f - try avoid leaking the recipient's node_id

Author: jkczyz

lightning/src/routing/router.rs

@@ -90,11 +90,21 @@ impl< G: Deref<Target = NetworkGraph<L>> + Clone, L: Deref, S: Deref, SP: Sized,
 		&self, recipient: PublicKey, first_hops: Vec<ChannelDetails>, tlvs: ReceiveTlvs,
 		amount_msats: u64, entropy_source: &ES, secp_ctx: &Secp256k1<T>
 	) -> Result<Vec<(BlindedPayInfo, BlindedPath)>, ()> {
+		// Ensure peers have at least three channels so that it is more difficult to infer the
+		// recipient's node_id.
+		const MIN_PEER_CHANNELS: usize = 3;
+		let network_graph = self.network_graph.deref().read_only();
+
 		first_hops.into_iter()
 			.filter(|details| details.is_public)
 			.filter(|details| details.counterparty.features.supports_route_blinding())
 			.filter(|details| amount_msats >= details.inbound_htlc_minimum_msat.unwrap_or(0))
 			.filter(|details| amount_msats <= details.inbound_htlc_maximum_msat.unwrap_or(0))
+			.filter(|details| network_graph
+					.node(&NodeId::from_pubkey(&details.counterparty.node_id))
+					.map(|node_info| node_info.channels.len() >= MIN_PEER_CHANNELS)
+					.unwrap_or(false)
+			)
 			.map(|details| {
 				let short_channel_id = details.get_inbound_payment_scid().unwrap();
 				let payment_relay: PaymentRelay = details.counterparty.forwarding_info.unwrap().into();