title
How to open Dotsama XCMP HRPM channel

Overview

This document describes all technical steps required to open a channel to any arbitrary chain.

Please adapt this to the variation of governance, business value and discussion forums according to the target chains.

This guide contains examples and links with guiding explanations on how to modify this for the next channel.

Assumptions

This guide assumes the following conditions:

You can get a minimum of 30 KSM and up to 70 KSM equivalent to handle end to end process
You are aware of how to use Polkadotjs and open relevant chains
You have a basic understanding of Dotsama encodings and the basics of XCM
You are aware of how Root transactions can be executed on the target chain
Transaction execution starts from Root unless stated otherwise

Identity and communication mediums

Create on chain and off chain identity on polkassembly
Login to https://matrix.to/#/#kusama:matrix.parity.io to observe discussions
Each chain may have its own chat to find

Minimum amount of native tokens for relay tip

Check that the chains involved have enough relay native tokens.

As of now this is in Storage -> configuration -> activeConfig related to channels.

The minimal amount of relay native token required is hrmpSenderDeposit + hrmpRecipientDeposit. It's recommended to have 2x the minimal amount.

Chain accounts can be obtained by mapping a parachain id to an account via substrate-js-utilities

Send Request to open channel to counterparty parachain

Example, 0x290001010002100004000000000b0060defb740513000000000b0060defb74050006000700f2052a01383c00e8030000e8030000009001000d0100040001009d20.

It will request to open hrmp to other parachain

It will execute a request to open a channel (half of future duplex).

Details

A message will be sent to the relay and pay all fees in the relay native(example, KSM) tokens.

Ensure the transaction is executed from Native (Parachain itself) originType

Ensure the function DepositAsset will deposit to the relevant Parachain identifier (spending chain). Specifically 0, X1(Parachain(2087)).

Ensure requireWeightAtMost is safely larger (e.g. 2-3x) than the weight of the transact.

Developer -> [Runtime Calls](https://polkadot.js.org/apps/?rpc=wss%3A%2F%2Frpc.ibp.network%2Fkusama#/runtime) -> TransactionPaymentCallApi -> queryCallInfo -> weight but strictly (and if possible safely) less than requireWeightAtMost.

requireWeightAtMost should be equivalent or less than in BuyExecution (you can compare it to the queryCallInfo.partialFee of the call and make BuyExecution 10x+ larger than this). In case of failure to do so, XCM will fail with TooExpensive

Do not set requireWeightAtMost too big as you will get dmpQueue.OverweightEnqueued. requireWeightAtMost has some similar semantics to requireWeightMinimum. It is not clear if the message will be retried automatically. For a sanity check navigate to configuration -> activeConfig -> umpMaxIndividualWeight and see if it is way higher than the weight of our transact.

NOTE: above details apply to other requests too.

For additional safety consider scheduling the transact messages instead of executing immediately.

0x3c00e8030000e803000000900100.

Check that:

The Transact message contains a proper existing parachain recipient.
proposedMaxCapacity is less or equal to Storage -> configuration -> activeConfig hrmpChannelMaxCapacity
proposedMaxMessageSize is less or equal to hrmpChannelMaxMessageSize here.
hrmpMaxParachain*Channels is not exceeded by any participant chains.

Counterparty chain to accept our request and request back

Encode the preimage above via Democracy -> Submit preimage.

Then Submit proposal.

https://polkadot.js.org/apps/?rpc=wss%3A%2F%2Fkarura-rpc-3.aca-api.network%2Fws#/extrinsics/decode/0x33000101000210000400000000070010a5d4e81300000000070010a5d4e800060003009435775c1802083c01270800003c0027080000e8030000009001000d010004000100411f

Details

Find the latest proposal or successful referenda to open channels and compare differences with our message. Things change so the further examples are likely to be out of date.