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::{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)]
73 pub enum ClosureDescriptor {
74 /// Closure generated from ChannelManager::force_close_channel or receiving a peer error
75 /// message by ChannelManager::handle_error
77 /// If the error is coming from the peer, there should be a human-readable msg
78 peer_msg: Option<String>,
80 /// Closure generated from receiving a peer's ClosingSigned message. Note the shutdown
81 /// sequence might have been initially initiated by us.
83 /// Closure generated from receiving chain::Watch's CommitmentTxBroadcast event.
84 CommitmentTxBroadcasted,
85 /// Closure generated from processing an event, likely a HTLC forward/relay/reception.
89 /// Closure generated from ChannelManager::peer_disconnected.
93 impl Writeable for ClosureDescriptor {
94 fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ::std::io::Error> {
96 ClosureDescriptor::ForceClosed { peer_msg } => {
98 if let Some(peer_msg) = peer_msg {
100 let bytes = peer_msg.clone().into_bytes();
101 (bytes.len() as u64).write(writer)?;
102 for b in bytes.iter() {
109 ClosureDescriptor::CooperativeClosure => 1u8.write(writer)?,
110 ClosureDescriptor::CommitmentTxBroadcasted => 2u8.write(writer)?,
111 ClosureDescriptor::ProcessingError { err } => {
113 let bytes = err.clone().into_bytes();
114 (bytes.len() as u64).write(writer)?;
115 for b in bytes.iter() {
119 ClosureDescriptor::DisconnectedPeer => 4u8.write(writer)?,
125 impl Readable for ClosureDescriptor {
126 fn read<R: ::std::io::Read>(reader: &mut R) -> Result<Self, DecodeError> {
127 Ok(match <u8 as Readable>::read(reader)? {
129 let peer_msg = match <u8 as Readable>::read(reader)? {
131 let bytes_len: u64 = Readable::read(reader)?;
132 let mut bytes: Vec<u8> = Vec::with_capacity(bytes_len as usize);
133 for _ in 0..bytes_len {
134 bytes.push(Readable::read(reader)?);
136 let err = String::from_utf8(bytes).unwrap();
140 _ => return Err(DecodeError::InvalidValue),
142 ClosureDescriptor::ForceClosed { peer_msg }
144 1 => ClosureDescriptor::CooperativeClosure,
145 2 => ClosureDescriptor::CommitmentTxBroadcasted,
147 let bytes_len: u64 = Readable::read(reader)?;
148 let mut bytes: Vec<u8> = Vec::with_capacity(bytes_len as usize);
149 for _ in 0..bytes_len {
150 bytes.push(Readable::read(reader)?);
152 let err = String::from_utf8(bytes).unwrap();
153 ClosureDescriptor::ProcessingError { err }
155 4 => ClosureDescriptor::DisconnectedPeer,
156 _ => return Err(DecodeError::InvalidValue),
161 /// An Event which you should probably take some action in response to.
163 /// Note that while Writeable and Readable are implemented for Event, you probably shouldn't use
164 /// them directly as they don't round-trip exactly (for example FundingGenerationReady is never
165 /// written as it makes no sense to respond to it after reconnecting to peers).
166 #[derive(Clone, Debug)]
168 /// Used to indicate that the client should generate a funding transaction with the given
169 /// parameters and then call ChannelManager::funding_transaction_generated.
170 /// Generated in ChannelManager message handling.
171 /// Note that *all inputs* in the funding transaction must spend SegWit outputs or your
172 /// counterparty can steal your funds!
173 FundingGenerationReady {
174 /// The random channel_id we picked which you'll need to pass into
175 /// ChannelManager::funding_transaction_generated.
176 temporary_channel_id: [u8; 32],
177 /// The value, in satoshis, that the output should have.
178 channel_value_satoshis: u64,
179 /// The script which should be used in the transaction output.
180 output_script: Script,
181 /// The value passed in to ChannelManager::create_channel
182 user_channel_id: u64,
184 /// Indicates we've received money! Just gotta dig out that payment preimage and feed it to
185 /// ChannelManager::claim_funds to get it....
186 /// Note that if the preimage is not known or the amount paid is incorrect, you should call
187 /// ChannelManager::fail_htlc_backwards to free up resources for this HTLC and avoid
188 /// network congestion.
189 /// The amount paid should be considered 'incorrect' when it is less than or more than twice
190 /// the amount expected.
191 /// If you fail to call either ChannelManager::claim_funds or
192 /// ChannelManager::fail_htlc_backwards within the HTLC's timeout, the HTLC will be
193 /// automatically failed.
195 /// The hash for which the preimage should be handed to the ChannelManager.
196 payment_hash: PaymentHash,
197 /// The value, in thousandths of a satoshi, that this payment is for. Note that you must
198 /// compare this to the expected value before accepting the payment (as otherwise you are
199 /// providing proof-of-payment for less than the value you expected!).
201 /// Information for claiming this received payment, based on whether the purpose of the
202 /// payment is to pay an invoice or to send a spontaneous payment.
203 purpose: PaymentPurpose,
205 /// Indicates an outbound payment we made succeeded (i.e. it made it all the way to its target
206 /// and we got back the payment preimage for it).
208 /// Note for MPP payments: in rare cases, this event may be preceded by a `PaymentFailed` event.
209 /// In this situation, you SHOULD treat this payment as having succeeded.
211 /// The preimage to the hash given to ChannelManager::send_payment.
212 /// Note that this serves as a payment receipt, if you wish to have such a thing, you must
213 /// store it somehow!
214 payment_preimage: PaymentPreimage,
216 /// Indicates an outbound payment we made failed. Probably some intermediary node dropped
217 /// something. You may wish to retry with a different route.
219 /// The hash which was given to ChannelManager::send_payment.
220 payment_hash: PaymentHash,
221 /// Indicates the payment was rejected for some reason by the recipient. This implies that
222 /// the payment has failed, not just the route in question. If this is not set, you may
223 /// retry the payment via a different route.
224 rejected_by_dest: bool,
225 /// Any failure information conveyed via the Onion return packet by a node along the failed
228 /// Should be applied to the [`NetworkGraph`] so that routing decisions can take into
229 /// account the update. [`NetGraphMsgHandler`] is capable of doing this.
231 /// [`NetworkGraph`]: crate::routing::network_graph::NetworkGraph
232 /// [`NetGraphMsgHandler`]: crate::routing::network_graph::NetGraphMsgHandler
233 network_update: Option<NetworkUpdate>,
234 /// For both single-path and multi-path payments, this is set if all paths of the payment have
235 /// failed. This will be set to false if (1) this is an MPP payment and (2) other parts of the
236 /// larger MPP payment were still in flight when this event was generated.
237 all_paths_failed: bool,
239 error_code: Option<u16>,
241 error_data: Option<Vec<u8>>,
243 /// Used to indicate that ChannelManager::process_pending_htlc_forwards should be called at a
244 /// time in the future.
245 PendingHTLCsForwardable {
246 /// The minimum amount of time that should be waited prior to calling
247 /// process_pending_htlc_forwards. To increase the effort required to correlate payments,
248 /// you should wait a random amount of time in roughly the range (now + time_forwardable,
249 /// now + 5*time_forwardable).
250 time_forwardable: Duration,
252 /// Used to indicate that an output which you should know how to spend was confirmed on chain
253 /// and is now spendable.
254 /// Such an output will *not* ever be spent by rust-lightning, and are not at risk of your
255 /// counterparty spending them due to some kind of timeout. Thus, you need to store them
256 /// somewhere and spend them when you create on-chain transactions.
258 /// The outputs which you should store as spendable by you.
259 outputs: Vec<SpendableOutputDescriptor>,
261 /// This event is generated when a payment has been successfully forwarded through us and a
262 /// forwarding fee earned.
264 /// The fee, in milli-satoshis, which was earned as a result of the payment.
266 /// Note that if we force-closed the channel over which we forwarded an HTLC while the HTLC
267 /// was pending, the amount the next hop claimed will have been rounded down to the nearest
268 /// whole satoshi. Thus, the fee calculated here may be higher than expected as we still
269 /// claimed the full value in millisatoshis from the source. In this case,
270 /// `claim_from_onchain_tx` will be set.
272 /// If the channel which sent us the payment has been force-closed, we will claim the funds
273 /// via an on-chain transaction. In that case we do not yet know the on-chain transaction
274 /// fees which we will spend and will instead set this to `None`. It is possible duplicate
275 /// `PaymentForwarded` events are generated for the same payment iff `fee_earned_msat` is
277 fee_earned_msat: Option<u64>,
278 /// If this is `true`, the forwarded HTLC was claimed by our counterparty via an on-chain
280 claim_from_onchain_tx: bool,
282 /// Used to indicate that a channel with the given `channel_id` is in the process of closure.
283 /// Note that if you try to force-close multiple times a channel through
284 /// [`ChannelManager::force_close_channel`] before receiving the corresponding monitor
285 /// event for the broadcast of the commitment transaction, multiple `ChannelClosed` events
286 /// can be generated.
288 /// The channel_id which has been barren from further off-chain updates but
289 /// funding output might still be not resolved yet.
290 channel_id: [u8; 32],
291 /// A machine-readable error message
292 err: ClosureDescriptor
296 impl Writeable for Event {
297 fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
299 &Event::FundingGenerationReady { .. } => {
301 // We never write out FundingGenerationReady events as, upon disconnection, peers
302 // drop any channels which have not yet exchanged funding_signed.
304 &Event::PaymentReceived { ref payment_hash, ref amt, ref purpose } => {
306 let mut payment_secret = None;
307 let mut user_payment_id = None;
308 let payment_preimage;
310 PaymentPurpose::InvoicePayment { payment_preimage: preimage, payment_secret: secret, user_payment_id: id } => {
311 payment_secret = Some(secret);
312 payment_preimage = *preimage;
313 user_payment_id = Some(id);
315 PaymentPurpose::SpontaneousPayment(preimage) => {
316 payment_preimage = Some(*preimage);
319 write_tlv_fields!(writer, {
320 (0, payment_hash, required),
321 (2, payment_secret, option),
323 (6, user_payment_id, option),
324 (8, payment_preimage, option),
327 &Event::PaymentSent { ref payment_preimage } => {
329 write_tlv_fields!(writer, {
330 (0, payment_preimage, required),
333 &Event::PaymentFailed { ref payment_hash, ref rejected_by_dest, ref network_update, ref all_paths_failed,
341 error_code.write(writer)?;
343 error_data.write(writer)?;
344 write_tlv_fields!(writer, {
345 (0, payment_hash, required),
346 (1, network_update, option),
347 (2, rejected_by_dest, required),
348 (3, all_paths_failed, required),
351 &Event::PendingHTLCsForwardable { time_forwardable: _ } => {
353 write_tlv_fields!(writer, {});
354 // We don't write the time_fordwardable out at all, as we presume when the user
355 // deserializes us at least that much time has elapsed.
357 &Event::SpendableOutputs { ref outputs } => {
359 write_tlv_fields!(writer, {
360 (0, VecWriteWrapper(outputs), required),
363 &Event::PaymentForwarded { fee_earned_msat, claim_from_onchain_tx } => {
365 write_tlv_fields!(writer, {
366 (0, fee_earned_msat, option),
367 (2, claim_from_onchain_tx, required),
370 &Event::ChannelClosed { ref channel_id, ref err } => {
372 channel_id.write(writer)?;
374 write_tlv_fields!(writer, {});
380 impl MaybeReadable for Event {
381 fn read<R: io::Read>(reader: &mut R) -> Result<Option<Self>, msgs::DecodeError> {
382 match Readable::read(reader)? {
386 let mut payment_hash = PaymentHash([0; 32]);
387 let mut payment_preimage = None;
388 let mut payment_secret = None;
390 let mut user_payment_id = None;
391 read_tlv_fields!(reader, {
392 (0, payment_hash, required),
393 (2, payment_secret, option),
395 (6, user_payment_id, option),
396 (8, payment_preimage, option),
398 let purpose = match payment_secret {
399 Some(secret) => PaymentPurpose::InvoicePayment {
401 payment_secret: secret,
402 user_payment_id: if let Some(id) = user_payment_id {
404 } else { return Err(msgs::DecodeError::InvalidValue) }
406 None if payment_preimage.is_some() => PaymentPurpose::SpontaneousPayment(payment_preimage.unwrap()),
407 None => return Err(msgs::DecodeError::InvalidValue),
409 Ok(Some(Event::PaymentReceived {
419 let mut payment_preimage = PaymentPreimage([0; 32]);
420 read_tlv_fields!(reader, {
421 (0, payment_preimage, required),
423 Ok(Some(Event::PaymentSent {
432 let error_code = Readable::read(reader)?;
434 let error_data = Readable::read(reader)?;
435 let mut payment_hash = PaymentHash([0; 32]);
436 let mut rejected_by_dest = false;
437 let mut network_update = None;
438 let mut all_paths_failed = Some(true);
439 read_tlv_fields!(reader, {
440 (0, payment_hash, required),
441 (1, network_update, ignorable),
442 (2, rejected_by_dest, required),
443 (3, all_paths_failed, option),
445 Ok(Some(Event::PaymentFailed {
449 all_paths_failed: all_paths_failed.unwrap(),
460 read_tlv_fields!(reader, {});
461 Ok(Some(Event::PendingHTLCsForwardable {
462 time_forwardable: Duration::from_secs(0)
469 let mut outputs = VecReadWrapper(Vec::new());
470 read_tlv_fields!(reader, {
471 (0, outputs, required),
473 Ok(Some(Event::SpendableOutputs { outputs: outputs.0 }))
479 let mut fee_earned_msat = None;
480 let mut claim_from_onchain_tx = false;
481 read_tlv_fields!(reader, {
482 (0, fee_earned_msat, option),
483 (2, claim_from_onchain_tx, required),
485 Ok(Some(Event::PaymentForwarded { fee_earned_msat, claim_from_onchain_tx }))
490 let channel_id = Readable::read(reader)?;
491 let err = Readable::read(reader)?;
492 read_tlv_fields!(reader, {});
493 Ok(Some(Event::ChannelClosed { channel_id, err}))
495 // Versions prior to 0.0.100 did not ignore odd types, instead returning InvalidValue.
496 x if x % 2 == 1 => Ok(None),
497 _ => Err(msgs::DecodeError::InvalidValue)
502 /// An event generated by ChannelManager which indicates a message should be sent to a peer (or
503 /// broadcast to most peers).
504 /// These events are handled by PeerManager::process_events if you are using a PeerManager.
505 #[derive(Clone, Debug)]
506 pub enum MessageSendEvent {
507 /// Used to indicate that we've accepted a channel open and should send the accept_channel
508 /// message provided to the given peer.
510 /// The node_id of the node which should receive this message
512 /// The message which should be sent.
513 msg: msgs::AcceptChannel,
515 /// Used to indicate that we've initiated a channel open and should send the open_channel
516 /// message provided to the given peer.
518 /// The node_id of the node which should receive this message
520 /// The message which should be sent.
521 msg: msgs::OpenChannel,
523 /// Used to indicate that a funding_created message should be sent to the peer with the given node_id.
525 /// The node_id of the node which should receive this message
527 /// The message which should be sent.
528 msg: msgs::FundingCreated,
530 /// Used to indicate that a funding_signed message should be sent to the peer with the given node_id.
532 /// The node_id of the node which should receive this message
534 /// The message which should be sent.
535 msg: msgs::FundingSigned,
537 /// Used to indicate that a funding_locked message should be sent to the peer with the given node_id.
539 /// The node_id of the node which should receive these message(s)
541 /// The funding_locked message which should be sent.
542 msg: msgs::FundingLocked,
544 /// Used to indicate that an announcement_signatures message should be sent to the peer with the given node_id.
545 SendAnnouncementSignatures {
546 /// The node_id of the node which should receive these message(s)
548 /// The announcement_signatures message which should be sent.
549 msg: msgs::AnnouncementSignatures,
551 /// Used to indicate that a series of HTLC update messages, as well as a commitment_signed
552 /// message should be sent to the peer with the given node_id.
554 /// The node_id of the node which should receive these message(s)
556 /// The update messages which should be sent. ALL messages in the struct should be sent!
557 updates: msgs::CommitmentUpdate,
559 /// Used to indicate that a revoke_and_ack message should be sent to the peer with the given node_id.
561 /// The node_id of the node which should receive this message
563 /// The message which should be sent.
564 msg: msgs::RevokeAndACK,
566 /// Used to indicate that a closing_signed message should be sent to the peer with the given node_id.
568 /// The node_id of the node which should receive this message
570 /// The message which should be sent.
571 msg: msgs::ClosingSigned,
573 /// Used to indicate that a shutdown message should be sent to the peer with the given node_id.
575 /// The node_id of the node which should receive this message
577 /// The message which should be sent.
580 /// Used to indicate that a channel_reestablish message should be sent to the peer with the given node_id.
581 SendChannelReestablish {
582 /// The node_id of the node which should receive this message
584 /// The message which should be sent.
585 msg: msgs::ChannelReestablish,
587 /// Used to indicate that a channel_announcement and channel_update should be broadcast to all
588 /// peers (except the peer with node_id either msg.contents.node_id_1 or msg.contents.node_id_2).
590 /// Note that after doing so, you very likely (unless you did so very recently) want to call
591 /// ChannelManager::broadcast_node_announcement to trigger a BroadcastNodeAnnouncement event.
592 /// This ensures that any nodes which see our channel_announcement also have a relevant
593 /// node_announcement, including relevant feature flags which may be important for routing
594 /// through or to us.
595 BroadcastChannelAnnouncement {
596 /// The channel_announcement which should be sent.
597 msg: msgs::ChannelAnnouncement,
598 /// The followup channel_update which should be sent.
599 update_msg: msgs::ChannelUpdate,
601 /// Used to indicate that a node_announcement should be broadcast to all peers.
602 BroadcastNodeAnnouncement {
603 /// The node_announcement which should be sent.
604 msg: msgs::NodeAnnouncement,
606 /// Used to indicate that a channel_update should be broadcast to all peers.
607 BroadcastChannelUpdate {
608 /// The channel_update which should be sent.
609 msg: msgs::ChannelUpdate,
611 /// Used to indicate that a channel_update should be sent to a single peer.
612 /// In contrast to [`Self::BroadcastChannelUpdate`], this is used when the channel is a
613 /// private channel and we shouldn't be informing all of our peers of channel parameters.
615 /// The node_id of the node which should receive this message
617 /// The channel_update which should be sent.
618 msg: msgs::ChannelUpdate,
620 /// Broadcast an error downstream to be handled
622 /// The node_id of the node which should receive this message
624 /// The action which should be taken.
625 action: msgs::ErrorAction
627 /// Query a peer for channels with funding transaction UTXOs in a block range.
628 SendChannelRangeQuery {
629 /// The node_id of this message recipient
631 /// The query_channel_range which should be sent.
632 msg: msgs::QueryChannelRange,
634 /// Request routing gossip messages from a peer for a list of channels identified by
635 /// their short_channel_ids.
637 /// The node_id of this message recipient
639 /// The query_short_channel_ids which should be sent.
640 msg: msgs::QueryShortChannelIds,
642 /// Sends a reply to a channel range query. This may be one of several SendReplyChannelRange events
643 /// emitted during processing of the query.
644 SendReplyChannelRange {
645 /// The node_id of this message recipient
647 /// The reply_channel_range which should be sent.
648 msg: msgs::ReplyChannelRange,
652 /// A trait indicating an object may generate message send events
653 pub trait MessageSendEventsProvider {
654 /// Gets the list of pending events which were generated by previous actions, clearing the list
656 fn get_and_clear_pending_msg_events(&self) -> Vec<MessageSendEvent>;
659 /// A trait indicating an object may generate events.
661 /// Events are processed by passing an [`EventHandler`] to [`process_pending_events`].
665 /// See [`process_pending_events`] for requirements around event processing.
667 /// When using this trait, [`process_pending_events`] will call [`handle_event`] for each pending
668 /// event since the last invocation. The handler must either act upon the event immediately
669 /// or preserve it for later handling.
671 /// Note, handlers may call back into the provider and thus deadlocking must be avoided. Be sure to
672 /// consult the provider's documentation on the implication of processing events and how a handler
673 /// may safely use the provider (e.g., see [`ChannelManager::process_pending_events`] and
674 /// [`ChainMonitor::process_pending_events`]).
676 /// (C-not implementable) As there is likely no reason for a user to implement this trait on their
679 /// [`process_pending_events`]: Self::process_pending_events
680 /// [`handle_event`]: EventHandler::handle_event
681 /// [`ChannelManager::process_pending_events`]: crate::ln::channelmanager::ChannelManager#method.process_pending_events
682 /// [`ChainMonitor::process_pending_events`]: crate::chain::chainmonitor::ChainMonitor#method.process_pending_events
683 pub trait EventsProvider {
684 /// Processes any events generated since the last call using the given event handler.
686 /// Subsequent calls must only process new events. However, handlers must be capable of handling
687 /// duplicate events across process restarts. This may occur if the provider was recovered from
688 /// an old state (i.e., it hadn't been successfully persisted after processing pending events).
689 fn process_pending_events<H: Deref>(&self, handler: H) where H::Target: EventHandler;
692 /// A trait implemented for objects handling events from [`EventsProvider`].
693 pub trait EventHandler {
694 /// Handles the given [`Event`].
696 /// See [`EventsProvider`] for details that must be considered when implementing this method.
697 fn handle_event(&self, event: &Event);
700 impl<F> EventHandler for F where F: Fn(&Event) {
701 fn handle_event(&self, event: &Event) {