Configurable send origin in XCM handler

[shaunxw]

XCM handler module has dispatchable calls to send messages, but the origin must be root.

cumulus/pallets/xcm-handler/src/lib.rs

Lines 77 to 78 in d8126cd

	fn sudo_send_xcm(origin, dest: MultiLocation, message: Xcm) {
	ensure_root(origin)?;

It will be helpful to make the origin configurable, so that it can work with pallet-collective. For instance, config the send origin as EnsureRootOrHalfCouncil.

[bkchr]

As the name suggests, these are sudo related dispatchables for testing purposes not as a general way to send these messages.

[shaunxw]

Parachains needs to send upward message to init/accept HRMP channel requests. Before this issue solved, there is no way to add helper dispatchable calls to do these tasks. However it seems the issue cannot be solved in short term. Could you suggest a way if these testing sudo calls removed in the future?

[shaunxw]

Maybe we can add a more specific dispatchable call, which only sends upward Xcm::Transact message, to help parachains managing HRMP channels (or other future calls which checks ensure_parachain origin in relay chain). Like this:

fn send_upward_xcm_transact(origin, call: Vec<u8>) {
    T::SendOrigin::ensure_origin(origin)?;
    let msg = Xcm::Transact {
        origin_type: OriginKind::Native,
        call: call,
    };
    // send upward msg...
}

[bkchr]

Best is to ask @pepyakin on what he thinks about this.

[pepyakin]

I distanced a bit from XCM lately and not that well versed in the specifics of the pallet-collective, so I think @shawntabrizi is the man here.

However, I can note that this particular use case could be addressed using an intermediate pallet, which could accept calls from, e.g pallet-collective and manually prepare and send a message. Gross but works.

[shawntabrizi]

I think having a configurable origin is a fine change and doesn't really change the pallet. Probably you would want to remove the word sudo though

As for creating a root call, you can do so in Democracy with do_enact_proposal:

https://github.com/paritytech/substrate/blob/master/frame/democracy/src/lib.rs#L1540

Which can be executed by an collective as an ExternalMajorityOrigin. This is how Runtime Upgrades happen...

[shaunxw]

I think having a configurable origin is a fine change and doesn't really change the pallet. Probably you would want to remove the word sudo though

I'm happy to open a PR to do this. Will make these send xcm dispatchable calls use configurable origin and remove word sudo.