Merge pull request #1900 from tnull/2022-12-improve-confirm-docs

Improve `Confirm` docs

Author: TheBlueMatt

lightning/src/chain/mod.rs

@@ -107,31 +107,35 @@ pub trait Listen {
 	fn block_disconnected(&self, header: &BlockHeader, height: u32);
 }
 
-/// The `Confirm` trait is used to notify when transactions have been confirmed on chain or
-/// unconfirmed during a chain reorganization.
+/// The `Confirm` trait is used to notify LDK when relevant transactions have been confirmed on
+/// chain or unconfirmed during a chain reorganization.
 ///
 /// Clients sourcing chain data using a transaction-oriented API should prefer this interface over
-/// [`Listen`]. For instance, an Electrum client may implement [`Filter`] by subscribing to activity
-/// related to registered transactions and outputs. Upon notification, it would pass along the
-/// matching transactions using this interface.
+/// [`Listen`]. For instance, an Electrum-based transaction sync implementation may implement
+/// [`Filter`] to subscribe to relevant transactions and unspent outputs it should monitor for
+/// on-chain activity. Then, it needs to notify LDK via this interface upon observing any changes
+/// with reference to the confirmation status of the monitored objects.
 ///
 /// # Use
-///
 /// The intended use is as follows:
-/// - Call [`transactions_confirmed`] to process any on-chain activity of interest.
-/// - Call [`transaction_unconfirmed`] to process any transaction returned by [`get_relevant_txids`]
-///   that has been reorganized out of the chain.
-/// - Call [`best_block_updated`] whenever a new chain tip becomes available.
+/// - Call [`transactions_confirmed`] to notify LDK whenever any of the registered transactions or
+///   outputs are, respectively, confirmed or spent on chain.
+/// - Call [`transaction_unconfirmed`] to notify LDK whenever any transaction returned by
+///   [`get_relevant_txids`] is no longer confirmed in the block with the given block hash.
+/// - Call [`best_block_updated`] to notify LDK whenever a new chain tip becomes available.
 ///
 /// # Order
 ///
 /// Clients must call these methods in chain order. Specifically:
-/// - Transactions confirmed in a block must be given before transactions confirmed in a later
-///   block.
+/// - Transactions which are confirmed in a particular block must be given before transactions
+///   confirmed in a later block.
 /// - Dependent transactions within the same block must be given in topological order, possibly in
 ///   separate calls.
-/// - Unconfirmed transactions must be given after the original confirmations and before any
-///   reconfirmation.
+/// - All unconfirmed transactions must be given after the original confirmations and before *any*
+///   reconfirmations, i.e., [`transactions_confirmed`] and [`transaction_unconfirmed`] calls should
+///   never be interleaved, but always conduced *en bloc*.
+/// - Any reconfirmed transactions need to be explicitly unconfirmed before they are reconfirmed
+///   in regard to the new block.
 ///
 /// See individual method documentation for further details.
 ///
@@ -140,9 +144,9 @@ pub trait Listen {
 /// [`best_block_updated`]: Self::best_block_updated
 /// [`get_relevant_txids`]: Self::get_relevant_txids
 pub trait Confirm {
-	/// Processes transactions confirmed in a block with a given header and height.
+	/// Notifies LDK of transactions confirmed in a block with a given header and height.
 	///
-	/// Should be called for any transactions registered by [`Filter::register_tx`] or any
+	/// Must be called for any transactions registered by [`Filter::register_tx`] or any
 	/// transactions spending an output registered by [`Filter::register_output`]. Such transactions
 	/// appearing in the same block do not need to be included in the same call; instead, multiple
 	/// calls with additional transactions may be made so long as they are made in [chain order].
@@ -154,36 +158,36 @@ pub trait Confirm {
 	/// [chain order]: Confirm#order
 	/// [`best_block_updated`]: Self::best_block_updated
 	fn transactions_confirmed(&self, header: &BlockHeader, txdata: &TransactionData, height: u32);
-
-	/// Processes a transaction that is no longer confirmed as result of a chain reorganization.
+	/// Notifies LDK of a transaction that is no longer confirmed as result of a chain reorganization.
 	///
-	/// Should be called for any transaction returned by [`get_relevant_txids`] if it has been
-	/// reorganized out of the best chain. Once called, the given transaction will not be returned
+	/// Must be called for any transaction returned by [`get_relevant_txids`] if it has been
+	/// reorganized out of the best chain or if it is no longer confirmed in the block with the
+	/// given block hash. Once called, the given transaction will not be returned
 	/// by [`get_relevant_txids`], unless it has been reconfirmed via [`transactions_confirmed`].
 	///
 	/// [`get_relevant_txids`]: Self::get_relevant_txids
 	/// [`transactions_confirmed`]: Self::transactions_confirmed
 	fn transaction_unconfirmed(&self, txid: &Txid);
-
-	/// Processes an update to the best header connected at the given height.
+	/// Notifies LDK of an update to the best header connected at the given height.
 	///
-	/// Should be called when a new header is available but may be skipped for intermediary blocks
-	/// if they become available at the same time.
+	/// Must be called whenever a new chain tip becomes available. May be skipped for intermediary
+	/// blocks.
 	fn best_block_updated(&self, header: &BlockHeader, height: u32);
-
-	/// Returns transactions that should be monitored for reorganization out of the chain along
-	/// with the hash of the block as part of which had been previously confirmed.
+	/// Returns transactions that must be monitored for reorganization out of the chain along
+	/// with the hash of the block as part of which it had been previously confirmed.
 	///
 	/// Will include any transactions passed to [`transactions_confirmed`] that have insufficient
 	/// confirmations to be safe from a chain reorganization. Will not include any transactions
 	/// passed to [`transaction_unconfirmed`], unless later reconfirmed.
 	///
-	/// May be called to determine the subset of transactions that must still be monitored for
+	/// Must be called to determine the subset of transactions that must be monitored for
 	/// reorganization. Will be idempotent between calls but may change as a result of calls to the
-	/// other interface methods. Thus, this is useful to determine which transactions may need to be
-	/// given to [`transaction_unconfirmed`]. If any of the returned transactions are confirmed in
-	/// a block other than the one with the given hash, they need to be unconfirmed and reconfirmed
-	/// via [`transaction_unconfirmed`] and [`transactions_confirmed`], respectively.
+	/// other interface methods. Thus, this is useful to determine which transactions must be
+	/// given to [`transaction_unconfirmed`].
+	///
+	/// If any of the returned transactions are confirmed in a block other than the one with the
+	/// given hash, they need to be unconfirmed and reconfirmed via [`transaction_unconfirmed`] and
+	/// [`transactions_confirmed`], respectively.
 	///
 	/// [`transactions_confirmed`]: Self::transactions_confirmed
 	/// [`transaction_unconfirmed`]: Self::transaction_unconfirmed