Optimize offchain worker api by re-using http-client (#6454)

* Fix typo in offchain's docs

* Use Self keyword in AsyncApi::new()

* Move httpclient to be part of OffchainWorkers to optimize block import

* Fix compilation errors for tests

* Add wrapper struct for HyperClient

* Use lazy_static share SharedClient amongst OffchainWorkers. Remove the need to raise the fd limit

* Revert "Use lazy_static share SharedClient amongst OffchainWorkers. Remove the need to raise the fd limit"

This reverts commit 7af9749.

* Add lazy_static for tests

client/offchain/Cargo.toml

@@ -37,12 +37,12 @@ hyper-rustls = "0.20"
 
 [dev-dependencies]
 env_logger = "0.7.0"
-fdlimit = "0.1.4"
 sc-client-db = { version = "0.8.0-rc3", default-features = true, path = "../db/" }
 sc-transaction-pool = { version = "2.0.0-rc3", path = "../../client/transaction-pool" }
 sp-transaction-pool = { version = "2.0.0-rc3", path = "../../primitives/transaction-pool" }
 substrate-test-runtime-client = { version = "2.0.0-rc3", path = "../../test-utils/runtime/client" }
 tokio = "0.2"
+lazy_static = "1.4.0"
 
 [features]
 default = []

client/offchain/src/api.rs

@@ -31,6 +31,7 @@ use sp_core::offchain::{
 	OpaqueNetworkState, OpaquePeerId, OpaqueMultiaddr, StorageKind,
 };
 pub use sp_offchain::STORAGE_PREFIX;
+pub use http::SharedClient;
 
 #[cfg(not(target_os = "unknown"))]
 mod http;
@@ -260,8 +261,9 @@ impl AsyncApi {
 		db: S,
 		network_state: Arc<dyn NetworkStateInfo + Send + Sync>,
 		is_validator: bool,
-	) -> (Api<S>, AsyncApi) {
-		let (http_api, http_worker) = http::http();
+		shared_client: SharedClient,
+	) -> (Api<S>, Self) {
+		let (http_api, http_worker) = http::http(shared_client);
 
 		let api = Api {
 			db,
@@ -270,7 +272,7 @@ impl AsyncApi {
 			http: http_api,
 		};
 
-		let async_api = AsyncApi {
+		let async_api = Self {
 			http: Some(http_worker),
 		};
 
@@ -308,11 +310,14 @@ mod tests {
 		let _ = env_logger::try_init();
 		let db = LocalStorage::new_test();
 		let mock = Arc::new(MockNetworkStateInfo());
+		let shared_client = SharedClient::new();
+
 
 		AsyncApi::new(
 			db,
 			mock,
 			false,
+			shared_client,
 		)
 	}
 

client/offchain/src/api/http.rs

@@ -33,9 +33,22 @@ use log::error;
 use sp_core::offchain::{HttpRequestId, Timestamp, HttpRequestStatus, HttpError};
 use std::{convert::TryFrom, fmt, io::Read as _, pin::Pin, task::{Context, Poll}};
 use sp_utils::mpsc::{tracing_unbounded, TracingUnboundedSender, TracingUnboundedReceiver};
+use std::sync::Arc;
+use hyper::{Client as HyperClient, Body, client};
+use hyper_rustls::HttpsConnector;
+
+/// Wrapper struct used for keeping the hyper_rustls client running.
+#[derive(Clone)]
+pub struct SharedClient(Arc<HyperClient<HttpsConnector<client::HttpConnector>, Body>>);
+
+impl SharedClient {
+	pub fn new() -> Self {
+		Self(Arc::new(HyperClient::builder().build(HttpsConnector::new())))
+	}
+}
 
 /// Creates a pair of [`HttpApi`] and [`HttpWorker`].
-pub fn http() -> (HttpApi, HttpWorker) {
+pub fn http(shared_client: SharedClient) -> (HttpApi, HttpWorker) {
 	let (to_worker, from_api) = tracing_unbounded("mpsc_ocw_to_worker");
 	let (to_api, from_worker) = tracing_unbounded("mpsc_ocw_to_api");
 
@@ -51,7 +64,7 @@ pub fn http() -> (HttpApi, HttpWorker) {
 	let engine = HttpWorker {
 		to_api,
 		from_api,
-		http_client: hyper::Client::builder().build(hyper_rustls::HttpsConnector::new()),
+		http_client: shared_client.0,
 		requests: Vec::new(),
 	};
 
@@ -551,7 +564,7 @@ pub struct HttpWorker {
 	/// Used to receive messages from the `HttpApi`.
 	from_api: TracingUnboundedReceiver<ApiToWorker>,
 	/// The engine that runs HTTP requests.
-	http_client: hyper::Client<hyper_rustls::HttpsConnector<hyper::client::HttpConnector>, hyper::Body>,
+	http_client: Arc<HyperClient<HttpsConnector<client::HttpConnector>, Body>>,
 	/// HTTP requests that are being worked on by the engine.
 	requests: Vec<(HttpRequestId, HttpWorkerRequest)>,
 }
@@ -685,21 +698,23 @@ impl fmt::Debug for HttpWorkerRequest {
 mod tests {
 	use core::convert::Infallible;
 	use crate::api::timestamp;
-	use super::http;
+	use super::{http, SharedClient};
 	use sp_core::offchain::{HttpError, HttpRequestId, HttpRequestStatus, Duration};
 	use futures::future;
+	use lazy_static::lazy_static;
+
+	// Using lazy_static to avoid spawning lots of different SharedClients,
+	// as spawning a SharedClient is CPU-intensive and opens lots of fds.
+	lazy_static! {
+		static ref SHARED_CLIENT: SharedClient = SharedClient::new();
+	}
 
 	// Returns an `HttpApi` whose worker is ran in the background, and a `SocketAddr` to an HTTP
 	// server that runs in the background as well.
 	macro_rules! build_api_server {
 		() => {{
-			// We spawn quite a bit of HTTP servers here due to how async API
-			// works for offchain workers, so be sure to raise the FD limit
-			// (particularly useful for macOS where the default soft limit may
-			// not be enough).
-			fdlimit::raise_fd_limit();
-
-			let (api, worker) = http();
+			let hyper_client = SHARED_CLIENT.clone();
+			let (api, worker) = http(hyper_client.clone());
 
 			let (addr_tx, addr_rx) = std::sync::mpsc::channel();
 			std::thread::spawn(move || {

client/offchain/src/api/http_dummy.rs

@@ -19,8 +19,18 @@
 use sp_core::offchain::{HttpRequestId, Timestamp, HttpRequestStatus, HttpError};
 use std::{future::Future, pin::Pin, task::Context, task::Poll};
 
+/// Wrapper struct (wrapping nothing in case of http_dummy) used for keeping the hyper_rustls client running.
+#[derive(Clone)]
+pub struct SharedClient;
+
+impl SharedClient {
+	pub fn new() -> Self {
+		Self
+	}
+}
+
 /// Creates a pair of [`HttpApi`] and [`HttpWorker`].
-pub fn http() -> (HttpApi, HttpWorker) {
+pub fn http(_: SharedClient) -> (HttpApi, HttpWorker) {
 	(HttpApi, HttpWorker)
 }
 

client/offchain/src/lib.rs

@@ -19,7 +19,7 @@
 //! The offchain workers is a special function of the runtime that
 //! gets executed after block is imported. During execution
 //! it's able to asynchronously submit extrinsics that will either
-//! be propagated to other nodes added to the next block
+//! be propagated to other nodes or added to the next block
 //! produced by the node as unsigned transactions.
 //!
 //! Offchain workers can be used for computation-heavy tasks
@@ -46,6 +46,7 @@ use sp_runtime::{generic::BlockId, traits::{self, Header}};
 use futures::{prelude::*, future::ready};
 
 mod api;
+use api::SharedClient;
 
 pub use sp_offchain::{OffchainWorkerApi, STORAGE_PREFIX};
 
@@ -55,16 +56,19 @@ pub struct OffchainWorkers<Client, Storage, Block: traits::Block> {
 	db: Storage,
 	_block: PhantomData<Block>,
 	thread_pool: Mutex<ThreadPool>,
+	shared_client: SharedClient,
 }
 
 impl<Client, Storage, Block: traits::Block> OffchainWorkers<Client, Storage, Block> {
 	/// Creates new `OffchainWorkers`.
 	pub fn new(client: Arc<Client>, db: Storage) -> Self {
+		let shared_client = SharedClient::new();
 		Self {
 			client,
 			db,
 			_block: PhantomData,
 			thread_pool: Mutex::new(ThreadPool::new(num_cpus::get())),
+			shared_client,
 		}
 	}
 }
@@ -120,6 +124,7 @@ impl<Client, Storage, Block> OffchainWorkers<
 				self.db.clone(),
 				network_state.clone(),
 				is_validator,
+				self.shared_client.clone(),
 			);
 			debug!("Spawning offchain workers at {:?}", at);
 			let header = header.clone();