Cross Token Network Payments

[ulope]

trafficstars

Abstract

We want to support single payments that cross token network boundaries.

Motivation

TBD

Specification

• Implementation in Raiden itself External makes little sense b/c of difficulties with synchronizing, restartability etc.

• Raiden Node:

  • Swap will happen in mediator state machine (https://github.com/raiden-network/raiden/issues/6515)
  • The API needs to gain an endpoint that supports payments across TNs (#6516)
  • Cross network payment messages will contain the per hop token network route information
    • Ideally existing single token payments will remain backwards compatible
    • The new format should be enabled using capabilities
  • Nodes will opt in to providing swaps and inform the PFS via a new message (e.g. PFSSwapUpdate) (#6511)
    • CLI option to enable token pairs and set rate premium (#6514)
    • The message will contain a rate premium the node requires over uniswap base. (#6511)
    • The PFS will update the base rate from uniswap every block (https://github.com/raiden-network/raiden-services/issues/853)
    • The swap update need to have a validity period and be re-published before it expires. If not the PFS will remove the swap ability. (#6511)

• PFS:

  • PFS will gain ability to find paths between multiple token networks (raiden-network/raiden-services#851)
  • The route returned by the PFS will contain the applicable per-hop token network per hop. (raiden-network/raiden-services#852, #6512)

• WebUI:

  • An interface is needed

• MVP constraints:

  • Only uniswap as rate source for now
  • Only one rate premium per token pair for both directions
  • Only payments across TNs of the same TNR will be supported
  • PFS will use a fixed amount when querying the rates (amount TBD), i.e. we don't account for slippage for now

• Possible expansions:

  • Per path request rate calculation
  • Nodes can constrain the max slippage
  • Cross TNR payments
  • Payments with oneself
  • Cross blockchain payments

Backwards Compatibility

Ideally payments within a single TN continue to use the same message format and therefore remain backwards compatible. Should be decided based on implementation effort.