Add Rococo People <> Rococo Bulletin bridge support to Rococo Bridge …

…Hub (#2540)

This PR adds [Rococo
People](#2281) <> [Rococo
Bulletin](https://github.com/zdave-parity/polkadot-bulletin-chain) to
the Rococo Bridge Hub code. There's a couple of things left to do here:
- [x] add remaining tests - it'd need some refactoring in the
`bridge-hub-test-utils` - will do in a separate PR;
- [x] actually run benchmarks for new messaging pallet (do we have bot
nowadays?).

The reason why I'm opening it before this ^^^ is ready, is that I'd like
to hear others opinion on how to deal with hacks with that bridge.
Initially I was assuming that Rococo Bulletin will be the 1:1 copy of
the Polkadot Bulletin (to avoid maintaining multiple
runtimes/releases/...), so you can see many `PolkadotBulletin` mentions
in this PR, even though we are going to bridge with the parallel chain
(`RococoBulletin`). That's because e.g. pallet names from
`construct_runtime` are affecting runtime storage keys and bridges are
using runtime storage proofs => it is important to use names that the
Bulletin chain expects.

But in the end, this hack won't work - we can't use Polkadot Bulletin
runtime to bridge with Rococo Bridge Hub, because Polkadot Bulletin
expects Polkadot Bridge hub to use `1002` parachain id and Rococo Bridge
Hub seats on the `1013`. This also affects storage keys using in
bridging, so I had to add the [`rococo`
feature](https://github.com/svyatonik/polkadot-bulletin-chain/blob/add-bridge-pallets/runtime/Cargo.toml#L198)
to the Bulletin chain. So now we can actually alter its runtime and
adapt it for Rococo.

So the question here is - what's better for us here
- to leave everything as is (seems hacky and non-trivial);
- change Bulletin chain runtime when `rococo` feature is used - e.g. use
proper names there (`WithPolkadotGrandpa` -> `WithRococoGrandpa`, ...)
- add another set of pallets to the Bulletin chain runtime to bridge
with Rococo and never use them in production. Similar to hack that we
had in Rococo/Wococo

cc @acatangiu @bkontur @serban300 

also cc @joepetrowski as the main "client" of this bridge

---

A couple words on how this bridge is different from the Rococo <>
Westend bridge:
- it is a bridge with a chain that uses GRANDPA finality, not the
parachain finality (hence the tests needs to be changed);
- it is a fee-free bridge. So
`AllowExplicitUnpaidExecutionFrom<Equals<SiblingPeople>>` + we are not
paying any rewards to relayers (apart from compensating transaction
costs).

---------

Signed-off-by: dependabot[bot] <support@github.com>
Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>
Co-authored-by: Adrian Catangiu <adrian@parity.io>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Andrei Sandu <54316454+sandreim@users.noreply.github.com>
Co-authored-by: Egor_P <egor@parity.io>
Co-authored-by: command-bot <>

bridges/modules/messages/src/weights_ext.rs

@@ -60,7 +60,8 @@ pub fn ensure_weights_are_correct<W: WeightInfoExt>() {
 	// W::receive_messages_delivery_proof_messages_overhead(1).ref_time() may be zero because:
 	// there's no code that iterates over confirmed messages in confirmation transaction
 	assert_eq!(W::receive_messages_delivery_proof_messages_overhead(1).proof_size(), 0);
-	assert_ne!(W::receive_messages_delivery_proof_relayers_overhead(1).ref_time(), 0);
+	// W::receive_messages_delivery_proof_relayers_overhead(1).ref_time() may be zero because:
+	// runtime **can** choose not to pay any rewards to relayers
 	// W::receive_messages_delivery_proof_relayers_overhead(1).proof_size() is an exception
 	// it may or may not cause additional db reads, so proof size may vary
 	assert_ne!(W::storage_proof_size_overhead(1).ref_time(), 0);

bridges/primitives/chain-bridge-hub-rococo/src/lib.rs

@@ -76,6 +76,8 @@ pub const WITH_BRIDGE_HUB_ROCOCO_RELAYERS_PALLET_NAME: &str = "BridgeRelayers";
 
 /// Pallet index of `BridgeWestendMessages: pallet_bridge_messages::<Instance3>`.
 pub const WITH_BRIDGE_ROCOCO_TO_WESTEND_MESSAGES_PALLET_INDEX: u8 = 51;
+/// Pallet index of `BridgePolkadotBulletinMessages: pallet_bridge_messages::<Instance4>`.
+pub const WITH_BRIDGE_ROCOCO_TO_BULLETIN_MESSAGES_PALLET_INDEX: u8 = 61;
 
 decl_bridge_finality_runtime_apis!(bridge_hub_rococo);
 decl_bridge_messages_runtime_apis!(bridge_hub_rococo);

cumulus/parachains/runtimes/bridge-hubs/bridge-hub-rococo/Cargo.toml

@@ -87,11 +87,13 @@ parachains-common = { path = "../../../common", default-features = false }
 # Bridges
 bp-asset-hub-rococo = { path = "../../../../../bridges/primitives/chain-asset-hub-rococo", default-features = false }
 bp-asset-hub-westend = { path = "../../../../../bridges/primitives/chain-asset-hub-westend", default-features = false }
+bp-bridge-hub-polkadot = { path = "../../../../../bridges/primitives/chain-bridge-hub-polkadot", default-features = false }
 bp-bridge-hub-rococo = { path = "../../../../../bridges/primitives/chain-bridge-hub-rococo", default-features = false }
 bp-bridge-hub-westend = { path = "../../../../../bridges/primitives/chain-bridge-hub-westend", default-features = false }
 bp-header-chain = { path = "../../../../../bridges/primitives/header-chain", default-features = false }
 bp-messages = { path = "../../../../../bridges/primitives/messages", default-features = false }
 bp-parachains = { path = "../../../../../bridges/primitives/parachains", default-features = false }
+bp-polkadot-bulletin = { path = "../../../../../bridges/primitives/chain-polkadot-bulletin", default-features = false }
 bp-polkadot-core = { path = "../../../../../bridges/primitives/polkadot-core", default-features = false }
 bp-relayers = { path = "../../../../../bridges/primitives/relayers", default-features = false }
 bp-runtime = { path = "../../../../../bridges/primitives/runtime", default-features = false }
@@ -117,11 +119,13 @@ default = ["std"]
 std = [
 	"bp-asset-hub-rococo/std",
 	"bp-asset-hub-westend/std",
+	"bp-bridge-hub-polkadot/std",
 	"bp-bridge-hub-rococo/std",
 	"bp-bridge-hub-westend/std",
 	"bp-header-chain/std",
 	"bp-messages/std",
 	"bp-parachains/std",
+	"bp-polkadot-bulletin/std",
 	"bp-polkadot-core/std",
 	"bp-relayers/std",
 	"bp-rococo/std",

cumulus/parachains/runtimes/bridge-hubs/bridge-hub-rococo/src/bridge_common_config.rs

@@ -21,15 +21,20 @@
 //! For example, the messaging pallet needs to know the sending and receiving chains, but the
 //! GRANDPA tracking pallet only needs to be aware of one chain.
 
-use super::{weights, AccountId, Balance, Balances, BlockNumber, Runtime, RuntimeEvent};
+use super::{
+	weights, AccountId, Balance, Balances, BlockNumber, Runtime, RuntimeEvent, RuntimeOrigin,
+};
 use bp_parachains::SingleParaStoredHeaderDataBuilder;
+use bp_runtime::UnderlyingChainProvider;
+use bridge_runtime_common::messages::ThisChainWithMessages;
 use frame_support::{parameter_types, traits::ConstU32};
+use sp_runtime::RuntimeDebug;
 
 parameter_types! {
 	pub const RelayChainHeadersToKeep: u32 = 1024;
 	pub const ParachainHeadsToKeep: u32 = 64;
 
-	pub const WestendBridgeParachainPalletName: &'static str = "Paras";
+	pub const WestendBridgeParachainPalletName: &'static str = bp_westend::PARAS_PALLET_NAME;
 	pub const MaxWestendParaHeadDataSize: u32 = bp_westend::MAX_NESTED_PARACHAIN_HEAD_DATA_SIZE;
 
 	pub storage RequiredStakeForStakeAndSlash: Balance = 1_000_000;
@@ -78,3 +83,33 @@ impl pallet_bridge_relayers::Config for Runtime {
 	>;
 	type WeightInfo = weights::pallet_bridge_relayers::WeightInfo<Runtime>;
 }
+
+/// Add GRANDPA bridge pallet to track Rococo Bulletin chain.
+pub type BridgeGrandpaRococoBulletinInstance = pallet_bridge_grandpa::Instance4;
+impl pallet_bridge_grandpa::Config<BridgeGrandpaRococoBulletinInstance> for Runtime {
+	type RuntimeEvent = RuntimeEvent;
+	type BridgedChain = bp_polkadot_bulletin::PolkadotBulletin;
+	type MaxFreeMandatoryHeadersPerBlock = ConstU32<4>;
+	type HeadersToKeep = RelayChainHeadersToKeep;
+	// Technically this is incorrect - we have two pallet instances and ideally we shall
+	// benchmark every instance separately. But the benchmarking engine has a flaw - it
+	// messes with components. E.g. in Kusama maximal validators count is 1024 and in
+	// Bulletin chain it is 100. But benchmarking engine runs Bulletin benchmarks using
+	// components range, computed for Kusama => it causes an error.
+	//
+	// In practice, however, GRANDPA pallet works the same way for all bridged chains, so
+	// weights are also the same for both bridges.
+	type WeightInfo = weights::pallet_bridge_grandpa::WeightInfo<Runtime>;
+}
+
+/// BridgeHubRococo chain from message lane point of view.
+#[derive(RuntimeDebug, Clone, Copy)]
+pub struct BridgeHubRococo;
+
+impl UnderlyingChainProvider for BridgeHubRococo {
+	type Chain = bp_bridge_hub_rococo::BridgeHubRococo;
+}
+
+impl ThisChainWithMessages for BridgeHubRococo {
+	type RuntimeOrigin = RuntimeOrigin;
+}