parameters.
• Call the PFS to request the estimated fee for the transfer.
• Optionally, the PFS may or may not be paid for this request. If it is, then an IOU would be required by the PFS.
• Return the estimated fee value
• Write tests for this new endpoint.

[karlb]

To accurately estimate the fees, the PFS will have to find the route first. Since requesting a route from the PFS already returns a fee estimate along with the route, why do we need an additional endpoint?

To me it looks like we should display the fee to the user after asking the PFS for a route but before actually starting the payment.

[rakanalh]

Our API endpoints are stateless. What you're suggesting is that, we query the route from the PFS and somehow save it until the user hits the send button which then means that we can use that route. Provided the API statelessness, i would suggest we do it this way.