Introduce create_blinded_paths helpers in OffersMessageFlow

These functions will be used in the following commit to replace closure usage
in Flow trait functions.

Author: shaavan

lightning/src/ln/channelmanager.rs

@@ -2842,7 +2842,7 @@ pub const MIN_CLTV_EXPIRY_DELTA: u16 = 6*7;
 // scale them up to suit its security policy. At the network-level, we shouldn't constrain them too much,
 // while avoiding to introduce a DoS vector. Further, a low CTLV_FAR_FAR_AWAY could be a source of
 // routing failure for any HTLC sender picking up an LDK node among the first hops.
-pub(super) const CLTV_FAR_FAR_AWAY: u32 = 14 * 24 * 6;
+pub(crate) const CLTV_FAR_FAR_AWAY: u32 = 14 * 24 * 6;
 
 /// Minimum CLTV difference between the current block height and received inbound payments.
 /// Invoices generated for payment to us must set their `min_final_cltv_expiry_delta` field to at least

lightning/src/offers/flow.rs

@@ -14,19 +14,31 @@ use core::ops::Deref;
 use core::sync::atomic::{AtomicUsize, Ordering};
 use core::time::Duration;
 
-use bitcoin::block::Header;
-use bitcoin::constants::ChainHash;
-use bitcoin::secp256k1::{self, PublicKey, Secp256k1};
-
+use crate::blinded_path::message::{
+	BlindedMessagePath, MessageContext, MessageForwardNode, OffersContext,
+};
+use crate::blinded_path::payment::{
+	BlindedPaymentPath, PaymentConstraints, PaymentContext, UnauthenticatedReceiveTlvs,
+};
+use crate::chain::channelmonitor::LATENCY_GRACE_PERIOD_BLOCKS;
 use crate::chain::transaction::TransactionData;
 use crate::chain::{self, BestBlock};
+use crate::ln::channel_state::ChannelDetails;
+use crate::ln::channelmanager::{
+	ChainParameters, CLTV_FAR_FAR_AWAY, MAX_SHORT_LIVED_RELATIVE_EXPIRY,
+};
 use crate::ln::inbound_payment;
+use crate::offers::nonce::Nonce;
 use crate::onion_message::async_payments::AsyncPaymentsMessage;
 use crate::onion_message::messenger::{MessageRouter, MessageSendInstructions};
 use crate::onion_message::offers::OffersMessage;
 use crate::routing::router::Router;
 use crate::sign::EntropySource;
 use crate::sync::{Mutex, RwLock};
+use bitcoin::block::Header;
+use bitcoin::constants::ChainHash;
+use bitcoin::secp256k1::{self, PublicKey, Secp256k1};
+use lightning_invoice::PaymentSecret;
 
 #[cfg(feature = "dnssec")]
 use crate::onion_message::dns_resolution::DNSResolverMessage;
@@ -144,6 +156,110 @@ where
 	}
 }
 
+impl<ES: Deref, MR: Deref, R: Deref> OffersMessageFlow<ES, MR, R>
+where
+	ES::Target: EntropySource,
+	MR::Target: MessageRouter,
+	R::Target: Router,
+{
+	/// Creates a collection of blinded paths by delegating to [`MessageRouter`] based on
+	/// the path's intended lifetime.
+	///
+	/// Whether or not the path is compact depends on whether the path is short-lived or long-lived,
+	/// respectively, based on the given `absolute_expiry` as seconds since the Unix epoch. See
+	/// [`MAX_SHORT_LIVED_RELATIVE_EXPIRY`].
+	fn create_blinded_paths_using_absolute_expiry(
+		&self, context: OffersContext, absolute_expiry: Option<Duration>,
+		peers: Vec<MessageForwardNode>,
+	) -> Result<Vec<BlindedMessagePath>, ()> {
+		let now = self.duration_since_epoch();
+		let max_short_lived_absolute_expiry = now.saturating_add(MAX_SHORT_LIVED_RELATIVE_EXPIRY);
+
+		if absolute_expiry.unwrap_or(Duration::MAX) <= max_short_lived_absolute_expiry {
+			self.create_compact_blinded_paths(peers, context)
+		} else {
+			self.create_blinded_paths(peers, MessageContext::Offers(context))
+		}
+	}
+
+	/// Creates a collection of blinded paths by delegating to
+	/// [`MessageRouter::create_blinded_paths`].
+	///
+	/// Errors if the `MessageRouter` errors.
+	fn create_blinded_paths(
+		&self, peers: Vec<MessageForwardNode>, context: MessageContext,
+	) -> Result<Vec<BlindedMessagePath>, ()> {
+		let recipient = self.get_our_node_id();
+		let secp_ctx = &self.secp_ctx;
+
+		let peers = peers.into_iter().map(|node| node.node_id).collect();
+
+		self.message_router
+			.create_blinded_paths(recipient, context, peers, secp_ctx)
+			.and_then(|paths| (!paths.is_empty()).then(|| paths).ok_or(()))
+	}
+
+	/// Creates a collection of blinded paths by delegating to
+	/// [`MessageRouter::create_compact_blinded_paths`].
+	///
+	/// Errors if the `MessageRouter` errors.
+	fn create_compact_blinded_paths(
+		&self, peers: Vec<MessageForwardNode>, context: OffersContext,
+	) -> Result<Vec<BlindedMessagePath>, ()> {
+		let recipient = self.get_our_node_id();
+		let secp_ctx = &self.secp_ctx;
+
+		let peers = peers;
+
+		self.message_router
+			.create_compact_blinded_paths(
+				recipient,
+				MessageContext::Offers(context),
+				peers,
+				secp_ctx,
+			)
+			.and_then(|paths| (!paths.is_empty()).then(|| paths).ok_or(()))
+	}
+
+	/// Creates multi-hop blinded payment paths for the given `amount_msats` by delegating to
+	/// [`Router::create_blinded_payment_paths`].
+	fn create_blinded_payment_paths(
+		&self, usable_channels: Vec<ChannelDetails>, amount_msats: Option<u64>,
+		payment_secret: PaymentSecret, payment_context: PaymentContext,
+		relative_expiry_seconds: u32,
+	) -> Result<Vec<BlindedPaymentPath>, ()> {
+		let expanded_key = &self.inbound_payment_key;
+		let entropy = &*self.entropy_source;
+		let secp_ctx = &self.secp_ctx;
+
+		let first_hops = usable_channels;
+		let payee_node_id = self.get_our_node_id();
+
+		// Assume shorter than usual block times to avoid spuriously failing payments too early.
+		const SECONDS_PER_BLOCK: u32 = 9 * 60;
+		let relative_expiry_blocks = relative_expiry_seconds / SECONDS_PER_BLOCK;
+		let max_cltv_expiry = core::cmp::max(relative_expiry_blocks, CLTV_FAR_FAR_AWAY)
+			.saturating_add(LATENCY_GRACE_PERIOD_BLOCKS)
+			.saturating_add(self.best_block.read().unwrap().height);
+
+		let payee_tlvs = UnauthenticatedReceiveTlvs {
+			payment_secret,
+			payment_constraints: PaymentConstraints { max_cltv_expiry, htlc_minimum_msat: 1 },
+			payment_context,
+		};
+		let nonce = Nonce::from_entropy_source(entropy);
+		let payee_tlvs = payee_tlvs.authenticate(nonce, expanded_key);
+
+		self.router.create_blinded_payment_paths(
+			payee_node_id,
+			first_hops,
+			payee_tlvs,
+			amount_msats,
+			secp_ctx,
+		)
+	}
+}
+
 impl<ES: Deref, MR: Deref, R: Deref> chain::Listen for OffersMessageFlow<ES, MR, R>
 where
 	ES::Target: EntropySource,