Move code from sc-network-common back to sc-network (#13592)

* Move service tests to `client/network/tests`

These tests depend on `sc-network` and `sc-network-sync` so they should
live outside the crate.

* Move some configs from `sc-network-common` to `sc-network`

* Move `NetworkService` traits to `sc-network`

* Move request-responses to `sc-network`

* Remove more stuff

* Remove rest of configs from `sc-network-common` to `sc-network`

* Remove more stuff

* Fix warnings

* Update client/network/src/request_responses.rs

Co-authored-by: Dmitry Markin <dmitry@markin.tech>

* Fix cargo doc

---------

Co-authored-by: Dmitry Markin <dmitry@markin.tech>

substrate/client/network/src/utils.rs

@@ -0,0 +1,88 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+//! `sc-network` utilities
+
+use futures::{stream::unfold, FutureExt, Stream, StreamExt};
+use futures_timer::Delay;
+use linked_hash_set::LinkedHashSet;
+
+use std::{hash::Hash, num::NonZeroUsize, time::Duration};
+
+/// Creates a stream that returns a new value every `duration`.
+pub fn interval(duration: Duration) -> impl Stream<Item = ()> + Unpin {
+	unfold((), move |_| Delay::new(duration).map(|_| Some(((), ())))).map(drop)
+}
+
+/// Wrapper around `LinkedHashSet` with bounded growth.
+///
+/// In the limit, for each element inserted the oldest existing element will be removed.
+#[derive(Debug, Clone)]
+pub struct LruHashSet<T: Hash + Eq> {
+	set: LinkedHashSet<T>,
+	limit: NonZeroUsize,
+}
+
+impl<T: Hash + Eq> LruHashSet<T> {
+	/// Create a new `LruHashSet` with the given (exclusive) limit.
+	pub fn new(limit: NonZeroUsize) -> Self {
+		Self { set: LinkedHashSet::new(), limit }
+	}
+
+	/// Insert element into the set.
+	///
+	/// Returns `true` if this is a new element to the set, `false` otherwise.
+	/// Maintains the limit of the set by removing the oldest entry if necessary.
+	/// Inserting the same element will update its LRU position.
+	pub fn insert(&mut self, e: T) -> bool {
+		if self.set.insert(e) {
+			if self.set.len() == usize::from(self.limit) {
+				self.set.pop_front(); // remove oldest entry
+			}
+			return true
+		}
+		false
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn maintains_limit() {
+		let three = NonZeroUsize::new(3).unwrap();
+		let mut set = LruHashSet::<u8>::new(three);
+
+		// First element.
+		assert!(set.insert(1));
+		assert_eq!(vec![&1], set.set.iter().collect::<Vec<_>>());
+
+		// Second element.
+		assert!(set.insert(2));
+		assert_eq!(vec![&1, &2], set.set.iter().collect::<Vec<_>>());
+
+		// Inserting the same element updates its LRU position.
+		assert!(!set.insert(1));
+		assert_eq!(vec![&2, &1], set.set.iter().collect::<Vec<_>>());
+
+		// We reached the limit. The next element forces the oldest one out.
+		assert!(set.insert(3));
+		assert_eq!(vec![&1, &3], set.set.iter().collect::<Vec<_>>());
+	}
+}