Downward Message Processing implementation (#1859)

* DMP: data structures and plumbing

* DMP: Implement DMP logic in the router module

DMP: Integrate DMP parts into the inclusion module

* DMP: Introduce the max size limit for the size of a downward message

* DMP: Runtime API for accessing inbound messages

* OCD

Small clean ups

* DMP: fix the naming of the error

* DMP: add caution about a non-existent recipient

polkadot/parachain/src/primitives.rs

@@ -248,6 +248,11 @@ pub struct ValidationParams {
 	pub block_data: BlockData,
 	/// The current relay-chain block number.
 	pub relay_chain_height: RelayChainBlockNumber,
+	/// The MQC head for the DMQ.
+	///
+	/// The DMQ MQC head will be used by the validation function to authorize the downward messages
+	/// passed by the collator.
+	pub dmq_mqc_head: Hash,
 	/// The list of MQC heads for the inbound HRMP channels paired with the sender para ids. This
 	/// vector is sorted ascending by the para id and doesn't contain multiple entries with the same
 	/// sender.

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

@@ -97,6 +97,7 @@ fn execute_good_on_parent(execution_mode: ExecutionMode) {
 			block_data: GenericBlockData(block_data.encode()),
 			relay_chain_height: 1,
 			hrmp_mqc_heads: Vec::new(),
+			dmq_mqc_head: Default::default(),
 		},
 		&execution_mode,
 		sp_core::testing::TaskExecutor::new(),
@@ -135,6 +136,7 @@ fn execute_good_chain_on_parent() {
 				block_data: GenericBlockData(block_data.encode()),
 				relay_chain_height: number as RelayChainBlockNumber + 1,
 				hrmp_mqc_heads: Vec::new(),
+				dmq_mqc_head: Default::default(),
 			},
 			&execution_mode,
 			sp_core::testing::TaskExecutor::new(),
@@ -174,6 +176,7 @@ fn execute_bad_on_parent() {
 			block_data: GenericBlockData(block_data.encode()),
 			relay_chain_height: 1,
 			hrmp_mqc_heads: Vec::new(),
+			dmq_mqc_head: Default::default(),
 		},
 		&execution_mode,
 		sp_core::testing::TaskExecutor::new(),

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

@@ -43,6 +43,7 @@ fn terminates_on_timeout() {
 			parent_head: Default::default(),
 			relay_chain_height: 1,
 			hrmp_mqc_heads: Vec::new(),
+			dmq_mqc_head: Default::default(),
 		},
 		&execution_mode,
 		sp_core::testing::TaskExecutor::new(),
@@ -71,6 +72,7 @@ fn parallel_execution() {
 			parent_head: Default::default(),
 			relay_chain_height: 1,
 			hrmp_mqc_heads: Vec::new(),
+			dmq_mqc_head: Default::default(),
 		},
 		&execution_mode,
 		sp_core::testing::TaskExecutor::new(),
@@ -82,6 +84,7 @@ fn parallel_execution() {
 			parent_head: Default::default(),
 			relay_chain_height: 1,
 			hrmp_mqc_heads: Vec::new(),
+			dmq_mqc_head: Default::default(),
 		},
 		&execution_mode2,
 		sp_core::testing::TaskExecutor::new(),