+ * [`ChannelManager`] is parameterized by a number of components to achieve this.
+ * - [`chain::Watch`] (typically [`ChainMonitor`]) for on-chain monitoring and enforcement of each
+ * channel
+ * - [`BroadcasterInterface`] for broadcasting transactions related to opening, funding, and
+ * closing channels
+ * - [`EntropySource`] for providing random data needed for cryptographic operations
+ * - [`NodeSigner`] for cryptographic operations scoped to the node
+ * - [`SignerProvider`] for providing signers whose operations are scoped to individual channels
+ * - [`FeeEstimator`] to determine transaction fee rates needed to have a transaction mined in a
+ * timely manner
+ * - [`Router`] for finding payment paths when initiating and retrying payments
+ * - [`Logger`] for logging operational information of varying degrees
+ *
+ * Additionally, it implements the following traits:
+ * - [`ChannelMessageHandler`] to handle off-chain channel activity from peers
+ * - [`MessageSendEventsProvider`] to similarly send such messages to peers
+ * - [`OffersMessageHandler`] for BOLT 12 message handling and sending
+ * - [`EventsProvider`] to generate user-actionable [`Event`]s
+ * - [`chain::Listen`] and [`chain::Confirm`] for notification of on-chain activity
+ *
+ * Thus, [`ChannelManager`] is typically used to parameterize a [`MessageHandler`] and an
+ * [`OnionMessenger`]. The latter is required to support BOLT 12 functionality.
+ *
+ * # `ChannelManager` vs `ChannelMonitor`
+ *
+ * It's important to distinguish between the *off-chain* management and *on-chain* enforcement of
+ * lightning channels. [`ChannelManager`] exchanges messages with peers to manage the off-chain
+ * state of each channel. During this process, it generates a [`ChannelMonitor`] for each channel
+ * and a [`ChannelMonitorUpdate`] for each relevant change, notifying its parameterized
+ * [`chain::Watch`] of them.
+ *
+ * An implementation of [`chain::Watch`], such as [`ChainMonitor`], is responsible for aggregating
+ * these [`ChannelMonitor`]s and applying any [`ChannelMonitorUpdate`]s to them. It then monitors
+ * for any pertinent on-chain activity, enforcing claims as needed.
+ *
+ * This division of off-chain management and on-chain enforcement allows for interesting node
+ * setups. For instance, on-chain enforcement could be moved to a separate host or have added
+ * redundancy, possibly as a watchtower. See [`chain::Watch`] for the relevant interface.
+ *
+ * # Initialization
+ *
+ * Use [`ChannelManager::new`] with the most recent [`BlockHash`] when creating a fresh instance.
+ * Otherwise, if restarting, construct [`ChannelManagerReadArgs`] with the necessary parameters and
+ * references to any deserialized [`ChannelMonitor`]s that were previously persisted. Use this to
+ * deserialize the [`ChannelManager`] and feed it any new chain data since it was last online, as
+ * detailed in the [`ChannelManagerReadArgs`] documentation.
+ *
+ * ```
+ * use bitcoin::BlockHash;
+ * use bitcoin::network::constants::Network;
+ * use lightning::chain::BestBlock;
+ * # use lightning::chain::channelmonitor::ChannelMonitor;
+ * use lightning::ln::channelmanager::{ChainParameters, ChannelManager, ChannelManagerReadArgs};
+ * # use lightning::routing::gossip::NetworkGraph;
+ * use lightning::util::config::UserConfig;
+ * use lightning::util::ser::ReadableArgs;
+ *
+ * # fn read_channel_monitors() -> Vec<ChannelMonitor<lightning::sign::InMemorySigner>> { vec![] }
+ * # fn example<
+ * # 'a,
+ * # L: lightning::util::logger::Logger,
+ * # ES: lightning::sign::EntropySource,
+ * # S: for <'b> lightning::routing::scoring::LockableScore<'b, ScoreLookUp = SL>,
+ * # SL: lightning::routing::scoring::ScoreLookUp<ScoreParams = SP>,
+ * # SP: Sized,
+ * # R: lightning::io::Read,
+ * # >(
+ * # fee_estimator: &dyn lightning::chain::chaininterface::FeeEstimator,
+ * # chain_monitor: &dyn lightning::chain::Watch<lightning::sign::InMemorySigner>,
+ * # tx_broadcaster: &dyn lightning::chain::chaininterface::BroadcasterInterface,
+ * # router: &lightning::routing::router::DefaultRouter<&NetworkGraph<&'a L>, &'a L, &ES, &S, SP, SL>,
+ * # logger: &L,
+ * # entropy_source: &ES,
+ * # node_signer: &dyn lightning::sign::NodeSigner,
+ * # signer_provider: &lightning::sign::DynSignerProvider,
+ * # best_block: lightning::chain::BestBlock,
+ * # current_timestamp: u32,
+ * # mut reader: R,
+ * # ) -> Result<(), lightning::ln::msgs::DecodeError> {
+ * Fresh start with no channels
+ * let params = ChainParameters {
+ * network: Network::Bitcoin,
+ * best_block,
+ * };
+ * let default_config = UserConfig::default();
+ * let channel_manager = ChannelManager::new(
+ * fee_estimator, chain_monitor, tx_broadcaster, router, logger, entropy_source, node_signer,
+ * signer_provider, default_config, params, current_timestamp
+ * );
+ *
+ * Restart from deserialized data
+ * let mut channel_monitors = read_channel_monitors();
+ * let args = ChannelManagerReadArgs::new(
+ * entropy_source, node_signer, signer_provider, fee_estimator, chain_monitor, tx_broadcaster,
+ * router, logger, default_config, channel_monitors.iter_mut().collect()
+ * );
+ * let (block_hash, channel_manager) =
+ * <(BlockHash, ChannelManager<_, _, _, _, _, _, _, _>)>::read(&mut reader, args)?;
+ *
+ * Update the ChannelManager and ChannelMonitors with the latest chain data
+ * ...
+ *
+ * Move the monitors to the ChannelManager's chain::Watch parameter
+ * for monitor in channel_monitors {
+ * chain_monitor.watch_channel(monitor.get_funding_txo().0, monitor);
+ * }
+ * # Ok(())
+ * # }
+ * ```
+ *
+ * # Operation
+ *
+ * The following is required for [`ChannelManager`] to function properly:
+ * - Handle messages from peers using its [`ChannelMessageHandler`] implementation (typically
+ * called by [`PeerManager::read_event`] when processing network I/O)
+ * - Send messages to peers obtained via its [`MessageSendEventsProvider`] implementation
+ * (typically initiated when [`PeerManager::process_events`] is called)
+ * - Feed on-chain activity using either its [`chain::Listen`] or [`chain::Confirm`] implementation
+ * as documented by those traits
+ * - Perform any periodic channel and payment checks by calling [`timer_tick_occurred`] roughly
+ * every minute
+ * - Persist to disk whenever [`get_and_clear_needs_persistence`] returns `true` using a
+ * [`Persister`] such as a [`KVStore`] implementation
+ * - Handle [`Event`]s obtained via its [`EventsProvider`] implementation
+ *
+ * The [`Future`] returned by [`get_event_or_persistence_needed_future`] is useful in determining
+ * when the last two requirements need to be checked.
+ *
+ * The [`lightning-block-sync`] and [`lightning-transaction-sync`] crates provide utilities that
+ * simplify feeding in on-chain activity using the [`chain::Listen`] and [`chain::Confirm`] traits,
+ * respectively. The remaining requirements can be met using the [`lightning-background-processor`]
+ * crate. For languages other than Rust, the availability of similar utilities may vary.
+ *
+ * # Channels
+ *
+ * [`ChannelManager`]'s primary function involves managing a channel state. Without channels,
+ * payments can't be sent. Use [`list_channels`] or [`list_usable_channels`] for a snapshot of the
+ * currently open channels.
+ *
+ * ```
+ * # use lightning::ln::channelmanager::AChannelManager;
+ * #
+ * # fn example<T: AChannelManager>(channel_manager: T) {
+ * # let channel_manager = channel_manager.get_cm();
+ * let channels = channel_manager.list_usable_channels();
+ * for details in channels {
+ * println!(\"{:?}\", details);
+ * }
+ * # }
+ * ```
+ *
+ * Each channel is identified using a [`ChannelId`], which will change throughout the channel's
+ * life cycle. Additionally, channels are assigned a `user_channel_id`, which is given in
+ * [`Event`]s associated with the channel and serves as a fixed identifier but is otherwise unused
+ * by [`ChannelManager`].
+ *
+ * ## Opening Channels
+ *
+ * To an open a channel with a peer, call [`create_channel`]. This will initiate the process of
+ * opening an outbound channel, which requires self-funding when handling
+ * [`Event::FundingGenerationReady`].
+ *
+ * ```
+ * # use bitcoin::{ScriptBuf, Transaction};
+ * # use bitcoin::secp256k1::PublicKey;
+ * # use lightning::ln::channelmanager::AChannelManager;
+ * # use lightning::events::{Event, EventsProvider};
+ * #
+ * # trait Wallet {
+ * # fn create_funding_transaction(
+ * # &self, _amount_sats: u64, _output_script: ScriptBuf
+ * # ) -> Transaction;
+ * # }
+ * #
+ * # fn example<T: AChannelManager, W: Wallet>(channel_manager: T, wallet: W, peer_id: PublicKey) {
+ * # let channel_manager = channel_manager.get_cm();
+ * let value_sats = 1_000_000;
+ * let push_msats = 10_000_000;
+ * match channel_manager.create_channel(peer_id, value_sats, push_msats, 42, None, None) {
+ * Ok(channel_id) => println!(\"Opening channel {}\", channel_id),
+ * Err(e) => println!(\"Error opening channel: {:?}\", e),
+ * }
+ *
+ * On the event processing thread once the peer has responded
+ * channel_manager.process_pending_events(&|event| match event {
+ * Event::FundingGenerationReady {
+ * temporary_channel_id, counterparty_node_id, channel_value_satoshis, output_script,
+ * user_channel_id, ..
+ * } => {
+ * assert_eq!(user_channel_id, 42);
+ * let funding_transaction = wallet.create_funding_transaction(
+ * channel_value_satoshis, output_script
+ * );
+ * match channel_manager.funding_transaction_generated(
+ * &temporary_channel_id, &counterparty_node_id, funding_transaction
+ * ) {
+ * Ok(()) => println!(\"Funding channel {}\", temporary_channel_id),
+ * Err(e) => println!(\"Error funding channel {}: {:?}\", temporary_channel_id, e),
+ * }
+ * },
+ * Event::ChannelPending { channel_id, user_channel_id, former_temporary_channel_id, .. } => {
+ * assert_eq!(user_channel_id, 42);
+ * println!(
+ * \"Channel {} now {} pending (funding transaction has been broadcasted)\", channel_id,
+ * former_temporary_channel_id.unwrap()
+ * );
+ * },
+ * Event::ChannelReady { channel_id, user_channel_id, .. } => {
+ * assert_eq!(user_channel_id, 42);
+ * println!(\"Channel {} ready\", channel_id);
+ * },
+ * ...
+ * # _ => {},
+ * });
+ * # }
+ * ```
+ *
+ * ## Accepting Channels
+ *
+ * Inbound channels are initiated by peers and are automatically accepted unless [`ChannelManager`]
+ * has [`UserConfig::manually_accept_inbound_channels`] set. In that case, the channel may be
+ * either accepted or rejected when handling [`Event::OpenChannelRequest`].
+ *
+ * ```
+ * # use bitcoin::secp256k1::PublicKey;
+ * # use lightning::ln::channelmanager::AChannelManager;
+ * # use lightning::events::{Event, EventsProvider};
+ * #
+ * # fn is_trusted(counterparty_node_id: PublicKey) -> bool {
+ * # // ...
+ * # unimplemented!()
+ * # }
+ * #
+ * # fn example<T: AChannelManager>(channel_manager: T) {
+ * # let channel_manager = channel_manager.get_cm();
+ * channel_manager.process_pending_events(&|event| match event {
+ * Event::OpenChannelRequest { temporary_channel_id, counterparty_node_id, .. } => {
+ * if !is_trusted(counterparty_node_id) {
+ * match channel_manager.force_close_without_broadcasting_txn(
+ * &temporary_channel_id, &counterparty_node_id
+ * ) {
+ * Ok(()) => println!(\"Rejecting channel {}\", temporary_channel_id),
+ * Err(e) => println!(\"Error rejecting channel {}: {:?}\", temporary_channel_id, e),
+ * }
+ * return;
+ * }
+ *
+ * let user_channel_id = 43;
+ * match channel_manager.accept_inbound_channel(
+ * &temporary_channel_id, &counterparty_node_id, user_channel_id
+ * ) {
+ * Ok(()) => println!(\"Accepting channel {}\", temporary_channel_id),
+ * Err(e) => println!(\"Error accepting channel {}: {:?}\", temporary_channel_id, e),
+ * }
+ * },
+ * ...
+ * # _ => {},
+ * });
+ * # }
+ * ```
+ *
+ * ## Closing Channels
+ *
+ * There are two ways to close a channel: either cooperatively using [`close_channel`] or
+ * unilaterally using [`force_close_broadcasting_latest_txn`]. The former is ideal as it makes for
+ * lower fees and immediate access to funds. However, the latter may be necessary if the
+ * counterparty isn't behaving properly or has gone offline. [`Event::ChannelClosed`] is generated
+ * once the channel has been closed successfully.
+ *
+ * ```
+ * # use bitcoin::secp256k1::PublicKey;
+ * # use lightning::ln::types::ChannelId;
+ * # use lightning::ln::channelmanager::AChannelManager;
+ * # use lightning::events::{Event, EventsProvider};
+ * #
+ * # fn example<T: AChannelManager>(
+ * # channel_manager: T, channel_id: ChannelId, counterparty_node_id: PublicKey
+ * # ) {
+ * # let channel_manager = channel_manager.get_cm();
+ * match channel_manager.close_channel(&channel_id, &counterparty_node_id) {
+ * Ok(()) => println!(\"Closing channel {}\", channel_id),
+ * Err(e) => println!(\"Error closing channel {}: {:?}\", channel_id, e),
+ * }
+ *
+ * On the event processing thread
+ * channel_manager.process_pending_events(&|event| match event {
+ * Event::ChannelClosed { channel_id, user_channel_id, .. } => {
+ * assert_eq!(user_channel_id, 42);
+ * println!(\"Channel {} closed\", channel_id);
+ * },
+ * ...
+ * # _ => {},
+ * });
+ * # }
+ * ```
+ *
+ * # Payments
+ *
+ * [`ChannelManager`] is responsible for sending, forwarding, and receiving payments through its
+ * channels. A payment is typically initiated from a [BOLT 11] invoice or a [BOLT 12] offer, though
+ * spontaneous (i.e., keysend) payments are also possible. Incoming payments don't require
+ * maintaining any additional state as [`ChannelManager`] can reconstruct the [`PaymentPreimage`]
+ * from the [`PaymentSecret`]. Sending payments, however, require tracking in order to retry failed
+ * HTLCs.
+ *
+ * After a payment is initiated, it will appear in [`list_recent_payments`] until a short time
+ * after either an [`Event::PaymentSent`] or [`Event::PaymentFailed`] is handled. Failed HTLCs
+ * for a payment will be retried according to the payment's [`Retry`] strategy or until
+ * [`abandon_payment`] is called.
+ *
+ * ## BOLT 11 Invoices
+ *
+ * The [`lightning-invoice`] crate is useful for creating BOLT 11 invoices. Specifically, use the
+ * functions in its `utils` module for constructing invoices that are compatible with
+ * [`ChannelManager`]. These functions serve as a convenience for building invoices with the
+ * [`PaymentHash`] and [`PaymentSecret`] returned from [`create_inbound_payment`]. To provide your
+ * own [`PaymentHash`], use [`create_inbound_payment_for_hash`] or the corresponding functions in
+ * the [`lightning-invoice`] `utils` module.
+ *
+ * [`ChannelManager`] generates an [`Event::PaymentClaimable`] once the full payment has been
+ * received. Call [`claim_funds`] to release the [`PaymentPreimage`], which in turn will result in
+ * an [`Event::PaymentClaimed`].
+ *
+ * ```
+ * # use lightning::events::{Event, EventsProvider, PaymentPurpose};
+ * # use lightning::ln::channelmanager::AChannelManager;
+ * #
+ * # fn example<T: AChannelManager>(channel_manager: T) {
+ * # let channel_manager = channel_manager.get_cm();
+ * Or use utils::create_invoice_from_channelmanager
+ * let known_payment_hash = match channel_manager.create_inbound_payment(
+ * Some(10_000_000), 3600, None
+ * ) {
+ * Ok((payment_hash, _payment_secret)) => {
+ * println!(\"Creating inbound payment {}\", payment_hash);
+ * payment_hash
+ * },
+ * Err(()) => panic!(\"Error creating inbound payment\"),
+ * };
+ *
+ * On the event processing thread
+ * channel_manager.process_pending_events(&|event| match event {
+ * Event::PaymentClaimable { payment_hash, purpose, .. } => match purpose {
+ * PaymentPurpose::Bolt11InvoicePayment { payment_preimage: Some(payment_preimage), .. } => {
+ * assert_eq!(payment_hash, known_payment_hash);
+ * println!(\"Claiming payment {}\", payment_hash);
+ * channel_manager.claim_funds(payment_preimage);
+ * },
+ * PaymentPurpose::Bolt11InvoicePayment { payment_preimage: None, .. } => {
+ * println!(\"Unknown payment hash: {}\", payment_hash);
+ * },
+ * PaymentPurpose::SpontaneousPayment(payment_preimage) => {
+ * assert_ne!(payment_hash, known_payment_hash);
+ * println!(\"Claiming spontaneous payment {}\", payment_hash);
+ * channel_manager.claim_funds(payment_preimage);
+ * },
+ * ...
+ * # _ => {},
+ * },
+ * Event::PaymentClaimed { payment_hash, amount_msat, .. } => {
+ * assert_eq!(payment_hash, known_payment_hash);
+ * println!(\"Claimed {} msats\", amount_msat);
+ * },
+ * ...
+ * # _ => {},
+ * });
+ * # }
+ * ```
+ *
+ * For paying an invoice, [`lightning-invoice`] provides a `payment` module with convenience
+ * functions for use with [`send_payment`].
+ *
+ * ```
+ * # use lightning::events::{Event, EventsProvider};
+ * # use lightning::ln::types::PaymentHash;
+ * # use lightning::ln::channelmanager::{AChannelManager, PaymentId, RecentPaymentDetails, RecipientOnionFields, Retry};
+ * # use lightning::routing::router::RouteParameters;
+ * #
+ * # fn example<T: AChannelManager>(
+ * # channel_manager: T, payment_hash: PaymentHash, recipient_onion: RecipientOnionFields,
+ * # route_params: RouteParameters, retry: Retry
+ * # ) {
+ * # let channel_manager = channel_manager.get_cm();
+ * let (payment_hash, recipient_onion, route_params) =
+ * payment::payment_parameters_from_invoice(&invoice);
+ * let payment_id = PaymentId([42; 32]);
+ * match channel_manager.send_payment(
+ * payment_hash, recipient_onion, payment_id, route_params, retry
+ * ) {
+ * Ok(()) => println!(\"Sending payment with hash {}\", payment_hash),
+ * Err(e) => println!(\"Failed sending payment with hash {}: {:?}\", payment_hash, e),
+ * }
+ *
+ * let expected_payment_id = payment_id;
+ * let expected_payment_hash = payment_hash;
+ * assert!(
+ * channel_manager.list_recent_payments().iter().find(|details| matches!(
+ * details,
+ * RecentPaymentDetails::Pending {
+ * payment_id: expected_payment_id,
+ * payment_hash: expected_payment_hash,
+ * ..
+ * }
+ * )).is_some()
+ * );
+ *
+ * On the event processing thread
+ * channel_manager.process_pending_events(&|event| match event {
+ * Event::PaymentSent { payment_hash, .. } => println!(\"Paid {}\", payment_hash),
+ * Event::PaymentFailed { payment_hash, .. } => println!(\"Failed paying {}\", payment_hash),
+ * ...
+ * # _ => {},
+ * });
+ * # }
+ * ```
+ *
+ * ## BOLT 12 Offers
+ *
+ * The [`offers`] module is useful for creating BOLT 12 offers. An [`Offer`] is a precursor to a
+ * [`Bolt12Invoice`], which must first be requested by the payer. The interchange of these messages
+ * as defined in the specification is handled by [`ChannelManager`] and its implementation of
+ * [`OffersMessageHandler`]. However, this only works with an [`Offer`] created using a builder
+ * returned by [`create_offer_builder`]. With this approach, BOLT 12 offers and invoices are
+ * stateless just as BOLT 11 invoices are.
+ *
+ * ```
+ * # use lightning::events::{Event, EventsProvider, PaymentPurpose};
+ * # use lightning::ln::channelmanager::AChannelManager;
+ * # use lightning::offers::parse::Bolt12SemanticError;
+ * #
+ * # fn example<T: AChannelManager>(channel_manager: T) -> Result<(), Bolt12SemanticError> {
+ * # let channel_manager = channel_manager.get_cm();
+ * let offer = channel_manager
+ * .create_offer_builder()?
+ * # ;
+ * # // Needed for compiling for c_bindings
+ * # let builder: lightning::offers::offer::OfferBuilder<_, _> = offer.into();
+ * # let offer = builder
+ * .description(\"coffee\".to_string())
+ * .amount_msats(10_000_000)
+ * .build()?;
+ * let bech32_offer = offer.to_string();
+ *
+ * On the event processing thread
+ * channel_manager.process_pending_events(&|event| match event {
+ * Event::PaymentClaimable { payment_hash, purpose, .. } => match purpose {
+ * PaymentPurpose::Bolt12OfferPayment { payment_preimage: Some(payment_preimage), .. } => {
+ * println!(\"Claiming payment {}\", payment_hash);
+ * channel_manager.claim_funds(payment_preimage);
+ * },
+ * PaymentPurpose::Bolt12OfferPayment { payment_preimage: None, .. } => {
+ * println!(\"Unknown payment hash: {}\", payment_hash);
+ * },
+ * ...
+ * # _ => {},
+ * },
+ * Event::PaymentClaimed { payment_hash, amount_msat, .. } => {
+ * println!(\"Claimed {} msats\", amount_msat);
+ * },
+ * ...
+ * # _ => {},
+ * });
+ * # Ok(())
+ * # }
+ * ```
+ *
+ * Use [`pay_for_offer`] to initiated payment, which sends an [`InvoiceRequest`] for an [`Offer`]
+ * and pays the [`Bolt12Invoice`] response. In addition to success and failure events,
+ * [`ChannelManager`] may also generate an [`Event::InvoiceRequestFailed`].
+ *
+ * ```
+ * # use lightning::events::{Event, EventsProvider};
+ * # use lightning::ln::channelmanager::{AChannelManager, PaymentId, RecentPaymentDetails, Retry};
+ * # use lightning::offers::offer::Offer;
+ * #
+ * # fn example<T: AChannelManager>(
+ * # channel_manager: T, offer: &Offer, quantity: Option<u64>, amount_msats: Option<u64>,
+ * # payer_note: Option<String>, retry: Retry, max_total_routing_fee_msat: Option<u64>
+ * # ) {
+ * # let channel_manager = channel_manager.get_cm();
+ * let payment_id = PaymentId([42; 32]);
+ * match channel_manager.pay_for_offer(
+ * offer, quantity, amount_msats, payer_note, payment_id, retry, max_total_routing_fee_msat
+ * ) {
+ * Ok(()) => println!(\"Requesting invoice for offer\"),
+ * Err(e) => println!(\"Unable to request invoice for offer: {:?}\", e),
+ * }
+ *
+ * First the payment will be waiting on an invoice
+ * let expected_payment_id = payment_id;
+ * assert!(
+ * channel_manager.list_recent_payments().iter().find(|details| matches!(
+ * details,
+ * RecentPaymentDetails::AwaitingInvoice { payment_id: expected_payment_id }
+ * )).is_some()
+ * );
+ *
+ * Once the invoice is received, a payment will be sent
+ * assert!(
+ * channel_manager.list_recent_payments().iter().find(|details| matches!(
+ * details,
+ * RecentPaymentDetails::Pending { payment_id: expected_payment_id, .. }
+ * )).is_some()
+ * );
+ *
+ * On the event processing thread
+ * channel_manager.process_pending_events(&|event| match event {
+ * Event::PaymentSent { payment_id: Some(payment_id), .. } => println!(\"Paid {}\", payment_id),
+ * Event::PaymentFailed { payment_id, .. } => println!(\"Failed paying {}\", payment_id),
+ * Event::InvoiceRequestFailed { payment_id, .. } => println!(\"Failed paying {}\", payment_id),
+ * ...
+ * # _ => {},
+ * });
+ * # }
+ * ```
+ *
+ * ## BOLT 12 Refunds
+ *
+ * A [`Refund`] is a request for an invoice to be paid. Like *paying* for an [`Offer`], *creating*
+ * a [`Refund`] involves maintaining state since it represents a future outbound payment.
+ * Therefore, use [`create_refund_builder`] when creating one, otherwise [`ChannelManager`] will
+ * refuse to pay any corresponding [`Bolt12Invoice`] that it receives.
+ *
+ * ```
+ * # use core::time::Duration;
+ * # use lightning::events::{Event, EventsProvider};
+ * # use lightning::ln::channelmanager::{AChannelManager, PaymentId, RecentPaymentDetails, Retry};
+ * # use lightning::offers::parse::Bolt12SemanticError;
+ * #
+ * # fn example<T: AChannelManager>(
+ * # channel_manager: T, amount_msats: u64, absolute_expiry: Duration, retry: Retry,
+ * # max_total_routing_fee_msat: Option<u64>
+ * # ) -> Result<(), Bolt12SemanticError> {
+ * # let channel_manager = channel_manager.get_cm();
+ * let payment_id = PaymentId([42; 32]);
+ * let refund = channel_manager
+ * .create_refund_builder(
+ * amount_msats, absolute_expiry, payment_id, retry, max_total_routing_fee_msat
+ * )?
+ * # ;
+ * # // Needed for compiling for c_bindings
+ * # let builder: lightning::offers::refund::RefundBuilder<_> = refund.into();
+ * # let refund = builder
+ * .description(\"coffee\".to_string())
+ * .payer_note(\"refund for order 1234\".to_string())
+ * .build()?;
+ * let bech32_refund = refund.to_string();
+ *
+ * First the payment will be waiting on an invoice
+ * let expected_payment_id = payment_id;
+ * assert!(
+ * channel_manager.list_recent_payments().iter().find(|details| matches!(
+ * details,
+ * RecentPaymentDetails::AwaitingInvoice { payment_id: expected_payment_id }
+ * )).is_some()
+ * );
+ *
+ * Once the invoice is received, a payment will be sent
+ * assert!(
+ * channel_manager.list_recent_payments().iter().find(|details| matches!(
+ * details,
+ * RecentPaymentDetails::Pending { payment_id: expected_payment_id, .. }
+ * )).is_some()
+ * );
+ *
+ * On the event processing thread
+ * channel_manager.process_pending_events(&|event| match event {
+ * Event::PaymentSent { payment_id: Some(payment_id), .. } => println!(\"Paid {}\", payment_id),
+ * Event::PaymentFailed { payment_id, .. } => println!(\"Failed paying {}\", payment_id),
+ * ...
+ * # _ => {},
+ * });
+ * # Ok(())
+ * # }
+ * ```
+ *
+ * Use [`request_refund_payment`] to send a [`Bolt12Invoice`] for receiving the refund. Similar to
+ * creating* an [`Offer`], this is stateless as it represents an inbound payment.
+ *
+ * ```
+ * # use lightning::events::{Event, EventsProvider, PaymentPurpose};
+ * # use lightning::ln::channelmanager::AChannelManager;
+ * # use lightning::offers::refund::Refund;
+ * #
+ * # fn example<T: AChannelManager>(channel_manager: T, refund: &Refund) {
+ * # let channel_manager = channel_manager.get_cm();
+ * let known_payment_hash = match channel_manager.request_refund_payment(refund) {
+ * Ok(invoice) => {
+ * let payment_hash = invoice.payment_hash();
+ * println!(\"Requesting refund payment {}\", payment_hash);
+ * payment_hash
+ * },
+ * Err(e) => panic!(\"Unable to request payment for refund: {:?}\", e),
+ * };
+ *
+ * On the event processing thread
+ * channel_manager.process_pending_events(&|event| match event {
+ * Event::PaymentClaimable { payment_hash, purpose, .. } => match purpose {
+ * \tPaymentPurpose::Bolt12RefundPayment { payment_preimage: Some(payment_preimage), .. } => {
+ * assert_eq!(payment_hash, known_payment_hash);
+ * println!(\"Claiming payment {}\", payment_hash);
+ * channel_manager.claim_funds(payment_preimage);
+ * },
+ * \tPaymentPurpose::Bolt12RefundPayment { payment_preimage: None, .. } => {
+ * println!(\"Unknown payment hash: {}\", payment_hash);
+ * \t},
+ * ...
+ * # _ => {},
+ * },
+ * Event::PaymentClaimed { payment_hash, amount_msat, .. } => {
+ * assert_eq!(payment_hash, known_payment_hash);
+ * println!(\"Claimed {} msats\", amount_msat);
+ * },
+ * ...
+ * # _ => {},
+ * });
+ * # }
+ * ```
+ *
+ * # Persistence