[rust-lightning] / lightning / src / util / events.rs

// This file is Copyright its original authors, visible in version control
// history.
//
// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
// You may not use this file except in accordance with one or both of these
// licenses.

//! Events are returned from various bits in the library which indicate some action must be taken
//! by the client.
//!
//! Because we don't have a built-in runtime, it's up to the client to call events at a time in the
//! future, as well as generate and broadcast funding transactions handle payment preimages and a
//! few other things.

use chain::keysinterface::SpendableOutputDescriptor;
use ln::channelmanager::PaymentId;
use ln::channel::FUNDING_CONF_DEADLINE_BLOCKS;
use ln::features::ChannelTypeFeatures;
use ln::msgs;
use ln::msgs::DecodeError;
use ln::{PaymentPreimage, PaymentHash, PaymentSecret};
use routing::gossip::NetworkUpdate;
use util::ser::{BigSize, FixedLengthReader, Writeable, Writer, MaybeReadable, Readable, VecReadWrapper, VecWriteWrapper};
use routing::router::{RouteHop, RouteParameters};

use bitcoin::Transaction;
use bitcoin::blockdata::script::Script;
use bitcoin::hashes::Hash;
use bitcoin::hashes::sha256::Hash as Sha256;
use bitcoin::secp256k1::PublicKey;
use io;
use prelude::*;
use core::time::Duration;
use core::ops::Deref;
use sync::Arc;

/// Some information provided on receipt of payment depends on whether the payment received is a
/// spontaneous payment or a "conventional" lightning payment that's paying an invoice.
#[derive(Clone, Debug)]
pub enum PaymentPurpose {
        /// Information for receiving a payment that we generated an invoice for.
        InvoicePayment {
                /// The preimage to the payment_hash, if the payment hash (and secret) were fetched via
                /// [`ChannelManager::create_inbound_payment`]. If provided, this can be handed directly to
                /// [`ChannelManager::claim_funds`].
                ///
                /// [`ChannelManager::create_inbound_payment`]: crate::ln::channelmanager::ChannelManager::create_inbound_payment
                /// [`ChannelManager::claim_funds`]: crate::ln::channelmanager::ChannelManager::claim_funds
                payment_preimage: Option<PaymentPreimage>,
                /// The "payment secret". This authenticates the sender to the recipient, preventing a
                /// number of deanonymization attacks during the routing process.
                /// It is provided here for your reference, however its accuracy is enforced directly by
                /// [`ChannelManager`] using the values you previously provided to
                /// [`ChannelManager::create_inbound_payment`] or
                /// [`ChannelManager::create_inbound_payment_for_hash`].
                ///
                /// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
                /// [`ChannelManager::create_inbound_payment`]: crate::ln::channelmanager::ChannelManager::create_inbound_payment
                /// [`ChannelManager::create_inbound_payment_for_hash`]: crate::ln::channelmanager::ChannelManager::create_inbound_payment_for_hash
                payment_secret: PaymentSecret,
        },
        /// Because this is a spontaneous payment, the payer generated their own preimage rather than us
        /// (the payee) providing a preimage.
        SpontaneousPayment(PaymentPreimage),
}

impl_writeable_tlv_based_enum!(PaymentPurpose,
        (0, InvoicePayment) => {
                (0, payment_preimage, option),
                (2, payment_secret, required),
        };
        (2, SpontaneousPayment)
);

#[derive(Clone, Debug, PartialEq)]
/// The reason the channel was closed. See individual variants more details.
pub enum ClosureReason {
        /// Closure generated from receiving a peer error message.
        ///
        /// Our counterparty may have broadcasted their latest commitment state, and we have
        /// as well.
        CounterpartyForceClosed {
                /// The error which the peer sent us.
                ///
                /// The string should be sanitized before it is used (e.g emitted to logs
                /// or printed to stdout). Otherwise, a well crafted error message may exploit
                /// a security vulnerability in the terminal emulator or the logging subsystem.
                peer_msg: String,
        },
        /// Closure generated from [`ChannelManager::force_close_channel`], called by the user.
        ///
        /// [`ChannelManager::force_close_channel`]: crate::ln::channelmanager::ChannelManager::force_close_channel.
        HolderForceClosed,
        /// The channel was closed after negotiating a cooperative close and we've now broadcasted
        /// the cooperative close transaction. Note the shutdown may have been initiated by us.
        //TODO: split between CounterpartyInitiated/LocallyInitiated
        CooperativeClosure,
        /// A commitment transaction was confirmed on chain, closing the channel. Most likely this
        /// commitment transaction came from our counterparty, but it may also have come from
        /// a copy of our own `ChannelMonitor`.
        CommitmentTxConfirmed,
        /// The funding transaction failed to confirm in a timely manner on an inbound channel.
        FundingTimedOut,
        /// Closure generated from processing an event, likely a HTLC forward/relay/reception.
        ProcessingError {
                /// A developer-readable error message which we generated.
                err: String,
        },
        /// The peer disconnected prior to funding completing. In this case the spec mandates that we
        /// forget the channel entirely - we can attempt again if the peer reconnects.
        ///
        /// In LDK versions prior to 0.0.107 this could also occur if we were unable to connect to the
        /// peer because of mutual incompatibility between us and our channel counterparty.
        DisconnectedPeer,
        /// Closure generated from `ChannelManager::read` if the ChannelMonitor is newer than
        /// the ChannelManager deserialized.
        OutdatedChannelManager
}

impl core::fmt::Display for ClosureReason {
        fn fmt(&self, f: &mut core::fmt::Formatter) -> Result<(), core::fmt::Error> {
                f.write_str("Channel closed because ")?;
                match self {
                        ClosureReason::CounterpartyForceClosed { peer_msg } => {
                                f.write_str("counterparty force-closed with message ")?;
                                f.write_str(&peer_msg)
                        },
                        ClosureReason::HolderForceClosed => f.write_str("user manually force-closed the channel"),
                        ClosureReason::CooperativeClosure => f.write_str("the channel was cooperatively closed"),
                        ClosureReason::CommitmentTxConfirmed => f.write_str("commitment or closing transaction was confirmed on chain."),
                        ClosureReason::FundingTimedOut => write!(f, "funding transaction failed to confirm within {} blocks", FUNDING_CONF_DEADLINE_BLOCKS),
                        ClosureReason::ProcessingError { err } => {
                                f.write_str("of an exception: ")?;
                                f.write_str(&err)
                        },
                        ClosureReason::DisconnectedPeer => f.write_str("the peer disconnected prior to the channel being funded"),
                        ClosureReason::OutdatedChannelManager => f.write_str("the ChannelManager read from disk was stale compared to ChannelMonitor(s)"),
                }
        }
}

impl_writeable_tlv_based_enum_upgradable!(ClosureReason,
        (0, CounterpartyForceClosed) => { (1, peer_msg, required) },
        (1, FundingTimedOut) => {},
        (2, HolderForceClosed) => {},
        (6, CommitmentTxConfirmed) => {},
        (4, CooperativeClosure) => {},
        (8, ProcessingError) => { (1, err, required) },
        (10, DisconnectedPeer) => {},
        (12, OutdatedChannelManager) => {},
);

/// An Event which you should probably take some action in response to.
///
/// Note that while Writeable and Readable are implemented for Event, you probably shouldn't use
/// them directly as they don't round-trip exactly (for example FundingGenerationReady is never
/// written as it makes no sense to respond to it after reconnecting to peers).
#[derive(Clone, Debug)]
pub enum Event {
        /// Used to indicate that the client should generate a funding transaction with the given
        /// parameters and then call [`ChannelManager::funding_transaction_generated`].
        /// Generated in [`ChannelManager`] message handling.
        /// Note that *all inputs* in the funding transaction must spend SegWit outputs or your
        /// counterparty can steal your funds!
        ///
        /// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
        /// [`ChannelManager::funding_transaction_generated`]: crate::ln::channelmanager::ChannelManager::funding_transaction_generated
        FundingGenerationReady {
                /// The random channel_id we picked which you'll need to pass into
                /// [`ChannelManager::funding_transaction_generated`].
                ///
                /// [`ChannelManager::funding_transaction_generated`]: crate::ln::channelmanager::ChannelManager::funding_transaction_generated
                temporary_channel_id: [u8; 32],
                /// The counterparty's node_id, which you'll need to pass back into
                /// [`ChannelManager::funding_transaction_generated`].
                ///
                /// [`ChannelManager::funding_transaction_generated`]: crate::ln::channelmanager::ChannelManager::funding_transaction_generated
                counterparty_node_id: PublicKey,
                /// The value, in satoshis, that the output should have.
                channel_value_satoshis: u64,
                /// The script which should be used in the transaction output.
                output_script: Script,
                /// The `user_channel_id` value passed in to [`ChannelManager::create_channel`], or 0 for
                /// an inbound channel.
                ///
                /// [`ChannelManager::create_channel`]: crate::ln::channelmanager::ChannelManager::create_channel
                user_channel_id: u64,
        },
        /// Indicates we've received (an offer of) money! Just gotta dig out that payment preimage and
        /// feed it to [`ChannelManager::claim_funds`] to get it....
        ///
        /// Note that if the preimage is not known, you should call
        /// [`ChannelManager::fail_htlc_backwards`] to free up resources for this HTLC and avoid
        /// network congestion.
        /// If you fail to call either [`ChannelManager::claim_funds`] or
        /// [`ChannelManager::fail_htlc_backwards`] within the HTLC's timeout, the HTLC will be
        /// automatically failed.
        ///
        /// # Note
        /// LDK will not stop an inbound payment from being paid multiple times, so multiple
        /// `PaymentReceived` events may be generated for the same payment.
        ///
        /// [`ChannelManager::claim_funds`]: crate::ln::channelmanager::ChannelManager::claim_funds
        /// [`ChannelManager::fail_htlc_backwards`]: crate::ln::channelmanager::ChannelManager::fail_htlc_backwards
        PaymentReceived {
                /// The hash for which the preimage should be handed to the ChannelManager. Note that LDK will
                /// not stop you from registering duplicate payment hashes for inbound payments.
                payment_hash: PaymentHash,
                /// The value, in thousandths of a satoshi, that this payment is for.
                amount_msat: u64,
                /// Information for claiming this received payment, based on whether the purpose of the
                /// payment is to pay an invoice or to send a spontaneous payment.
                purpose: PaymentPurpose,
        },
        /// Indicates a payment has been claimed and we've received money!
        ///
        /// This most likely occurs when [`ChannelManager::claim_funds`] has been called in response
        /// to an [`Event::PaymentReceived`]. However, if we previously crashed during a
        /// [`ChannelManager::claim_funds`] call you may see this event without a corresponding
        /// [`Event::PaymentReceived`] event.
        ///
        /// # Note
        /// LDK will not stop an inbound payment from being paid multiple times, so multiple
        /// `PaymentReceived` events may be generated for the same payment. If you then call
        /// [`ChannelManager::claim_funds`] twice for the same [`Event::PaymentReceived`] you may get
        /// multiple `PaymentClaimed` events.
        ///
        /// [`ChannelManager::claim_funds`]: crate::ln::channelmanager::ChannelManager::claim_funds
        PaymentClaimed {
                /// The payment hash of the claimed payment. Note that LDK will not stop you from
                /// registering duplicate payment hashes for inbound payments.
                payment_hash: PaymentHash,
                /// The value, in thousandths of a satoshi, that this payment is for.
                amount_msat: u64,
                /// The purpose of this claimed payment, i.e. whether the payment was for an invoice or a
                /// spontaneous payment.
                purpose: PaymentPurpose,
        },
        /// Indicates an outbound payment we made succeeded (i.e. it made it all the way to its target
        /// and we got back the payment preimage for it).
        ///
        /// Note for MPP payments: in rare cases, this event may be preceded by a `PaymentPathFailed`
        /// event. In this situation, you SHOULD treat this payment as having succeeded.
        PaymentSent {
                /// The id returned by [`ChannelManager::send_payment`] and used with
                /// [`ChannelManager::retry_payment`].
                ///
                /// [`ChannelManager::send_payment`]: crate::ln::channelmanager::ChannelManager::send_payment
                /// [`ChannelManager::retry_payment`]: crate::ln::channelmanager::ChannelManager::retry_payment
                payment_id: Option<PaymentId>,
                /// The preimage to the hash given to ChannelManager::send_payment.
                /// Note that this serves as a payment receipt, if you wish to have such a thing, you must
                /// store it somehow!
                payment_preimage: PaymentPreimage,
                /// The hash that was given to [`ChannelManager::send_payment`].
                ///
                /// [`ChannelManager::send_payment`]: crate::ln::channelmanager::ChannelManager::send_payment
                payment_hash: PaymentHash,
                /// The total fee which was spent at intermediate hops in this payment, across all paths.
                ///
                /// Note that, like [`Route::get_total_fees`] this does *not* include any potential
                /// overpayment to the recipient node.
                ///
                /// If the recipient or an intermediate node misbehaves and gives us free money, this may
                /// overstate the amount paid, though this is unlikely.
                ///
                /// [`Route::get_total_fees`]: crate::routing::router::Route::get_total_fees
                fee_paid_msat: Option<u64>,
        },
        /// Indicates an outbound payment failed. Individual [`Event::PaymentPathFailed`] events
        /// provide failure information for each MPP part in the payment.
        ///
        /// This event is provided once there are no further pending HTLCs for the payment and the
        /// payment is no longer retryable, either due to a several-block timeout or because
        /// [`ChannelManager::abandon_payment`] was previously called for the corresponding payment.
        ///
        /// [`ChannelManager::abandon_payment`]: crate::ln::channelmanager::ChannelManager::abandon_payment
        PaymentFailed {
                /// The id returned by [`ChannelManager::send_payment`] and used with
                /// [`ChannelManager::retry_payment`] and [`ChannelManager::abandon_payment`].
                ///
                /// [`ChannelManager::send_payment`]: crate::ln::channelmanager::ChannelManager::send_payment
                /// [`ChannelManager::retry_payment`]: crate::ln::channelmanager::ChannelManager::retry_payment
                /// [`ChannelManager::abandon_payment`]: crate::ln::channelmanager::ChannelManager::abandon_payment
                payment_id: PaymentId,
                /// The hash that was given to [`ChannelManager::send_payment`].
                ///
                /// [`ChannelManager::send_payment`]: crate::ln::channelmanager::ChannelManager::send_payment
                payment_hash: PaymentHash,
        },
        /// Indicates that a path for an outbound payment was successful.
        ///
        /// Always generated after [`Event::PaymentSent`] and thus useful for scoring channels. See
        /// [`Event::PaymentSent`] for obtaining the payment preimage.
        PaymentPathSuccessful {
                /// The id returned by [`ChannelManager::send_payment`] and used with
                /// [`ChannelManager::retry_payment`].
                ///
                /// [`ChannelManager::send_payment`]: crate::ln::channelmanager::ChannelManager::send_payment
                /// [`ChannelManager::retry_payment`]: crate::ln::channelmanager::ChannelManager::retry_payment
                payment_id: PaymentId,
                /// The hash that was given to [`ChannelManager::send_payment`].
                ///
                /// [`ChannelManager::send_payment`]: crate::ln::channelmanager::ChannelManager::send_payment
                payment_hash: Option<PaymentHash>,
                /// The payment path that was successful.
                ///
                /// May contain a closed channel if the HTLC sent along the path was fulfilled on chain.
                path: Vec<RouteHop>,
        },
        /// Indicates an outbound HTLC we sent failed. Probably some intermediary node dropped
        /// something. You may wish to retry with a different route.
        ///
        /// Note that this does *not* indicate that all paths for an MPP payment have failed, see
        /// [`Event::PaymentFailed`] and [`all_paths_failed`].
        ///
        /// [`all_paths_failed`]: Self::PaymentPathFailed::all_paths_failed
        PaymentPathFailed {
                /// The id returned by [`ChannelManager::send_payment`] and used with
                /// [`ChannelManager::retry_payment`] and [`ChannelManager::abandon_payment`].
                ///
                /// [`ChannelManager::send_payment`]: crate::ln::channelmanager::ChannelManager::send_payment
                /// [`ChannelManager::retry_payment`]: crate::ln::channelmanager::ChannelManager::retry_payment
                /// [`ChannelManager::abandon_payment`]: crate::ln::channelmanager::ChannelManager::abandon_payment
                payment_id: Option<PaymentId>,
                /// The hash that was given to [`ChannelManager::send_payment`].
                ///
                /// [`ChannelManager::send_payment`]: crate::ln::channelmanager::ChannelManager::send_payment
                payment_hash: PaymentHash,
                /// Indicates the payment was rejected for some reason by the recipient. This implies that
                /// the payment has failed, not just the route in question. If this is not set, you may
                /// retry the payment via a different route.
                rejected_by_dest: bool,
                /// Any failure information conveyed via the Onion return packet by a node along the failed
                /// payment route.
                ///
                /// Should be applied to the [`NetworkGraph`] so that routing decisions can take into
                /// account the update.
                ///
                /// [`NetworkGraph`]: crate::routing::gossip::NetworkGraph
                network_update: Option<NetworkUpdate>,
                /// For both single-path and multi-path payments, this is set if all paths of the payment have
                /// failed. This will be set to false if (1) this is an MPP payment and (2) other parts of the
                /// larger MPP payment were still in flight when this event was generated.
                ///
                /// Note that if you are retrying individual MPP parts, using this value to determine if a
                /// payment has fully failed is race-y. Because multiple failures can happen prior to events
                /// being processed, you may retry in response to a first failure, with a second failure
                /// (with `all_paths_failed` set) still pending. Then, when the second failure is processed
                /// you will see `all_paths_failed` set even though the retry of the first failure still
                /// has an associated in-flight HTLC. See (1) for an example of such a failure.
                ///
                /// If you wish to retry individual MPP parts and learn when a payment has failed, you must
                /// call [`ChannelManager::abandon_payment`] and wait for a [`Event::PaymentFailed`] event.
                ///
                /// (1) <https://github.com/lightningdevkit/rust-lightning/issues/1164>
                ///
                /// [`ChannelManager::abandon_payment`]: crate::ln::channelmanager::ChannelManager::abandon_payment
                all_paths_failed: bool,
                /// The payment path that failed.
                path: Vec<RouteHop>,
                /// The channel responsible for the failed payment path.
                ///
                /// Note that for route hints or for the first hop in a path this may be an SCID alias and
                /// may not refer to a channel in the public network graph. These aliases may also collide
                /// with channels in the public network graph.
                ///
                /// If this is `Some`, then the corresponding channel should be avoided when the payment is
                /// retried. May be `None` for older [`Event`] serializations.
                short_channel_id: Option<u64>,
                /// Parameters needed to compute a new [`Route`] when retrying the failed payment path.
                ///
                /// See [`find_route`] for details.
                ///
                /// [`Route`]: crate::routing::router::Route
                /// [`find_route`]: crate::routing::router::find_route
                retry: Option<RouteParameters>,
#[cfg(test)]
                error_code: Option<u16>,
#[cfg(test)]
                error_data: Option<Vec<u8>>,
        },
        /// Indicates that a probe payment we sent returned successful, i.e., only failed at the destination.
        ProbeSuccessful {
                /// The id returned by [`ChannelManager::send_probe`].
                ///
                /// [`ChannelManager::send_probe`]: crate::ln::channelmanager::ChannelManager::send_probe
                payment_id: PaymentId,
                /// The hash generated by [`ChannelManager::send_probe`].
                ///
                /// [`ChannelManager::send_probe`]: crate::ln::channelmanager::ChannelManager::send_probe
                payment_hash: PaymentHash,
                /// The payment path that was successful.
                path: Vec<RouteHop>,
        },
        /// Indicates that a probe payment we sent failed at an intermediary node on the path.
        ProbeFailed {
                /// The id returned by [`ChannelManager::send_probe`].
                ///
                /// [`ChannelManager::send_probe`]: crate::ln::channelmanager::ChannelManager::send_probe
                payment_id: PaymentId,
                /// The hash generated by [`ChannelManager::send_probe`].
                ///
                /// [`ChannelManager::send_probe`]: crate::ln::channelmanager::ChannelManager::send_probe
                payment_hash: PaymentHash,
                /// The payment path that failed.
                path: Vec<RouteHop>,
                /// The channel responsible for the failed probe.
                ///
                /// Note that for route hints or for the first hop in a path this may be an SCID alias and
                /// may not refer to a channel in the public network graph. These aliases may also collide
                /// with channels in the public network graph.
                short_channel_id: Option<u64>,
        },
        /// Used to indicate that [`ChannelManager::process_pending_htlc_forwards`] should be called at
        /// a time in the future.
        ///
        /// [`ChannelManager::process_pending_htlc_forwards`]: crate::ln::channelmanager::ChannelManager::process_pending_htlc_forwards
        PendingHTLCsForwardable {
                /// The minimum amount of time that should be waited prior to calling
                /// process_pending_htlc_forwards. To increase the effort required to correlate payments,
                /// you should wait a random amount of time in roughly the range (now + time_forwardable,
                /// now + 5*time_forwardable).
                time_forwardable: Duration,
        },
        /// Used to indicate that an output which you should know how to spend was confirmed on chain
        /// and is now spendable.
        /// Such an output will *not* ever be spent by rust-lightning, and are not at risk of your
        /// counterparty spending them due to some kind of timeout. Thus, you need to store them
        /// somewhere and spend them when you create on-chain transactions.
        SpendableOutputs {
                /// The outputs which you should store as spendable by you.
                outputs: Vec<SpendableOutputDescriptor>,
        },
        /// This event is generated when a payment has been successfully forwarded through us and a
        /// forwarding fee earned.
        PaymentForwarded {
                /// The incoming channel between the previous node and us. This is only `None` for events
                /// generated or serialized by versions prior to 0.0.107.
                prev_channel_id: Option<[u8; 32]>,
                /// The outgoing channel between the next node and us. This is only `None` for events
                /// generated or serialized by versions prior to 0.0.107.
                next_channel_id: Option<[u8; 32]>,
                /// The fee, in milli-satoshis, which was earned as a result of the payment.
                ///
                /// Note that if we force-closed the channel over which we forwarded an HTLC while the HTLC
                /// was pending, the amount the next hop claimed will have been rounded down to the nearest
                /// whole satoshi. Thus, the fee calculated here may be higher than expected as we still
                /// claimed the full value in millisatoshis from the source. In this case,
                /// `claim_from_onchain_tx` will be set.
                ///
                /// If the channel which sent us the payment has been force-closed, we will claim the funds
                /// via an on-chain transaction. In that case we do not yet know the on-chain transaction
                /// fees which we will spend and will instead set this to `None`. It is possible duplicate
                /// `PaymentForwarded` events are generated for the same payment iff `fee_earned_msat` is
                /// `None`.
                fee_earned_msat: Option<u64>,
                /// If this is `true`, the forwarded HTLC was claimed by our counterparty via an on-chain
                /// transaction.
                claim_from_onchain_tx: bool,
        },
        /// Used to indicate that a previously opened channel with the given `channel_id` is in the
        /// process of closure.
        ChannelClosed  {
                /// The channel_id of the channel which has been closed. Note that on-chain transactions
                /// resolving the channel are likely still awaiting confirmation.
                channel_id: [u8; 32],
                /// The `user_channel_id` value passed in to [`ChannelManager::create_channel`] for outbound
                /// channels, or to [`ChannelManager::accept_inbound_channel`] for inbound channels if
                /// [`UserConfig::manually_accept_inbound_channels`] config flag is set to true. Otherwise
                /// `user_channel_id` will be 0 for an inbound channel.
                /// This will always be zero for objects serialized with LDK versions prior to 0.0.102.
                ///
                /// [`ChannelManager::create_channel`]: crate::ln::channelmanager::ChannelManager::create_channel
                /// [`ChannelManager::accept_inbound_channel`]: crate::ln::channelmanager::ChannelManager::accept_inbound_channel
                /// [`UserConfig::manually_accept_inbound_channels`]: crate::util::config::UserConfig::manually_accept_inbound_channels
                user_channel_id: u64,
                /// The reason the channel was closed.
                reason: ClosureReason
        },
        /// Used to indicate to the user that they can abandon the funding transaction and recycle the
        /// inputs for another purpose.
        DiscardFunding {
                /// The channel_id of the channel which has been closed.
                channel_id: [u8; 32],
                /// The full transaction received from the user
                transaction: Transaction
        },
        /// Indicates a request to open a new channel by a peer.
        ///
        /// To accept the request, call [`ChannelManager::accept_inbound_channel`]. To reject the
        /// request, call [`ChannelManager::force_close_without_broadcasting_txn`].
        ///
        /// The event is only triggered when a new open channel request is received and the
        /// [`UserConfig::manually_accept_inbound_channels`] config flag is set to true.
        ///
        /// [`ChannelManager::accept_inbound_channel`]: crate::ln::channelmanager::ChannelManager::accept_inbound_channel
        /// [`ChannelManager::force_close_without_broadcasting_txn`]: crate::ln::channelmanager::ChannelManager::force_close_without_broadcasting_txn
        /// [`UserConfig::manually_accept_inbound_channels`]: crate::util::config::UserConfig::manually_accept_inbound_channels
        OpenChannelRequest {
                /// The temporary channel ID of the channel requested to be opened.
                ///
                /// When responding to the request, the `temporary_channel_id` should be passed
                /// back to the ChannelManager through [`ChannelManager::accept_inbound_channel`] to accept,
                /// or through [`ChannelManager::force_close_without_broadcasting_txn`] to reject.
                ///
                /// [`ChannelManager::accept_inbound_channel`]: crate::ln::channelmanager::ChannelManager::accept_inbound_channel
                /// [`ChannelManager::force_close_without_broadcasting_txn`]: crate::ln::channelmanager::ChannelManager::force_close_without_broadcasting_txn
                temporary_channel_id: [u8; 32],
                /// The node_id of the counterparty requesting to open the channel.
                ///
                /// When responding to the request, the `counterparty_node_id` should be passed
                /// back to the `ChannelManager` through [`ChannelManager::accept_inbound_channel`] to
                /// accept the request, or through [`ChannelManager::force_close_without_broadcasting_txn`] to reject the
                /// request.
                ///
                /// [`ChannelManager::accept_inbound_channel`]: crate::ln::channelmanager::ChannelManager::accept_inbound_channel
                /// [`ChannelManager::force_close_without_broadcasting_txn`]: crate::ln::channelmanager::ChannelManager::force_close_without_broadcasting_txn
                counterparty_node_id: PublicKey,
                /// The channel value of the requested channel.
                funding_satoshis: u64,
                /// Our starting balance in the channel if the request is accepted, in milli-satoshi.
                push_msat: u64,
                /// The features that this channel will operate with. If you reject the channel, a
                /// well-behaved counterparty may automatically re-attempt the channel with a new set of
                /// feature flags.
                ///
                /// Note that if [`ChannelTypeFeatures::supports_scid_privacy`] returns true on this type,
                /// the resulting [`ChannelManager`] will not be readable by versions of LDK prior to
                /// 0.0.106.
                ///
                /// Furthermore, note that if [`ChannelTypeFeatures::supports_zero_conf`] returns true on this type,
                /// the resulting [`ChannelManager`] will not be readable by versions of LDK prior to
                /// 0.0.107. Channels setting this type also need to get manually accepted via
                /// [`crate::ln::channelmanager::ChannelManager::accept_inbound_channel_from_trusted_peer_0conf`],
                /// or will be rejected otherwise.
                ///
                /// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
                channel_type: ChannelTypeFeatures,
        },
}

impl Writeable for Event {
        fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
                match self {
                        &Event::FundingGenerationReady { .. } => {
                                0u8.write(writer)?;
                                // We never write out FundingGenerationReady events as, upon disconnection, peers
                                // drop any channels which have not yet exchanged funding_signed.
                        },
                        &Event::PaymentReceived { ref payment_hash, ref amount_msat, ref purpose } => {
                                1u8.write(writer)?;
                                let mut payment_secret = None;
                                let payment_preimage;
                                match &purpose {
                                        PaymentPurpose::InvoicePayment { payment_preimage: preimage, payment_secret: secret } => {
                                                payment_secret = Some(secret);
                                                payment_preimage = *preimage;
                                        },
                                        PaymentPurpose::SpontaneousPayment(preimage) => {
                                                payment_preimage = Some(*preimage);
                                        }
                                }
                                write_tlv_fields!(writer, {
                                        (0, payment_hash, required),
                                        (2, payment_secret, option),
                                        (4, amount_msat, required),
                                        (6, 0u64, required), // user_payment_id required for compatibility with 0.0.103 and earlier
                                        (8, payment_preimage, option),
                                });
                        },
                        &Event::PaymentSent { ref payment_id, ref payment_preimage, ref payment_hash, ref fee_paid_msat } => {
                                2u8.write(writer)?;
                                write_tlv_fields!(writer, {
                                        (0, payment_preimage, required),
                                        (1, payment_hash, required),
                                        (3, payment_id, option),
                                        (5, fee_paid_msat, option),
                                });
                        },
                        &Event::PaymentPathFailed {
                                ref payment_id, ref payment_hash, ref rejected_by_dest, ref network_update,
                                ref all_paths_failed, ref path, ref short_channel_id, ref retry,
                                #[cfg(test)]
                                ref error_code,
                                #[cfg(test)]
                                ref error_data,
                        } => {
                                3u8.write(writer)?;
                                #[cfg(test)]
                                error_code.write(writer)?;
                                #[cfg(test)]
                                error_data.write(writer)?;
                                write_tlv_fields!(writer, {
                                        (0, payment_hash, required),
                                        (1, network_update, option),
                                        (2, rejected_by_dest, required),
                                        (3, all_paths_failed, required),
                                        (5, path, vec_type),
                                        (7, short_channel_id, option),
                                        (9, retry, option),
                                        (11, payment_id, option),
                                });
                        },
                        &Event::PendingHTLCsForwardable { time_forwardable: _ } => {
                                4u8.write(writer)?;
                                // Note that we now ignore these on the read end as we'll re-generate them in
                                // ChannelManager, we write them here only for backwards compatibility.
                        },
                        &Event::SpendableOutputs { ref outputs } => {
                                5u8.write(writer)?;
                                write_tlv_fields!(writer, {
                                        (0, VecWriteWrapper(outputs), required),
                                });
                        },
                        &Event::PaymentForwarded { fee_earned_msat, prev_channel_id, claim_from_onchain_tx, next_channel_id } => {
                                7u8.write(writer)?;
                                write_tlv_fields!(writer, {
                                        (0, fee_earned_msat, option),
                                        (1, prev_channel_id, option),
                                        (2, claim_from_onchain_tx, required),
                                        (3, next_channel_id, option),
                                });
                        },
                        &Event::ChannelClosed { ref channel_id, ref user_channel_id, ref reason } => {
                                9u8.write(writer)?;
                                write_tlv_fields!(writer, {
                                        (0, channel_id, required),
                                        (1, user_channel_id, required),
                                        (2, reason, required)
                                });
                        },
                        &Event::DiscardFunding { ref channel_id, ref transaction } => {
                                11u8.write(writer)?;
                                write_tlv_fields!(writer, {
                                        (0, channel_id, required),
                                        (2, transaction, required)
                                })
                        },
                        &Event::PaymentPathSuccessful { ref payment_id, ref payment_hash, ref path } => {
                                13u8.write(writer)?;
                                write_tlv_fields!(writer, {
                                        (0, payment_id, required),
                                        (2, payment_hash, option),
                                        (4, path, vec_type)
                                })
                        },
                        &Event::PaymentFailed { ref payment_id, ref payment_hash } => {
                                15u8.write(writer)?;
                                write_tlv_fields!(writer, {
                                        (0, payment_id, required),
                                        (2, payment_hash, required),
                                })
                        },
                        &Event::OpenChannelRequest { .. } => {
                                17u8.write(writer)?;
                                // We never write the OpenChannelRequest events as, upon disconnection, peers
                                // drop any channels which have not yet exchanged funding_signed.
                        },
                        &Event::PaymentClaimed { ref payment_hash, ref amount_msat, ref purpose } => {
                                19u8.write(writer)?;
                                write_tlv_fields!(writer, {
                                        (0, payment_hash, required),
                                        (2, purpose, required),
                                        (4, amount_msat, required),
                                });
                        },
                        &Event::ProbeSuccessful { ref payment_id, ref payment_hash, ref path } => {
                                21u8.write(writer)?;
                                write_tlv_fields!(writer, {
                                        (0, payment_id, required),
                                        (2, payment_hash, required),
                                        (4, path, vec_type)
                                })
                        },
                        &Event::ProbeFailed { ref payment_id, ref payment_hash, ref path, ref short_channel_id } => {
                                23u8.write(writer)?;
                                write_tlv_fields!(writer, {
                                        (0, payment_id, required),
                                        (2, payment_hash, required),
                                        (4, path, vec_type),
                                        (6, short_channel_id, option),
                                })
                        },
                        // Note that, going forward, all new events must only write data inside of
                        // `write_tlv_fields`. Versions 0.0.101+ will ignore odd-numbered events that write
                        // data via `write_tlv_fields`.
                }
                Ok(())
        }
}
impl MaybeReadable for Event {
        fn read<R: io::Read>(reader: &mut R) -> Result<Option<Self>, msgs::DecodeError> {
                match Readable::read(reader)? {
                        // Note that we do not write a length-prefixed TLV for FundingGenerationReady events,
                        // unlike all other events, thus we return immediately here.
                        0u8 => Ok(None),
                        1u8 => {
                                let f = || {
                                        let mut payment_hash = PaymentHash([0; 32]);
                                        let mut payment_preimage = None;
                                        let mut payment_secret = None;
                                        let mut amount_msat = 0;
                                        let mut _user_payment_id = None::<u64>; // For compatibility with 0.0.103 and earlier
                                        read_tlv_fields!(reader, {
                                                (0, payment_hash, required),
                                                (2, payment_secret, option),
                                                (4, amount_msat, required),
                                                (6, _user_payment_id, option),
                                                (8, payment_preimage, option),
                                        });
                                        let purpose = match payment_secret {
                                                Some(secret) => PaymentPurpose::InvoicePayment {
                                                        payment_preimage,
                                                        payment_secret: secret
                                                },
                                                None if payment_preimage.is_some() => PaymentPurpose::SpontaneousPayment(payment_preimage.unwrap()),
                                                None => return Err(msgs::DecodeError::InvalidValue),
                                        };
                                        Ok(Some(Event::PaymentReceived {
                                                payment_hash,
                                                amount_msat,
                                                purpose,
                                        }))
                                };
                                f()
                        },
                        2u8 => {
                                let f = || {
                                        let mut payment_preimage = PaymentPreimage([0; 32]);
                                        let mut payment_hash = None;
                                        let mut payment_id = None;
                                        let mut fee_paid_msat = None;
                                        read_tlv_fields!(reader, {
                                                (0, payment_preimage, required),
                                                (1, payment_hash, option),
                                                (3, payment_id, option),
                                                (5, fee_paid_msat, option),
                                        });
                                        if payment_hash.is_none() {
                                                payment_hash = Some(PaymentHash(Sha256::hash(&payment_preimage.0[..]).into_inner()));
                                        }
                                        Ok(Some(Event::PaymentSent {
                                                payment_id,
                                                payment_preimage,
                                                payment_hash: payment_hash.unwrap(),
                                                fee_paid_msat,
                                        }))
                                };
                                f()
                        },
                        3u8 => {
                                let f = || {
                                        #[cfg(test)]
                                        let error_code = Readable::read(reader)?;
                                        #[cfg(test)]
                                        let error_data = Readable::read(reader)?;
                                        let mut payment_hash = PaymentHash([0; 32]);
                                        let mut rejected_by_dest = false;
                                        let mut network_update = None;
                                        let mut all_paths_failed = Some(true);
                                        let mut path: Option<Vec<RouteHop>> = Some(vec![]);
                                        let mut short_channel_id = None;
                                        let mut retry = None;
                                        let mut payment_id = None;
                                        read_tlv_fields!(reader, {
                                                (0, payment_hash, required),
                                                (1, network_update, ignorable),
                                                (2, rejected_by_dest, required),
                                                (3, all_paths_failed, option),
                                                (5, path, vec_type),
                                                (7, short_channel_id, option),
                                                (9, retry, option),
                                                (11, payment_id, option),
                                        });
                                        Ok(Some(Event::PaymentPathFailed {
                                                payment_id,
                                                payment_hash,
                                                rejected_by_dest,
                                                network_update,
                                                all_paths_failed: all_paths_failed.unwrap(),
                                                path: path.unwrap(),
                                                short_channel_id,
                                                retry,
                                                #[cfg(test)]
                                                error_code,
                                                #[cfg(test)]
                                                error_data,
                                        }))
                                };
                                f()
                        },
                        4u8 => Ok(None),
                        5u8 => {
                                let f = || {
                                        let mut outputs = VecReadWrapper(Vec::new());
                                        read_tlv_fields!(reader, {
                                                (0, outputs, required),
                                        });
                                        Ok(Some(Event::SpendableOutputs { outputs: outputs.0 }))
                                };
                                f()
                        },
                        7u8 => {
                                let f = || {
                                        let mut fee_earned_msat = None;
                                        let mut prev_channel_id = None;
                                        let mut claim_from_onchain_tx = false;
                                        let mut next_channel_id = None;
                                        read_tlv_fields!(reader, {
                                                (0, fee_earned_msat, option),
                                                (1, prev_channel_id, option),
                                                (2, claim_from_onchain_tx, required),
                                                (3, next_channel_id, option),
                                        });
                                        Ok(Some(Event::PaymentForwarded { fee_earned_msat, prev_channel_id, claim_from_onchain_tx, next_channel_id }))
                                };
                                f()
                        },
                        9u8 => {
                                let f = || {
                                        let mut channel_id = [0; 32];
                                        let mut reason = None;
                                        let mut user_channel_id_opt = None;
                                        read_tlv_fields!(reader, {
                                                (0, channel_id, required),
                                                (1, user_channel_id_opt, option),
                                                (2, reason, ignorable),
                                        });
                                        if reason.is_none() { return Ok(None); }
                                        let user_channel_id = if let Some(id) = user_channel_id_opt { id } else { 0 };
                                        Ok(Some(Event::ChannelClosed { channel_id, user_channel_id, reason: reason.unwrap() }))
                                };
                                f()
                        },
                        11u8 => {
                                let f = || {
                                        let mut channel_id = [0; 32];
                                        let mut transaction = Transaction{ version: 2, lock_time: 0, input: Vec::new(), output: Vec::new() };
                                        read_tlv_fields!(reader, {
                                                (0, channel_id, required),
                                                (2, transaction, required),
                                        });
                                        Ok(Some(Event::DiscardFunding { channel_id, transaction } ))
                                };
                                f()
                        },
                        13u8 => {
                                let f = || {
                                        let mut payment_id = PaymentId([0; 32]);
                                        let mut payment_hash = None;
                                        let mut path: Option<Vec<RouteHop>> = Some(vec![]);
                                        read_tlv_fields!(reader, {
                                                (0, payment_id, required),
                                                (2, payment_hash, option),
                                                (4, path, vec_type),
                                        });
                                        Ok(Some(Event::PaymentPathSuccessful {
                                                payment_id,
                                                payment_hash,
                                                path: path.unwrap(),
                                        }))
                                };
                                f()
                        },
                        15u8 => {
                                let f = || {
                                        let mut payment_hash = PaymentHash([0; 32]);
                                        let mut payment_id = PaymentId([0; 32]);
                                        read_tlv_fields!(reader, {
                                                (0, payment_id, required),
                                                (2, payment_hash, required),
                                        });
                                        Ok(Some(Event::PaymentFailed {
                                                payment_id,
                                                payment_hash,
                                        }))
                                };
                                f()
                        },
                        17u8 => {
                                // Value 17 is used for `Event::OpenChannelRequest`.
                                Ok(None)
                        },
                        19u8 => {
                                let f = || {
                                        let mut payment_hash = PaymentHash([0; 32]);
                                        let mut purpose = None;
                                        let mut amount_msat = 0;
                                        read_tlv_fields!(reader, {
                                                (0, payment_hash, required),
                                                (2, purpose, ignorable),
                                                (4, amount_msat, required),
                                        });
                                        if purpose.is_none() { return Ok(None); }
                                        Ok(Some(Event::PaymentClaimed {
                                                payment_hash,
                                                purpose: purpose.unwrap(),
                                                amount_msat,
                                        }))
                                };
                                f()
                        },
                        21u8 => {
                                let f = || {
                                        let mut payment_id = PaymentId([0; 32]);
                                        let mut payment_hash = PaymentHash([0; 32]);
                                        let mut path: Option<Vec<RouteHop>> = Some(vec![]);
                                        read_tlv_fields!(reader, {
                                                (0, payment_id, required),
                                                (2, payment_hash, required),
                                                (4, path, vec_type),
                                        });
                                        Ok(Some(Event::ProbeSuccessful {
                                                payment_id,
                                                payment_hash,
                                                path: path.unwrap(),
                                        }))
                                };
                                f()
                        },
                        23u8 => {
                                let f = || {
                                        let mut payment_id = PaymentId([0; 32]);
                                        let mut payment_hash = PaymentHash([0; 32]);
                                        let mut path: Option<Vec<RouteHop>> = Some(vec![]);
                                        let mut short_channel_id = None;
                                        read_tlv_fields!(reader, {
                                                (0, payment_id, required),
                                                (2, payment_hash, required),
                                                (4, path, vec_type),
                                                (6, short_channel_id, option),
                                        });
                                        Ok(Some(Event::ProbeFailed{
                                                payment_id,
                                                payment_hash,
                                                path: path.unwrap(),
                                                short_channel_id,
                                        }))
                                };
                                f()
                        },
                        // Versions prior to 0.0.100 did not ignore odd types, instead returning InvalidValue.
                        // Version 0.0.100 failed to properly ignore odd types, possibly resulting in corrupt
                        // reads.
                        x if x % 2 == 1 => {
                                // If the event is of unknown type, assume it was written with `write_tlv_fields`,
                                // which prefixes the whole thing with a length BigSize. Because the event is
                                // odd-type unknown, we should treat it as `Ok(None)` even if it has some TLV
                                // fields that are even. Thus, we avoid using `read_tlv_fields` and simply read
                                // exactly the number of bytes specified, ignoring them entirely.
                                let tlv_len: BigSize = Readable::read(reader)?;
                                FixedLengthReader::new(reader, tlv_len.0)
                                        .eat_remaining().map_err(|_| msgs::DecodeError::ShortRead)?;
                                Ok(None)
                        },
                        _ => Err(msgs::DecodeError::InvalidValue)
                }
        }
}

/// An event generated by ChannelManager which indicates a message should be sent to a peer (or
/// broadcast to most peers).
/// These events are handled by PeerManager::process_events if you are using a PeerManager.
#[derive(Clone, Debug)]
pub enum MessageSendEvent {
        /// Used to indicate that we've accepted a channel open and should send the accept_channel
        /// message provided to the given peer.
        SendAcceptChannel {
                /// The node_id of the node which should receive this message
                node_id: PublicKey,
                /// The message which should be sent.
                msg: msgs::AcceptChannel,
        },
        /// Used to indicate that we've initiated a channel open and should send the open_channel
        /// message provided to the given peer.
        SendOpenChannel {
                /// The node_id of the node which should receive this message
                node_id: PublicKey,
                /// The message which should be sent.
                msg: msgs::OpenChannel,
        },
        /// Used to indicate that a funding_created message should be sent to the peer with the given node_id.
        SendFundingCreated {
                /// The node_id of the node which should receive this message
                node_id: PublicKey,
                /// The message which should be sent.
                msg: msgs::FundingCreated,
        },
        /// Used to indicate that a funding_signed message should be sent to the peer with the given node_id.
        SendFundingSigned {
                /// The node_id of the node which should receive this message
                node_id: PublicKey,
                /// The message which should be sent.
                msg: msgs::FundingSigned,
        },
        /// Used to indicate that a channel_ready message should be sent to the peer with the given node_id.
        SendChannelReady {
                /// The node_id of the node which should receive these message(s)
                node_id: PublicKey,
                /// The channel_ready message which should be sent.
                msg: msgs::ChannelReady,
        },
        /// Used to indicate that an announcement_signatures message should be sent to the peer with the given node_id.
        SendAnnouncementSignatures {
                /// The node_id of the node which should receive these message(s)
                node_id: PublicKey,
                /// The announcement_signatures message which should be sent.
                msg: msgs::AnnouncementSignatures,
        },
        /// Used to indicate that a series of HTLC update messages, as well as a commitment_signed
        /// message should be sent to the peer with the given node_id.
        UpdateHTLCs {
                /// The node_id of the node which should receive these message(s)
                node_id: PublicKey,
                /// The update messages which should be sent. ALL messages in the struct should be sent!
                updates: msgs::CommitmentUpdate,
        },
        /// Used to indicate that a revoke_and_ack message should be sent to the peer with the given node_id.
        SendRevokeAndACK {
                /// The node_id of the node which should receive this message
                node_id: PublicKey,
                /// The message which should be sent.
                msg: msgs::RevokeAndACK,
        },
        /// Used to indicate that a closing_signed message should be sent to the peer with the given node_id.
        SendClosingSigned {
                /// The node_id of the node which should receive this message
                node_id: PublicKey,
                /// The message which should be sent.
                msg: msgs::ClosingSigned,
        },
        /// Used to indicate that a shutdown message should be sent to the peer with the given node_id.
        SendShutdown {
                /// The node_id of the node which should receive this message
                node_id: PublicKey,
                /// The message which should be sent.
                msg: msgs::Shutdown,
        },
        /// Used to indicate that a channel_reestablish message should be sent to the peer with the given node_id.
        SendChannelReestablish {
                /// The node_id of the node which should receive this message
                node_id: PublicKey,
                /// The message which should be sent.
                msg: msgs::ChannelReestablish,
        },
        /// Used to indicate that a channel_announcement and channel_update should be broadcast to all
        /// peers (except the peer with node_id either msg.contents.node_id_1 or msg.contents.node_id_2).
        ///
        /// Note that after doing so, you very likely (unless you did so very recently) want to call
        /// ChannelManager::broadcast_node_announcement to trigger a BroadcastNodeAnnouncement event.
        /// This ensures that any nodes which see our channel_announcement also have a relevant
        /// node_announcement, including relevant feature flags which may be important for routing
        /// through or to us.
        BroadcastChannelAnnouncement {
                /// The channel_announcement which should be sent.
                msg: msgs::ChannelAnnouncement,
                /// The followup channel_update which should be sent.
                update_msg: msgs::ChannelUpdate,
        },
        /// Used to indicate that a node_announcement should be broadcast to all peers.
        BroadcastNodeAnnouncement {
                /// The node_announcement which should be sent.
                msg: msgs::NodeAnnouncement,
        },
        /// Used to indicate that a channel_update should be broadcast to all peers.
        BroadcastChannelUpdate {
                /// The channel_update which should be sent.
                msg: msgs::ChannelUpdate,
        },
        /// Used to indicate that a channel_update should be sent to a single peer.
        /// In contrast to [`Self::BroadcastChannelUpdate`], this is used when the channel is a
        /// private channel and we shouldn't be informing all of our peers of channel parameters.
        SendChannelUpdate {
                /// The node_id of the node which should receive this message
                node_id: PublicKey,
                /// The channel_update which should be sent.
                msg: msgs::ChannelUpdate,
        },
        /// Broadcast an error downstream to be handled
        HandleError {
                /// The node_id of the node which should receive this message
                node_id: PublicKey,
                /// The action which should be taken.
                action: msgs::ErrorAction
        },
        /// Query a peer for channels with funding transaction UTXOs in a block range.
        SendChannelRangeQuery {
                /// The node_id of this message recipient
                node_id: PublicKey,
                /// The query_channel_range which should be sent.
                msg: msgs::QueryChannelRange,
        },
        /// Request routing gossip messages from a peer for a list of channels identified by
        /// their short_channel_ids.
        SendShortIdsQuery {
                /// The node_id of this message recipient
                node_id: PublicKey,
                /// The query_short_channel_ids which should be sent.
                msg: msgs::QueryShortChannelIds,
        },
        /// Sends a reply to a channel range query. This may be one of several SendReplyChannelRange events
        /// emitted during processing of the query.
        SendReplyChannelRange {
                /// The node_id of this message recipient
                node_id: PublicKey,
                /// The reply_channel_range which should be sent.
                msg: msgs::ReplyChannelRange,
        },
        /// Sends a timestamp filter for inbound gossip. This should be sent on each new connection to
        /// enable receiving gossip messages from the peer.
        SendGossipTimestampFilter {
                /// The node_id of this message recipient
                node_id: PublicKey,
                /// The gossip_timestamp_filter which should be sent.
                msg: msgs::GossipTimestampFilter,
        },
}

/// A trait indicating an object may generate message send events
pub trait MessageSendEventsProvider {
        /// Gets the list of pending events which were generated by previous actions, clearing the list
        /// in the process.
        fn get_and_clear_pending_msg_events(&self) -> Vec<MessageSendEvent>;
}

/// A trait indicating an object may generate events.
///
/// Events are processed by passing an [`EventHandler`] to [`process_pending_events`].
///
/// # Requirements
///
/// See [`process_pending_events`] for requirements around event processing.
///
/// When using this trait, [`process_pending_events`] will call [`handle_event`] for each pending
/// event since the last invocation. The handler must either act upon the event immediately
/// or preserve it for later handling.
///
/// Note, handlers may call back into the provider and thus deadlocking must be avoided. Be sure to
/// consult the provider's documentation on the implication of processing events and how a handler
/// may safely use the provider (e.g., see [`ChannelManager::process_pending_events`] and
/// [`ChainMonitor::process_pending_events`]).
///
/// (C-not implementable) As there is likely no reason for a user to implement this trait on their
/// own type(s).
///
/// [`process_pending_events`]: Self::process_pending_events
/// [`handle_event`]: EventHandler::handle_event
/// [`ChannelManager::process_pending_events`]: crate::ln::channelmanager::ChannelManager#method.process_pending_events
/// [`ChainMonitor::process_pending_events`]: crate::chain::chainmonitor::ChainMonitor#method.process_pending_events
pub trait EventsProvider {
        /// Processes any events generated since the last call using the given event handler.
        ///
        /// Subsequent calls must only process new events. However, handlers must be capable of handling
        /// duplicate events across process restarts. This may occur if the provider was recovered from
        /// an old state (i.e., it hadn't been successfully persisted after processing pending events).
        fn process_pending_events<H: Deref>(&self, handler: H) where H::Target: EventHandler;
}

/// A trait implemented for objects handling events from [`EventsProvider`].
pub trait EventHandler {
        /// Handles the given [`Event`].
        ///
        /// See [`EventsProvider`] for details that must be considered when implementing this method.
        fn handle_event(&self, event: &Event);
}

impl<F> EventHandler for F where F: Fn(&Event) {
        fn handle_event(&self, event: &Event) {
                self(event)
        }
}

impl<T: EventHandler> EventHandler for Arc<T> {
        fn handle_event(&self, event: &Event) {
                self.deref().handle_event(event)
        }
}