Introduce structured, span-based observability through Logger interface

This change allows users to create hierarchical span objects through the
Logger interface for specific computations, such as the handling of
HTLCs. These span objects will be held in LDK across the corresponding
lifetimes before being dropped, providing insight in durations and
latencies.

Author: wvanlint

lightning-dns-resolver/src/lib.rs

@@ -176,7 +176,7 @@ mod test {
 	use lightning::sign::{KeysManager, NodeSigner, Recipient};
 	use lightning::types::features::InitFeatures;
 	use lightning::types::payment::PaymentHash;
-	use lightning::util::logger::Logger;
+	use lightning::util::logger::{Logger, Span};
 
 	use lightning::{
 		commitment_signed_dance, expect_payment_claimed, expect_pending_htlcs_forwardable,
@@ -191,9 +191,13 @@ mod test {
 		node: &'static str,
 	}
 	impl Logger for TestLogger {
+		type UserSpan = ();
+
 		fn log(&self, record: lightning::util::logger::Record) {
 			eprintln!("{}: {}", self.node, record.args);
 		}
+
+		fn start(&self, _span: Span, _parent: Option<&()>) -> () {}
 	}
 	impl Deref for TestLogger {
 		type Target = TestLogger;

lightning-net-tokio/src/lib.rs

@@ -640,6 +640,8 @@ mod tests {
 
 	pub struct TestLogger();
 	impl lightning::util::logger::Logger for TestLogger {
+		type UserSpan = ();
+
 		fn log(&self, record: lightning::util::logger::Record) {
 			println!(
 				"{:<5} [{} : {}, {}] {}",
@@ -650,6 +652,8 @@ mod tests {
 				record.args
 			);
 		}
+
+		fn start(&self, _span: lightning::util::logger::Span, _parent: Option<&()>) -> () {}
 	}
 
 	struct MsgHandler {

lightning-rapid-gossip-sync/src/lib.rs

@@ -51,10 +51,12 @@
 //! use lightning::routing::gossip::NetworkGraph;
 //! use lightning_rapid_gossip_sync::RapidGossipSync;
 //!
-//! # use lightning::util::logger::{Logger, Record};
+//! # use lightning::util::logger::{Logger, Record, Span};
 //! # struct FakeLogger {}
 //! # impl Logger for FakeLogger {
+//! #     type UserSpan = ();
 //! #     fn log(&self, record: Record) { }
+//! #     fn start(&self, _span: Span, parent: Option<&()>) -> () {}
 //! # }
 //! # let logger = FakeLogger {};
 //!

lightning/src/chain/channelmonitor.rs

@@ -48,7 +48,7 @@ use crate::sign::{ChannelDerivationParameters, HTLCDescriptor, SpendableOutputDe
 use crate::chain::onchaintx::{ClaimEvent, FeerateStrategy, OnchainTxHandler};
 use crate::chain::package::{CounterpartyOfferedHTLCOutput, CounterpartyReceivedHTLCOutput, HolderFundingOutput, HolderHTLCOutput, PackageSolvingData, PackageTemplate, RevokedOutput, RevokedHTLCOutput};
 use crate::chain::Filter;
-use crate::util::logger::{Logger, Record};
+use crate::util::logger::{Logger, Record, Span};
 use crate::util::persist::MonitorName;
 use crate::util::ser::{Readable, ReadableArgs, RequiredWrapper, MaybeReadable, UpgradableRequired, Writer, Writeable, U48};
 use crate::util::byte_utils;
@@ -1471,12 +1471,18 @@ pub(crate) struct WithChannelMonitor<'a, L: Deref> where L::Target: Logger {
 }
 
 impl<'a, L: Deref> Logger for WithChannelMonitor<'a, L> where L::Target: Logger {
+	type UserSpan = <<L as Deref>::Target as Logger>::UserSpan;
+
 	fn log(&self, mut record: Record) {
 		record.peer_id = self.peer_id;
 		record.channel_id = self.channel_id;
 		record.payment_hash = self.payment_hash;
 		self.logger.log(record)
 	}
+
+	fn start(&self, span: Span, parent: Option<&Self::UserSpan>) -> Self::UserSpan {
+		self.logger.start(span, parent)
+	}
 }
 
 impl<'a, L: Deref> WithChannelMonitor<'a, L> where L::Target: Logger {