rpc: Expose the subscription ID for RpcClientT (#733)

* rpc: Extend `RpcClientT` to return the subscription ID

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc: Return `RpcSubscriptionId` for jsonrpsee clients

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc: Expose subscription ID via subxt subscription

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* examples: Adjust example to return subscription ID

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc: Add structure for subscription stream and subscription id

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

examples/examples/custom_rpc_client.rs

@@ -68,7 +68,8 @@ impl RpcClientT for MyLoggingClient {
         let res = RawValue::from_string("[]".to_string()).unwrap();
         let stream = futures::stream::once(async move { Ok(res) });
         let stream: Pin<Box<dyn futures::Stream<Item = _> + Send>> = Box::pin(stream);
-        Box::pin(std::future::ready(Ok(stream)))
+        // This subscription does not provide an ID.
+        Box::pin(std::future::ready(Ok(RpcSubscription { stream, id: None })))
     }
 }
 

subxt/src/rpc/jsonrpsee_impl.rs

@@ -12,14 +12,18 @@ use futures::stream::{
     StreamExt,
     TryStreamExt,
 };
-use jsonrpsee::core::{
-    client::{
-        Client,
-        ClientT,
-        SubscriptionClientT,
+use jsonrpsee::{
+    core::{
+        client::{
+            Client,
+            ClientT,
+            SubscriptionClientT,
+            SubscriptionKind,
+        },
+        traits::ToRpcParams,
+        Error as JsonRpseeError,
     },
-    traits::ToRpcParams,
-    Error as JsonRpseeError,
+    types::SubscriptionId,
 };
 use serde_json::value::RawValue;
 
@@ -52,17 +56,26 @@ impl RpcClientT for Client {
         unsub: &'a str,
     ) -> RpcFuture<'a, RpcSubscription> {
         Box::pin(async move {
-            let sub = SubscriptionClientT::subscribe::<Box<RawValue>, _>(
+            let stream = SubscriptionClientT::subscribe::<Box<RawValue>, _>(
                 self,
                 sub,
                 Params(params),
                 unsub,
             )
             .await
-            .map_err(|e| RpcError::ClientError(Box::new(e)))?
-            .map_err(|e| RpcError::ClientError(Box::new(e)))
-            .boxed();
-            Ok(sub)
+            .map_err(|e| RpcError::ClientError(Box::new(e)))?;
+
+            let id = match stream.kind() {
+                SubscriptionKind::Subscription(SubscriptionId::Str(id)) => {
+                    Some(id.clone().into_owned())
+                }
+                _ => None,
+            };
+
+            let stream = stream
+                .map_err(|e| RpcError::ClientError(Box::new(e)))
+                .boxed();
+            Ok(RpcSubscription { stream, id })
         })
     }
 }

subxt/src/rpc/mod.rs

@@ -67,6 +67,8 @@ pub use rpc_client_t::{
     RpcClientT,
     RpcFuture,
     RpcSubscription,
+    RpcSubscriptionId,
+    RpcSubscriptionStream,
 };
 
 pub use rpc_client::{

subxt/src/rpc/rpc_client.rs

@@ -5,6 +5,7 @@
 use super::{
     RpcClientT,
     RpcSubscription,
+    RpcSubscriptionId,
 };
 use crate::error::Error;
 use futures::{
@@ -185,6 +186,11 @@ impl<Res> Subscription<Res> {
             _marker: std::marker::PhantomData,
         }
     }
+
+    /// Obtain the ID associated with this subscription.
+    pub fn subscription_id(&self) -> Option<&RpcSubscriptionId> {
+        self.inner.id.as_ref()
+    }
 }
 
 impl<Res: DeserializeOwned> Subscription<Res> {
@@ -203,7 +209,7 @@ impl<Res: DeserializeOwned> Stream for Subscription<Res> {
         mut self: Pin<&mut Self>,
         cx: &mut std::task::Context<'_>,
     ) -> Poll<Option<Self::Item>> {
-        let res = futures::ready!(self.inner.poll_next_unpin(cx));
+        let res = futures::ready!(self.inner.stream.poll_next_unpin(cx));
 
         // Decode the inner RawValue to the type we're expecting and map
         // any errors to the right shape:

subxt/src/rpc/rpc_client_t.rs

@@ -59,6 +59,17 @@ pub trait RpcClientT: Send + Sync + 'static {
 pub type RpcFuture<'a, T> =
     Pin<Box<dyn Future<Output = Result<T, RpcError>> + Send + 'a>>;
 
+/// The RPC subscription returned from [`RpcClientT`]'s `subscription` method.
+pub struct RpcSubscription {
+    /// The subscription stream.
+    pub stream: RpcSubscriptionStream,
+    /// The ID associated with the subscription.
+    pub id: Option<RpcSubscriptionId>,
+}
+
 /// The inner subscription stream returned from our [`RpcClientT`]'s `subscription` method.
-pub type RpcSubscription =
+pub type RpcSubscriptionStream =
     Pin<Box<dyn Stream<Item = Result<Box<RawValue>, RpcError>> + Send + 'static>>;
+
+/// The ID associated with the [`RpcClientT`]'s `subscription`.
+pub type RpcSubscriptionId = String;