Downward & Upward messages (#1266)

* Downward messages, the front-end.

* Move types around to make them accessible from Parachains

* Fix compilation

* Fix branch

* Make it compile for Cumulus

* Update the branch names

* Add default generic parameter

* Implement `Partialeq`

* Move upward messages into the `ValidationResult`

* Support disabling of the runtime api

* Update branch

* Adds support for handling downward messages

* Implement sending XCMP messages as up/downward messages

* service: update to latest ServiceBuilder changes

* Make it compile

* Initial commit

Forked at: ef2aa428d7
Parent branch: origin/master

* Update substrate branch to cecton-update-polkadot-substrate

* Update substrate & polkadot to cumulus-branch

* Reset branch

* Update primitives/src/parachain.rs

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

* Update runtime/common/src/parachains.rs

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

* Update runtime/common/src/parachains.rs

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

* Minor fixes

* Fix wasm build

Co-authored-by: Gav Wood <gavin@parity.io>
Co-authored-by: André Silva <andre.beat@gmail.com>
Co-authored-by: Cecile Tonglet <cecile.tonglet@cecton.com>
Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

polkadot/Cargo.lock

@@ -4319,6 +4319,16 @@ dependencies = [
  "tokio 0.2.21",
 ]
 
+[[package]]
+name = "polkadot-core-primitives"
+version = "0.7.30"
+dependencies = [
+ "parity-scale-codec",
+ "sp-core",
+ "sp-runtime",
+ "sp-std",
+]
+
 [[package]]
 name = "polkadot-erasure-coding"
 version = "0.8.13"
@@ -4446,13 +4456,13 @@ dependencies = [
  "log 0.4.8",
  "parity-scale-codec",
  "parking_lot 0.10.2",
+ "polkadot-core-primitives",
  "sc-executor",
  "serde",
  "shared_memory",
  "sp-core",
  "sp-externalities",
  "sp-io",
- "sp-runtime-interface",
  "sp-std",
  "sp-wasm-interface",
 ]
@@ -4464,6 +4474,7 @@ dependencies = [
  "bitvec",
  "frame-system",
  "parity-scale-codec",
+ "polkadot-core-primitives",
  "polkadot-parachain",
  "pretty_assertions",
  "serde",
@@ -8043,6 +8054,7 @@ dependencies = [
  "parity-scale-codec",
  "polkadot-parachain",
  "sp-io",
+ "sp-std",
  "substrate-wasm-builder-runner 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "tiny-keccak 1.5.0",
 ]
@@ -8070,6 +8082,7 @@ dependencies = [
  "parity-scale-codec",
  "polkadot-parachain",
  "sp-io",
+ "sp-std",
  "substrate-wasm-builder-runner 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "tiny-keccak 1.5.0",
 ]

polkadot/Cargo.toml

@@ -26,6 +26,7 @@ members = [
 	"availability-store",
 	"cli",
 	"collator",
+	"core-primitives",
 	"erasure-coding",
 	"network",
 	"network/test",

polkadot/availability-store/src/lib.rs

@@ -33,7 +33,7 @@ use polkadot_primitives::{
 	},
 };
 use sp_runtime::traits::HashFor;
-use sp_blockchain::{Result as ClientResult};
+use sp_blockchain::Result as ClientResult;
 use client::{
 	BlockchainEvents, BlockBackend,
 };
@@ -58,7 +58,7 @@ use worker::{
 	Worker, WorkerHandle, IncludedParachainBlocks, WorkerMsg, MakeAvailable, Chunks
 };
 
-use store::{Store as InnerStore};
+use store::Store as InnerStore;
 
 const LOG_TARGET: &str = "availability";
 

polkadot/availability-store/src/store.rs

@@ -18,7 +18,7 @@
 use kvdb_rocksdb::{Database, DatabaseConfig};
 use kvdb::{KeyValueDB, DBTransaction};
 use codec::{Encode, Decode};
-use polkadot_erasure_coding::{self as erasure};
+use polkadot_erasure_coding as erasure;
 use polkadot_primitives::{
 	Hash,
 	parachain::{

polkadot/collator/src/lib.rs

@@ -56,7 +56,7 @@ use sc_client_api::{StateBackend, BlockchainEvents};
 use sp_blockchain::HeaderBackend;
 use sp_core::Pair;
 use polkadot_primitives::{
-	BlockId, Hash, Block,
+	BlockId, Hash, Block, DownwardMessage,
 	parachain::{
 		self, BlockData, DutyRoster, HeadData, Id as ParaId,
 		PoVBlock, ValidatorId, CollatorPair, LocalValidationData, GlobalValidationSchedule,
@@ -150,6 +150,7 @@ pub trait ParachainContext: Clone {
 		relay_parent: Hash,
 		global_validation: GlobalValidationSchedule,
 		local_validation: LocalValidationData,
+		downward_messages: Vec<DownwardMessage>,
 	) -> Self::ProduceCandidate;
 }
 
@@ -159,6 +160,7 @@ pub async fn collate<P>(
 	local_id: ParaId,
 	global_validation: GlobalValidationSchedule,
 	local_validation_data: LocalValidationData,
+	downward_messages: Vec<DownwardMessage>,
 	mut para_context: P,
 	key: Arc<CollatorPair>,
 ) -> Option<parachain::Collation>
@@ -170,6 +172,7 @@ pub async fn collate<P>(
 		relay_parent,
 		global_validation,
 		local_validation_data,
+		downward_messages,
 	).await?;
 
 	let pov_block = PoVBlock {
@@ -317,6 +320,7 @@ fn build_collator_service<P, C, R, Extrinsic>(
 					Some(local_validation) => local_validation,
 					None => return future::Either::Left(future::ok(())),
 				};
+				let downward_messages = try_fr!(api.downward_messages(&id, para_id));
 
 				let validators = try_fr!(api.validators(&id));
 
@@ -331,6 +335,7 @@ fn build_collator_service<P, C, R, Extrinsic>(
 					para_id,
 					global_validation,
 					local_validation,
+					downward_messages,
 					parachain_context,
 					key,
 				).map(move |collation| {
@@ -470,6 +475,7 @@ mod tests {
 			_relay_parent: Hash,
 			_global: GlobalValidationSchedule,
 			_local_validation: LocalValidationData,
+			_: Vec<DownwardMessage>,
 		) -> Self::ProduceCandidate {
 			// send messages right back.
 			future::ready(Some((

polkadot/core-primitives/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "polkadot-core-primitives"
+version = "0.7.30"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2018"
+
+[dependencies]
+sp-core = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
+sp-std = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
+sp-runtime = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
+codec = { package = "parity-scale-codec", version = "1.3.0", default-features = false, features = [ "derive" ] }
+
+[features]
+default = [ "std" ]
+std = [
+	"sp-core/std",
+	"sp-runtime/std",
+	"sp-std/std",
+	"codec/std",
+]

polkadot/core-primitives/src/lib.rs

@@ -0,0 +1,96 @@
+// Copyright 2020 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Polkadot is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+//! Core Polkadot types.
+//!
+//! These core Polkadot types are used by the relay chain and the Parachains.
+
+use sp_runtime::{generic, MultiSignature, traits::{Verify, BlakeTwo256, IdentifyAccount}};
+
+/// The block number type used by Polkadot.
+/// 32-bits will allow for 136 years of blocks assuming 1 block per second.
+pub type BlockNumber = u32;
+
+/// An instant or duration in time.
+pub type Moment = u64;
+
+/// Alias to type for a signature for a transaction on the relay chain. This allows one of several
+/// kinds of underlying crypto to be used, so isn't a fixed size when encoded.
+pub type Signature = MultiSignature;
+
+/// Alias to the public key used for this chain, actually a `MultiSigner`. Like the signature, this
+/// also isn't a fixed size when encoded, as different cryptos have different size public keys.
+pub type AccountPublic = <Signature as Verify>::Signer;
+
+/// Alias to the opaque account ID type for this chain, actually a `AccountId32`. This is always
+/// 32 bytes.
+pub type AccountId = <AccountPublic as IdentifyAccount>::AccountId;
+
+/// The type for looking up accounts. We don't expect more than 4 billion of them.
+pub type AccountIndex = u32;
+
+/// Identifier for a chain. 32-bit should be plenty.
+pub type ChainId = u32;
+
+/// A hash of some data used by the relay chain.
+pub type Hash = sp_core::H256;
+
+/// Index of a transaction in the relay chain. 32-bit should be plenty.
+pub type Nonce = u32;
+
+/// The balance of an account.
+/// 128-bits (or 38 significant decimal figures) will allow for 10m currency (10^7) at a resolution
+/// to all for one second's worth of an annualised 50% reward be paid to a unit holder (10^11 unit
+/// denomination), or 10^18 total atomic units, to grow at 50%/year for 51 years (10^9 multiplier)
+/// for an eventual total of 10^27 units (27 significant decimal figures).
+/// We round denomination to 10^12 (12 sdf), and leave the other redundancy at the upper end so
+/// that 32 bits may be multiplied with a balance in 128 bits without worrying about overflow.
+pub type Balance = u128;
+
+/// Header type.
+pub type Header = generic::Header<BlockNumber, BlakeTwo256>;
+/// Block type.
+pub type Block = generic::Block<Header, UncheckedExtrinsic>;
+/// Block ID.
+pub type BlockId = generic::BlockId<Block>;
+
+/// Opaque, encoded, unchecked extrinsic.
+pub use sp_runtime::OpaqueExtrinsic as UncheckedExtrinsic;
+
+/// The information that goes alongside a transfer_into_parachain operation. Entirely opaque, it
+/// will generally be used for identifying the reason for the transfer. Typically it will hold the
+/// destination account to which the transfer should be credited. If still more information is
+/// needed, then this should be a hash with the pre-image presented via an off-chain mechanism on
+/// the parachain.
+pub type Remark = [u8; 32];
+
+/// These are special "control" messages that can be passed from the Relaychain to a parachain.
+/// They should be handled by all parachains.
+#[derive(codec::Encode, codec::Decode, Clone, sp_runtime::RuntimeDebug, PartialEq)]
+pub enum DownwardMessage<AccountId = crate::AccountId> {
+	/// Some funds were transferred into the parachain's account. The hash is the identifier that
+	/// was given with the transfer.
+	TransferInto(AccountId, Balance, Remark),
+	/// An opaque blob of data. The relay chain must somehow know how to form this so that the
+	/// destination parachain does something sensible.
+	///
+	/// NOTE: Be very careful not to allow users to place arbitrary size information in here.
+	Opaque(sp_std::vec::Vec<u8>),
+	/// XCMP message for the Parachain.
+	XCMPMessage(sp_std::vec::Vec<u8>),
+}

polkadot/network/src/protocol/tests.rs

@@ -185,6 +185,9 @@ sp_api::mock_impl_runtime_apis! {
 				parent_hash: Default::default(),
 			}
 		}
+		fn downward_messages(_: ParaId) -> Vec<polkadot_primitives::DownwardMessage> {
+			Vec::new()
+		}
 	}
 }
 

polkadot/parachain/Cargo.toml

@@ -13,11 +13,11 @@ codec = { package = "parity-scale-codec", version = "1.1.0", default-features =
 sp-std = { package = "sp-std", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-core = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-wasm-interface = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
+polkadot-core-primitives = { path = "../core-primitives", default-features = false }
 
 # all optional crates.
 derive_more = { version = "0.99.2", optional = true }
 serde = { version = "1.0.102", default-features = false, features = [ "derive" ], optional = true }
-sp-runtime-interface = { git = "https://github.com/paritytech/substrate", branch = "master", optional = true, default-features = false }
 sp-externalities = { git = "https://github.com/paritytech/substrate", branch = "master", optional = true }
 sc-executor = { git = "https://github.com/paritytech/substrate", branch = "master", optional = true }
 sp-io = { git = "https://github.com/paritytech/substrate", branch = "master", optional = true }
@@ -29,7 +29,7 @@ shared_memory = { version = "0.10.0", optional = true }
 
 [features]
 default = ["std"]
-wasm-api = ["sp-runtime-interface"]
+wasm-api = []
 std = [
 	"codec/std",
 	"derive_more",
@@ -39,8 +39,8 @@ std = [
 	"sp-core/std",
 	"parking_lot",
 	"log",
-	"sp-runtime-interface/std",
 	"sp-externalities",
 	"sc-executor",
 	"sp-io",
+	"polkadot-core-primitives/std",
 ]

polkadot/parachain/src/primitives.rs

@@ -28,9 +28,8 @@ use serde::{Serialize, Deserialize};
 #[cfg(feature = "std")]
 use sp_core::bytes;
 
-/// The block number of the relay chain.
+/// Block number type used by the relay chain.
-/// 32-bits will allow for 136 years of blocks assuming 1 block per second.
+pub use polkadot_core_primitives::BlockNumber as RelayChainBlockNumber;
-pub type RelayChainBlockNumber = u32;
 
 /// Parachain head data included in the chain.
 #[derive(PartialEq, Eq, Clone, PartialOrd, Ord, Encode, Decode, RuntimeDebug)]
@@ -186,10 +185,6 @@ impl sp_std::convert::TryFrom<u8> for ParachainDispatchOrigin {
 
 /// A message from a parachain to its Relay Chain.
 #[derive(Clone, PartialEq, Eq, Encode, Decode)]
-#[cfg_attr(
-	any(feature = "std", feature = "wasm-api"),
-	derive(sp_runtime_interface::pass_by::PassByCodec,
-))]
 #[cfg_attr(feature = "std", derive(Debug))]
 pub struct UpwardMessage {
 	/// The origin for the message to be sent from.
@@ -212,13 +207,13 @@ pub struct ValidationParams {
 	/// The maximum head-data size permitted, in bytes.
 	pub max_head_data_size: u32,
 	/// The current relay-chain block number.
-	pub relay_chain_height: RelayChainBlockNumber,
+	pub relay_chain_height: polkadot_core_primitives::BlockNumber,
 	/// Whether a code upgrade is allowed or not, and at which height the upgrade
 	/// would be applied after, if so. The parachain logic should apply any upgrade
 	/// issued in this block after the first block
 	/// with `relay_chain_height` at least this value, if `Some`. if `None`, issue
 	/// no upgrade.
-	pub code_upgrade_allowed: Option<RelayChainBlockNumber>,
+	pub code_upgrade_allowed: Option<polkadot_core_primitives::BlockNumber>,
 }
 
 /// The result of parachain validation.
@@ -230,4 +225,10 @@ pub struct ValidationResult {
 	pub head_data: HeadData,
 	/// An update to the validation code that should be scheduled in the relay chain.
 	pub new_validation_code: Option<ValidationCode>,
+	/// Upward messages send by the Parachain.
+	pub upward_messages: Vec<UpwardMessage>,
+	/// Number of downward messages that were processed by the Parachain.
+	///
+	/// It is expected that the Parachain processes them from first to last.
+	pub processed_downward_messages: u32,
 }

polkadot/parachain/src/wasm_api.rs

@@ -16,29 +16,6 @@
 
 //! Utilities for writing parachain WASM.
 
-#[cfg(any(feature = "std", all(not(feature = "std"), feature = "wasm-api")))]
-use crate::primitives::UpwardMessage;
-#[cfg(any(feature = "std", all(not(feature = "std"), feature = "wasm-api")))]
-use sp_runtime_interface::runtime_interface;
-#[cfg(feature = "std")]
-use sp_externalities::ExternalitiesExt;
-
-/// The parachain api for posting messages.
-// Either activate on `std` to get access to the `HostFunctions` or when `wasm-api` is given and on
-// `no_std`.
-#[cfg(any(feature = "std", all(not(feature = "std"), feature = "wasm-api")))]
-#[runtime_interface]
-pub trait Parachain {
-	/// Post a message to this parachain's relay chain.
-	#[allow(dead_code)]
-	fn post_upward_message(&mut self, msg: UpwardMessage) {
-		self.extension::<crate::wasm_executor::ParachainExt>()
-			.expect("No `ParachainExt` associated with the current context.")
-			.post_upward_message(msg)
-			.expect("Failed to post upward message")
-	}
-}
-
 /// Load the validation params from memory when implementing a Rust parachain.
 ///
 /// Offset and length must have been provided by the validation

polkadot/parachain/src/wasm_executor/mod.rs

@@ -21,12 +21,12 @@
 //! a WASM VM for re-execution of a parachain candidate.
 
 use std::any::{TypeId, Any};
-use crate::primitives::{ValidationParams, ValidationResult, UpwardMessage};
+use crate::primitives::{ValidationParams, ValidationResult};
 use codec::{Decode, Encode};
 use sp_core::storage::ChildInfo;
 use sp_core::traits::CallInWasm;
-use sp_wasm_interface::HostFunctions as _;
 use sp_externalities::Extensions;
+use sp_wasm_interface::HostFunctions as _;
 
 #[cfg(not(any(target_os = "android", target_os = "unknown")))]
 pub use validation_host::{run_worker, ValidationPool, EXECUTION_TIMEOUT_SEC};
@@ -37,18 +37,6 @@ mod validation_host;
 const MAX_RUNTIME_MEM: usize = 1024 * 1024 * 1024; // 1 GiB
 const MAX_CODE_MEM: usize = 16 * 1024 * 1024; // 16 MiB
 
-sp_externalities::decl_extension! {
-	/// The extension that is registered at the `Externalities` when validating a parachain state
-	/// transition.
-	pub(crate) struct ParachainExt(Box<dyn Externalities>);
-}
-
-impl ParachainExt {
-	pub fn new<T: Externalities + 'static>(ext: T) -> Self {
-		Self(Box::new(ext))
-	}
-}
-
 /// A stub validation-pool defined when compiling for Android or WASM.
 #[cfg(any(target_os = "android", target_os = "unknown"))]
 #[derive(Clone)]
@@ -124,32 +112,25 @@ impl std::error::Error for Error {
 	}
 }
 
-/// Externalities for parachain validation.
-pub trait Externalities: Send {
-	/// Called when a message is to be posted to the parachain's relay chain.
-	fn post_upward_message(&mut self, message: UpwardMessage) -> Result<(), String>;
-}
-
 /// Validate a candidate under the given validation code.
 ///
 /// This will fail if the validation code is not a proper parachain validation module.
-pub fn validate_candidate<E: Externalities + 'static>(
+pub fn validate_candidate(
 	validation_code: &[u8],
 	params: ValidationParams,
-	ext: E,
 	options: ExecutionMode<'_>,
 ) -> Result<ValidationResult, Error> {
 	match options {
 		ExecutionMode::Local => {
-			validate_candidate_internal(validation_code, &params.encode(), ext)
+			validate_candidate_internal(validation_code, &params.encode())
 		},
 		#[cfg(not(any(target_os = "android", target_os = "unknown")))]
 		ExecutionMode::Remote(pool) => {
-			pool.validate_candidate(validation_code, params, ext, false)
+			pool.validate_candidate(validation_code, params, false)
 		},
 		#[cfg(not(any(target_os = "android", target_os = "unknown")))]
 		ExecutionMode::RemoteTest(pool) => {
-			pool.validate_candidate(validation_code, params, ext, true)
+			pool.validate_candidate(validation_code, params, true)
 		},
 		#[cfg(any(target_os = "android", target_os = "unknown"))]
 		ExecutionMode::Remote(pool) =>
@@ -165,21 +146,16 @@ pub fn validate_candidate<E: Externalities + 'static>(
 }
 
 /// The host functions provided by the wasm executor to the parachain wasm blob.
-type HostFunctions = (
+type HostFunctions = sp_io::SubstrateHostFunctions;
-	sp_io::SubstrateHostFunctions,
-	crate::wasm_api::parachain::HostFunctions,
-);
 
 /// Validate a candidate under the given validation code.
 ///
 /// This will fail if the validation code is not a proper parachain validation module.
-pub fn validate_candidate_internal<E: Externalities + 'static>(
+pub fn validate_candidate_internal(
 	validation_code: &[u8],
 	encoded_call_data: &[u8],
-	externalities: E,
 ) -> Result<ValidationResult, Error> {
 	let mut extensions = Extensions::new();
-	extensions.register(ParachainExt::new(externalities));
 	extensions.register(sp_core::traits::TaskExecutorExt(sp_core::tasks::executor()));
 
 	let mut ext = ValidationExternalities(extensions);

polkadot/parachain/src/wasm_executor/validation_host.rs

@@ -16,18 +16,15 @@
 
 #![cfg(not(any(target_os = "android", target_os = "unknown")))]
 
-use std::{process, env, sync::Arc, sync::atomic, mem};
+use std::{process, env, sync::Arc, sync::atomic};
-use codec::{Decode, Encode, EncodeAppend};
+use codec::{Decode, Encode};
-use crate::primitives::{ValidationParams, ValidationResult, UpwardMessage};
+use crate::primitives::{ValidationParams, ValidationResult};
-use super::{validate_candidate_internal, Error, Externalities};
+use super::{validate_candidate_internal, Error};
 use super::{MAX_CODE_MEM, MAX_RUNTIME_MEM};
 use shared_memory::{SharedMem, SharedMemConf, EventState, WriteLockable, EventWait, EventSet};
 use parking_lot::Mutex;
 use log::{debug, trace};
 
-// Message data limit
-const MAX_MESSAGE_MEM: usize = 16 * 1024 * 1024; // 16 MiB
-
 const WORKER_ARGS_TEST: &[&'static str] = &["--nocapture", "validation_worker"];
 /// CLI Argument to start in validation worker mode.
 const WORKER_ARG: &'static str = "validation-worker";
@@ -40,27 +37,6 @@ pub const EXECUTION_TIMEOUT_SEC: u64 =  30;
 #[cfg(not(debug_assertions))]
 pub const EXECUTION_TIMEOUT_SEC: u64 =  5;
 
-#[derive(Default)]
-struct WorkerExternalitiesInner {
-	up_data: Vec<u8>,
-}
-
-#[derive(Default, Clone)]
-struct WorkerExternalities {
-	inner: Arc<Mutex<WorkerExternalitiesInner>>,
-}
-
-impl Externalities for WorkerExternalities {
-	fn post_upward_message(&mut self, message: UpwardMessage) -> Result<(), String> {
-		let mut inner = self.inner.lock();
-		inner.up_data = <Vec::<UpwardMessage> as EncodeAppend>::append_or_new(
-			mem::replace(&mut inner.up_data, Vec::new()),
-			std::iter::once(message),
-		).map_err(|e| e.what())?;
-		Ok(())
-	}
-}
-
 enum Event {
 	CandidateReady = 0,
 	ResultReady = 1,
@@ -87,21 +63,20 @@ impl ValidationPool {
 	/// free validation host.
 	///
 	/// This will fail if the validation code is not a proper parachain validation module.
-	pub fn validate_candidate<E: Externalities>(
+	pub fn validate_candidate(
 		&self,
 		validation_code: &[u8],
 		params: ValidationParams,
-		externalities: E,
 		test_mode: bool,
 	) -> Result<ValidationResult, Error> {
 		for host in self.hosts.iter() {
 			if let Some(mut host) = host.try_lock() {
-				return host.validate_candidate(validation_code, params, externalities, test_mode);
+				return host.validate_candidate(validation_code, params, test_mode);
 			}
 		}
 
 		// all workers are busy, just wait for the first one
-		self.hosts[0].lock().validate_candidate(validation_code, params, externalities, test_mode)
+		self.hosts[0].lock().validate_candidate(validation_code, params, test_mode)
 	}
 }
 
@@ -116,8 +91,6 @@ pub fn run_worker(mem_id: &str) -> Result<(), String> {
 		}
 	};
 
-	let worker_ext = WorkerExternalities::default();
-
 	let exit = Arc::new(atomic::AtomicBool::new(false));
 	// spawn parent monitor thread
 	let watch_exit = exit.clone();
@@ -166,21 +139,11 @@ pub fn run_worker(mem_id: &str) -> Result<(), String> {
 				let (call_data, _) = rest.split_at_mut(MAX_RUNTIME_MEM);
 				let (call_data, _) = call_data.split_at_mut(header.params_size as usize);
 
-				let result = validate_candidate_internal(code, call_data, worker_ext.clone());
+				let result = validate_candidate_internal(code, call_data);
 				debug!("{} Candidate validated: {:?}", process::id(), result);
 
 				match result {
-					Ok(r) => {
+					Ok(r) => ValidationResultHeader::Ok(r),
-						let inner = worker_ext.inner.lock();
-						let up_data = &inner.up_data;
-						let up_len = up_data.len();
-
-						if up_len > MAX_MESSAGE_MEM {
-							ValidationResultHeader::Error("Message data is too large".into())
-						} else {
-							ValidationResultHeader::Ok(r)
-						}
-					},
 					Err(e) => ValidationResultHeader::Error(e.to_string()),
 				}
 			};
@@ -226,7 +189,7 @@ impl Drop for ValidationHost {
 
 impl ValidationHost {
 	fn create_memory() -> Result<SharedMem, Error> {
-		let mem_size = MAX_RUNTIME_MEM + MAX_CODE_MEM + MAX_MESSAGE_MEM + 1024;
+		let mem_size = MAX_RUNTIME_MEM + MAX_CODE_MEM + 1024;
 		let mem_config = SharedMemConf::default()
 			.set_size(mem_size)
 			.add_lock(shared_memory::LockType::Mutex, 0, mem_size)?
@@ -268,11 +231,10 @@ impl ValidationHost {
 	/// Validate a candidate under the given validation code.
 	///
 	/// This will fail if the validation code is not a proper parachain validation module.
-	pub fn validate_candidate<E: Externalities>(
+	pub fn validate_candidate(
 		&mut self,
 		validation_code: &[u8],
 		params: ValidationParams,
-		mut externalities: E,
 		test_mode: bool,
 	) -> Result<ValidationResult, Error> {
 		if validation_code.len() > MAX_CODE_MEM {
@@ -322,24 +284,11 @@ impl ValidationHost {
 		{
 			debug!("{} Reading results", self.id);
 			let data: &[u8] = &**memory.wlock_as_slice(0)?;
-			let (header_buf, rest) = data.split_at(1024);
+			let (header_buf, _) = data.split_at(1024);
-			let (_, rest) = rest.split_at(MAX_CODE_MEM);
-			let (_, message_data) = rest.split_at(MAX_RUNTIME_MEM);
 			let mut header_buf: &[u8] = header_buf;
-			let mut message_data: &[u8] = message_data;
 			let header = ValidationResultHeader::decode(&mut header_buf).unwrap();
 			match header {
-				ValidationResultHeader::Ok(result) => {
+				ValidationResultHeader::Ok(result) => Ok(result),
-					let upwards = Vec::<UpwardMessage>::decode(&mut message_data)
-						.map_err(|e|
-							Error::External(
-								format!("Could not decode upward messages: {}", e.what())
-							)
-						)?;
-					upwards.into_iter().try_for_each(|msg| externalities.post_upward_message(msg))?;
-
-					Ok(result)
-				}
 				ValidationResultHeader::Error(message) => {
 					debug!("{} Validation error: {}", self.id, message);
 					Err(Error::External(message).into())

polkadot/parachain/test-parachains/adder/Cargo.toml

@@ -9,6 +9,7 @@ build = "build.rs"
 [dependencies]
 parachain = { package = "polkadot-parachain", path = "../../", default-features = false, features = [ "wasm-api" ] }
 codec = { package = "parity-scale-codec", version = "1.3.0", default-features = false, features = ["derive"] }
+sp-std = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 tiny-keccak = "1.5.0"
 dlmalloc = { version = "0.1.3", features = [ "global" ] }
 
@@ -20,4 +21,7 @@ wasm-builder-runner = { package = "substrate-wasm-builder-runner", version = "1.
 
 [features]
 default = [ "std" ]
-std = ["parachain/std"]
+std = [
+	"parachain/std",
+	"sp-std/std",
+]

polkadot/parachain/test-parachains/adder/collator/src/main.rs

@@ -23,7 +23,7 @@ use adder::{HeadData as AdderHead, BlockData as AdderBody};
 use sp_core::Pair;
 use codec::{Encode, Decode};
 use primitives::{
-	Hash,
+	Hash, DownwardMessage,
 	parachain::{HeadData, BlockData, Id as ParaId, LocalValidationData, GlobalValidationSchedule},
 };
 use collator::{ParachainContext, Network, BuildParachainContext, Cli, SubstrateCli};
@@ -60,6 +60,7 @@ impl ParachainContext for AdderContext {
 		_relay_parent: Hash,
 		_global_validation: GlobalValidationSchedule,
 		local_validation: LocalValidationData,
+		_: Vec<DownwardMessage>,
 	) -> Self::ProduceCandidate
 	{
 		let adder_head = match AdderHead::decode(&mut &local_validation.parent_head.0[..]).ok() {

polkadot/parachain/test-parachains/adder/src/wasm_validation.rs

@@ -21,22 +21,6 @@ use core::{intrinsics, panic};
 use parachain::primitives::{ValidationResult, HeadData as GenericHeadData};
 use codec::{Encode, Decode};
 
-#[panic_handler]
-#[no_mangle]
-pub fn panic(_info: &panic::PanicInfo) -> ! {
-	unsafe {
-		intrinsics::abort()
-	}
-}
-
-#[alloc_error_handler]
-#[no_mangle]
-pub fn oom(_: core::alloc::Layout) -> ! {
-	unsafe {
-		intrinsics::abort();
-	}
-}
-
 #[no_mangle]
 pub extern fn validate_block(params: *const u8, len: usize) -> u64 {
 	let params = unsafe { parachain::load_params(params, len) };
@@ -53,6 +37,8 @@ pub extern fn validate_block(params: *const u8, len: usize) -> u64 {
 			&ValidationResult {
 				head_data: GenericHeadData(new_head.encode()),
 				new_validation_code: None,
+				upward_messages: sp_std::vec::Vec::new(),
+				processed_downward_messages: 0,
 			}
 		),
 		Err(_) => panic!("execution failure"),

polkadot/parachain/test-parachains/code-upgrader/Cargo.toml

@@ -9,6 +9,7 @@ build = "build.rs"
 [dependencies]
 parachain = { package = "polkadot-parachain", path = "../../", default-features = false, features = [ "wasm-api" ] }
 codec = { package = "parity-scale-codec", version = "1.1.0", default-features = false, features = ["derive"] }
+sp-std = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 tiny-keccak = "1.5.0"
 dlmalloc = { version = "0.1.3", features = [ "global" ] }
 
@@ -20,4 +21,7 @@ wasm-builder-runner = { package = "substrate-wasm-builder-runner", version = "1.
 
 [features]
 default = [ "std" ]
-std = ["parachain/std"]
+std = [
+	"parachain/std",
+	"sp-std/std",
+]

polkadot/parachain/test-parachains/code-upgrader/src/wasm_validation.rs

@@ -21,22 +21,6 @@ use core::{intrinsics, panic};
 use parachain::primitives::{ValidationResult, HeadData as GenericHeadData};
 use codec::{Encode, Decode};
 
-#[panic_handler]
-#[no_mangle]
-pub fn panic(_info: &panic::PanicInfo) -> ! {
-	unsafe {
-		intrinsics::abort()
-	}
-}
-
-#[alloc_error_handler]
-#[no_mangle]
-pub fn oom(_: core::alloc::Layout) -> ! {
-	unsafe {
-		intrinsics::abort();
-	}
-}
-
 #[no_mangle]
 pub extern fn validate_block(params: *const u8, len: usize) -> u64 {
 	let params = unsafe { parachain::load_params(params, len) };
@@ -64,6 +48,8 @@ pub extern fn validate_block(params: *const u8, len: usize) -> u64 {
 			&ValidationResult {
 				head_data: GenericHeadData(output.head_data.encode()),
 				new_validation_code: output.new_validation_code,
+				upward_messages: sp_std::vec::Vec::new(),
+				processed_downward_messages: 0,
 			}
 		),
 		Err(_) => panic!("execution failure"),

polkadot/parachain/test-parachains/tests/adder/mod.rs

@@ -16,15 +16,11 @@
 
 //! Basic parachain that adds a number as part of its state.
 
-use crate::{
+use parachain::primitives::{
-	DummyExt,
-	parachain,
-	parachain::primitives::{
 	RelayChainBlockNumber,
 	BlockData as GenericBlockData,
 	HeadData as GenericHeadData,
 	ValidationParams,
-	},
 };
 use codec::{Decode, Encode};
 
@@ -83,7 +79,6 @@ pub fn execute_good_on_parent() {
 			relay_chain_height: 1,
 			code_upgrade_allowed: None,
 		},
-		DummyExt,
 		parachain::wasm_executor::ExecutionMode::RemoteTest(&pool),
 	).unwrap();
 
@@ -123,7 +118,6 @@ fn execute_good_chain_on_parent() {
 				relay_chain_height: number as RelayChainBlockNumber + 1,
 				code_upgrade_allowed: None,
 			},
-			DummyExt,
 			parachain::wasm_executor::ExecutionMode::RemoteTest(&pool),
 		).unwrap();
 
@@ -164,7 +158,6 @@ fn execute_bad_on_parent() {
 			relay_chain_height: 1,
 			code_upgrade_allowed: None,
 		},
-		DummyExt,
 		parachain::wasm_executor::ExecutionMode::RemoteTest(&pool),
 	).unwrap_err();
 }

polkadot/parachain/test-parachains/tests/code_upgrader/mod.rs

@@ -16,15 +16,10 @@
 
 //! Basic parachain that adds a number as part of its state.
 
-use parachain;
+use parachain::primitives::{
-
-use crate::{
-	DummyExt,
-	parachain::primitives::{
 	BlockData as GenericBlockData,
 	HeadData as GenericHeadData,
 	ValidationParams, ValidationCode,
-	},
 };
 use codec::{Decode, Encode};
 use code_upgrader::{hash_state, HeadData, BlockData, State};
@@ -56,7 +51,6 @@ pub fn execute_good_no_upgrade() {
 			relay_chain_height: 1,
 			code_upgrade_allowed: None,
 		},
-		DummyExt,
 		parachain::wasm_executor::ExecutionMode::RemoteTest(&pool),
 	).unwrap();
 
@@ -93,7 +87,6 @@ pub fn execute_good_with_upgrade() {
 			relay_chain_height: 1,
 			code_upgrade_allowed: Some(20),
 		},
-		DummyExt,
 		parachain::wasm_executor::ExecutionMode::RemoteTest(&pool),
 	).unwrap();
 
@@ -137,7 +130,6 @@ pub fn code_upgrade_not_allowed() {
 			relay_chain_height: 1,
 			code_upgrade_allowed: None,
 		},
-		DummyExt,
 		parachain::wasm_executor::ExecutionMode::RemoteTest(&pool),
 	).unwrap();
 }
@@ -168,7 +160,6 @@ pub fn applies_code_upgrade_after_delay() {
 				relay_chain_height: 1,
 				code_upgrade_allowed: Some(2),
 			},
-			DummyExt,
 			parachain::wasm_executor::ExecutionMode::RemoteTest(&pool),
 		).unwrap();
 
@@ -204,7 +195,6 @@ pub fn applies_code_upgrade_after_delay() {
 				relay_chain_height: 2,
 				code_upgrade_allowed: None,
 			},
-			DummyExt,
 			parachain::wasm_executor::ExecutionMode::RemoteTest(&pool),
 		).unwrap();
 

polkadot/parachain/test-parachains/tests/lib.rs

@@ -18,16 +18,7 @@ mod adder;
 mod code_upgrader;
 mod wasm_executor;
 
-use parachain::{
+use parachain::wasm_executor::run_worker;
-	self, primitives::UpwardMessage, wasm_executor::{Externalities, run_worker},
-};
-
-struct DummyExt;
-impl Externalities for DummyExt {
-	fn post_upward_message(&mut self, _: UpwardMessage) -> Result<(), String> {
-		Ok(())
-	}
-}
 
 // This is not an actual test, but rather an entry point for out-of process WASM executor.
 // When executing tests the executor spawns currently executing binary, which happens to be test binary.

polkadot/parachain/test-parachains/tests/wasm_executor/mod.rs

@@ -16,9 +16,8 @@
 
 //! Basic parachain that adds a number as part of its state.
 
-use parachain;
+use crate::adder;
-use crate::{adder, DummyExt};
+use parachain::{
-use crate::parachain::{
 	primitives::{BlockData, ValidationParams},
 	wasm_executor::EXECUTION_TIMEOUT_SEC,
 };
@@ -40,7 +39,6 @@ fn terminates_on_timeout() {
 			relay_chain_height: 1,
 			code_upgrade_allowed: None,
 		},
-		DummyExt,
 		parachain::wasm_executor::ExecutionMode::RemoteTest(&pool),
 	);
 	match result {
@@ -70,7 +68,6 @@ fn parallel_execution() {
 			relay_chain_height: 1,
 			code_upgrade_allowed: None,
 		},
-		DummyExt,
 		parachain::wasm_executor::ExecutionMode::RemoteTest(&pool2),
 	).ok());
 	let _ = parachain::wasm_executor::validate_candidate(
@@ -83,7 +80,6 @@ fn parallel_execution() {
 			relay_chain_height: 1,
 			code_upgrade_allowed: None,
 		},
-		DummyExt,
 		parachain::wasm_executor::ExecutionMode::RemoteTest(&pool),
 	);
 	thread.join().unwrap();

polkadot/primitives/Cargo.toml

@@ -8,7 +8,6 @@ edition = "2018"
 serde = { version = "1.0.102", optional = true, features = ["derive"] }
 parity-scale-codec = { version = "1.3.0", default-features = false, features = ["bit-vec", "derive"] }
 primitives = { package = "sp-core", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
-system = { package = "frame-system", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 inherents = { package = "sp-inherents", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 application-crypto = { package = "sp-application-crypto", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sp-api = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
@@ -17,8 +16,10 @@ sp-std = { package = "sp-std", git = "https://github.com/paritytech/substrate",
 sp-staking = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 runtime_primitives = { package = "sp-runtime", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 polkadot-parachain = { path = "../parachain", default-features = false }
+polkadot-core-primitives = { path = "../core-primitives", default-features = false }
 trie = { package = "sp-trie", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 bitvec = { version = "0.17.4", default-features = false, features = ["alloc"] }
+frame-system = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 
 [dev-dependencies]
 sp-serializer = { git = "https://github.com/paritytech/substrate", branch = "master" }
@@ -27,9 +28,9 @@ pretty_assertions = "0.5.1"
 [features]
 default = ["std"]
 std = [
+	"application-crypto/std",
 	"parity-scale-codec/std",
 	"primitives/std",
-	"system/std",
 	"inherents/std",
 	"trie/std",
 	"sp-api/std",
@@ -39,5 +40,7 @@ std = [
 	"runtime_primitives/std",
 	"serde",
 	"polkadot-parachain/std",
+	"polkadot-core-primitives/std",
 	"bitvec/std",
+	"frame-system/std",
 ]

polkadot/primitives/src/lib.rs

@@ -20,63 +20,14 @@
 
 #![cfg_attr(not(feature = "std"), no_std)]
 
-use runtime_primitives::{generic, MultiSignature};
 pub use runtime_primitives::traits::{BlakeTwo256, Hash as HashT, Verify, IdentifyAccount};
+pub use polkadot_core_primitives::*;
 
 pub mod inclusion_inherent;
 pub mod parachain;
 
 pub use parity_scale_codec::Compact;
 
-/// An index to a block.
-pub type BlockNumber = polkadot_parachain::primitives::RelayChainBlockNumber;
-
-/// An instant or duration in time.
-pub type Moment = u64;
-
-/// Alias to type for a signature for a transaction on the relay chain. This allows one of several
-/// kinds of underlying crypto to be used, so isn't a fixed size when encoded.
-pub type Signature = MultiSignature;
-
-/// Alias to the public key used for this chain, actually a `MultiSigner`. Like the signature, this
-/// also isn't a fixed size when encoded, as different cryptos have different size public keys.
-pub type AccountPublic = <Signature as Verify>::Signer;
-
-/// Alias to the opaque account ID type for this chain, actually a `AccountId32`. This is always
-/// 32 bytes.
-pub type AccountId = <AccountPublic as IdentifyAccount>::AccountId;
-
-/// The type for looking up accounts. We don't expect more than 4 billion of them.
-pub type AccountIndex = u32;
-
-/// Identifier for a chain. 32-bit should be plenty.
-pub type ChainId = u32;
-
-/// A hash of some data used by the relay chain.
-pub type Hash = primitives::H256;
-
-/// Index of a transaction in the relay chain. 32-bit should be plenty.
-pub type Nonce = u32;
-
-/// The balance of an account.
-/// 128-bits (or 38 significant decimal figures) will allow for 10m currency (10^7) at a resolution
-/// to all for one second's worth of an annualised 50% reward be paid to a unit holder (10^11 unit
-/// denomination), or 10^18 total atomic units, to grow at 50%/year for 51 years (10^9 multiplier)
-/// for an eventual total of 10^27 units (27 significant decimal figures).
-/// We round denomination to 10^12 (12 sdf), and leave the other redundancy at the upper end so
-/// that 32 bits may be multiplied with a balance in 128 bits without worrying about overflow.
-pub type Balance = u128;
-
-/// Header type.
-pub type Header = generic::Header<BlockNumber, BlakeTwo256>;
-/// Block type.
-pub type Block = generic::Block<Header, UncheckedExtrinsic>;
-/// Block ID.
-pub type BlockId = generic::BlockId<Block>;
-
-/// Opaque, encoded, unchecked extrinsic.
-pub use runtime_primitives::OpaqueExtrinsic as UncheckedExtrinsic;
-
 /// Custom validity errors used in Polkadot while validating transactions.
 #[repr(u8)]
 pub enum ValidityError {
@@ -118,7 +69,7 @@ pub mod fisherman {
 	/// An `AppCrypto` type to allow submitting signed transactions using the fisherman
 	/// application key as signer.
 	pub struct FishermanAppCrypto;
-	impl system::offchain::AppCrypto<<Signature as Verify>::Signer, Signature> for FishermanAppCrypto {
+	impl frame_system::offchain::AppCrypto<<Signature as Verify>::Signer, Signature> for FishermanAppCrypto {
 		type RuntimeAppPublic = FishermanId;
 		type GenericSignature = primitives::sr25519::Signature;
 		type GenericPublic = primitives::sr25519::Public;

polkadot/primitives/src/parachain.rs

@@ -32,6 +32,7 @@ use primitives::RuntimeDebug;
 use runtime_primitives::traits::{AppVerify, Block as BlockT};
 use inherents::InherentIdentifier;
 use application_crypto::KeyTypeId;
+use polkadot_core_primitives::DownwardMessage;
 
 pub use polkadot_parachain::primitives::{
 	Id, ParachainDispatchOrigin, LOWEST_USER_ID, UpwardMessage, HeadData, BlockData,
@@ -220,6 +221,10 @@ pub struct CandidateCommitments<H = Hash> {
 	pub erasure_root: H,
 	/// New validation code.
 	pub new_validation_code: Option<ValidationCode>,
+	/// Number of `DownwardMessage`'s that were processed by the Parachain.
+	///
+	/// It is expected that the Parachain processes them from first to last.
+	pub processed_downward_messages: u32,
 }
 
 /// Get a collator signature payload on a relay-parent, block-data combo.
@@ -814,6 +819,8 @@ sp_api::decl_runtime_apis! {
 			-> Option<Vec<AbridgedCandidateReceipt>>;
 		/// Get a `SigningContext` with current `SessionIndex` and parent hash.
 		fn signing_context() -> SigningContext;
+		/// Get the `DownwardMessage`'s for the given parachain.
+		fn downward_messages(id: Id) -> Vec<DownwardMessage>;
 	}
 }
 

polkadot/runtime/common/src/parachains.rs

@@ -34,7 +34,7 @@ use sp_staking::{
 };
 use frame_support::{
 	traits::KeyOwnerProofSystem,
-	dispatch::{IsSubType},
+	dispatch::IsSubType,
 	weights::{DispatchClass, Weight},
 };
 use primitives::{
@@ -47,14 +47,13 @@ use primitives::{
 		LocalValidationData, Scheduling, ValidityAttestation, NEW_HEADS_IDENTIFIER, PARACHAIN_KEY_TYPE_ID,
 		ValidatorSignature, SigningContext, HeadData, ValidationCode,
 	},
+	Remark, DownwardMessage
 };
 use frame_support::{
 	Parameter, dispatch::DispatchResult, decl_storage, decl_module, decl_error, ensure,
 	traits::{Currency, Get, WithdrawReason, ExistenceRequirement, Randomness},
 };
-use sp_runtime::{
+use sp_runtime::transaction_validity::InvalidTransaction;
-	transaction_validity::InvalidTransaction,
-};
 
 use inherents::{ProvideInherent, InherentData, MakeFatalError, InherentIdentifier};
 
@@ -91,6 +90,18 @@ impl<N: Saturating + One + PartialOrd + PartialEq + Clone> Iterator for BlockNum
 pub trait ParachainCurrency<AccountId> {
 	fn free_balance(para_id: ParaId) -> Balance;
 	fn deduct(para_id: ParaId, amount: Balance) -> DispatchResult;
+	fn transfer_in(
+		source: &AccountId,
+		dest: ParaId,
+		amount: Balance,
+		existence_requirement: ExistenceRequirement,
+	) -> DispatchResult;
+	fn transfer_out(
+		source: ParaId,
+		dest: &AccountId,
+		amount: Balance,
+		existence_requirement: ExistenceRequirement,
+	) -> DispatchResult;
 }
 
 impl<AccountId, T: Currency<AccountId>> ParachainCurrency<AccountId> for T where
@@ -102,6 +113,8 @@ impl<AccountId, T: Currency<AccountId>> ParachainCurrency<AccountId> for T where
 		T::free_balance(&para_account).into()
 	}
 
+	// TODO: this should really be the same API as `withdraw`, having NegativeImbalance as an
+	//   associated type.
 	fn deduct(para_id: ParaId, amount: Balance) -> DispatchResult {
 		let para_account = para_id.into_account();
 
@@ -115,6 +128,24 @@ impl<AccountId, T: Currency<AccountId>> ParachainCurrency<AccountId> for T where
 
 		Ok(())
 	}
+
+	fn transfer_in(
+		source: &AccountId,
+		dest: ParaId,
+		amount: Balance,
+		existence_requirement: ExistenceRequirement,
+	) -> DispatchResult {
+		T::transfer(source, &dest.into_account(), amount.into(), existence_requirement)
+	}
+
+	fn transfer_out(
+		source: ParaId,
+		dest: &AccountId,
+		amount: Balance,
+		existence_requirement: ExistenceRequirement,
+	) -> DispatchResult {
+		T::transfer(&source.into_account(), dest, amount.into(), existence_requirement)
+	}
 }
 
 /// Interface to the persistent (stash) identities of the current validators.
@@ -226,12 +257,14 @@ pub trait Trait: CreateSignedTransaction<Call<Self>> + attestations::Trait + ses
 	type AuthorityId: system::offchain::AppCrypto<Self::Public, Self::Signature>;
 
 	/// The outer origin type.
-	type Origin: From<Origin> + From<system::RawOrigin<Self::AccountId>>;
+	type Origin: From<Origin>
+		+ From<<Self as system::Trait>::Origin>
+		+ Into<result::Result<Origin, <Self as Trait>::Origin>>;
 
 	/// The outer call dispatch type.
 	type Call: Parameter + Dispatchable<Origin=<Self as Trait>::Origin> + From<Call<Self>>;
 
-	/// Some way of interacting with balances for fees.
+	/// Some way of interacting with balances for fees and transfers.
 	type ParachainCurrency: ParachainCurrency<Self::AccountId>;
 
 	/// Polkadot in practice will always use the `BlockNumber` type.
@@ -345,6 +378,8 @@ impl<Offender: Clone> Offence<Offender> for DoubleVoteOffence<Offender> {
 	}
 }
 
+/// Total number of individual messages allowed in the relay-chain -> parachain message queue.
+const MAX_DOWNWARD_QUEUE_COUNT: usize = 10;
 /// Total number of individual messages allowed in the parachain -> relay-chain message queue.
 const MAX_QUEUE_COUNT: usize = 100;
 /// Total size of messages allowed in the parachain -> relay-chain message queue before which no
@@ -445,8 +480,7 @@ impl<N: Ord + Copy> ParaPastCodeMeta<N> {
 }
 
 decl_storage! {
-	trait Store for Module<T: Trait> as Parachains
+	trait Store for Module<T: Trait> as Parachains {
-	{
 		/// All authorities' keys at the moment.
 		pub Authorities get(fn authorities): Vec<ValidatorId>;
 		/// The active code of a currently-registered parachain.
@@ -484,6 +518,9 @@ decl_storage! {
 		///
 		/// `None` if not yet updated.
 		pub DidUpdate: Option<Vec<ParaId>>;
+
+		/// Messages waiting to be delivered from the Relay chain into the parachain.
+		pub DownwardMessageQueue: map hasher(twox_64_concat) ParaId => Vec<DownwardMessage<T::AccountId>>;
 	}
 	add_extra_genesis {
 		config(authorities): Vec<ValidatorId>;
@@ -531,6 +568,8 @@ decl_error! {
 		CannotPayFees,
 		/// Unexpected relay-parent for a candidate receipt.
 		UnexpectedRelayParent,
+		/// Downward message queue is full for the Parachain.
+		DownwardMessageQueueFull,
 	}
 }
 
@@ -596,6 +635,11 @@ decl_module! {
 							WATERMARK_QUEUE_SIZE,
 						)?;
 
+						Self::remove_processed_downward_messages(
+							id,
+							head.candidate.commitments.processed_downward_messages as usize,
+						);
+
 						let id = head.parachain_index();
 						proceeded.push(id);
 						last_id = Some(id);
@@ -668,6 +712,36 @@ decl_module! {
 
 			Ok(())
 		}
+
+		/// Transfer some tokens into a parachain and leave a message in the downward queue for it.
+		#[weight = 100_000]
+		pub fn transfer_to_parachain(
+			origin,
+			to: ParaId,
+			amount: Balance,
+			remark: Remark,
+		) {
+			let who = ensure_signed(origin)?;
+			let downward_queue_count = DownwardMessageQueue::<T>::decode_len(to).unwrap_or(0);
+			ensure!(downward_queue_count < MAX_DOWNWARD_QUEUE_COUNT, Error::<T>::DownwardMessageQueueFull);
+			T::ParachainCurrency::transfer_in(&who, to, amount, ExistenceRequirement::AllowDeath)?;
+			DownwardMessageQueue::<T>::append(to, DownwardMessage::TransferInto(who, amount, remark));
+		}
+
+		/// Send a XCMP message to the given parachain.
+		///
+		/// The origin must be another parachain.
+		#[weight = 100_000]
+		pub fn send_xcmp_message(
+			origin,
+			to: ParaId,
+			msg: Vec<u8>,
+		) {
+			ensure_parachain(<T as Trait>::Origin::from(origin))?;
+			let downward_queue_count = DownwardMessageQueue::<T>::decode_len(to).unwrap_or(0);
+			ensure!(downward_queue_count < MAX_DOWNWARD_QUEUE_COUNT, Error::<T>::DownwardMessageQueueFull);
+			DownwardMessageQueue::<T>::append(to, DownwardMessage::XCMPMessage(msg));
+		}
 	}
 }
 
@@ -814,11 +888,11 @@ impl<T: Trait> Module<T> {
 		if let Ok(message_call) = <T as Trait>::Call::decode(&mut &data[..]) {
 			let origin: <T as Trait>::Origin = match origin {
 				ParachainDispatchOrigin::Signed =>
-					system::RawOrigin::Signed(id.into_account()).into(),
+					<T as Trait>::Origin::from(<T as system::Trait>::Origin::from(system::RawOrigin::Signed(id.into_account()))),
 				ParachainDispatchOrigin::Parachain =>
 					Origin::Parachain(id).into(),
 				ParachainDispatchOrigin::Root =>
-					system::RawOrigin::Root.into(),
+					<T as Trait>::Origin::from(<T as system::Trait>::Origin::from(system::RawOrigin::Root)),
 			};
 			let _ok = message_call.dispatch(origin).is_ok();
 			// Not much to do with the result as it is. It's up to the parachain to ensure that the
@@ -862,6 +936,17 @@ impl<T: Trait> Module<T> {
 		Ok(())
 	}
 
+	/// Remove processed downward messages from the `DownwardMessageQueue`.
+	fn remove_processed_downward_messages(id: ParaId, processed: usize) {
+		DownwardMessageQueue::<T>::mutate(id, |v| {
+			if processed > v.len() {
+				v.clear();
+			} else {
+				*v = v.split_off(processed);
+			}
+		});
+	}
+
 	/// Update routing information from the parachain heads. This queues upwards
 	/// messages to the relay chain as well.
 	fn update_routing(
@@ -1079,6 +1164,11 @@ impl<T: Trait> Module<T> {
 		})
 	}
 
+	/// Returns the `DownwardMessage`'s for the given parachain.
+	pub fn downward_messages(id: ParaId) -> Vec<DownwardMessage<T::AccountId>> {
+		DownwardMessageQueue::<T>::get(id)
+	}
+
 	/// Get the local validation data for a particular parent w.r.t. the current
 	/// block height.
 	pub fn current_local_validation_data(id: &ParaId) -> Option<LocalValidationData> {
@@ -1113,8 +1203,7 @@ impl<T: Trait> Module<T> {
 		schedule: &GlobalValidationSchedule,
 		attested_candidates: &[AttestedCandidate],
 		active_parachains: &[(ParaId, Option<(CollatorId, Retriable)>)]
-	) -> sp_std::result::Result<IncludedBlocks<T>, sp_runtime::DispatchError>
+	) -> sp_std::result::Result<IncludedBlocks<T>, sp_runtime::DispatchError> {
-	{
 		// returns groups of slices that have the same chain ID.
 		// assumes the inner slice is sorted by id.
 		struct GroupedDutyIter<'a> {
@@ -3511,4 +3600,40 @@ mod tests {
 			}
 		});
 	}
+
+	#[test]
+	fn downward_message_removal_works() {
+		let id = ParaId::from(0);
+
+		// That the list of egress queue roots is in ascending order by `ParaId`.
+		let parachains = vec![
+			(id, vec![].into(), vec![].into()),
+		];
+
+		new_test_ext(parachains).execute_with(|| {
+			run_to_block(2);
+
+			DownwardMessageQueue::<Test>::insert(
+				&id,
+				vec![
+					DownwardMessage::Opaque(vec![1]),
+					DownwardMessage::Opaque(vec![2]),
+					DownwardMessage::Opaque(vec![3])
+				]
+			);
+
+			let mut raw_candidate = raw_candidate(id);
+			raw_candidate.commitments.processed_downward_messages = 2;
+
+			let candidate = make_blank_attested(raw_candidate);
+			let mut candidates = vec![candidate];
+			candidates.iter_mut().for_each(make_attestations);
+
+			assert_ok!(Parachains::set_heads(Origin::none(), candidates));
+			assert_eq!(
+				vec![DownwardMessage::Opaque(vec![3])],
+				DownwardMessageQueue::<Test>::get(&id),
+			);
+		});
+	}
 }

polkadot/runtime/common/src/registrar.rs

@@ -1074,6 +1074,7 @@ mod tests {
 				upward_messages: vec![],
 				erasure_root: [1; 32].into(),
 				new_validation_code: None,
+				processed_downward_messages: 0,
 			},
 		};
 		let (candidate, _) = candidate.abridge();

polkadot/runtime/kusama/Cargo.toml

@@ -66,9 +66,9 @@ utility = { package = "pallet-utility", git = "https://github.com/paritytech/sub
 vesting = { package = "pallet-vesting", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 
 frame-benchmarking = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false, optional = true }
-frame-system-benchmarking = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false, optional = true }
 pallet-offences-benchmarking = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false, optional = true }
 pallet-session-benchmarking = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false, optional = true }
+frame-system-benchmarking = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false, optional = true }
 hex-literal = { version = "0.2.1", optional = true }
 
 runtime-common = { package = "polkadot-runtime-common", path = "../common", default-features = false }
@@ -170,3 +170,9 @@ runtime-benchmarks = [
 	"pallet-session-benchmarking",
 	"hex-literal",
 ]
+# When enabled, the runtime api will not be build.
+#
+# This is required by Cumulus to access certain types of the
+# runtime without clashing with the runtime api exported functions
+# in WASM.
+disable-runtime-api = []

polkadot/runtime/kusama/src/lib.rs

@@ -88,7 +88,10 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	authoring_version: 2,
 	spec_version: 2013,
 	impl_version: 0,
+	#[cfg(not(feature = "disable-runtime-api"))]
 	apis: RUNTIME_API_VERSIONS,
+	#[cfg(feature = "disable-runtime-api")]
+	apis: version::create_apis_vec![[]],
 	transaction_version: 2,
 };
 
@@ -1005,6 +1008,7 @@ pub type Executive = executive::Executive<
 /// The payload being signed in the transactions.
 pub type SignedPayload = generic::SignedPayload<Call, SignedExtra>;
 
+#[cfg(not(feature = "disable-runtime-api"))]
 sp_api::impl_runtime_apis! {
 	impl sp_api::Core<Block> for Runtime {
 		fn version() -> RuntimeVersion {
@@ -1103,6 +1107,9 @@ sp_api::impl_runtime_apis! {
 		fn signing_context() -> SigningContext {
 			Parachains::signing_context()
 		}
+		fn downward_messages(id: parachain::Id) -> Vec<primitives::DownwardMessage> {
+			Parachains::downward_messages(id)
+		}
 	}
 
 	impl fg_primitives::GrandpaApi<Block> for Runtime {

polkadot/runtime/polkadot/Cargo.toml

@@ -60,8 +60,8 @@ system_rpc_runtime_api = { package = "frame-system-rpc-runtime-api", git = "http
 timestamp = { package = "pallet-timestamp", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 treasury = { package = "pallet-treasury", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 sudo = { package = "pallet-sudo", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
-utility = { package = "pallet-utility", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 vesting = { package = "pallet-vesting", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
+utility = { package = "pallet-utility", git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 
 frame-benchmarking = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false, optional = true }
 frame-system-benchmarking = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false, optional = true }
@@ -164,3 +164,9 @@ runtime-benchmarks = [
 	"pallet-session-benchmarking",
 	"hex-literal",
 ]
+# When enabled, the runtime api will not be build.
+#
+# This is required by Cumulus to access certain types of the
+# runtime without clashing with the runtime api exported functions
+# in WASM.
+disable-runtime-api = []

polkadot/runtime/polkadot/src/lib.rs

@@ -93,7 +93,10 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	authoring_version: 0,
 	spec_version: 13,
 	impl_version: 0,
+	#[cfg(not(feature = "disable-runtime-api"))]
 	apis: RUNTIME_API_VERSIONS,
+	#[cfg(feature = "disable-runtime-api")]
+	apis: version::create_apis_vec![[]],
 	transaction_version: 2,
 };
 
@@ -991,6 +994,7 @@ pub type Executive = executive::Executive<Runtime, Block, system::ChainContext<R
 /// The payload being signed in transactions.
 pub type SignedPayload = generic::SignedPayload<Call, SignedExtra>;
 
+#[cfg(not(feature = "disable-runtime-api"))]
 sp_api::impl_runtime_apis! {
 	impl sp_api::Core<Block> for Runtime {
 		fn version() -> RuntimeVersion {
@@ -1089,6 +1093,9 @@ sp_api::impl_runtime_apis! {
 		fn signing_context() -> SigningContext {
 			Parachains::signing_context()
 		}
+		fn downward_messages(id: parachain::Id) -> Vec<primitives::DownwardMessage> {
+			Parachains::downward_messages(id)
+		}
 	}
 
 	impl fg_primitives::GrandpaApi<Block> for Runtime {

polkadot/runtime/test-runtime/src/lib.rs

@@ -656,6 +656,9 @@ sp_api::impl_runtime_apis! {
 		fn signing_context() -> SigningContext {
 			Parachains::signing_context()
 		}
+		fn downward_messages(id: parachain::Id) -> Vec<primitives::DownwardMessage> {
+			Parachains::downward_messages(id)
+		}
 	}
 
 	impl fg_primitives::GrandpaApi<Block> for Runtime {

polkadot/runtime/westend/Cargo.toml

@@ -174,3 +174,9 @@ runtime-benchmarks = [
 	"pallet-session-benchmarking",
 	"hex-literal",
 ]
+# When enabled, the runtime api will not be build.
+#
+# This is required by Cumulus to access certain types of the
+# runtime without clashing with the runtime api exported functions
+# in WASM.
+disable-runtime-api = []

polkadot/runtime/westend/src/lib.rs

@@ -83,7 +83,10 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	authoring_version: 2,
 	spec_version: 33,
 	impl_version: 0,
+	#[cfg(not(feature = "disable-runtime-api"))]
 	apis: RUNTIME_API_VERSIONS,
+	#[cfg(feature = "disable-runtime-api")]
+	apis: version::create_apis_vec![[]],
 	transaction_version: 2,
 };
 
@@ -753,6 +756,7 @@ pub type Executive = executive::Executive<Runtime, Block, system::ChainContext<R
 /// The payload being signed in transactions.
 pub type SignedPayload = generic::SignedPayload<Call, SignedExtra>;
 
+#[cfg(not(feature = "disable-runtime-api"))]
 sp_api::impl_runtime_apis! {
 	impl sp_api::Core<Block> for Runtime {
 		fn version() -> RuntimeVersion {
@@ -851,6 +855,9 @@ sp_api::impl_runtime_apis! {
 		fn signing_context() -> SigningContext {
 			Parachains::signing_context()
 		}
+		fn downward_messages(id: parachain::Id) -> Vec<primitives::DownwardMessage> {
+			Parachains::downward_messages(id)
+		}
 	}
 
 	impl fg_primitives::GrandpaApi<Block> for Runtime {

polkadot/validation/src/error.rs

@@ -81,7 +81,10 @@ pub enum Error {
 	/// Block data is too big
 	#[display(fmt = "Block data is too big (maximum allowed size: {}, actual size: {})", size, max_size)]
 	BlockDataTooBig { size: u64, max_size: u64 },
-	Join(tokio::task::JoinError)
+	Join(tokio::task::JoinError),
+	/// Could not cover fee for an operation e.g. for sending `UpwardMessage`.
+	#[display(fmt = "Parachain could not cover fee for an operation e.g. for sending an `UpwardMessage`.")]
+	CouldNotCoverFee,
 }
 
 impl std::error::Error for Error {

polkadot/validation/src/pipeline.rs

@@ -17,8 +17,6 @@
 //! The pipeline of validation functions a parachain block must pass through before
 //! it can be voted for.
 
-use std::sync::Arc;
-
 use codec::Encode;
 use polkadot_erasure_coding as erasure;
 use polkadot_primitives::parachain::{
@@ -33,7 +31,6 @@ use parachain::{
 };
 use runtime_primitives::traits::{BlakeTwo256, Hash as HashT};
 use sp_api::ProvideRuntimeApi;
-use parking_lot::Mutex;
 use crate::Error;
 
 pub use parachain::wasm_executor::ValidationPool;
@@ -67,67 +64,6 @@ pub fn basic_checks(
 	Ok(())
 }
 
-struct ExternalitiesInner {
-	upward: Vec<UpwardMessage>,
-	fees_charged: Balance,
-	free_balance: Balance,
-	fee_schedule: FeeSchedule,
-}
-
-impl wasm_executor::Externalities for ExternalitiesInner {
-	fn post_upward_message(&mut self, message: UpwardMessage) -> Result<(), String> {
-		self.apply_message_fee(message.data.len())?;
-
-		self.upward.push(message);
-
-		Ok(())
-	}
-}
-
-impl ExternalitiesInner {
-	fn new(free_balance: Balance, fee_schedule: FeeSchedule) -> Self {
-		Self {
-			free_balance,
-			fee_schedule,
-			fees_charged: 0,
-			upward: Vec::new(),
-		}
-	}
-
-	fn apply_message_fee(&mut self, message_len: usize) -> Result<(), String> {
-		let fee = self.fee_schedule.compute_message_fee(message_len);
-		let new_fees_charged = self.fees_charged.saturating_add(fee);
-		if new_fees_charged > self.free_balance {
-			Err("could not cover fee.".into())
-		} else {
-			self.fees_charged = new_fees_charged;
-			Ok(())
-		}
-	}
-
-	// Returns the noted outputs of execution so far - upward messages and balances.
-	fn outputs(self) -> (Vec<UpwardMessage>, Balance) {
-		(self.upward, self.fees_charged)
-	}
-}
-
-#[derive(Clone)]
-struct Externalities(Arc<Mutex<ExternalitiesInner>>);
-
-impl Externalities {
-	fn new(free_balance: Balance, fee_schedule: FeeSchedule) -> Self {
-		Self(Arc::new(Mutex::new(
-			ExternalitiesInner::new(free_balance, fee_schedule)
-		)))
-	}
-}
-
-impl wasm_executor::Externalities for Externalities {
-	fn post_upward_message(&mut self, message: UpwardMessage) -> Result<(), String> {
-		self.0.lock().post_upward_message(message)
-	}
-}
-
 /// Data from a fully-outputted validation of a parachain candidate. This contains
 /// all outputs and commitments of the validation as well as all additional data to make available.
 pub struct FullOutput {
@@ -163,6 +99,7 @@ pub struct ValidatedCandidate<'a> {
 	local_validation: &'a LocalValidationData,
 	upward_messages: Vec<UpwardMessage>,
 	fees: Balance,
+	processed_downward_messages: u32,
 }
 
 impl<'a> ValidatedCandidate<'a> {
@@ -175,6 +112,7 @@ impl<'a> ValidatedCandidate<'a> {
 			local_validation,
 			upward_messages,
 			fees,
+			processed_downward_messages,
 		} = self;
 
 		let omitted_validation = OmittedValidationData {
@@ -212,6 +150,7 @@ impl<'a> ValidatedCandidate<'a> {
 			fees,
 			erasure_root,
 			new_validation_code: None,
+			processed_downward_messages,
 		};
 
 		Ok(FullOutput {
@@ -223,6 +162,27 @@ impl<'a> ValidatedCandidate<'a> {
 	}
 }
 
+/// Validate that the given `UpwardMessage`s are covered by the given `free_balance`.
+///
+/// Will return an error if the `free_balance` does not cover the required fees to the
+/// given `msgs`. On success it returns the fees that need to be charged for the `msgs`.
+fn validate_upward_messages(
+	msgs: &[UpwardMessage],
+	fee_schedule: FeeSchedule,
+	free_balance: Balance,
+) -> Result<Balance, Error> {
+	msgs.iter().try_fold(Balance::from(0u128), |fees_charged, msg| {
+		let fees = fee_schedule.compute_message_fee(msg.data.len());
+		let fees_charged = fees_charged.saturating_add(fees);
+
+		if fees_charged > free_balance {
+			Err(Error::CouldNotCoverFee)
+		} else {
+			Ok(fees_charged)
+		}
+	})
+}
+
 /// Does full checks of a collation, with provided PoV-block and contextual data.
 pub fn validate<'a>(
 	validation_pool: Option<&'_ ValidationPool>,
@@ -258,28 +218,26 @@ pub fn validate<'a>(
 		.map(ExecutionMode::Remote)
 		.unwrap_or(ExecutionMode::Local);
 
-	let ext = Externalities::new(local_validation.balance, fee_schedule);
 	match wasm_executor::validate_candidate(
 		&validation_code.0,
 		params,
-		ext.clone(),
 		execution_mode,
 	) {
 		Ok(result) => {
 			if result.head_data == collation.head_data {
-				let (upward_messages, fees) = Arc::try_unwrap(ext.0)
+				let fees = validate_upward_messages(
-					.map_err(|_| "<non-unique>")
+					&result.upward_messages,
-					.expect("Wasm executor drops passed externalities on completion; \
+					fee_schedule,
-						call has concluded; qed")
+					local_validation.balance,
-					.into_inner()
+				)?;
-					.outputs();
 
 				Ok(ValidatedCandidate {
 					pov_block,
 					global_validation,
 					local_validation,
-					upward_messages,
+					upward_messages: result.upward_messages,
 					fees,
+					processed_downward_messages: result.processed_downward_messages,
 				})
 			} else {
 				Err(Error::HeadDataMismatch)
@@ -368,37 +326,34 @@ pub fn full_output_validation_with_api<P>(
 #[cfg(test)]
 mod tests {
 	use super::*;
-	use parachain::wasm_executor::Externalities as ExternalitiesTrait;
 	use parachain::primitives::ParachainDispatchOrigin;
 
+	fn add_msg(size: usize, msgs: &mut Vec<UpwardMessage>) {
+		let msg = UpwardMessage { data: vec![0; size], origin: ParachainDispatchOrigin::Parachain };
+		msgs.push(msg);
+	}
+
 	#[test]
-	fn ext_checks_fees_and_updates_correctly() {
+	fn validate_upward_messages_works() {
-		let mut ext = ExternalitiesInner {
+		let fee_schedule = FeeSchedule {
-			upward: vec![
-				UpwardMessage { data: vec![42], origin: ParachainDispatchOrigin::Parachain },
-			],
-			fees_charged: 0,
-			free_balance: 1_000_000,
-			fee_schedule: FeeSchedule {
 			base: 1000,
 			per_byte: 10,
-			},
 		};
+		let free_balance = 1_000_000;
+		let mut msgs = Vec::new();
 
-		ext.apply_message_fee(100).unwrap();
+		add_msg(100, &mut msgs);
-		assert_eq!(ext.fees_charged, 2000);
+		assert_eq!(2000, validate_upward_messages(&msgs, fee_schedule, free_balance).unwrap());
 
-		ext.post_upward_message(UpwardMessage {
+		add_msg(100, &mut msgs);
-			origin: ParachainDispatchOrigin::Signed,
+		assert_eq!(4000, validate_upward_messages(&msgs, fee_schedule, free_balance).unwrap());
-			data: vec![0u8; 100],
-		}).unwrap();
-		assert_eq!(ext.fees_charged, 4000);
 
-
+		add_msg((1_000_000 - 4000 - 1000) / 10, &mut msgs);
-		ext.apply_message_fee((1_000_000 - 4000 - 1000) / 10).unwrap();
+		assert_eq!(1_000_000, validate_upward_messages(&msgs, fee_schedule, free_balance).unwrap());
-		assert_eq!(ext.fees_charged, 1_000_000);
 
 		// cannot pay fee.
-		assert!(ext.apply_message_fee(1).is_err());
+		add_msg(1, &mut msgs);
+		let err = validate_upward_messages(&msgs, fee_schedule, free_balance).unwrap_err();
+		assert!(matches!(err, Error::CouldNotCoverFee));
 	}
 }

polkadot/validation/src/validation_service/mod.rs

@@ -704,6 +704,9 @@ mod tests {
 			fn signing_context() -> SigningContext {
 				Default::default()
 			}
+			fn downward_messages(_: ParaId) -> Vec<polkadot_primitives::DownwardMessage> {
+				Vec::new()
+			}
 		}
 	}