From c3e809f0e5b9916f7c4bc66261310f5a26b692a9 Mon Sep 17 00:00:00 2001
From: Svyatoslav Nikolsky <svyatonik@gmail.com>
Date: Wed, 17 Feb 2021 15:09:02 +0300
Subject: [PATCH] ForbidOutboundMessages and ForbidInboundMessages (#735)

---
 .../message-lane/src/source_chain.rs          | 56 +++++++++++++++++++
 .../message-lane/src/target_chain.rs          | 29 ++++++++++
 bridges/primitives/runtime/src/lib.rs         |  6 ++
 3 files changed, 91 insertions(+)

diff --git a/bridges/primitives/message-lane/src/source_chain.rs b/bridges/primitives/message-lane/src/source_chain.rs
index 1bb0d591586f9..d0dc36bb69352 100644
--- a/bridges/primitives/message-lane/src/source_chain.rs
+++ b/bridges/primitives/message-lane/src/source_chain.rs
@@ -134,3 +134,59 @@ pub trait MessageDeliveryAndDispatchPayment<AccountId, Balance> {
 		0
 	}
 }
+
+/// Structure that may be used in place of `TargetHeaderChain`, `LaneMessageVerifier` and
+/// `MessageDeliveryAndDispatchPayment` on chains, where outbound messages are forbidden.
+pub struct ForbidOutboundMessages;
+
+/// Error message that is used in `ForbidOutboundMessages` implementation.
+const ALL_OUTBOUND_MESSAGES_REJECTED: &str = "This chain is configured to reject all outbound messages";
+
+impl<Payload, AccountId> TargetHeaderChain<Payload, AccountId> for ForbidOutboundMessages {
+	type Error = &'static str;
+
+	type MessagesDeliveryProof = ();
+
+	fn verify_message(_payload: &Payload) -> Result<(), Self::Error> {
+		Err(ALL_OUTBOUND_MESSAGES_REJECTED)
+	}
+
+	fn verify_messages_delivery_proof(
+		_proof: Self::MessagesDeliveryProof,
+	) -> Result<(LaneId, InboundLaneData<AccountId>), Self::Error> {
+		Err(ALL_OUTBOUND_MESSAGES_REJECTED)
+	}
+}
+
+impl<Submitter, Payload, Fee> LaneMessageVerifier<Submitter, Payload, Fee> for ForbidOutboundMessages {
+	type Error = &'static str;
+
+	fn verify_message(
+		_submitter: &Sender<Submitter>,
+		_delivery_and_dispatch_fee: &Fee,
+		_lane: &LaneId,
+		_outbound_data: &OutboundLaneData,
+		_payload: &Payload,
+	) -> Result<(), Self::Error> {
+		Err(ALL_OUTBOUND_MESSAGES_REJECTED)
+	}
+}
+
+impl<AccountId, Balance> MessageDeliveryAndDispatchPayment<AccountId, Balance> for ForbidOutboundMessages {
+	type Error = &'static str;
+
+	fn pay_delivery_and_dispatch_fee(
+		_submitter: &Sender<AccountId>,
+		_fee: &Balance,
+		_relayer_fund_account: &AccountId,
+	) -> Result<(), Self::Error> {
+		Err(ALL_OUTBOUND_MESSAGES_REJECTED)
+	}
+
+	fn pay_relayers_rewards(
+		_confirmation_relayer: &AccountId,
+		_relayers_rewards: RelayersRewards<AccountId, Balance>,
+		_relayer_fund_account: &AccountId,
+	) {
+	}
+}
diff --git a/bridges/primitives/message-lane/src/target_chain.rs b/bridges/primitives/message-lane/src/target_chain.rs
index 825fe67c54915..765ce64f63b39 100644
--- a/bridges/primitives/message-lane/src/target_chain.rs
+++ b/bridges/primitives/message-lane/src/target_chain.rs
@@ -129,3 +129,32 @@ impl<DispatchPayload: Decode, Fee> From<MessageData<Fee>> for DispatchMessageDat
 		}
 	}
 }
+
+/// Structure that may be used in place of `SourceHeaderChain` and `MessageDispatch` on chains,
+/// where inbound messages are forbidden.
+pub struct ForbidInboundMessages;
+
+/// Error message that is used in `ForbidOutboundMessages` implementation.
+const ALL_INBOUND_MESSAGES_REJECTED: &str = "This chain is configured to reject all inbound messages";
+
+impl<Fee> SourceHeaderChain<Fee> for ForbidInboundMessages {
+	type Error = &'static str;
+	type MessagesProof = ();
+
+	fn verify_messages_proof(
+		_proof: Self::MessagesProof,
+		_messages_count: u32,
+	) -> Result<ProvedMessages<Message<Fee>>, Self::Error> {
+		Err(ALL_INBOUND_MESSAGES_REJECTED)
+	}
+}
+
+impl<Fee> MessageDispatch<Fee> for ForbidInboundMessages {
+	type DispatchPayload = ();
+
+	fn dispatch_weight(_message: &DispatchMessage<Self::DispatchPayload, Fee>) -> Weight {
+		Weight::MAX
+	}
+
+	fn dispatch(_message: DispatchMessage<Self::DispatchPayload, Fee>) {}
+}
diff --git a/bridges/primitives/runtime/src/lib.rs b/bridges/primitives/runtime/src/lib.rs
index 058c510c1b526..6612e26c37dca 100644
--- a/bridges/primitives/runtime/src/lib.rs
+++ b/bridges/primitives/runtime/src/lib.rs
@@ -112,6 +112,12 @@ pub trait Size {
 	fn size_hint(&self) -> u32;
 }
 
+impl Size for () {
+	fn size_hint(&self) -> u32 {
+		0
+	}
+}
+
 /// Pre-computed size.
 pub struct PreComputedSize(pub usize);