Open HRMP channel between Moonbeam and Acala

TL:DR

Similar to other HRMP channel proposals, we propose to open an HRMP channel between Moonbeam and Acala.

Summary

We propose to open a bi-directional channel between Moonbeam and Acala. Initially, the main use case will be to transfer GLMR and ACA/aUSD between the two chains, but it can be further expanded to other use cases.

Proposal

There is no on-chain proposal yet; #TBD.

Technical details:

The procedure for opening the channels is as follows:

  1. Acala: democracy proposal to open the Acala to Moonbeam HRMP channel
  2. Moonbeam: democracy batched proposal to
    • Open Moonbeam to Acala HRMP channel
    • Accept Acala to Moonbeam HRMP channel
    • Register ACA & aUSD assets as XC-20s
  3. Acala: democracy proposal to accept Moonbeam to Acala HRMP channel
  4. Polkadot: wait one session after each acceptance for each channel to be opened
  5. XCM based cross-chain transfer will be possible at this stage

The extrinsics that need to be executed on the relay chain , are:

  • For step 1: hrmp.hrmpInitOpenChannel(recipient: 2004, proposedMaxCapacity: 1000, proposedMaxMessageSize: 102400) , which its hex-encoded call data is 0x3c00d4070000e803000000900100
  • For step 2 (open channel to Acala) hrmp.hrmpInitOpenChannel(recipient: 2000, proposedMaxCapacity: 1000, proposedMaxMessageSize: 102400) , which its hex-encoded call data is 0x3c00d0070000e803000000900100
  • For step 2 (accept channel from Acala): hrmp.hrmpAcceptOpenChannel(sender: 2000) , which hex-encoded call data is 0x3c01d0070000
  • For step 3: hrmp.hrmpAcceptOpenChannel(sender: 2004) , which its hex-encoded call data is 0x3c01d4070000

The proposedMaxCapacity and proposedMaxMessageSize are set to the values of Polkadot’s configuration.activeConfig.hrmpChannelMaxCapacity and configuration.activeConfig.hrmpChannelMaxMessageSize values, respectively.

These extrinsics need to be called from the parachain’s sovereign account as origin, via a democracy proposal. The proposal will use polkadotXcm pallet to send XCM message to the Relay Chain with the following items:

  • Withdraw asset: take funds out of the Sovereign Account of the origin parachain (in the relay chain) to a holding state
  • Buy execution: buys execution time from the relay chain, to execute the XCM message
  • Transact: provides the call data to be executed
  • Deposit asset (optional): refunds the leftover funds after the execution. If this is not provided, no refunds will be carried out

As a prerequisite, the parachain’s sovereign account must contain at least 20 DOT to be locked as collateral (10 for each channel direction), plus some DOT to pay for XCM execution fees. This depends on the approval of Referendum 61.

5 Likes