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// Copyright 2019-2024 ChainSafe Systems
// SPDX-License-Identifier: Apache-2.0, MIT
//! Subscription related types and traits for server implementations.
//!
//! Most of the code in this module comes from the `jsonrpsee` crate.
//! See <https://github.com/paritytech/jsonrpsee/blob/v0.21.0/core/src/server/subscription.rs>.
//! We slightly customized it from the original design to support Filecoin `pubsub` specification.
//! The principal changed types are the `PendingSubscriptionSink` and `SubscriptionSink`, adding an `u64` channel identifier member.
//!
//! The remaining types and methods must be duplicated because they are private.
//!
//! The sequence diagram of a channel lifetime is as follows:
//! ```text
//! ┌─────────────┐ ┌─────────────┐
//! │ WS Client │ │ Node │
//! └─────────────┘ └─────────────┘
//! │ │
//! │ ┌────────────────────────────────┐ │
//! │──┤ Subscription message ├───────────────────────────────▶ │
//! │ │ │ │
//! │ │{ jsonrpc:'2.0', │ │
//! │ │ id:<id>, │ │
//! │ │ method:'Filecoin.ChainNotify',│ │
//! │ │ params:[] } │ │
//! │ └────────────────────────────────┘ │
//! │ ┌────────────────────────────────┐ │
//! │ ◀───────────────────────────────┤ Opened channel message ├──│
//! │ │ │ │
//! │ │{ jsonrpc:'2.0', │ │
//! │ │ result:<channId>, │ │
//! │ │ id:<id> } │ │
//! │ └────────────────────────────────┘ │
//! │ │
//! │ │
//! │ ┌────────────────────────────────┐ │
//! │ ◀───────────────────────────────┤ Notification message ├──│
//! │ │ │ │
//! │ │{ jsonrpc:'2.0', │ │
//! │ │ method:'xrpc.ch.val', │ │
//! │ │ params:[<channId>,<payload>] }│ │
//! │ └────────────────────────────────┘ │
//! │ │
//! │ │
//! │ │
//! │ After a few notifications │
//! │ ┌────────────────────────────────┐ │
//! │──┤ Cancel subscription ├───────────────────────────────▶ │
//! │ │ │ │
//! │ │{ jsonrpc:'2.0', │ │
//! │ │ method:'xrpc.cancel', │ │
//! │ │ params:[<id>], │ │
//! │ │ id:null } │ │
//! │ └────────────────────────────────┘ │
//! │ ┌────────────────────────────────┐ │
//! │ ◀───────────────────────────────┤ Closed channel message ├──│
//! │ │ │ │
//! │ │{ jsonrpc:'2.0', │ │
//! │ │ method:'xrpc.ch.close', │ │
//! │ │ params:[<channId>] } │ │
//! │ └────────────────────────────────┘ │
//! ```
use ahash::HashMap;
use jsonrpsee::{
server::{
IntoSubscriptionCloseResponse, MethodCallback, Methods, RegisterMethodError,
ResponsePayload,
},
types::{error::ErrorCode, ErrorObjectOwned, Id, Params},
ConnectionId, MethodResponse, MethodSink,
};
use parking_lot::Mutex;
use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::Arc;
use tokio::sync::broadcast::error::RecvError;
use tokio::sync::{mpsc, oneshot};
use super::error::ServerError;
pub const NOTIF_METHOD_NAME: &str = "xrpc.ch.val";
pub const CANCEL_METHOD_NAME: &str = "xrpc.cancel";
pub type ChannelId = u64;
/// Type-alias for subscribers.
pub type Subscribers =
Arc<Mutex<HashMap<(ConnectionId, Id<'static>), (MethodSink, mpsc::Receiver<()>, ChannelId)>>>;
/// Represents a single subscription that is waiting to be accepted or rejected.
///
/// If this is dropped without calling `PendingSubscription::reject` or `PendingSubscriptionSink::accept`
/// a default error is sent out as response to the subscription call.
///
/// Thus, if you want a customized error message then `PendingSubscription::reject` must be called.
#[derive(Debug)]
#[must_use = "PendingSubscriptionSink does nothing unless `accept` or `reject` is called"]
pub struct PendingSubscriptionSink {
/// Sink.
pub(crate) inner: MethodSink,
/// `MethodCallback`.
pub(crate) method: &'static str,
/// Shared Mutex of subscriptions for this method.
pub(crate) subscribers: Subscribers,
/// ID of the `subscription call` (i.e. not the same as subscription id) which is used
/// to reply to subscription method call and must only be used once.
pub(crate) id: Id<'static>,
/// Sender to answer the subscribe call.
pub(crate) subscribe: oneshot::Sender<MethodResponse>,
/// Channel identifier.
pub(crate) channel_id: ChannelId,
/// Connection identifier.
pub(crate) connection_id: ConnectionId,
}
impl PendingSubscriptionSink {
/// Attempt to accept the subscription and respond the subscription method call.
///
/// # Panics
///
/// Panics if the subscription response exceeded the `max_response_size`.
pub async fn accept(self) -> Result<SubscriptionSink, String> {
let channel_id = self.channel_id();
let id = self.id.clone();
let response = MethodResponse::subscription_response(
self.id,
ResponsePayload::success_borrowed(&channel_id),
self.inner.max_response_size() as usize,
);
let success = response.is_success();
// Ideally the message should be sent only once.
//
// The same message is sent twice here because one is sent directly to the transport layer and
// the other one is sent internally to accept the subscription.
self.inner
.send(response.to_result())
.await
.map_err(|e| e.to_string())?;
self.subscribe
.send(response)
.map_err(|e| format!("accept error: {}", e.as_result()))?;
if success {
let (tx, rx) = mpsc::channel(1);
self.subscribers.lock().insert(
(self.connection_id, id),
(self.inner.clone(), rx, self.channel_id),
);
tracing::debug!(
"Accepting subscription (conn_id={}, chann_id={})",
self.connection_id.0,
self.channel_id
);
Ok(SubscriptionSink {
inner: self.inner,
method: self.method,
unsubscribe: IsUnsubscribed(tx),
channel_id: self.channel_id,
})
} else {
panic!("The subscription response was too big; adjust the `max_response_size` or change Subscription ID generation");
}
}
/// Returns the channel identifier
pub fn channel_id(&self) -> ChannelId {
self.channel_id
}
}
/// Represents a subscription until it is unsubscribed.
#[derive(Debug, Clone)]
pub struct IsUnsubscribed(mpsc::Sender<()>);
impl IsUnsubscribed {
/// Wrapper over [`tokio::sync::mpsc::Sender::closed`]
pub async fn unsubscribed(&self) {
self.0.closed().await;
}
}
/// Represents a single subscription that hasn't been processed yet.
#[derive(Debug, Clone)]
pub struct SubscriptionSink {
/// Sink.
inner: MethodSink,
/// `MethodCallback`.
method: &'static str,
/// A future that fires once the unsubscribe method has been called.
unsubscribe: IsUnsubscribed,
/// Channel identifier.
channel_id: ChannelId,
}
impl SubscriptionSink {
/// Get the method name.
pub fn method_name(&self) -> &str {
self.method
}
/// Get the channel ID.
pub fn channel_id(&self) -> ChannelId {
self.channel_id
}
/// Send out a response on the subscription and wait until there is capacity.
///
///
/// Returns
/// - `Ok(())` if the message could be sent.
/// - `Err(unsent_msg)` if the connection or subscription was closed.
///
/// # Cancel safety
///
/// This method is cancel-safe and dropping a future loses its spot in the waiting queue.
pub async fn send(&self, msg: String) -> Result<(), String> {
// Only possible to trigger when the connection is dropped.
if self.is_closed() {
return Err(format!("disconnect error: {}", msg));
}
self.inner.send(msg).await.map_err(|e| e.to_string())
}
/// Returns whether the subscription is closed.
pub fn is_closed(&self) -> bool {
self.inner.is_closed()
}
/// Completes when the subscription has been closed.
pub async fn closed(&self) {
// Both are cancel-safe thus ok to use select here.
tokio::select! {
_ = self.inner.closed() => (),
_ = self.unsubscribe.unsubscribed() => (),
}
}
}
fn create_notif_message(
sink: &SubscriptionSink,
result: &impl serde::Serialize,
) -> anyhow::Result<String> {
let method = sink.method_name();
let channel_id = sink.channel_id();
let result = serde_json::to_string(result)?;
let msg =
format!(r#"{{"jsonrpc":"2.0","method":"{method}","params":[{channel_id},{result}]}}"#,);
tracing::debug!("Sending notification: {}", msg);
Ok(msg)
}
fn close_payload(channel_id: ChannelId) -> serde_json::Value {
serde_json::json!({
"jsonrpc":"2.0",
"method":"xrpc.ch.close",
"params":[channel_id]
})
}
fn close_channel_response(channel_id: ChannelId) -> MethodResponse {
MethodResponse::response(
Id::Null,
ResponsePayload::success(close_payload(channel_id)),
1024,
)
}
#[derive(Debug, Clone)]
pub struct RpcModule {
id_provider: Arc<AtomicU64>,
channels: Subscribers,
methods: Methods,
}
impl From<RpcModule> for Methods {
fn from(module: RpcModule) -> Methods {
module.methods
}
}
impl Default for RpcModule {
fn default() -> Self {
let mut methods = Methods::default();
let channels = Subscribers::default();
methods
.verify_and_insert(
CANCEL_METHOD_NAME,
MethodCallback::Unsubscription(Arc::new({
let channels = channels.clone();
move |id,
params: Params,
connection_id: ConnectionId,
_max_response,
_extensions| {
let cb = || {
let arr: [Id<'_>; 1] = params.parse()?;
let sub_id = arr[0].clone().into_owned();
tracing::debug!("Got cancel request (id={sub_id})");
let opt = channels.lock().remove(&(connection_id, sub_id));
match opt {
Some((_, _, channel_id)) => {
Ok::<ChannelId, ServerError>(channel_id)
}
None => Err::<ChannelId, ServerError>(ServerError::from(
anyhow::anyhow!("channel not found"),
)),
}
};
let result = cb();
match result {
Ok(channel_id) => {
let resp = close_channel_response(channel_id);
tracing::debug!("Sending close message: {}", resp.as_result());
resp
}
Err(e) => {
let error: ErrorObjectOwned = e.into();
MethodResponse::error(id, error)
}
}
}
})),
)
.expect("Inserting a method into an empty methods map is infallible.");
Self {
id_provider: Arc::new(AtomicU64::new(0)),
channels,
methods,
}
}
}
impl RpcModule {
pub fn register_channel<R, F>(
&mut self,
subscribe_method_name: &'static str,
callback: F,
) -> Result<&mut MethodCallback, RegisterMethodError>
where
F: (Fn(Params) -> tokio::sync::broadcast::Receiver<R>) + Send + Sync + 'static,
R: serde::Serialize + Clone + Send + 'static,
{
self.register_channel_raw(subscribe_method_name, {
move |params, pending| {
let mut receiver = callback(params);
tokio::spawn(async move {
let sink = pending.accept().await.unwrap();
tracing::debug!("Channel created: chann_id={}", sink.channel_id);
loop {
tokio::select! {
action = receiver.recv() => {
match action {
Ok(msg) => {
match create_notif_message(&sink, &msg) {
Ok(msg) => {
// This fails only if the connection is closed
if sink.send(msg).await.is_err() {
break;
}
}
Err(e) => {
tracing::error!("Failed to serialize channel message: {:?}", e);
break;
}
}
}
Err(RecvError::Closed) => {
let _ = sink.send(close_payload(sink.channel_id()).to_string()).await;
break;
}
Err(RecvError::Lagged(_)) => {
}
}
},
_ = sink.closed() => {
break;
}
}
}
tracing::debug!("Send notification task ended (chann_id={})", sink.channel_id);
});
}
})
}
fn register_channel_raw<R, F>(
&mut self,
subscribe_method_name: &'static str,
callback: F,
) -> Result<&mut MethodCallback, RegisterMethodError>
where
F: (Fn(Params, PendingSubscriptionSink) -> R) + Send + Sync + 'static,
R: IntoSubscriptionCloseResponse,
{
self.methods.verify_method_name(subscribe_method_name)?;
let subscribers = self.channels.clone();
// Subscribe
self.methods.verify_and_insert(
subscribe_method_name,
MethodCallback::Subscription(Arc::new({
let id_provider = self.id_provider.clone();
move |id, params, method_sink, conn, _extensions| {
let channel_id = id_provider.fetch_add(1, Ordering::Relaxed);
// response to the subscription call.
let (tx, rx) = oneshot::channel();
let sink = PendingSubscriptionSink {
inner: method_sink.clone(),
method: NOTIF_METHOD_NAME,
subscribers: subscribers.clone(),
id: id.clone().into_owned(),
subscribe: tx,
channel_id,
connection_id: conn.conn_id,
};
callback(params, sink);
let id = id.clone().into_owned();
Box::pin(async move {
match rx.await {
Ok(rp) => rp,
Err(_) => MethodResponse::error(id, ErrorCode::InternalError),
}
})
}
})),
)
}
}