Add support for versioned notification for HRMP pallet

[bkontur]

Closes: #4003 (please see for the problem description)

TODO

• add more tests covering WrapVersion corner cases (e.g. para has lower version, ...)
• regenerate benchmarks runtime_parachains::hrmp (fix for Rococo is here: HRMP - set DefaultChannelSizeAndCapacityWithSystem with dynamic values according to the ActiveConfig #4332)

Questions / possible improvements

• A WrapVersion implementation for pallet_xcm initiates version discovery with note_unknown_version, there is possibility to avoid this overhead in this HRMP case to create new WrapVersion adapter for pallet_xcm which would not use note_unknown_version. Is it worth to do it or not?
• There's a possibility to decouple XCM functionality from the HRMP pallet, allowing any relay chain to generate its own notifications. This approach wouldn't restrict notifications solely to the XCM. However, it's uncertain whether it's worthwhile or desirable to do so? It means making HRMP pallet more generic. E.g. hiding HRMP notifications behind some trait:

   trait HrmpNotifications {
  
   	fn on_channel_open_request(
   		sender: ParaId,
   		proposed_max_capacity: u32,
   		proposed_max_message_size: u32) -> primitives::DownwardMessage;
  
   	fn on_channel_accepted(recipient: ParaId) -> primitives::DownwardMessage;
  
   	fn on_channel_closing(initiator: ParaId, sender: ParaId, recipient: ParaId) -> primitives::DownwardMessage;
   }
  

  and then we could have whatever adapter, impl HrmpNotifications for VersionedXcmHrmpNotifications {...},

   impl parachains_hrmp::Config for Runtime {
   ..
   	type HrmpNotifications = VersionedXcmHrmpNotifications;
   ..
   }
  

[bkontur]

bot help

[bkontur]

bot bench polkadot-pallet --runtime=rococo --pallet=runtime_parachains::hrmp
bot bench polkadot-pallet --runtime=westend --pallet=runtime_parachains::hrmp

[bkontur]

bot bench polkadot-pallet --runtime=rococo --pallet=runtime_parachains::hrmp

[bkontur]

bot clean

[bkontur]

bot bench polkadot-pallet --runtime=rococo --pallet=runtime_parachains::hrmp
bot bench polkadot-pallet --runtime=westend --pallet=runtime_parachains::hrmp

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The CI pipeline was cancelled due to failure one of the required jobs.
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[command-bot]

@bkontur Command "$PIPELINE_SCRIPTS_DIR/commands/bench/bench.sh" --subcommand=pallet --runtime=rococo --target_dir=polkadot --pallet=runtime_parachains::hrmp has finished. Result: https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/6106217 has finished. If any artifacts were generated, you can download them from https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/6106217/artifacts/download.

[command-bot]

@bkontur Command "$PIPELINE_SCRIPTS_DIR/commands/bench/bench.sh" --subcommand=pallet --runtime=westend --target_dir=polkadot --pallet=runtime_parachains::hrmp has finished. Result: https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/6106218 has finished. If any artifacts were generated, you can download them from https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/6106218/artifacts/download.

[franciscoaguirre]

So if your runtime is a parachain you just put (), right?
What does it mean to concern oneself about versions? Is it allowing older versions of XCM?

[bkontur]

So if your runtime is a parachain you just put (), right?

The HRMP pallet is dedicated to relay chain runtimes, I don't think that any parachain runtime uses this HRMP pallet.

What does it mean to concern oneself about versions? Is it allowing older versions of XCM?

The problem could arise from a higher version on the relay chain than on the receiving parachain. For example, imagine that we update Polkadot with xcm::v5, but Polimec still uses xcm::v4. Without this fix, they could lose messages because they would not be able to decode xcm::v5.

[bkontur]

Perhaps it could be possible to replace most of the functionality related to the WrapVersion with just the SendXcm trait. In this scenario, the HRMP pallet would use type XcmSender = ChildParachainRouter, potentially simplifying things. However, this approach would introduce another layer of complexity, particularly regarding handling transport fees. Nevertheless, I think these HRMP notifications are treated as system notifications, which is why they are sent directly by dmp::Pallet::<T>::queue_downward_message.