Implement BlocksClient for working with blocks (#671)

* rpc: Fill in any missing finalized blocks

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

* tests: Move fill blocks test to RPC location

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

* events: Remove the fill in strategy

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

* blocks: Introduce blocks client

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

* client: Enable the block API

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

* blocks: Simplify `subscribe_finalized_headers` method

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

* tests: Add tests for `subscribe_finalized_headers`

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

* blocks: Implement `subscribe_headers`

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

* tests: Add tests for `subscribe_headers`

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

* tests: Move `missing_block_headers_will_be_filled_in` to blocks

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

* events: Use the new subscribe to blocks

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

* blocks: Change API to return future similar to events

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

* events: Use blocks API for subscribing to blocks

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

* Update subxt/src/blocks/blocks_client.rs

Co-authored-by: James Wilson <james@jsdw.me>

* blocks: Simplify docs for `subscribe_finalized_headers`

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

* blocks: Use `PhantomDataSendSync` to avoid other bounds on `T: Config`

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

* blocks: Add docs for best blocks

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

* blocks: Avoid one clone for the `client.rpc()`

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

* Update testing/integration-tests/src/blocks/mod.rs

Co-authored-by: Niklas Adolfsson <niklasadolfsson1@gmail.com>

* blocks: Improve `subscribe_headers` doc

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

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>
Co-authored-by: James Wilson <james@jsdw.me>
Co-authored-by: Niklas Adolfsson <niklasadolfsson1@gmail.com>

subxt/src/blocks/blocks_client.rs

@@ -0,0 +1,152 @@
+// Copyright 2019-2022 Parity Technologies (UK) Ltd.
+// This file is dual-licensed as Apache-2.0 or GPL-3.0.
+// see LICENSE for license details.
+
+use crate::{
+    client::OnlineClientT,
+    error::Error,
+    utils::PhantomDataSendSync,
+    Config,
+};
+use derivative::Derivative;
+use futures::{
+    future::Either,
+    stream,
+    Stream,
+    StreamExt,
+};
+use sp_runtime::traits::Header;
+use std::future::Future;
+
+/// A client for working with blocks.
+#[derive(Derivative)]
+#[derivative(Clone(bound = "Client: Clone"))]
+pub struct BlocksClient<T, Client> {
+    client: Client,
+    _marker: PhantomDataSendSync<T>,
+}
+
+impl<T, Client> BlocksClient<T, Client> {
+    /// Create a new [`BlocksClient`].
+    pub fn new(client: Client) -> Self {
+        Self {
+            client,
+            _marker: PhantomDataSendSync::new(),
+        }
+    }
+}
+
+impl<T, Client> BlocksClient<T, Client>
+where
+    T: Config,
+    Client: OnlineClientT<T>,
+{
+    /// Subscribe to new best block headers.
+    ///
+    /// # Note
+    ///
+    /// This does not produce all the blocks from the chain, just the best blocks.
+    /// The best block is selected by the consensus algorithm.
+    /// This calls under the hood the `chain_subscribeNewHeads` RPC method, if you need
+    /// a subscription of all the blocks please use the `chain_subscribeAllHeads` method.
+    ///
+    /// These blocks haven't necessarily been finalised yet. Prefer
+    /// [`BlocksClient::subscribe_finalized_headers()`] if that is important.
+    pub fn subscribe_headers(
+        &self,
+    ) -> impl Future<Output = Result<impl Stream<Item = Result<T::Header, Error>>, Error>>
+           + Send
+           + 'static {
+        let client = self.client.clone();
+        async move { client.rpc().subscribe_blocks().await }
+    }
+
+    /// Subscribe to finalized block headers.
+    ///
+    /// While the Substrate RPC method does not guarantee that all finalized block headers are
+    /// provided, this function does.
+    /// ```
+    pub fn subscribe_finalized_headers(
+        &self,
+    ) -> impl Future<Output = Result<impl Stream<Item = Result<T::Header, Error>>, Error>>
+           + Send
+           + 'static {
+        let client = self.client.clone();
+        async move { subscribe_finalized_headers(client).await }
+    }
+}
+
+async fn subscribe_finalized_headers<T, Client>(
+    client: Client,
+) -> Result<impl Stream<Item = Result<T::Header, Error>>, Error>
+where
+    T: Config,
+    Client: OnlineClientT<T>,
+{
+    // Fetch the last finalised block details immediately, so that we'll get
+    // all blocks after this one.
+    let last_finalized_block_hash = client.rpc().finalized_head().await?;
+    let last_finalized_block_num = client
+        .rpc()
+        .header(Some(last_finalized_block_hash))
+        .await?
+        .map(|h| (*h.number()).into());
+
+    let sub = client.rpc().subscribe_finalized_blocks().await?;
+
+    // Adjust the subscription stream to fill in any missing blocks.
+    Ok(
+        subscribe_to_block_headers_filling_in_gaps(client, last_finalized_block_num, sub)
+            .boxed(),
+    )
+}
+
+/// Note: This is exposed for testing but is not considered stable and may change
+/// without notice in a patch release.
+#[doc(hidden)]
+pub fn subscribe_to_block_headers_filling_in_gaps<T, Client, S, E>(
+    client: Client,
+    mut last_block_num: Option<u64>,
+    sub: S,
+) -> impl Stream<Item = Result<T::Header, Error>> + Send
+where
+    T: Config,
+    Client: OnlineClientT<T>,
+    S: Stream<Item = Result<T::Header, E>> + Send,
+    E: Into<Error> + Send + 'static,
+{
+    sub.flat_map(move |s| {
+        let client = client.clone();
+
+        // Get the header, or return a stream containing just the error.
+        let header = match s {
+            Ok(header) => header,
+            Err(e) => return Either::Left(stream::once(async { Err(e.into()) })),
+        };
+
+        // We want all previous details up to, but not including this current block num.
+        let end_block_num = (*header.number()).into();
+
+        // This is one after the last block we returned details for last time.
+        let start_block_num = last_block_num.map(|n| n + 1).unwrap_or(end_block_num);
+
+        // Iterate over all of the previous blocks we need headers for, ignoring the current block
+        // (which we already have the header info for):
+        let previous_headers = stream::iter(start_block_num..end_block_num)
+            .then(move |n| {
+                let rpc = client.rpc().clone();
+                async move {
+                    let hash = rpc.block_hash(Some(n.into())).await?;
+                    let header = rpc.header(hash).await?;
+                    Ok::<_, Error>(header)
+                }
+            })
+            .filter_map(|h| async { h.transpose() });
+
+        // On the next iteration, we'll get details starting just after this end block.
+        last_block_num = Some(end_block_num);
+
+        // Return a combination of any previous headers plus the new header.
+        Either::Right(previous_headers.chain(stream::once(async { Ok(header) })))
+    })
+}

subxt/src/blocks/mod.rs

@@ -0,0 +1,12 @@
+// Copyright 2019-2022 Parity Technologies (UK) Ltd.
+// This file is dual-licensed as Apache-2.0 or GPL-3.0.
+// see LICENSE for license details.
+
+//! This module exposes the necessary functionality for working with events.
+
+mod blocks_client;
+
+pub use blocks_client::{
+    subscribe_to_block_headers_filling_in_gaps,
+    BlocksClient,
+};

subxt/src/client/offline_client.rs

@@ -3,6 +3,7 @@
 // see LICENSE for license details.
 
 use crate::{
+    blocks::BlocksClient,
     constants::ConstantsClient,
     events::EventsClient,
     rpc::RuntimeVersion,
@@ -43,6 +44,11 @@ pub trait OfflineClientT<T: Config>: Clone + Send + Sync + 'static {
     fn constants(&self) -> ConstantsClient<T, Self> {
         ConstantsClient::new(self.clone())
     }
+
+    /// Work with blocks.
+    fn blocks(&self) -> BlocksClient<T, Self> {
+        BlocksClient::new(self.clone())
+    }
 }
 
 /// A client that is capable of performing offline-only operations.

subxt/src/client/online_client.rs

@@ -7,6 +7,7 @@ use super::{
     OfflineClientT,
 };
 use crate::{
+    blocks::BlocksClient,
     constants::ConstantsClient,
     error::Error,
     events::EventsClient,
@@ -203,6 +204,11 @@ impl<T: Config> OnlineClient<T> {
     pub fn constants(&self) -> ConstantsClient<T, Self> {
         <Self as OfflineClientT<T>>::constants(self)
     }
+
+    /// Work with blocks.
+    pub fn blocks(&self) -> BlocksClient<T, Self> {
+        <Self as OfflineClientT<T>>::blocks(self)
+    }
 }
 
 impl<T: Config> OfflineClientT<T> for OnlineClient<T> {

subxt/src/events/event_subscription.rs

@@ -8,7 +8,6 @@ use crate::{
     client::OnlineClientT,
     error::Error,
     events::EventsClient,
-    rpc::Subscription,
     Config,
 };
 use derivative::Derivative;
@@ -40,7 +39,7 @@ pub type FinalizedEventSub<Header> = BoxStream<'static, Result<Header, Error>>;
 /// A Subscription. This forms a part of the `EventSubscription` type handed back
 /// in codegen from `subscribe`, and is exposed to be used in codegen.
 #[doc(hidden)]
-pub type EventSub<Item> = Subscription<Item>;
+pub type EventSub<Item> = BoxStream<'static, Result<Item, Error>>;
 
 /// A subscription to events that implements [`Stream`], and returns [`Events`] objects for each block.
 #[derive(Derivative)]

subxt/src/events/events_client.rs

@@ -14,17 +14,10 @@ use crate::{
     Config,
 };
 use derivative::Derivative;
-use futures::{
-    future::Either,
-    stream,
-    Stream,
-    StreamExt,
-};
 use sp_core::{
     storage::StorageKey,
     twox_128,
 };
-use sp_runtime::traits::Header;
 use std::future::Future;
 
 /// A client for working with events.
@@ -96,7 +89,10 @@ where
     ) -> impl Future<
         Output = Result<EventSubscription<T, Client, EventSub<T::Header>>, Error>,
     > + Send
-           + 'static {
+           + 'static
+    where
+        Client: Send + Sync + 'static,
+    {
         let client = self.client.clone();
         async move { subscribe(client).await }
     }
@@ -157,8 +153,8 @@ where
     T: Config,
     Client: OnlineClientT<T>,
 {
-    let block_subscription = client.rpc().subscribe_blocks().await?;
-    Ok(EventSubscription::new(client, block_subscription))
+    let block_subscription = client.blocks().subscribe_headers().await?;
+    Ok(EventSubscription::new(client, Box::pin(block_subscription)))
 }
 
 /// Subscribe to events from finalized blocks.
@@ -169,78 +165,10 @@ where
     T: Config,
     Client: OnlineClientT<T>,
 {
-    // fetch the last finalised block details immediately, so that we'll get
-    // events for each block after this one.
-    let last_finalized_block_hash = client.rpc().finalized_head().await?;
-    let last_finalized_block_number = client
-        .rpc()
-        .header(Some(last_finalized_block_hash))
-        .await?
-        .map(|h| (*h.number()).into());
-
-    let sub = client.rpc().subscribe_finalized_blocks().await?;
-
-    // Fill in any gaps between the block above and the finalized blocks reported.
-    let block_subscription = subscribe_to_block_headers_filling_in_gaps(
-        client.clone(),
-        last_finalized_block_number,
-        sub,
-    );
-
+    let block_subscription = client.blocks().subscribe_finalized_headers().await?;
     Ok(EventSubscription::new(client, Box::pin(block_subscription)))
 }
 
-/// Note: This is exposed for testing but is not considered stable and may change
-/// without notice in a patch release.
-#[doc(hidden)]
-pub fn subscribe_to_block_headers_filling_in_gaps<T, Client, S, E>(
-    client: Client,
-    mut last_block_num: Option<u64>,
-    sub: S,
-) -> impl Stream<Item = Result<T::Header, Error>> + Send
-where
-    T: Config,
-    Client: OnlineClientT<T> + Send + Sync,
-    S: Stream<Item = Result<T::Header, E>> + Send,
-    E: Into<Error> + Send + 'static,
-{
-    sub.flat_map(move |s| {
-        let client = client.clone();
-
-        // Get the header, or return a stream containing just the error. Our EventSubscription
-        // stream will return `None` as soon as it hits an error like this.
-        let header = match s {
-            Ok(header) => header,
-            Err(e) => return Either::Left(stream::once(async { Err(e.into()) })),
-        };
-
-        // We want all previous details up to, but not including this current block num.
-        let end_block_num = (*header.number()).into();
-
-        // This is one after the last block we returned details for last time.
-        let start_block_num = last_block_num.map(|n| n + 1).unwrap_or(end_block_num);
-
-        // Iterate over all of the previous blocks we need headers for, ignoring the current block
-        // (which we already have the header info for):
-        let previous_headers = stream::iter(start_block_num..end_block_num)
-            .then(move |n| {
-                let client = client.clone();
-                async move {
-                    let hash = client.rpc().block_hash(Some(n.into())).await?;
-                    let header = client.rpc().header(hash).await?;
-                    Ok::<_, Error>(header)
-                }
-            })
-            .filter_map(|h| async { h.transpose() });
-
-        // On the next iteration, we'll get details starting just after this end block.
-        last_block_num = Some(end_block_num);
-
-        // Return a combination of any previous headers plus the new header.
-        Either::Right(previous_headers.chain(stream::once(async { Ok(header) })))
-    })
-}
-
 // The storage key needed to access events.
 fn system_events_key() -> StorageKey {
     let mut storage_key = twox_128(b"System").to_vec();

subxt/src/events/mod.rs

@@ -16,10 +16,7 @@ pub use event_subscription::{
     EventSubscription,
     FinalizedEventSub,
 };
-pub use events_client::{
-    subscribe_to_block_headers_filling_in_gaps,
-    EventsClient,
-};
+pub use events_client::EventsClient;
 pub use events_type::{
     EventDetails,
     Events,

subxt/src/lib.rs

@@ -135,6 +135,7 @@
 
 pub use subxt_macro::subxt;
 
+pub mod blocks;
 pub mod client;
 pub mod config;
 pub mod constants;
@@ -148,7 +149,7 @@ pub mod tx;
 pub mod utils;
 
 // Expose a few of the most common types at root,
-// but leave most types behind their respoctive modules.
+// but leave most types behind their respective modules.
 pub use crate::{
     client::{
         OfflineClient,