ethers-rs/ethers-providers/src/pubsub.rs

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use crate::{JsonRpcClient, Middleware, Provider};
use ethers_core::types::U256;
use futures_util::stream::Stream;
use pin_project::{pin_project, pinned_drop};
use serde::de::DeserializeOwned;
use serde_json::Value;
use std::{
marker::PhantomData,
pin::Pin,
task::{Context, Poll},
};
/// A transport implementation supporting pub sub subscriptions.
pub trait PubsubClient: JsonRpcClient {
/// The type of stream this transport returns
type NotificationStream: futures_core::Stream<Item = Value>;
/// Add a subscription to this transport
fn subscribe<T: Into<U256>>(&self, id: T) -> Result<Self::NotificationStream, Self::Error>;
/// Remove a subscription from this transport
fn unsubscribe<T: Into<U256>>(&self, id: T) -> Result<(), Self::Error>;
}
#[must_use = "subscriptions do nothing unless you stream them"]
#[pin_project(PinnedDrop)]
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/// Streams data from an installed filter via `eth_subscribe`
pub struct SubscriptionStream<'a, P: PubsubClient, R: DeserializeOwned> {
/// The subscription's installed id on the ethereum node
pub id: U256,
provider: &'a Provider<P>,
#[pin]
rx: P::NotificationStream,
ret: PhantomData<R>,
}
impl<'a, P, R> SubscriptionStream<'a, P, R>
where
P: PubsubClient,
R: DeserializeOwned,
{
/// Creates a new subscription stream for the provided subscription id
pub fn new(id: U256, provider: &'a Provider<P>) -> Result<Self, P::Error> {
// Call the underlying PubsubClient's subscribe
let rx = provider.as_ref().subscribe(id)?;
Ok(Self {
id,
provider,
rx,
ret: PhantomData,
})
}
/// Unsubscribes from the subscription
pub async fn unsubscribe(&self) -> Result<bool, crate::ProviderError> {
self.provider.unsubscribe(self.id).await
}
}
// Each subscription item is a serde_json::Value which must be decoded to the
// subscription's return type.
// TODO: Can this be replaced with an `rx.map` in the constructor?
impl<'a, P, R> Stream for SubscriptionStream<'a, P, R>
where
P: PubsubClient,
R: DeserializeOwned,
{
type Item = R;
fn poll_next(self: Pin<&mut Self>, ctx: &mut Context) -> Poll<Option<Self::Item>> {
let this = self.project();
match futures_util::ready!(this.rx.poll_next(ctx)) {
Some(item) => match serde_json::from_value(item) {
Ok(res) => Poll::Ready(Some(res)),
_ => Poll::Pending,
},
None => Poll::Pending,
}
}
}
#[pinned_drop]
impl<P, R> PinnedDrop for SubscriptionStream<'_, P, R>
where
P: PubsubClient,
R: DeserializeOwned,
{
fn drop(self: Pin<&mut Self>) {
// on drop it removes the handler from the websocket so that it stops
// getting populated. We need to call `unsubscribe` explicitly to cancel
// the subscription
let _ = (*self.provider).as_ref().unsubscribe(self.id);
}
}