Add LSPS5 DOS protections.

When handling an incoming LSPS5 request, the manager will check
if the counterparty is 'engaged' in some way before responding.
`Engaged` meaning = active channel | LSPS2 active operation | LSPS1 active operation.

Logic: `If not engaged then reject request;`

A single test is added only checking for the active channel condition,
because it's not super easy to get LSPS1-2 on the correct state to check this (yet).
Other tangential work is happening that will make this easier and more tests will come in the near future

Author: martinsaposnic

lightning-liquidity/src/lsps1/service.rs

@@ -174,6 +174,20 @@ where
 		&self.config
 	}
 
+	/// Returns whether the peer currently has any active LSPS1 order flows.
+	///
+	/// An order is considered active only after we have validated the client's
+	/// `CreateOrder` request and replied with a `CreateOrder` response containing
+	/// an `order_id`.
+	/// Pending requests that are still awaiting our response are deliberately NOT counted.
+	pub(crate) fn has_active_requests(&self, counterparty_node_id: &PublicKey) -> bool {
+		let outer_state_lock = self.per_peer_state.read().unwrap();
+		outer_state_lock.get(counterparty_node_id).map_or(false, |inner| {
+			let peer_state = inner.lock().unwrap();
+			!peer_state.outbound_channels_by_order_id.is_empty()
+		})
+	}
+
 	fn handle_get_info_request(
 		&self, request_id: LSPSRequestId, counterparty_node_id: &PublicKey,
 	) -> Result<(), LightningError> {

lightning-liquidity/src/lsps2/service.rs

@@ -566,6 +566,15 @@ where
 		&self.config
 	}
 
+	/// Returns whether the peer has any active LSPS2 requests.
+	pub(crate) fn has_active_requests(&self, counterparty_node_id: &PublicKey) -> bool {
+		let outer_state_lock = self.per_peer_state.read().unwrap();
+		outer_state_lock.get(counterparty_node_id).map_or(false, |inner| {
+			let peer_state = inner.lock().unwrap();
+			!peer_state.outbound_channels_by_intercept_scid.is_empty()
+		})
+	}
+
 	/// Used by LSP to inform a client requesting a JIT Channel the token they used is invalid.
 	///
 	/// Should be called in response to receiving a [`LSPS2ServiceEvent::GetInfo`] event.

lightning-liquidity/src/lsps5/client.rs

@@ -185,6 +185,9 @@ where
 	/// Also ensure the URL is valid, has HTTPS protocol, its length does not exceed [`MAX_WEBHOOK_URL_LENGTH`]
 	/// and that the URL points to a public host.
 	///
+	/// Your request may fail if you recently opened a channel or started an LSPS1 / LSPS2 flow.
+	/// Please retry shortly.
+	///
 	/// [`MAX_WEBHOOK_URL_LENGTH`]: super::msgs::MAX_WEBHOOK_URL_LENGTH
 	/// [`MAX_APP_NAME_LENGTH`]: super::msgs::MAX_APP_NAME_LENGTH
 	/// [`WebhookRegistered`]: super::event::LSPS5ClientEvent::WebhookRegistered

lightning-liquidity/src/lsps5/msgs.rs

@@ -53,6 +53,8 @@ pub const LSPS5_UNKNOWN_ERROR_CODE: i32 = 1000;
 pub const LSPS5_SERIALIZATION_ERROR_CODE: i32 = 1001;
 /// A notification was sent too frequently.
 pub const LSPS5_SLOW_DOWN_ERROR_CODE: i32 = 1002;
+/// A request was rejected because the client has no prior activity with the LSP (no open channel and no active LSPS1 or LSPS2 flow). The client should first open a channel
+pub const LSPS5_NO_PRIOR_ACTIVITY_ERROR_CODE: i32 = 1003;
 
 pub(crate) const LSPS5_SET_WEBHOOK_METHOD_NAME: &str = "lsps5.set_webhook";
 pub(crate) const LSPS5_LIST_WEBHOOKS_METHOD_NAME: &str = "lsps5.list_webhooks";
@@ -113,6 +115,10 @@ pub enum LSPS5ProtocolError {
 	///
 	/// [`NOTIFICATION_COOLDOWN_TIME`]: super::service::NOTIFICATION_COOLDOWN_TIME
 	SlowDownError,
+
+	/// Request rejected because the client has no prior activity with the LSP (no open channel and no active LSPS1 or LSPS2 flow). The client should first open a channel
+	/// or initiate an LSPS1/LSPS2 interaction before retrying.
+	NoPriorActivityError,
 }
 
 impl LSPS5ProtocolError {
@@ -129,6 +135,7 @@ impl LSPS5ProtocolError {
 			LSPS5ProtocolError::UnknownError => LSPS5_UNKNOWN_ERROR_CODE,
 			LSPS5ProtocolError::SerializationError => LSPS5_SERIALIZATION_ERROR_CODE,
 			LSPS5ProtocolError::SlowDownError => LSPS5_SLOW_DOWN_ERROR_CODE,
+			LSPS5ProtocolError::NoPriorActivityError => LSPS5_NO_PRIOR_ACTIVITY_ERROR_CODE,
 		}
 	}
 	/// The error message for the LSPS5 protocol error.
@@ -145,6 +152,9 @@ impl LSPS5ProtocolError {
 				"Error serializing LSPS5 webhook notification"
 			},
 			LSPS5ProtocolError::SlowDownError => "Notification sent too frequently",
+			LSPS5ProtocolError::NoPriorActivityError => {
+				"Request rejected due to no prior activity with the LSP"
+			},
 		}
 	}
 }
@@ -249,6 +259,9 @@ impl From<LSPSResponseError> for LSPS5ProtocolError {
 			LSPS5_UNSUPPORTED_PROTOCOL_ERROR_CODE => LSPS5ProtocolError::UnsupportedProtocol,
 			LSPS5_TOO_MANY_WEBHOOKS_ERROR_CODE => LSPS5ProtocolError::TooManyWebhooks,
 			LSPS5_APP_NAME_NOT_FOUND_ERROR_CODE => LSPS5ProtocolError::AppNameNotFound,
+			LSPS5_SERIALIZATION_ERROR_CODE => LSPS5ProtocolError::SerializationError,
+			LSPS5_SLOW_DOWN_ERROR_CODE => LSPS5ProtocolError::SlowDownError,
+			LSPS5_NO_PRIOR_ACTIVITY_ERROR_CODE => LSPS5ProtocolError::NoPriorActivityError,
 			_ => LSPS5ProtocolError::UnknownError,
 		}
 	}
@@ -640,6 +653,12 @@ pub enum LSPS5Request {
 	RemoveWebhook(RemoveWebhookRequest),
 }
 
+impl LSPS5Request {
+	pub(crate) fn is_state_allocating(&self) -> bool {
+		matches!(self, LSPS5Request::SetWebhook(_))
+	}
+}
+
 /// An LSPS5 protocol response.
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum LSPS5Response {

lightning-liquidity/src/lsps5/service.rs

@@ -149,6 +149,34 @@ where
 		}
 	}
 
+	/// Enforces the prior-activity requirement for state-allocating LSPS5 requests (e.g.
+	/// `lsps5.set_webhook`), rejecting and replying with `NoPriorActivityError` if not met.
+	pub(crate) fn enforce_prior_activity_or_reject(
+		&self, client_id: &PublicKey, lsps2_has_active_requests: bool, lsps1_has_activity: bool,
+		request_id: LSPSRequestId,
+	) -> Result<(), LightningError> {
+		let can_accept = self.client_has_open_channel(client_id)
+			|| lsps2_has_active_requests
+			|| lsps1_has_activity;
+
+		let mut message_queue_notifier = self.pending_messages.notifier();
+		if !can_accept {
+			let error = LSPS5ProtocolError::NoPriorActivityError;
+			let msg = LSPS5Message::Response(
+				request_id,
+				LSPS5Response::SetWebhookError(error.clone().into()),
+			)
+			.into();
+			message_queue_notifier.enqueue(&client_id, msg);
+			return Err(LightningError {
+				err: error.message().into(),
+				action: ErrorAction::IgnoreAndLog(Level::Info),
+			});
+		} else {
+			Ok(())
+		}
+	}
+
 	fn check_prune_stale_webhooks<'a>(
 		&self, outer_state_lock: &mut RwLockWriteGuard<'a, HashMap<PublicKey, PeerState>>,
 	) {

lightning-liquidity/src/manager.rs

@@ -568,6 +568,29 @@ where
 			LSPSMessage::LSPS5(msg @ LSPS5Message::Request(..)) => {
 				match &self.lsps5_service_handler {
 					Some(lsps5_service_handler) => {
+						if let LSPS5Message::Request(ref req_id, ref req) = msg {
+							if req.is_state_allocating() {
+								let lsps2_has_active_requests = self
+									.lsps2_service_handler
+									.as_ref()
+									.map_or(false, |h| h.has_active_requests(sender_node_id));
+								#[cfg(lsps1_service)]
+								let lsps1_has_active_requests = self
+									.lsps1_service_handler
+									.as_ref()
+									.map_or(false, |h| h.has_active_requests(sender_node_id));
+								#[cfg(not(lsps1_service))]
+								let lsps1_has_active_requests = false;
+
+								lsps5_service_handler.enforce_prior_activity_or_reject(
+									sender_node_id,
+									lsps2_has_active_requests,
+									lsps1_has_active_requests,
+									req_id.clone(),
+								)?
+							}
+						}
+
 						lsps5_service_handler.handle_message(msg, sender_node_id)?;
 					},
 					None => {