Add benchmark of deserializing a NetworkGraph.

NetworkGraph is one of the largest structures we generally
deserialize, so it makes for a good benchmark, even if it isn't the
most complicated one.

As of this commit, on an Intel 2687W v3, these benchmarks take:

test routing::network_graph::benches::read_network_graph  ... bench: 2,101,420,078 ns/iter (+/- 6,649,020)
test routing::network_graph::benches::write_network_graph ... bench: 344,696,835 ns/iter (+/- 229,061)

lightning/src/routing/network_graph.rs

@@ -2424,3 +2424,30 @@ mod tests {
 		assert!(result.is_err());
 	}
 }
+
+#[cfg(all(test, feature = "unstable"))]
+mod benches {
+	use super::*;
+
+	use test::Bencher;
+	use std::io::Read;
+
+	#[bench]
+	fn read_network_graph(bench: &mut Bencher) {
+		let mut d = ::routing::router::test_utils::get_route_file().unwrap();
+		let mut v = Vec::new();
+		d.read_to_end(&mut v).unwrap();
+		bench.iter(|| {
+			let _ = NetworkGraph::read(&mut std::io::Cursor::new(&v)).unwrap();
+		});
+	}
+
+	#[bench]
+	fn write_network_graph(bench: &mut Bencher) {
+		let mut d = ::routing::router::test_utils::get_route_file().unwrap();
+		let net_graph = NetworkGraph::read(&mut d).unwrap();
+		bench.iter(|| {
+			let _ = net_graph.encode();
+		});
+	}
+}

lightning/src/routing/router.rs

@@ -3856,30 +3856,6 @@ mod tests {
 		}
 	}
 
-	use std::fs::File;
-	use util::ser::Readable;
-	/// Tries to open a network graph file, or panics with a URL to fetch it.
-	pub(super) fn get_route_file() -> Result<std::fs::File, std::io::Error> {
-		let res = File::open("net_graph-2021-05-27.bin") // By default we're run in RL/lightning
-			.or_else(|_| File::open("lightning/net_graph-2021-05-27.bin")) // We may be run manually in RL/
-			.or_else(|_| { // Fall back to guessing based on the binary location
-				// path is likely something like .../rust-lightning/target/debug/deps/lightning-...
-				let mut path = std::env::current_exe().unwrap();
-				path.pop(); // lightning-...
-				path.pop(); // deps
-				path.pop(); // debug
-				path.pop(); // target
-				path.push("lightning");
-				path.push("net_graph-2021-05-27.bin");
-				eprintln!("{}", path.to_str().unwrap());
-				File::open(path)
-			});
-		#[cfg(require_route_graph_test)]
-		return Ok(res.expect("Didn't have route graph and was configured to require it"));
-		#[cfg(not(require_route_graph_test))]
-		return res;
-	}
-
 	pub(super) fn random_init_seed() -> u64 {
 		// Because the default HashMap in std pulls OS randomness, we can use it as a (bad) RNG.
 		use core::hash::{BuildHasher, Hasher};
@@ -3887,13 +3863,14 @@ mod tests {
 		println!("Using seed of {}", seed);
 		seed
 	}
+	use util::ser::Readable;
 
 	#[test]
 	fn generate_routes() {
-		let mut d = match get_route_file() {
+		let mut d = match super::test_utils::get_route_file() {
 			Ok(f) => f,
-			Err(_) => {
+			Err(e) => {
-				eprintln!("Please fetch https://bitcoin.ninja/ldk-net_graph-45d86ead641d-2021-05-27.bin and place it at lightning/net_graph-2021-05-27.bin");
+				eprintln!("{}", e);
 				return;
 			},
 		};
@@ -3917,10 +3894,10 @@ mod tests {
 
 	#[test]
 	fn generate_routes_mpp() {
-		let mut d = match get_route_file() {
+		let mut d = match super::test_utils::get_route_file() {
 			Ok(f) => f,
-			Err(_) => {
+			Err(e) => {
-				eprintln!("Please fetch https://bitcoin.ninja/ldk-net_graph-45d86ead641d-2021-05-27.bin and place it at lightning/net_graph-2021-05-27.bin");
+				eprintln!("{}", e);
 				return;
 			},
 		};
@@ -3943,12 +3920,38 @@ mod tests {
 	}
 }
 
+#[cfg(test)]
+pub(crate) mod test_utils {
+	use std::fs::File;
+	/// Tries to open a network graph file, or panics with a URL to fetch it.
+	pub(crate) fn get_route_file() -> Result<std::fs::File, &'static str> {
+		let res = File::open("net_graph-2021-05-27.bin") // By default we're run in RL/lightning
+			.or_else(|_| File::open("lightning/net_graph-2021-05-27.bin")) // We may be run manually in RL/
+			.or_else(|_| { // Fall back to guessing based on the binary location
+				// path is likely something like .../rust-lightning/target/debug/deps/lightning-...
+				let mut path = std::env::current_exe().unwrap();
+				path.pop(); // lightning-...
+				path.pop(); // deps
+				path.pop(); // debug
+				path.pop(); // target
+				path.push("lightning");
+				path.push("net_graph-2021-05-27.bin");
+				eprintln!("{}", path.to_str().unwrap());
+				File::open(path)
+			})
+		.map_err(|_| "Please fetch https://bitcoin.ninja/ldk-net_graph-45d86ead641d-2021-05-27.bin and place it at lightning/net_graph-2021-05-27.bin");
+		#[cfg(require_route_graph_test)]
+		return Ok(res.unwrap());
+		#[cfg(not(require_route_graph_test))]
+		return res;
+	}
+}
+
 #[cfg(all(test, feature = "unstable"))]
 mod benches {
 	use super::*;
 	use util::logger::{Logger, Record};
 
-	use prelude::*;
 	use test::Bencher;
 
 	struct DummyLogger {}
@@ -3958,8 +3961,7 @@ mod benches {
 
 	#[bench]
 	fn generate_routes(bench: &mut Bencher) {
-		let mut d = tests::get_route_file()
+		let mut d = test_utils::get_route_file().unwrap();
-			.expect("Please fetch https://bitcoin.ninja/ldk-net_graph-45d86ead641d-2021-05-27.bin and place it at lightning/net_graph-2021-05-27.bin");
 		let graph = NetworkGraph::read(&mut d).unwrap();
 
 		// First, get 100 (source, destination) pairs for which route-getting actually succeeds...
@@ -3990,8 +3992,7 @@ mod benches {
 
 	#[bench]
 	fn generate_mpp_routes(bench: &mut Bencher) {
-		let mut d = tests::get_route_file()
+		let mut d = test_utils::get_route_file().unwrap();
-			.expect("Please fetch https://bitcoin.ninja/ldk-net_graph-45d86ead641d-2021-05-27.bin and place it at lightning/net_graph-2021-05-27.bin");
 		let graph = NetworkGraph::read(&mut d).unwrap();
 
 		// First, get 100 (source, destination) pairs for which route-getting actually succeeds...