Add danger_funding_transaction_generated

..under `ChannelManager`. It replicates the functionality of the
original `funding_transaction_generated` in the same module but without
checking if the witness data is set in the funding transction inputs.

lightning/src/ln/channelmanager.rs

@@ -4618,6 +4618,53 @@ where
 		self.batch_funding_transaction_generated(&[(temporary_channel_id, counterparty_node_id)], funding_transaction)
 	}
 
+
+	/// Dangerous: This method wont check if the funding transaction
+	/// is signed ie. if the witness data is empty or not. It is the
+	/// caller's responsibility to ensure that the funding transaction
+	/// is final.
+	///
+	/// If you wish to use a safer method, use [`ChannelManager::funding_transaction_generated`]
+	///
+	/// Call this upon creation of a funding transaction for the given channel.
+	///
+	/// 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::APIMisuseError`] 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`].
+	///
+	/// May panic if the output found in the funding transaction is duplicative with some other
+	/// channel (note that this should be trivially prevented by using unique funding transaction
+	/// keys per-channel).
+	///
+	/// Do NOT broadcast the funding transaction yourself. When we have safely received our
+	/// counterparty's signature the funding transaction will automatically be broadcast via the
+	/// [`BroadcasterInterface`] provided when this `ChannelManager` was constructed.
+	///
+	/// Note that this includes RBF or similar transaction replacement strategies - lightning does
+	/// not currently support replacing a funding transaction on an existing channel. Instead,
+	/// create a new channel with a conflicting funding transaction.
+	///
+	/// Note to keep the miner incentives aligned in moving the blockchain forward, we recommend
+	/// the wallet software generating the funding transaction to apply anti-fee sniping as
+	/// implemented by Bitcoin Core wallet. See <https://bitcoinops.org/en/topics/fee-sniping/>
+	/// for more details.
+	///
+	/// [`Event::FundingGenerationReady`]: crate::events::Event::FundingGenerationReady
+	/// [`Event::ChannelClosed`]: crate::events::Event::ChannelClosed
+	/// [`ChannelManager::funding_transaction_generated`]: crate::ln::channelmanager::ChannelManager::funding_transaction_generated
+	pub fn danger_funding_transaction_generated(&self, temporary_channel_id: &ChannelId, counterparty_node_id: &PublicKey, funding_transaction: Transaction) -> Result<(), APIError> {
+		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop(self);
+
+		let temporary_channels = &[(temporary_channel_id, counterparty_node_id)];
+		return self.batch_funding_transaction_generated_intern(temporary_channels, funding_transaction);
+
+	}
+
 	/// Call this upon creation of a batch funding transaction for the given channels.
 	///
 	/// Return values are identical to [`Self::funding_transaction_generated`], respective to
@@ -4641,6 +4688,13 @@ where
 				}
 			}
 		}
+		if result != Ok(()) { return result; }
+
+		return self.batch_funding_transaction_generated_intern(temporary_channels, funding_transaction);
+	}
+
+	fn batch_funding_transaction_generated_intern(&self, temporary_channels: &[(&ChannelId, &PublicKey)], funding_transaction: Transaction) -> Result<(), APIError> {
+		let mut result = Ok(());
 		if funding_transaction.output.len() > u16::max_value() as usize {
 			result = result.and(Err(APIError::APIMisuseError {
 				err: "Transaction had more than 2^16 outputs, which is not supported".to_owned()

lightning/src/ln/functional_test_utils.rs

@@ -1133,6 +1133,39 @@ pub fn create_coinbase_funding_transaction<'a, 'b, 'c>(node: &Node<'a, 'b, 'c>,
 	internal_create_funding_transaction(node, expected_counterparty_node_id, expected_chan_value, expected_user_chan_id, true)
 }
 
+pub fn create_funding_tx_without_witness_data<'a, 'b, 'c>(node: &Node<'a, 'b, 'c>,
+	expected_counterparty_node_id: &PublicKey, expected_chan_value: u64, expected_user_chan_id: u128) -> (ChannelId, Transaction, OutPoint) {
+	let chan_id = *node.network_chan_count.borrow();
+
+	let events = node.node.get_and_clear_pending_events();
+	assert_eq!(events.len(), 1);
+	match events[0] {
+		Event::FundingGenerationReady { ref temporary_channel_id, ref counterparty_node_id, ref channel_value_satoshis, ref output_script, user_channel_id } => {
+			assert_eq!(counterparty_node_id, expected_counterparty_node_id);
+			assert_eq!(*channel_value_satoshis, expected_chan_value);
+			assert_eq!(user_channel_id, expected_user_chan_id);
+
+			let dummy_outpoint = bitcoin::OutPoint { txid: bitcoin::Txid::from_slice(&[1; 32]).unwrap(), vout: 0 };
+			let dummy_script_sig = bitcoin::ScriptBuf::new();
+			let dummy_sequence = bitcoin::Sequence::ZERO;
+			let dummy_witness = bitcoin::Witness::new();
+			let input = vec![TxIn {
+					previous_output: dummy_outpoint,
+					script_sig: dummy_script_sig,
+					sequence: dummy_sequence,
+					witness: dummy_witness,
+				}];
+
+			let tx = Transaction { version: chan_id as i32, lock_time: LockTime::ZERO, input, output: vec![TxOut {
+				value: *channel_value_satoshis, script_pubkey: output_script.clone(),
+			}]};
+			let funding_outpoint = OutPoint { txid: tx.txid(), index: 0 };
+			(*temporary_channel_id, tx, funding_outpoint)
+		},
+		_ => panic!("Unexpected event"),
+	}
+}
+
 fn internal_create_funding_transaction<'a, 'b, 'c>(node: &Node<'a, 'b, 'c>,
 	expected_counterparty_node_id: &PublicKey, expected_chan_value: u64, expected_user_chan_id: u128,
 	coinbase: bool) -> (ChannelId, Transaction, OutPoint) {

lightning/src/ln/functional_tests.rs

@@ -3743,6 +3743,33 @@ fn test_peer_disconnected_before_funding_broadcasted() {
 		, [nodes[0].node.get_our_node_id()], 1000000);
 }
 
+#[test]
+fn test_danger_funding_transaction_generated() {
+	let chanmon_cfgs = create_chanmon_cfgs(2);
+	let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
+	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
+	let nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+
+	let expected_temporary_channel_id = nodes[0].node.create_channel(nodes[1].node.get_our_node_id(), 1_000_000, 500_000_000, 42, None, None).unwrap();
+	let open_channel = get_event_msg!(nodes[0], MessageSendEvent::SendOpenChannel, nodes[1].node.get_our_node_id());
+	nodes[1].node.handle_open_channel(&nodes[0].node.get_our_node_id(), &open_channel);
+	let accept_channel = get_event_msg!(nodes[1], MessageSendEvent::SendAcceptChannel, nodes[0].node.get_our_node_id());
+	nodes[0].node.handle_accept_channel(&nodes[1].node.get_our_node_id(), &accept_channel);
+
+	let (temporary_channel_id, tx, _funding_output) = create_funding_tx_without_witness_data(&nodes[0], &nodes[1].node.get_our_node_id(), 1_000_000, 42);
+	assert_eq!(temporary_channel_id, expected_temporary_channel_id);
+
+	assert!(nodes[0].node.funding_transaction_generated(&temporary_channel_id, &nodes[1].node.get_our_node_id(), tx.clone()).is_err());
+	assert!(nodes[0].node.danger_funding_transaction_generated(&temporary_channel_id, &nodes[1].node.get_our_node_id(), tx.clone()).is_ok());
+	let node_0_msg_events = nodes[0].node.get_and_clear_pending_msg_events();
+	match node_0_msg_events[0] {
+		MessageSendEvent::SendFundingCreated { ref node_id, .. } => {
+			assert_eq!(node_id, &nodes[1].node.get_our_node_id());
+		},
+		_ => panic!("Unexpected event"),
+	}
+}
+
 #[test]
 fn test_simple_peer_disconnect() {
 	// Test that we can reconnect when there are no lost messages