README.md

Upward/ Downward native-token transfers

Working example for polkadot-v0.9.13 to transfer the native token from the relay-chain to the parachain via the xcm-pallet and vice-versa. The message format is very generic, hence the correct extrinsics for those transfers are shown below.

Preliminaries

The relay chain must have marked encointer as a trusted teleporter, which is not yet the case. This polkadot fork contains slightly amended westend and rococo runtimes, where encointer is a trusted teleporter.

• Polkadot relay chain: https://github.com/encointer/polkadot/tree/v0.9.13-trusted-encointer

• For debugging it greatly helps to pass -lxcm=trace to the collator. a subsequent less 9944.log | grep xcm, neatly displays all XCM steps.

Downwards Tx

Send from Alice on the relay chain to Ferdie on the parachain.

Upwards Token Tx

Send from Alice on the parachain to Ferdie on the relay chain.

Note: The relay chain tracks teleported assets. Hence, we must perform a downward transfer before we do the upward transfer such that the total token stream in parachain direction remains positive. Otherwise, we get a NotWithdrawable error upon the upward transfer on the relay chain side. In production system this condition always holds as the parachain starts with 0 tokens anyhow.

Related Resources

• Shawn Tabrizi's XCM workshop at sub0 and the corresponding resources.