1 // This file is Copyright its original authors, visible in version control
4 // This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
5 // or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
7 // You may not use this file except in accordance with one or both of these
10 //! Events are returned from various bits in the library which indicate some action must be taken
13 //! Because we don't have a built-in runtime, it's up to the client to call events at a time in the
14 //! future, as well as generate and broadcast funding transactions handle payment preimages and a
17 use chain::keysinterface::SpendableOutputDescriptor;
19 use ln::msgs::DecodeError;
20 use ln::{PaymentPreimage, PaymentHash, PaymentSecret};
21 use routing::network_graph::NetworkUpdate;
22 use util::ser::{BigSize, FixedLengthReader, Writeable, Writer, MaybeReadable, Readable, VecReadWrapper, VecWriteWrapper};
24 use bitcoin::blockdata::script::Script;
26 use bitcoin::secp256k1::key::PublicKey;
30 use core::time::Duration;
33 /// Some information provided on receipt of payment depends on whether the payment received is a
34 /// spontaneous payment or a "conventional" lightning payment that's paying an invoice.
35 #[derive(Clone, Debug)]
36 pub enum PaymentPurpose {
37 /// Information for receiving a payment that we generated an invoice for.
39 /// The preimage to the payment_hash, if the payment hash (and secret) were fetched via
40 /// [`ChannelManager::create_inbound_payment`]. If provided, this can be handed directly to
41 /// [`ChannelManager::claim_funds`].
43 /// [`ChannelManager::create_inbound_payment`]: crate::ln::channelmanager::ChannelManager::create_inbound_payment
44 /// [`ChannelManager::claim_funds`]: crate::ln::channelmanager::ChannelManager::claim_funds
45 payment_preimage: Option<PaymentPreimage>,
46 /// The "payment secret". This authenticates the sender to the recipient, preventing a
47 /// number of deanonymization attacks during the routing process.
48 /// It is provided here for your reference, however its accuracy is enforced directly by
49 /// [`ChannelManager`] using the values you previously provided to
50 /// [`ChannelManager::create_inbound_payment`] or
51 /// [`ChannelManager::create_inbound_payment_for_hash`].
53 /// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
54 /// [`ChannelManager::create_inbound_payment`]: crate::ln::channelmanager::ChannelManager::create_inbound_payment
55 /// [`ChannelManager::create_inbound_payment_for_hash`]: crate::ln::channelmanager::ChannelManager::create_inbound_payment_for_hash
56 payment_secret: PaymentSecret,
57 /// This is the `user_payment_id` which was provided to
58 /// [`ChannelManager::create_inbound_payment_for_hash`] or
59 /// [`ChannelManager::create_inbound_payment`]. It has no meaning inside of LDK and is
60 /// simply copied here. It may be used to correlate PaymentReceived events with invoice
61 /// metadata stored elsewhere.
63 /// [`ChannelManager::create_inbound_payment`]: crate::ln::channelmanager::ChannelManager::create_inbound_payment
64 /// [`ChannelManager::create_inbound_payment_for_hash`]: crate::ln::channelmanager::ChannelManager::create_inbound_payment_for_hash
67 /// Because this is a spontaneous payment, the payer generated their own preimage rather than us
68 /// (the payee) providing a preimage.
69 SpontaneousPayment(PaymentPreimage),
72 #[derive(Clone, Debug, PartialEq)]
73 /// The reason the channel was closed. See individual variants more details.
74 pub enum ClosureReason {
75 /// Closure generated from receiving a peer error message.
77 /// Our counterparty may have broadcasted their latest commitment state, and we have
79 CounterpartyForceClosed {
80 /// The error which the peer sent us.
82 /// The string should be sanitized before it is used (e.g emitted to logs
83 /// or printed to stdout). Otherwise, a well crafted error message may exploit
84 /// a security vulnerability in the terminal emulator or the logging subsystem.
87 /// Closure generated from [`ChannelManager::force_close_channel`], called by the user.
89 /// [`ChannelManager::force_close_channel`]: crate::ln::channelmanager::ChannelManager::force_close_channel.
91 /// The channel was closed after negotiating a cooperative close and we've now broadcasted
92 /// the cooperative close transaction. Note the shutdown may have been initiated by us.
93 //TODO: split between CounterpartyInitiated/LocallyInitiated
95 /// A commitment transaction was confirmed on chain, closing the channel. Most likely this
96 /// commitment transaction came from our counterparty, but it may also have come from
97 /// a copy of our own `ChannelMonitor`.
98 CommitmentTxConfirmed,
99 /// Closure generated from processing an event, likely a HTLC forward/relay/reception.
101 /// A developer-readable error message which we generated.
104 /// The `PeerManager` informed us that we've disconnected from the peer. We close channels
105 /// if the `PeerManager` informed us that it is unlikely we'll be able to connect to the
106 /// peer again in the future or if the peer disconnected before we finished negotiating
107 /// the channel open. The first case may be caused by incompatible features which our
108 /// counterparty, or we, require.
109 //TODO: split between PeerUnconnectable/PeerDisconnected ?
111 /// Closure generated from `ChannelManager::read` if the ChannelMonitor is newer than
112 /// the ChannelManager deserialized.
113 OutdatedChannelManager
116 impl_writeable_tlv_based_enum_upgradable!(ClosureReason,
117 (0, CounterpartyForceClosed) => { (1, peer_msg, required) },
118 (2, HolderForceClosed) => {},
119 (6, CommitmentTxConfirmed) => {},
120 (4, CooperativeClosure) => {},
121 (8, ProcessingError) => { (1, err, required) },
122 (10, DisconnectedPeer) => {},
123 (12, OutdatedChannelManager) => {},
126 /// An Event which you should probably take some action in response to.
128 /// Note that while Writeable and Readable are implemented for Event, you probably shouldn't use
129 /// them directly as they don't round-trip exactly (for example FundingGenerationReady is never
130 /// written as it makes no sense to respond to it after reconnecting to peers).
131 #[derive(Clone, Debug)]
133 /// Used to indicate that the client should generate a funding transaction with the given
134 /// parameters and then call ChannelManager::funding_transaction_generated.
135 /// Generated in ChannelManager message handling.
136 /// Note that *all inputs* in the funding transaction must spend SegWit outputs or your
137 /// counterparty can steal your funds!
138 FundingGenerationReady {
139 /// The random channel_id we picked which you'll need to pass into
140 /// ChannelManager::funding_transaction_generated.
141 temporary_channel_id: [u8; 32],
142 /// The value, in satoshis, that the output should have.
143 channel_value_satoshis: u64,
144 /// The script which should be used in the transaction output.
145 output_script: Script,
146 /// The value passed in to ChannelManager::create_channel
147 user_channel_id: u64,
149 /// Indicates we've received money! Just gotta dig out that payment preimage and feed it to
150 /// ChannelManager::claim_funds to get it....
151 /// Note that if the preimage is not known or the amount paid is incorrect, you should call
152 /// ChannelManager::fail_htlc_backwards to free up resources for this HTLC and avoid
153 /// network congestion.
154 /// The amount paid should be considered 'incorrect' when it is less than or more than twice
155 /// the amount expected.
156 /// If you fail to call either ChannelManager::claim_funds or
157 /// ChannelManager::fail_htlc_backwards within the HTLC's timeout, the HTLC will be
158 /// automatically failed.
160 /// The hash for which the preimage should be handed to the ChannelManager.
161 payment_hash: PaymentHash,
162 /// The value, in thousandths of a satoshi, that this payment is for. Note that you must
163 /// compare this to the expected value before accepting the payment (as otherwise you are
164 /// providing proof-of-payment for less than the value you expected!).
166 /// Information for claiming this received payment, based on whether the purpose of the
167 /// payment is to pay an invoice or to send a spontaneous payment.
168 purpose: PaymentPurpose,
170 /// Indicates an outbound payment we made succeeded (i.e. it made it all the way to its target
171 /// and we got back the payment preimage for it).
173 /// Note for MPP payments: in rare cases, this event may be preceded by a `PaymentFailed` event.
174 /// In this situation, you SHOULD treat this payment as having succeeded.
176 /// The preimage to the hash given to ChannelManager::send_payment.
177 /// Note that this serves as a payment receipt, if you wish to have such a thing, you must
178 /// store it somehow!
179 payment_preimage: PaymentPreimage,
181 /// Indicates an outbound payment we made failed. Probably some intermediary node dropped
182 /// something. You may wish to retry with a different route.
184 /// The hash which was given to ChannelManager::send_payment.
185 payment_hash: PaymentHash,
186 /// Indicates the payment was rejected for some reason by the recipient. This implies that
187 /// the payment has failed, not just the route in question. If this is not set, you may
188 /// retry the payment via a different route.
189 rejected_by_dest: bool,
190 /// Any failure information conveyed via the Onion return packet by a node along the failed
193 /// Should be applied to the [`NetworkGraph`] so that routing decisions can take into
194 /// account the update. [`NetGraphMsgHandler`] is capable of doing this.
196 /// [`NetworkGraph`]: crate::routing::network_graph::NetworkGraph
197 /// [`NetGraphMsgHandler`]: crate::routing::network_graph::NetGraphMsgHandler
198 network_update: Option<NetworkUpdate>,
199 /// For both single-path and multi-path payments, this is set if all paths of the payment have
200 /// failed. This will be set to false if (1) this is an MPP payment and (2) other parts of the
201 /// larger MPP payment were still in flight when this event was generated.
202 all_paths_failed: bool,
204 error_code: Option<u16>,
206 error_data: Option<Vec<u8>>,
208 /// Used to indicate that ChannelManager::process_pending_htlc_forwards should be called at a
209 /// time in the future.
210 PendingHTLCsForwardable {
211 /// The minimum amount of time that should be waited prior to calling
212 /// process_pending_htlc_forwards. To increase the effort required to correlate payments,
213 /// you should wait a random amount of time in roughly the range (now + time_forwardable,
214 /// now + 5*time_forwardable).
215 time_forwardable: Duration,
217 /// Used to indicate that an output which you should know how to spend was confirmed on chain
218 /// and is now spendable.
219 /// Such an output will *not* ever be spent by rust-lightning, and are not at risk of your
220 /// counterparty spending them due to some kind of timeout. Thus, you need to store them
221 /// somewhere and spend them when you create on-chain transactions.
223 /// The outputs which you should store as spendable by you.
224 outputs: Vec<SpendableOutputDescriptor>,
226 /// This event is generated when a payment has been successfully forwarded through us and a
227 /// forwarding fee earned.
229 /// The fee, in milli-satoshis, which was earned as a result of the payment.
231 /// Note that if we force-closed the channel over which we forwarded an HTLC while the HTLC
232 /// was pending, the amount the next hop claimed will have been rounded down to the nearest
233 /// whole satoshi. Thus, the fee calculated here may be higher than expected as we still
234 /// claimed the full value in millisatoshis from the source. In this case,
235 /// `claim_from_onchain_tx` will be set.
237 /// If the channel which sent us the payment has been force-closed, we will claim the funds
238 /// via an on-chain transaction. In that case we do not yet know the on-chain transaction
239 /// fees which we will spend and will instead set this to `None`. It is possible duplicate
240 /// `PaymentForwarded` events are generated for the same payment iff `fee_earned_msat` is
242 fee_earned_msat: Option<u64>,
243 /// If this is `true`, the forwarded HTLC was claimed by our counterparty via an on-chain
245 claim_from_onchain_tx: bool,
247 /// Used to indicate that a channel with the given `channel_id` is in the process of closure.
249 /// The channel_id of the channel which has been closed. Note that on-chain transactions
250 /// resolving the channel are likely still awaiting confirmation.
251 channel_id: [u8; 32],
252 /// The reason the channel was closed.
253 reason: ClosureReason
257 impl Writeable for Event {
258 fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
260 &Event::FundingGenerationReady { .. } => {
262 // We never write out FundingGenerationReady events as, upon disconnection, peers
263 // drop any channels which have not yet exchanged funding_signed.
265 &Event::PaymentReceived { ref payment_hash, ref amt, ref purpose } => {
267 let mut payment_secret = None;
268 let mut user_payment_id = None;
269 let payment_preimage;
271 PaymentPurpose::InvoicePayment { payment_preimage: preimage, payment_secret: secret, user_payment_id: id } => {
272 payment_secret = Some(secret);
273 payment_preimage = *preimage;
274 user_payment_id = Some(id);
276 PaymentPurpose::SpontaneousPayment(preimage) => {
277 payment_preimage = Some(*preimage);
280 write_tlv_fields!(writer, {
281 (0, payment_hash, required),
282 (2, payment_secret, option),
284 (6, user_payment_id, option),
285 (8, payment_preimage, option),
288 &Event::PaymentSent { ref payment_preimage } => {
290 write_tlv_fields!(writer, {
291 (0, payment_preimage, required),
294 &Event::PaymentFailed { ref payment_hash, ref rejected_by_dest, ref network_update, ref all_paths_failed,
302 error_code.write(writer)?;
304 error_data.write(writer)?;
305 write_tlv_fields!(writer, {
306 (0, payment_hash, required),
307 (1, network_update, option),
308 (2, rejected_by_dest, required),
309 (3, all_paths_failed, required),
312 &Event::PendingHTLCsForwardable { time_forwardable: _ } => {
314 write_tlv_fields!(writer, {});
315 // We don't write the time_fordwardable out at all, as we presume when the user
316 // deserializes us at least that much time has elapsed.
318 &Event::SpendableOutputs { ref outputs } => {
320 write_tlv_fields!(writer, {
321 (0, VecWriteWrapper(outputs), required),
324 &Event::PaymentForwarded { fee_earned_msat, claim_from_onchain_tx } => {
326 write_tlv_fields!(writer, {
327 (0, fee_earned_msat, option),
328 (2, claim_from_onchain_tx, required),
331 &Event::ChannelClosed { ref channel_id, ref reason } => {
333 write_tlv_fields!(writer, {
334 (0, channel_id, required),
335 (2, reason, required)
338 // Note that, going forward, all new events must only write data inside of
339 // `write_tlv_fields`. Versions 0.0.101+ will ignore odd-numbered events that write
340 // data via `write_tlv_fields`.
345 impl MaybeReadable for Event {
346 fn read<R: io::Read>(reader: &mut R) -> Result<Option<Self>, msgs::DecodeError> {
347 match Readable::read(reader)? {
348 // Note that we do not write a length-prefixed TLV for FundingGenerationReady events,
349 // unlike all other events, thus we return immediately here.
353 let mut payment_hash = PaymentHash([0; 32]);
354 let mut payment_preimage = None;
355 let mut payment_secret = None;
357 let mut user_payment_id = None;
358 read_tlv_fields!(reader, {
359 (0, payment_hash, required),
360 (2, payment_secret, option),
362 (6, user_payment_id, option),
363 (8, payment_preimage, option),
365 let purpose = match payment_secret {
366 Some(secret) => PaymentPurpose::InvoicePayment {
368 payment_secret: secret,
369 user_payment_id: if let Some(id) = user_payment_id {
371 } else { return Err(msgs::DecodeError::InvalidValue) }
373 None if payment_preimage.is_some() => PaymentPurpose::SpontaneousPayment(payment_preimage.unwrap()),
374 None => return Err(msgs::DecodeError::InvalidValue),
376 Ok(Some(Event::PaymentReceived {
386 let mut payment_preimage = PaymentPreimage([0; 32]);
387 read_tlv_fields!(reader, {
388 (0, payment_preimage, required),
390 Ok(Some(Event::PaymentSent {
399 let error_code = Readable::read(reader)?;
401 let error_data = Readable::read(reader)?;
402 let mut payment_hash = PaymentHash([0; 32]);
403 let mut rejected_by_dest = false;
404 let mut network_update = None;
405 let mut all_paths_failed = Some(true);
406 read_tlv_fields!(reader, {
407 (0, payment_hash, required),
408 (1, network_update, ignorable),
409 (2, rejected_by_dest, required),
410 (3, all_paths_failed, option),
412 Ok(Some(Event::PaymentFailed {
416 all_paths_failed: all_paths_failed.unwrap(),
427 read_tlv_fields!(reader, {});
428 Ok(Some(Event::PendingHTLCsForwardable {
429 time_forwardable: Duration::from_secs(0)
436 let mut outputs = VecReadWrapper(Vec::new());
437 read_tlv_fields!(reader, {
438 (0, outputs, required),
440 Ok(Some(Event::SpendableOutputs { outputs: outputs.0 }))
446 let mut fee_earned_msat = None;
447 let mut claim_from_onchain_tx = false;
448 read_tlv_fields!(reader, {
449 (0, fee_earned_msat, option),
450 (2, claim_from_onchain_tx, required),
452 Ok(Some(Event::PaymentForwarded { fee_earned_msat, claim_from_onchain_tx }))
457 let mut channel_id = [0; 32];
458 let mut reason = None;
459 read_tlv_fields!(reader, {
460 (0, channel_id, required),
461 (2, reason, ignorable),
463 if reason.is_none() { return Ok(None); }
464 Ok(Some(Event::ChannelClosed { channel_id, reason: reason.unwrap() }))
466 // Versions prior to 0.0.100 did not ignore odd types, instead returning InvalidValue.
467 // Version 0.0.100 failed to properly ignore odd types, possibly resulting in corrupt
470 // If the event is of unknown type, assume it was written with `write_tlv_fields`,
471 // which prefixes the whole thing with a length BigSize. Because the event is
472 // odd-type unknown, we should treat it as `Ok(None)` even if it has some TLV
473 // fields that are even. Thus, we avoid using `read_tlv_fields` and simply read
474 // exactly the number of bytes specified, ignoring them entirely.
475 let tlv_len: BigSize = Readable::read(reader)?;
476 FixedLengthReader::new(reader, tlv_len.0)
477 .eat_remaining().map_err(|_| msgs::DecodeError::ShortRead)?;
480 _ => Err(msgs::DecodeError::InvalidValue)
485 /// An event generated by ChannelManager which indicates a message should be sent to a peer (or
486 /// broadcast to most peers).
487 /// These events are handled by PeerManager::process_events if you are using a PeerManager.
488 #[derive(Clone, Debug)]
489 pub enum MessageSendEvent {
490 /// Used to indicate that we've accepted a channel open and should send the accept_channel
491 /// message provided to the given peer.
493 /// The node_id of the node which should receive this message
495 /// The message which should be sent.
496 msg: msgs::AcceptChannel,
498 /// Used to indicate that we've initiated a channel open and should send the open_channel
499 /// message provided to the given peer.
501 /// The node_id of the node which should receive this message
503 /// The message which should be sent.
504 msg: msgs::OpenChannel,
506 /// Used to indicate that a funding_created message should be sent to the peer with the given node_id.
508 /// The node_id of the node which should receive this message
510 /// The message which should be sent.
511 msg: msgs::FundingCreated,
513 /// Used to indicate that a funding_signed message should be sent to the peer with the given node_id.
515 /// The node_id of the node which should receive this message
517 /// The message which should be sent.
518 msg: msgs::FundingSigned,
520 /// Used to indicate that a funding_locked message should be sent to the peer with the given node_id.
522 /// The node_id of the node which should receive these message(s)
524 /// The funding_locked message which should be sent.
525 msg: msgs::FundingLocked,
527 /// Used to indicate that an announcement_signatures message should be sent to the peer with the given node_id.
528 SendAnnouncementSignatures {
529 /// The node_id of the node which should receive these message(s)
531 /// The announcement_signatures message which should be sent.
532 msg: msgs::AnnouncementSignatures,
534 /// Used to indicate that a series of HTLC update messages, as well as a commitment_signed
535 /// message should be sent to the peer with the given node_id.
537 /// The node_id of the node which should receive these message(s)
539 /// The update messages which should be sent. ALL messages in the struct should be sent!
540 updates: msgs::CommitmentUpdate,
542 /// Used to indicate that a revoke_and_ack message should be sent to the peer with the given node_id.
544 /// The node_id of the node which should receive this message
546 /// The message which should be sent.
547 msg: msgs::RevokeAndACK,
549 /// Used to indicate that a closing_signed message should be sent to the peer with the given node_id.
551 /// The node_id of the node which should receive this message
553 /// The message which should be sent.
554 msg: msgs::ClosingSigned,
556 /// Used to indicate that a shutdown message should be sent to the peer with the given node_id.
558 /// The node_id of the node which should receive this message
560 /// The message which should be sent.
563 /// Used to indicate that a channel_reestablish message should be sent to the peer with the given node_id.
564 SendChannelReestablish {
565 /// The node_id of the node which should receive this message
567 /// The message which should be sent.
568 msg: msgs::ChannelReestablish,
570 /// Used to indicate that a channel_announcement and channel_update should be broadcast to all
571 /// peers (except the peer with node_id either msg.contents.node_id_1 or msg.contents.node_id_2).
573 /// Note that after doing so, you very likely (unless you did so very recently) want to call
574 /// ChannelManager::broadcast_node_announcement to trigger a BroadcastNodeAnnouncement event.
575 /// This ensures that any nodes which see our channel_announcement also have a relevant
576 /// node_announcement, including relevant feature flags which may be important for routing
577 /// through or to us.
578 BroadcastChannelAnnouncement {
579 /// The channel_announcement which should be sent.
580 msg: msgs::ChannelAnnouncement,
581 /// The followup channel_update which should be sent.
582 update_msg: msgs::ChannelUpdate,
584 /// Used to indicate that a node_announcement should be broadcast to all peers.
585 BroadcastNodeAnnouncement {
586 /// The node_announcement which should be sent.
587 msg: msgs::NodeAnnouncement,
589 /// Used to indicate that a channel_update should be broadcast to all peers.
590 BroadcastChannelUpdate {
591 /// The channel_update which should be sent.
592 msg: msgs::ChannelUpdate,
594 /// Used to indicate that a channel_update should be sent to a single peer.
595 /// In contrast to [`Self::BroadcastChannelUpdate`], this is used when the channel is a
596 /// private channel and we shouldn't be informing all of our peers of channel parameters.
598 /// The node_id of the node which should receive this message
600 /// The channel_update which should be sent.
601 msg: msgs::ChannelUpdate,
603 /// Broadcast an error downstream to be handled
605 /// The node_id of the node which should receive this message
607 /// The action which should be taken.
608 action: msgs::ErrorAction
610 /// Query a peer for channels with funding transaction UTXOs in a block range.
611 SendChannelRangeQuery {
612 /// The node_id of this message recipient
614 /// The query_channel_range which should be sent.
615 msg: msgs::QueryChannelRange,
617 /// Request routing gossip messages from a peer for a list of channels identified by
618 /// their short_channel_ids.
620 /// The node_id of this message recipient
622 /// The query_short_channel_ids which should be sent.
623 msg: msgs::QueryShortChannelIds,
625 /// Sends a reply to a channel range query. This may be one of several SendReplyChannelRange events
626 /// emitted during processing of the query.
627 SendReplyChannelRange {
628 /// The node_id of this message recipient
630 /// The reply_channel_range which should be sent.
631 msg: msgs::ReplyChannelRange,
635 /// A trait indicating an object may generate message send events
636 pub trait MessageSendEventsProvider {
637 /// Gets the list of pending events which were generated by previous actions, clearing the list
639 fn get_and_clear_pending_msg_events(&self) -> Vec<MessageSendEvent>;
642 /// A trait indicating an object may generate events.
644 /// Events are processed by passing an [`EventHandler`] to [`process_pending_events`].
648 /// See [`process_pending_events`] for requirements around event processing.
650 /// When using this trait, [`process_pending_events`] will call [`handle_event`] for each pending
651 /// event since the last invocation. The handler must either act upon the event immediately
652 /// or preserve it for later handling.
654 /// Note, handlers may call back into the provider and thus deadlocking must be avoided. Be sure to
655 /// consult the provider's documentation on the implication of processing events and how a handler
656 /// may safely use the provider (e.g., see [`ChannelManager::process_pending_events`] and
657 /// [`ChainMonitor::process_pending_events`]).
659 /// (C-not implementable) As there is likely no reason for a user to implement this trait on their
662 /// [`process_pending_events`]: Self::process_pending_events
663 /// [`handle_event`]: EventHandler::handle_event
664 /// [`ChannelManager::process_pending_events`]: crate::ln::channelmanager::ChannelManager#method.process_pending_events
665 /// [`ChainMonitor::process_pending_events`]: crate::chain::chainmonitor::ChainMonitor#method.process_pending_events
666 pub trait EventsProvider {
667 /// Processes any events generated since the last call using the given event handler.
669 /// Subsequent calls must only process new events. However, handlers must be capable of handling
670 /// duplicate events across process restarts. This may occur if the provider was recovered from
671 /// an old state (i.e., it hadn't been successfully persisted after processing pending events).
672 fn process_pending_events<H: Deref>(&self, handler: H) where H::Target: EventHandler;
675 /// A trait implemented for objects handling events from [`EventsProvider`].
676 pub trait EventHandler {
677 /// Handles the given [`Event`].
679 /// See [`EventsProvider`] for details that must be considered when implementing this method.
680 fn handle_event(&self, event: &Event);
683 impl<F> EventHandler for F where F: Fn(&Event) {
684 fn handle_event(&self, event: &Event) {