rpc: backpressured RPC server (bump jsonrpsee 0.20) (#1313)

This is a rather big change in jsonrpsee, the major things in this bump
are:
- Server backpressure (the subscription impls are modified to deal with
that)
- Allow custom error types / return types (remove jsonrpsee::core::Error
and jsonrpee::core::CallError)
- Bug fixes (graceful shutdown in particular not used by substrate
anyway)
   - Less dependencies for the clients in particular
   - Return type requires Clone in method call responses
   - Moved to tokio channels
   - Async subscription API (not used in this PR)

Major changes in this PR:
- The subscriptions are now bounded and if subscription can't keep up
with the server it is dropped
- CLI: add parameter to configure the jsonrpc server bounded message
buffer (default is 64)
- Add our own subscription helper to deal with the unbounded streams in
substrate

The most important things in this PR to review is the added helpers
functions in `substrate/client/rpc/src/utils.rs` and the rest is pretty
much chore.

Regarding the "bounded buffer limit" it may cause the server to handle
the JSON-RPC calls
slower than before.

The message size limit is bounded by "--rpc-response-size" thus "by
default 10MB * 64 = 640MB"
but the subscription message size is not covered by this limit and could
be capped as well.

Hopefully the last release prior to 1.0, sorry in advance for a big PR

Previous attempt: https://github.com/paritytech/substrate/pull/13992

Resolves https://github.com/paritytech/polkadot-sdk/issues/748, resolves
https://github.com/paritytech/polkadot-sdk/issues/627

substrate/client/service/src/config.rs

@@ -100,6 +100,8 @@ pub struct Configuration {
 	pub rpc_max_subs_per_conn: u32,
 	/// JSON-RPC server default port.
 	pub rpc_port: u16,
+	/// The number of messages the JSON-RPC server is allowed to keep in memory.
+	pub rpc_message_buffer_capacity: u32,
 	/// Prometheus endpoint configuration. `None` if disabled.
 	pub prometheus_config: Option<PrometheusConfig>,
 	/// Telemetry service URL. `None` if disabled.

substrate/client/service/src/lib.rs

@@ -37,7 +37,7 @@ mod task_manager;
 use std::{collections::HashMap, net::SocketAddr};
 
 use codec::{Decode, Encode};
-use futures::{channel::mpsc, pin_mut, FutureExt, StreamExt};
+use futures::{pin_mut, FutureExt, StreamExt};
 use jsonrpsee::{core::Error as JsonRpseeError, RpcModule};
 use log::{debug, error, warn};
 use sc_client_api::{blockchain::HeaderBackend, BlockBackend, BlockchainEvents, ProofProvider};
@@ -109,9 +109,15 @@ impl RpcHandlers {
 	pub async fn rpc_query(
 		&self,
 		json_query: &str,
-	) -> Result<(String, mpsc::UnboundedReceiver<String>), JsonRpseeError> {
+	) -> Result<(String, tokio::sync::mpsc::Receiver<String>), JsonRpseeError> {
+		// Because `tokio::sync::mpsc::channel` is used under the hood
+		// it will panic if it's set to usize::MAX.
+		//
+		// This limit is used to prevent panics and is large enough.
+		const TOKIO_MPSC_MAX_SIZE: usize = tokio::sync::Semaphore::MAX_PERMITS;
+
 		self.0
-			.raw_json_request(json_query)
+			.raw_json_request(json_query, TOKIO_MPSC_MAX_SIZE)
 			.await
 			.map(|(method_res, recv)| (method_res.result, recv))
 	}
@@ -394,6 +400,7 @@ where
 		max_payload_in_mb: config.rpc_max_request_size,
 		max_payload_out_mb: config.rpc_max_response_size,
 		max_subs_per_conn: config.rpc_max_subs_per_conn,
+		message_buffer_capacity: config.rpc_message_buffer_capacity,
 		rpc_api: gen_rpc_module(deny_unsafe(addr, &config.rpc_methods))?,
 		metrics,
 		id_provider: rpc_id_provider,