Merge pull request lightningdevkit#4015 from TheBlueMatt/2025-08-fst-funding

Fix panic when calling `batch_funding_transaction_generated` early

Author: tnull

fuzz/src/full_stack.rs

@@ -857,21 +857,15 @@ pub fn do_test(mut data: &[u8], logger: &Arc<dyn Logger>) {
 				}
 				if tx.version.0 <= 0xff && !channels.is_empty() {
 					let chans = channels.iter().map(|(a, b)| (a, b)).collect::<Vec<_>>();
-					if let Err(e) =
-						channelmanager.batch_funding_transaction_generated(&chans, tx.clone())
-					{
-						// It's possible the channel has been closed in the mean time, but any other
-						// failure may be a bug.
-						if let APIError::ChannelUnavailable { .. } = e {
-						} else {
-							panic!();
+					let res =
+						channelmanager.batch_funding_transaction_generated(&chans, tx.clone());
+					if res.is_ok() {
+						let funding_txid = tx.compute_txid();
+						for idx in 0..tx.output.len() {
+							let outpoint = OutPoint { txid: funding_txid, index: idx as u16 };
+							pending_funding_signatures.insert(outpoint, tx.clone());
 						}
 					}
-					let funding_txid = tx.compute_txid();
-					for idx in 0..tx.output.len() {
-						let outpoint = OutPoint { txid: funding_txid, index: idx as u16 };
-						pending_funding_signatures.insert(outpoint, tx.clone());
-					}
 				}
 			},
 			11 => {

lightning/src/ln/channel.rs

@@ -1551,6 +1551,22 @@ where
 		)
 	}
 
+	/// Returns true if this channel is waiting on a (batch) funding transaction to be provided.
+	///
+	/// If this method returns true, [`Self::into_unfunded_outbound_v1`] will also succeed.
+	pub fn ready_to_fund(&self) -> bool {
+		if !self.funding().is_outbound() {
+			return false;
+		}
+		match self.context().channel_state {
+			ChannelState::NegotiatingFunding(flags) => {
+				debug_assert!(matches!(self.phase, ChannelPhase::UnfundedOutboundV1(_)));
+				flags.is_our_init_sent() && flags.is_their_init_sent()
+			},
+			_ => false,
+		}
+	}
+
 	pub fn into_unfunded_outbound_v1(self) -> Result<OutboundV1Channel<SP>, Self> {
 		if let ChannelPhase::UnfundedOutboundV1(channel) = self.phase {
 			Ok(channel)