Make ChainWatchInterface::filter_block return only idxes, not refs

Instead of making the filter_block fn in the ChainWatchInterface
trait return both a list of indexes of transaction positions within
the block and references to the transactions themselves, return
only the list of indexes and then build the reference list at the
callsite.

While this may be slightly less effecient from a memory locality
perspective, it shouldn't be materially different.

This should make it more practical to generate bindings for
filter_block as it no longer needs to reference Rust Transaction
objects that are contained in a Rust Block object (which we'd
otherwise just pass over the FFI in fully-serialized form).

Author: TheBlueMatt

fuzz/src/router.rs

@@ -76,8 +76,8 @@ impl ChainWatchInterface for DummyChainWatcher {
 	fn install_watch_tx(&self, _txid: &Txid, _script_pub_key: &Script) { }
 	fn install_watch_outpoint(&self, _outpoint: (Txid, u32), _out_script: &Script) { }
 	fn watch_all_txn(&self) { }
-	fn filter_block<'a>(&self, _block: &'a Block) -> (Vec<&'a Transaction>, Vec<u32>) {
-		(Vec::new(), Vec::new())
+	fn filter_block(&self, _block: &Block) -> Vec<u32> {
+		Vec::new()
 	}
 	fn reentered(&self) -> usize { 0 }
 

lightning/src/chain/chaininterface.rs

@@ -53,9 +53,9 @@ pub trait ChainWatchInterface: Sync + Send {
 	/// final two the output within the transaction.
 	fn get_chain_utxo(&self, genesis_hash: BlockHash, unspent_tx_output_identifier: u64) -> Result<(Script, u64), ChainError>;
 
-	/// Gets the list of transactions and transaction indices that the ChainWatchInterface is
+	/// Gets the list of transaction indices within a given block that the ChainWatchInterface is
 	/// watching for.
-	fn filter_block<'a>(&self, block: &'a Block) -> (Vec<&'a Transaction>, Vec<u32>);
+	fn filter_block(&self, block: &Block) -> Vec<u32>;
 
 	/// Returns a usize that changes when the ChainWatchInterface's watched data is modified.
 	/// Users of `filter_block` should pre-save a copy of `reentered`'s return value and use it to
@@ -277,8 +277,12 @@ impl<'a, CL: Deref<Target = ChainListener + 'a> + 'a, C: Deref> BlockNotifier<'a
 	pub fn block_connected(&self, block: &Block, height: u32) {
 		let mut reentered = true;
 		while reentered {
-			let (matched, matched_index) = self.chain_monitor.filter_block(block);
-			reentered = self.block_connected_checked(&block.header, height, matched.as_slice(), matched_index.as_slice());
+			let matched_indexes = self.chain_monitor.filter_block(block);
+			let mut matched_txn = Vec::new();
+			for index in matched_indexes.iter() {
+				matched_txn.push(&block.txdata[*index as usize]);
+			}
+			reentered = self.block_connected_checked(&block.header, height, matched_txn.as_slice(), matched_indexes.as_slice());
 		}
 	}
 
@@ -357,19 +361,17 @@ impl ChainWatchInterface for ChainWatchInterfaceUtil {
 		Err(ChainError::NotSupported)
 	}
 
-	fn filter_block<'a>(&self, block: &'a Block) -> (Vec<&'a Transaction>, Vec<u32>) {
-		let mut matched = Vec::new();
+	fn filter_block(&self, block: &Block) -> Vec<u32> {
 		let mut matched_index = Vec::new();
 		{
 			let watched = self.watched.lock().unwrap();
 			for (index, transaction) in block.txdata.iter().enumerate() {
 				if self.does_match_tx_unguarded(transaction, &watched) {
-					matched.push(transaction);
 					matched_index.push(index as u32);
 				}
 			}
 		}
-		(matched, matched_index)
+		matched_index
 	}
 
 	fn reentered(&self) -> usize {

lightning/src/util/test_utils.rs

@@ -371,8 +371,8 @@ impl ChainWatchInterface for TestChainWatcher {
 	fn install_watch_tx(&self, _txid: &Txid, _script_pub_key: &Script) { }
 	fn install_watch_outpoint(&self, _outpoint: (Txid, u32), _out_script: &Script) { }
 	fn watch_all_txn(&self) { }
-	fn filter_block<'a>(&self, _block: &'a Block) -> (Vec<&'a Transaction>, Vec<u32>) {
-		(Vec::new(), Vec::new())
+	fn filter_block<'a>(&self, _block: &'a Block) -> Vec<u32> {
+		Vec::new()
 	}
 	fn reentered(&self) -> usize { 0 }