// Copyright 2019-2021 Parity Technologies (UK) Ltd.
//
// Permission is hereby granted, free of charge, to any
// person obtaining a copy of this software and associated
// documentation files (the "Software"), to deal in the
// Software without restriction, including without
// limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of
// the Software, and to permit persons to whom the Software
// is furnished to do so, subject to the following
// conditions:
//
// The above copyright notice and this permission notice
// shall be included in all copies or substantial portions
// of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
// ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
// TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
// PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
// SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
// IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

use std::future::Future;
use std::net::SocketAddr;
use std::pin::Pin;
use std::sync::Arc;
use std::task::{Context, Poll};
use std::time::Duration;

use crate::future::{FutureDriver, ServerHandle, StopMonitor};
use crate::types::error::{ErrorCode, ErrorObject, BATCHES_NOT_SUPPORTED_CODE, BATCHES_NOT_SUPPORTED_MSG};
use crate::types::{Id, Request};
use futures_channel::mpsc;
use futures_util::future::{join_all, Either, FutureExt};
use futures_util::io::{BufReader, BufWriter};
use futures_util::stream::StreamExt;
use jsonrpsee_core::id_providers::RandomIntegerIdProvider;
use jsonrpsee_core::middleware::Middleware;
use jsonrpsee_core::server::access_control::AccessControl;
use jsonrpsee_core::server::helpers::{collect_batch_response, prepare_error, BoundedSubscriptions, MethodSink};
use jsonrpsee_core::server::resource_limiting::Resources;
use jsonrpsee_core::server::rpc_module::{ConnState, ConnectionId, MethodKind, Methods};
use jsonrpsee_core::traits::IdProvider;
use jsonrpsee_core::{Error, TEN_MB_SIZE_BYTES};
use jsonrpsee_types::error::{reject_too_big_request, reject_too_many_subscriptions};
use jsonrpsee_types::Params;
use soketto::connection::Error as SokettoError;
use soketto::data::ByteSlice125;
use soketto::handshake::{server::Response, Server as SokettoServer};
use soketto::Sender;
use tokio::net::{TcpListener, TcpStream, ToSocketAddrs};
use tokio_stream::wrappers::IntervalStream;
use tokio_util::compat::{Compat, TokioAsyncReadCompatExt};

/// Default maximum connections allowed.
const MAX_CONNECTIONS: u64 = 100;

/// A WebSocket JSON RPC server.
pub struct Server<M> {
	listener: TcpListener,
	cfg: Settings,
	stop_monitor: StopMonitor,
	resources: Resources,
	middleware: M,
	id_provider: Arc<dyn IdProvider>,
}

impl<M> std::fmt::Debug for Server<M> {
	fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
		f.debug_struct("Server")
			.field("listener", &self.listener)
			.field("cfg", &self.cfg)
			.field("stop_monitor", &self.stop_monitor)
			.field("id_provider", &self.id_provider)
			.field("resources", &self.resources)
			.finish()
	}
}

impl<M: Middleware> Server<M> {
	/// Returns socket address to which the server is bound.
	pub fn local_addr(&self) -> Result<SocketAddr, Error> {
		self.listener.local_addr().map_err(Into::into)
	}

	/// Returns the handle to stop the running server.
	pub fn server_handle(&self) -> ServerHandle {
		self.stop_monitor.handle()
	}

	/// Start responding to connections requests. This will run on the tokio runtime until the server is stopped.
	pub fn start(mut self, methods: impl Into<Methods>) -> Result<ServerHandle, Error> {
		let methods = methods.into().initialize_resources(&self.resources)?;
		let handle = self.server_handle();

		match self.cfg.tokio_runtime.take() {
			Some(rt) => rt.spawn(self.start_inner(methods)),
			None => tokio::spawn(self.start_inner(methods)),
		};

		Ok(handle)
	}

	async fn start_inner(self, methods: Methods) {
		let stop_monitor = self.stop_monitor;
		let resources = self.resources;
		let middleware = self.middleware;

		let mut id = 0;
		let mut connections = FutureDriver::default();
		let mut incoming = Monitored::new(Incoming(self.listener), &stop_monitor);

		loop {
			match connections.select_with(&mut incoming).await {
				Ok((socket, _addr)) => {
					if let Err(e) = socket.set_nodelay(true) {
						tracing::error!("Could not set NODELAY on socket: {:?}", e);
						continue;
					}

					if connections.count() >= self.cfg.max_connections as usize {
						tracing::warn!("Too many connections. Try again in a while.");
						connections.add(Box::pin(handshake(socket, HandshakeResponse::Reject { status_code: 429 })));
						continue;
					}

					let methods = &methods;
					let cfg = &self.cfg;
					let id_provider = self.id_provider.clone();

					connections.add(Box::pin(handshake(
						socket,
						HandshakeResponse::Accept {
							conn_id: id,
							methods,
							resources: &resources,
							cfg,
							stop_monitor: &stop_monitor,
							middleware: middleware.clone(),
							id_provider,
						},
					)));

					tracing::info!("Accepting new connection, {}/{}", connections.count(), self.cfg.max_connections);

					id = id.wrapping_add(1);
				}
				Err(MonitoredError::Selector(err)) => {
					tracing::error!("Error while awaiting a new connection: {:?}", err);
				}
				Err(MonitoredError::Shutdown) => break,
			}
		}

		connections.await
	}
}

/// This is a glorified select listening for new messages, while also checking the `stop_receiver` signal.
struct Monitored<'a, F> {
	future: F,
	stop_monitor: &'a StopMonitor,
}

impl<'a, F> Monitored<'a, F> {
	fn new(future: F, stop_monitor: &'a StopMonitor) -> Self {
		Monitored { future, stop_monitor }
	}
}

enum MonitoredError<E> {
	Shutdown,
	Selector(E),
}

struct Incoming(TcpListener);

impl<'a> Future for Monitored<'a, Incoming> {
	type Output = Result<(TcpStream, SocketAddr), MonitoredError<std::io::Error>>;

	fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
		let this = Pin::into_inner(self);

		if this.stop_monitor.shutdown_requested() {
			return Poll::Ready(Err(MonitoredError::Shutdown));
		}

		this.future.0.poll_accept(cx).map_err(MonitoredError::Selector)
	}
}

impl<'a, 'f, F, T, E> Future for Monitored<'a, Pin<&'f mut F>>
where
	F: Future<Output = Result<T, E>>,
{
	type Output = Result<T, MonitoredError<E>>;

	fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
		let this = Pin::into_inner(self);

		if this.stop_monitor.shutdown_requested() {
			return Poll::Ready(Err(MonitoredError::Shutdown));
		}

		this.future.poll_unpin(cx).map_err(MonitoredError::Selector)
	}
}

enum HandshakeResponse<'a, M> {
	Reject {
		status_code: u16,
	},
	Accept {
		conn_id: ConnectionId,
		methods: &'a Methods,
		resources: &'a Resources,
		cfg: &'a Settings,
		stop_monitor: &'a StopMonitor,
		middleware: M,
		id_provider: Arc<dyn IdProvider>,
	},
}

async fn handshake<M>(socket: tokio::net::TcpStream, mode: HandshakeResponse<'_, M>) -> Result<(), Error>
where
	M: Middleware,
{
	// For each incoming background_task we perform a handshake.
	let mut server = SokettoServer::new(BufReader::new(BufWriter::new(socket.compat())));

	match mode {
		HandshakeResponse::Reject { status_code } => {
			// Forced rejection, don't need to read anything from the socket
			let reject = Response::Reject { status_code };
			server.send_response(&reject).await?;

			let (mut sender, _) = server.into_builder().finish();

			// Gracefully shut down the connection
			sender.close().await?;

			Ok(())
		}
		HandshakeResponse::Accept { conn_id, methods, resources, cfg, stop_monitor, middleware, id_provider } => {
			tracing::debug!("Accepting new connection: {}", conn_id);
			let key = {
				let req = server.receive_request().await?;

				let host = std::str::from_utf8(req.headers().host)
					.map_err(|_e| Error::HttpHeaderRejected("Host", "Invalid UTF-8".to_string()))?;
				let origin = req.headers().origin.and_then(|h| {
					let res = std::str::from_utf8(h).ok();
					if res.is_none() {
						tracing::warn!("Origin header invalid UTF-8; treated as no Origin header");
					}
					res
				});

				let host_check = cfg.access_control.verify_host(host);
				let origin_check = cfg.access_control.verify_origin(origin, host);

				host_check.and(origin_check).map(|()| req.key())
			};

			match key {
				Ok(key) => {
					let accept = Response::Accept { key, protocol: None };
					server.send_response(&accept).await?;
				}
				Err(err) => {
					tracing::warn!("Rejected connection: {:?}", err);
					let reject = Response::Reject { status_code: 403 };
					server.send_response(&reject).await?;

					return Err(err);
				}
			}

			let join_result = tokio::spawn(background_task(
				server,
				conn_id,
				methods.clone(),
				resources.clone(),
				cfg.max_request_body_size,
				cfg.max_response_body_size,
				cfg.batch_requests_supported,
				BoundedSubscriptions::new(cfg.max_subscriptions_per_connection),
				stop_monitor.clone(),
				middleware,
				id_provider,
				cfg.ping_interval,
			))
			.await;

			match join_result {
				Err(_) => Err(Error::Custom("Background task was aborted".into())),
				Ok(result) => result,
			}
		}
	}
}

async fn background_task(
	server: SokettoServer<'_, BufReader<BufWriter<Compat<tokio::net::TcpStream>>>>,
	conn_id: ConnectionId,
	methods: Methods,
	resources: Resources,
	max_request_body_size: u32,
	max_response_body_size: u32,
	batch_requests_supported: bool,
	bounded_subscriptions: BoundedSubscriptions,
	stop_server: StopMonitor,
	middleware: impl Middleware,
	id_provider: Arc<dyn IdProvider>,
	ping_interval: Duration,
) -> Result<(), Error> {
	// And we can finally transition to a websocket background_task.
	let mut builder = server.into_builder();
	builder.set_max_message_size(max_request_body_size as usize);
	let (mut sender, mut receiver) = builder.finish();
	let (tx, mut rx) = mpsc::unbounded::<String>();
	let bounded_subscriptions2 = bounded_subscriptions.clone();

	let stop_server2 = stop_server.clone();
	let sink = MethodSink::new_with_limit(tx, max_response_body_size);

	middleware.on_connect();

	// Send results back to the client.
	tokio::spawn(async move {
		// Received messages from the WebSocket.
		let mut rx_item = rx.next();

		// Interval to send out continuously `pings`.
		let ping_interval = IntervalStream::new(tokio::time::interval(ping_interval));
		tokio::pin!(ping_interval);
		let mut next_ping = ping_interval.next();

		while !stop_server2.shutdown_requested() {
			// Ensure select is cancel-safe by fetching and storing the `rx_item` that did not finish yet.
			// Note: Although, this is cancel-safe already, avoid using `select!` macro for future proofing.
			match futures_util::future::select(rx_item, next_ping).await {
				Either::Left((Some(response), ping)) => {
					// If websocket message send fail then terminate the connection.
					if let Err(err) = send_ws_message(&mut sender, response).await {
						tracing::warn!("WS send error: {}; terminate connection", err);
						break;
					}
					rx_item = rx.next();
					next_ping = ping;
				}
				// Nothing else to receive.
				Either::Left((None, _)) => break,

				// Handle timer intervals.
				Either::Right((_, next_rx)) => {
					if let Err(err) = send_ws_ping(&mut sender).await {
						tracing::warn!("WS send ping error: {}; terminate connection", err);
						break;
					}
					rx_item = next_rx;
					next_ping = ping_interval.next();
				}
			}
		}

		// Terminate connection and send close message.
		let _ = sender.close().await;

		// Notify all listeners and close down associated tasks.
		bounded_subscriptions2.close();
	});

	// Buffer for incoming data.
	let mut data = Vec::with_capacity(100);
	let mut method_executors = FutureDriver::default();
	let middleware = &middleware;

	let result = loop {
		data.clear();

		{
			// Need the extra scope to drop this pinned future and reclaim access to `data`
			let receive = async {
				// Identical loop to `soketto::receive_data` with debug logs for `Pong` frames.
				loop {
					match receiver.receive(&mut data).await? {
						soketto::Incoming::Data(d) => break Ok(d),
						soketto::Incoming::Pong(_) => tracing::debug!("recv pong"),
						_ => continue,
					}
				}
			};

			tokio::pin!(receive);

			if let Err(err) = method_executors.select_with(Monitored::new(receive, &stop_server)).await {
				match err {
					MonitoredError::Selector(SokettoError::Closed) => {
						tracing::debug!("WS transport error: remote peer terminated the connection: {}", conn_id);
						sink.close();
						break Ok(());
					}
					MonitoredError::Selector(SokettoError::MessageTooLarge { current, maximum }) => {
						tracing::warn!(
							"WS transport error: outgoing message is too big error ({} bytes, max is {})",
							current,
							maximum
						);
						sink.send_error(Id::Null, reject_too_big_request(max_request_body_size));
						continue;
					}
					// These errors can not be gracefully handled, so just log them and terminate the connection.
					MonitoredError::Selector(err) => {
						tracing::warn!("WS error: {}; terminate connection {}", err, conn_id);
						sink.close();
						break Err(err.into());
					}
					MonitoredError::Shutdown => break Ok(()),
				};
			};
		};

		tracing::debug!("recv {} bytes", data.len());

		let request_start = middleware.on_request();

		let first_non_whitespace = data.iter().find(|byte| !byte.is_ascii_whitespace());

		match first_non_whitespace {
			Some(b'{') => {
				if let Ok(req) = serde_json::from_slice::<Request>(&data) {
					tracing::debug!("recv method call={}", req.method);
					tracing::trace!("recv: req={:?}", req);

					let id = req.id.clone();
					let params = Params::new(req.params.map(|params| params.get()));

					middleware.on_call(&req.method);

					match methods.method_with_name(&req.method) {
						None => {
							sink.send_error(req.id, ErrorCode::MethodNotFound.into());
							middleware.on_response(request_start);
						}
						Some((name, method)) => match &method.inner() {
							MethodKind::Sync(callback) => match method.claim(name, &resources) {
								Ok(guard) => {
									let result = (callback)(id, params, &sink);

									middleware.on_result(name, result, request_start);
									middleware.on_response(request_start);
									drop(guard);
								}
								Err(err) => {
									tracing::error!(
										"[Methods::execute_with_resources] failed to lock resources: {:?}",
										err
									);
									sink.send_error(req.id, ErrorCode::ServerIsBusy.into());
									middleware.on_result(name, false, request_start);
									middleware.on_response(request_start);
								}
							},
							MethodKind::Async(callback) => match method.claim(name, &resources) {
								Ok(guard) => {
									let sink = sink.clone();
									let id = id.into_owned();
									let params = params.into_owned();

									let fut = async move {
										let result = (callback)(id, params, sink, conn_id, Some(guard)).await;
										middleware.on_result(name, result, request_start);
										middleware.on_response(request_start);
									};

									method_executors.add(fut.boxed());
								}
								Err(err) => {
									tracing::error!(
										"[Methods::execute_with_resources] failed to lock resources: {:?}",
										err
									);
									sink.send_error(req.id, ErrorCode::ServerIsBusy.into());
									middleware.on_result(name, false, request_start);
									middleware.on_response(request_start);
								}
							},
							MethodKind::Subscription(callback) => match method.claim(&req.method, &resources) {
								Ok(guard) => {
									let result = if let Some(cn) = bounded_subscriptions.acquire() {
										let conn_state =
											ConnState { conn_id, close_notify: cn, id_provider: &*id_provider };
										callback(id, params, sink.clone(), conn_state)
									} else {
										sink.send_error(
											req.id,
											reject_too_many_subscriptions(bounded_subscriptions.max()),
										);
										false
									};
									middleware.on_result(name, result, request_start);
									middleware.on_response(request_start);
									drop(guard);
								}
								Err(err) => {
									tracing::error!(
										"[Methods::execute_with_resources] failed to lock resources: {:?}",
										err
									);
									sink.send_error(req.id, ErrorCode::ServerIsBusy.into());
									middleware.on_result(name, false, request_start);
									middleware.on_response(request_start);
								}
							},
							MethodKind::Unsubscription(callback) => {
								// Don't adhere to any resource or subscription limits; always let unsubscribing happen!
								let result = callback(id, params, &sink, conn_id);
								middleware.on_result(name, result, request_start);
								middleware.on_response(request_start);
							}
						},
					}
				} else {
					let (id, code) = prepare_error(&data);
					sink.send_error(id, code.into());
					middleware.on_response(request_start);
				}
			}
			Some(b'[') => {
				// Make sure the following variables are not moved into async closure below.
				let d = std::mem::take(&mut data);
				let resources = &resources;
				let methods = &methods;
				let sink = sink.clone();
				let id_provider = id_provider.clone();
				let bounded_subscriptions2 = bounded_subscriptions.clone();

				let fut = async move {
					// Batch responses must be sent back as a single message so we read the results from each
					// request in the batch and read the results off of a new channel, `rx_batch`, and then send the
					// complete batch response back to the client over `tx`.
					let (tx_batch, mut rx_batch) = mpsc::unbounded();
					let sink_batch = MethodSink::new_with_limit(tx_batch, max_response_body_size);
					if let Ok(batch) = serde_json::from_slice::<Vec<Request>>(&d) {
						tracing::debug!("recv batch len={}", batch.len());
						tracing::trace!("recv: batch={:?}", batch);
						if !batch_requests_supported {
							sink.send_error(
								Id::Null,
								ErrorObject::borrowed(BATCHES_NOT_SUPPORTED_CODE, &BATCHES_NOT_SUPPORTED_MSG, None),
							);
							middleware.on_response(request_start);
						} else if !batch.is_empty() {
							join_all(batch.into_iter().filter_map(move |req| {
								let id = req.id.clone();
								let params = Params::new(req.params.map(|params| params.get()));
								let name = &req.method;

								match methods.method_with_name(name) {
									None => {
										sink_batch.send_error(req.id, ErrorCode::MethodNotFound.into());
										None
									}
									Some((name, method_callback)) => match &method_callback.inner() {
										MethodKind::Sync(callback) => match method_callback.claim(name, resources) {
											Ok(guard) => {
												let result = (callback)(id, params, &sink_batch);
												middleware.on_result(name, result, request_start);
												drop(guard);
												None
											}
											Err(err) => {
												tracing::error!(
													"[Methods::execute_with_resources] failed to lock resources: {:?}",
													err
												);
												sink_batch.send_error(req.id, ErrorCode::ServerIsBusy.into());
												middleware.on_result(&req.method, false, request_start);
												None
											}
										},
										MethodKind::Async(callback) => match method_callback
											.claim(&req.method, resources)
										{
											Ok(guard) => {
												let sink_batch = sink_batch.clone();
												let id = id.into_owned();
												let params = params.into_owned();

												Some(async move {
													let result =
														(callback)(id, params, sink_batch, conn_id, Some(guard)).await;
													middleware.on_result(&req.method, result, request_start);
												})
											}
											Err(err) => {
												tracing::error!(
													"[Methods::execute_with_resources] failed to lock resources: {:?}",
													err
												);
												sink_batch.send_error(req.id, ErrorCode::ServerIsBusy.into());
												middleware.on_result(&req.method, false, request_start);
												None
											}
										},
										MethodKind::Subscription(callback) => {
											match method_callback.claim(&req.method, resources) {
												Ok(guard) => {
													let result = if let Some(cn) = bounded_subscriptions2.acquire() {
														let conn_state = ConnState {
															conn_id,
															close_notify: cn,
															id_provider: &*id_provider,
														};
														callback(id, params, sink_batch.clone(), conn_state)
													} else {
														sink_batch.send_error(
															req.id,
															reject_too_many_subscriptions(bounded_subscriptions2.max()),
														);
														false
													};
													middleware.on_result(&req.method, result, request_start);
													drop(guard);
													None
												}
												Err(err) => {
													tracing::error!(
														"[Methods::execute_with_resources] failed to lock resources: {:?}",
														err
													);

													sink_batch.send_error(req.id, ErrorCode::ServerIsBusy.into());
													middleware.on_result(&req.method, false, request_start);
													None
												}
											}
										}
										MethodKind::Unsubscription(callback) => {
											// Don't adhere to any resource or subscription limits; always let unsubscribing happen!
											let result = callback(id, params, &sink_batch, conn_id);
											middleware.on_result(&req.method, result, request_start);
											None
										}
									},
								}
							}))
							.await;

							rx_batch.close();
							let results = collect_batch_response(rx_batch).await;

							if let Err(err) = sink.send_raw(results) {
								tracing::warn!("Error sending batch response to the client: {:?}", err)
							} else {
								middleware.on_response(request_start);
							}
						} else {
							sink.send_error(Id::Null, ErrorCode::InvalidRequest.into());
							middleware.on_response(request_start);
						}
					} else {
						let (id, code) = prepare_error(&d);
						sink.send_error(id, code.into());
						middleware.on_response(request_start);
					}
				};

				method_executors.add(Box::pin(fut));
			}
			_ => {
				sink.send_error(Id::Null, ErrorCode::ParseError.into());
			}
		}
	};

	middleware.on_disconnect();

	// Drive all running methods to completion.
	// **NOTE** Do not return early in this function. This `await` needs to run to guarantee
	// proper drop behaviour.
	method_executors.await;

	result
}

/// JSON-RPC Websocket server settings.
#[derive(Debug, Clone)]
struct Settings {
	/// Maximum size in bytes of a request.
	max_request_body_size: u32,
	/// Maximum size in bytes of a response.
	max_response_body_size: u32,
	/// Maximum number of incoming connections allowed.
	max_connections: u64,
	/// Maximum number of subscriptions per connection.
	max_subscriptions_per_connection: u32,
	/// Access control based on HTTP headers
	access_control: AccessControl,
	/// Whether batch requests are supported by this server or not.
	batch_requests_supported: bool,
	/// Custom tokio runtime to run the server on.
	tokio_runtime: Option<tokio::runtime::Handle>,
	/// The interval at which `Ping` frames are submitted.
	ping_interval: Duration,
}

impl Default for Settings {
	fn default() -> Self {
		Self {
			max_request_body_size: TEN_MB_SIZE_BYTES,
			max_response_body_size: TEN_MB_SIZE_BYTES,
			max_subscriptions_per_connection: 1024,
			max_connections: MAX_CONNECTIONS,
			batch_requests_supported: true,
			access_control: AccessControl::default(),
			tokio_runtime: None,
			ping_interval: Duration::from_secs(60),
		}
	}
}

/// Builder to configure and create a JSON-RPC Websocket server
#[derive(Debug)]
pub struct Builder<M = ()> {
	settings: Settings,
	resources: Resources,
	middleware: M,
	id_provider: Arc<dyn IdProvider>,
}

impl Default for Builder {
	fn default() -> Self {
		Builder {
			settings: Settings::default(),
			resources: Resources::default(),
			middleware: (),
			id_provider: Arc::new(RandomIntegerIdProvider),
		}
	}
}

impl Builder {
	/// Create a default server builder.
	pub fn new() -> Self {
		Self::default()
	}
}

impl<M> Builder<M> {
	/// Set the maximum size of a request body in bytes. Default is 10 MiB.
	pub fn max_request_body_size(mut self, size: u32) -> Self {
		self.settings.max_request_body_size = size;
		self
	}

	/// Set the maximum size of a response body in bytes. Default is 10 MiB.
	pub fn max_response_body_size(mut self, size: u32) -> Self {
		self.settings.max_response_body_size = size;
		self
	}

	/// Set the maximum number of connections allowed. Default is 100.
	pub fn max_connections(mut self, max: u64) -> Self {
		self.settings.max_connections = max;
		self
	}

	/// Enables or disables support of [batch requests](https://www.jsonrpc.org/specification#batch).
	/// By default, support is enabled.
	pub fn batch_requests_supported(mut self, supported: bool) -> Self {
		self.settings.batch_requests_supported = supported;
		self
	}

	/// Set the maximum number of connections allowed. Default is 1024.
	pub fn max_subscriptions_per_connection(mut self, max: u32) -> Self {
		self.settings.max_subscriptions_per_connection = max;
		self
	}

	/// Register a new resource kind. Errors if `label` is already registered, or if the number of
	/// registered resources on this server instance would exceed 8.
	///
	/// See the module documentation for [`resurce_limiting`](../jsonrpsee_utils/server/resource_limiting/index.html#resource-limiting)
	/// for details.
	pub fn register_resource(mut self, label: &'static str, capacity: u16, default: u16) -> Result<Self, Error> {
		self.resources.register(label, capacity, default)?;
		Ok(self)
	}

	/// Add a middleware to the builder [`Middleware`](../jsonrpsee_core/middleware/trait.Middleware.html).
	///
	/// ```
	/// use std::time::Instant;
	///
	/// use jsonrpsee_core::middleware::Middleware;
	/// use jsonrpsee_ws_server::WsServerBuilder;
	///
	/// #[derive(Clone)]
	/// struct MyMiddleware;
	///
	/// impl Middleware for MyMiddleware {
	///     type Instant = Instant;
	///
	///     fn on_request(&self) -> Instant {
	///         Instant::now()
	///     }
	///
	///     fn on_result(&self, name: &str, success: bool, started_at: Instant) {
	///         println!("Call to '{}' took {:?}", name, started_at.elapsed());
	///     }
	/// }
	///
	/// let builder = WsServerBuilder::new().set_middleware(MyMiddleware);
	/// ```
	pub fn set_middleware<T: Middleware>(self, middleware: T) -> Builder<T> {
		Builder { settings: self.settings, resources: self.resources, middleware, id_provider: self.id_provider }
	}

	/// Configure a custom [`tokio::runtime::Handle`] to run the server on.
	///
	/// Default: [`tokio::spawn`]
	pub fn custom_tokio_runtime(mut self, rt: tokio::runtime::Handle) -> Self {
		self.settings.tokio_runtime = Some(rt);
		self
	}

	/// Configure the interval at which pings are submitted.
	///
	/// This option is used to keep the connection alive, and is just submitting `Ping` frames,
	/// without making any assumptions about when a `Pong` frame should be received.
	///
	/// Default: 60 seconds.
	///
	/// # Examples
	///
	/// ```rust
	/// use std::time::Duration;
	/// use jsonrpsee_ws_server::WsServerBuilder;
	///
	/// // Set the ping interval to 10 seconds.
	/// let builder = WsServerBuilder::default().ping_interval(Duration::from_secs(10));
	/// ```
	pub fn ping_interval(mut self, interval: Duration) -> Self {
		self.settings.ping_interval = interval;
		self
	}

	/// Configure custom `subscription ID` provider for the server to use
	/// to when getting new subscription calls.
	///
	/// You may choose static dispatch or dynamic dispatch because
	/// `IdProvider` is implemented for `Box<T>`.
	///
	/// Default: [`RandomIntegerIdProvider`].
	///
	/// # Examples
	///
	/// ```rust
	/// use jsonrpsee_ws_server::{WsServerBuilder, RandomStringIdProvider, IdProvider};
	///
	/// // static dispatch
	/// let builder1 = WsServerBuilder::default().set_id_provider(RandomStringIdProvider::new(16));
	///
	/// // or dynamic dispatch
	/// let builder2 = WsServerBuilder::default().set_id_provider(Box::new(RandomStringIdProvider::new(16)));
	/// ```
	///
	pub fn set_id_provider<I: IdProvider + 'static>(mut self, id_provider: I) -> Self {
		self.id_provider = Arc::new(id_provider);
		self
	}

	/// Sets access control settings.
	pub fn set_access_control(mut self, acl: AccessControl) -> Self {
		self.settings.access_control = acl;
		self
	}

	/// Finalize the configuration of the server. Consumes the [`Builder`].
	///
	/// ```rust
	/// #[tokio::main]
	/// async fn main() {
	///   let listener = std::net::TcpListener::bind("127.0.0.1:0").unwrap();
	///   let occupied_addr = listener.local_addr().unwrap();
	///   let addrs: &[std::net::SocketAddr] = &[
	///       occupied_addr,
	///       "127.0.0.1:0".parse().unwrap(),
	///   ];
	///   assert!(jsonrpsee_ws_server::WsServerBuilder::default().build(occupied_addr).await.is_err());
	///   assert!(jsonrpsee_ws_server::WsServerBuilder::default().build(addrs).await.is_ok());
	/// }
	/// ```
	///
	pub async fn build(self, addrs: impl ToSocketAddrs) -> Result<Server<M>, Error> {
		let listener = TcpListener::bind(addrs).await?;
		let stop_monitor = StopMonitor::new();
		let resources = self.resources;
		Ok(Server {
			listener,
			cfg: self.settings,
			stop_monitor,
			resources,
			middleware: self.middleware,
			id_provider: self.id_provider,
		})
	}
}

async fn send_ws_message(
	sender: &mut Sender<BufReader<BufWriter<Compat<TcpStream>>>>,
	response: String,
) -> Result<(), Error> {
	tracing::debug!("send {} bytes", response.len());
	tracing::trace!("send: {}", response);
	sender.send_text_owned(response).await?;
	sender.flush().await.map_err(Into::into)
}

async fn send_ws_ping(sender: &mut Sender<BufReader<BufWriter<Compat<TcpStream>>>>) -> Result<(), Error> {
	tracing::debug!("send ping");
	// Submit empty slice as "optional" parameter.
	let slice: &[u8] = &[];
	// Byte slice fails if the provided slice is larger than 125 bytes.
	let byte_slice = ByteSlice125::try_from(slice).expect("Empty slice should fit into ByteSlice125");
	sender.send_ping(byte_slice).await?;
	sender.flush().await.map_err(Into::into)
}