Check if funding transaction is final for propagation

If the funding transaction is timelocked beyond the next block of
our best known chain tip, return an APIError instead of silently
failing at broadcast attempt.

Author: Antoine Riard

lightning/src/ln/channelmanager.rs

@@ -2783,6 +2783,9 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 	/// Returns an [`APIError::APIMisuseError`] if the funding_transaction spent non-SegWit outputs
 	/// or if no output was found which matches the parameters in [`Event::FundingGenerationReady`].
 	///
+	/// Returns [`APIError::APIMisueError`] if the funding transaction is not final for propagation
+	/// across the p2p network.
+	///
 	/// Returns [`APIError::ChannelUnavailable`] if a funding transaction has already been provided
 	/// for the channel or if the channel has been closed as indicated by [`Event::ChannelClosed`].
 	///
@@ -2810,6 +2813,15 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 				});
 			}
 		}
+		{
+			let height = self.best_block.read().unwrap().height();
+			// Transactions are evaluated as final by network mempools at the next block.
+			if funding_transaction.lock_time < 500_000_000 && funding_transaction.lock_time > height + 1 {
+				return Err(APIError::APIMisuseError {
+					err: "Funding transaction asbolute timelock is non-final".to_owned()
+				});
+			}
+		}
 		self.funding_transaction_generated_intern(temporary_channel_id, counterparty_node_id, funding_transaction, |chan, tx| {
 			let mut output_index = None;
 			let expected_spk = chan.get_funding_redeemscript().to_v0_p2wsh();