Add a trivial benchmark of calculating routes on today's graph

Sadly rust upstream never really figured out the benchmark story,
and it looks like the API we use here may not be long for this
world. Luckily, we can switch to criterion with largely the same
API if that happens before upstream finishes ongoing work with the
custom test framework stuff.

Sadly, it requires fetching the current network graph, which I did
using Val's route-testing script written to test the MPP router.

Author: TheBlueMatt

lightning/Cargo.toml

@@ -23,6 +23,7 @@ max_level_debug = []
 # Allow signing of local transactions that may have been revoked or will be revoked, for functional testing (e.g. justice tx handling).
 # This is unsafe to use in production because it may result in the counterparty publishing taking our funds.
 unsafe_revoked_tx_signing = []
+unstable = []
 
 [dependencies]
 bitcoin = "0.24"

lightning/src/lib.rs

@@ -27,6 +27,9 @@
 #![allow(bare_trait_objects)]
 #![allow(ellipsis_inclusive_range_patterns)]
 
+#![cfg_attr(all(test, feature = "unstable"), feature(test))]
+#[cfg(all(test, feature = "unstable"))] extern crate test;
+
 extern crate bitcoin;
 #[cfg(any(test, feature = "_test_utils"))] extern crate hex;
 #[cfg(any(test, feature = "fuzztarget", feature = "_test_utils"))] extern crate regex;

lightning/src/routing/router.rs

@@ -1279,3 +1279,47 @@ mod tests {
 		assert_eq!(route.paths[0][1].channel_features.le_flags(), &[0; 0]); // We can't learn any flags from invoices, sadly
 	}
 }
+
+#[cfg(all(test, feature = "unstable"))]
+mod benches {
+	use super::*;
+	use util::logger::{Logger, Record};
+
+	use std::fs::File;
+	use test::Bencher;
+
+	struct DummyLogger {}
+	impl Logger for DummyLogger {
+		fn log(&self, _record: &Record) {}
+	}
+
+	#[bench]
+	fn generate_routes(bench: &mut Bencher) {
+		let mut d = File::open("net_graph-2021-02-12.bin").expect("Please fetch https://bitcoin.ninja/ldk-net_graph-879e309c128-2020-02-12.bin and place it at lightning/net_graph-2021-02-12.bin");
+		let graph = NetworkGraph::read(&mut d).unwrap();
+
+		// First, get 100 (source, destination) pairs for which route-getting actually succeeds...
+		let mut path_endpoints = Vec::new();
+		let mut seed: usize = 0xdeadbeef;
+		'load_endpoints: for _ in 0..100 {
+			loop {
+				seed *= 0xdeadbeef;
+				let src = graph.get_nodes().keys().skip(seed % graph.get_nodes().len()).next().unwrap();
+				seed *= 0xdeadbeef;
+				let dst = graph.get_nodes().keys().skip(seed % graph.get_nodes().len()).next().unwrap();
+				if get_route(src, &graph, dst, None, &[], seed as u64 % 1_000_000, 42, &DummyLogger{}).is_ok() {
+					path_endpoints.push((src, dst));
+					continue 'load_endpoints;
+				}
+			}
+		}
+
+		// ...then benchmark finding paths between the nodes we learned.
+		let mut idx = 0;
+		bench.iter(|| {
+			let (src, dst) = path_endpoints[idx % path_endpoints.len()];
+			assert!(get_route(src, &graph, dst, None, &[], seed as u64 % 1_000_000, 42, &DummyLogger{}).is_ok());
+			idx += 1;
+		});
+	}
+}