A0-1610: Restore contract event support (#838)

* Restore contract event listening

* Authenticate when installing protoc on CI

This should reduce the number of failures caused by rate limiting.

* Bump aleph-client version

* Update contract event docs

* Improve cosmetics

* This reverts commit e21d155.

aleph-client/Cargo.toml

@@ -14,7 +14,7 @@ log = "0.4"
 serde_json = { version = "1.0" }
 thiserror = "1.0"
 contract-metadata = "2.0.0-beta"
-contract-transcode = "2.0.0-beta"
+contract-transcode = { git = "https://github.com/obrok/cargo-contract", branch = "send-sync-env-types" }
 ink_metadata = "4.0.0-beta"
 subxt = "0.25.0"
 futures = "0.3.25"
@@ -25,3 +25,6 @@ sp-core = { git = "https://github.com/Cardinal-Cryptography/substrate.git", bran
 sp-runtime = { git = "https://github.com/Cardinal-Cryptography/substrate.git", branch = "aleph-v0.9.32" }
 pallet-contracts-primitives = { git = "https://github.com/Cardinal-Cryptography/substrate.git", branch = "aleph-v0.9.32" }
 primitives = { path = "../primitives" }
+
+[dev-dependencies]
+tokio = "1.21"

aleph-client/src/contract/event.rs

@@ -0,0 +1,131 @@
+//! Utilities for listening for contract events.
+//!
+//! To use the module you will need to pass a connection, some contracts and an `UnboundedSender` to the
+//! [listen_contract_events] function. You most likely want to `tokio::spawn` the resulting future, so that it runs
+//! concurrently.
+//!
+//! ```no_run
+//! # use std::sync::Arc;
+//! # use std::sync::mpsc::channel;
+//! # use std::time::Duration;
+//! # use aleph_client::{AccountId, Connection, SignedConnection};
+//! # use aleph_client::contract::ContractInstance;
+//! # use aleph_client::contract::event::{listen_contract_events};
+//! # use anyhow::Result;
+//! use futures::{channel::mpsc::unbounded, StreamExt};
+//!
+//! # async fn example(conn: Connection, signed_conn: SignedConnection, address1: AccountId, address2: AccountId, path1: &str, path2: &str) -> Result<()> {
+//! // The `Arc` makes it possible to pass a reference to the contract to another thread
+//! let contract1 = Arc::new(ContractInstance::new(address1, path1)?);
+//! let contract2 = Arc::new(ContractInstance::new(address2, path2)?);
+//!
+//! let conn_copy = conn.clone();
+//! let contract1_copy = contract1.clone();
+//! let contract2_copy = contract2.clone();
+//!
+//! let (tx, mut rx) = unbounded();
+//! let listen = || async move {
+//!     listen_contract_events(&conn, &[contract1_copy.as_ref(), contract2_copy.as_ref()], tx).await?;
+//!     <Result<(), anyhow::Error>>::Ok(())
+//! };
+//! let join = tokio::spawn(listen());
+//!
+//! contract1.contract_exec0(&signed_conn, "some_method").await?;
+//! contract2.contract_exec0(&signed_conn, "some_other_method").await?;
+//!
+//! println!("Received event {:?}", rx.next().await);
+//!
+//! rx.close();
+//! join.await??;
+//!
+//! #   Ok(())
+//! # }
+//! ```
+
+use std::collections::HashMap;
+
+use anyhow::{bail, Result};
+use contract_transcode::Value;
+use futures::{channel::mpsc::UnboundedSender, StreamExt};
+
+use crate::{contract::ContractInstance, AccountId, Connection};
+
+/// Represents a single event emitted by a contract.
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub struct ContractEvent {
+    /// The address of the contract that emitted the event.
+    pub contract: AccountId,
+    /// The name of the event.
+    pub name: Option<String>,
+    /// Data contained in the event.
+    pub data: HashMap<String, Value>,
+}
+
+/// Starts an event listening loop.
+///
+/// Will send contract event and every error encountered while fetching through the provided [UnboundedSender].
+/// Only events coming from the address of one of the `contracts` will be decoded.
+///
+/// The loop will terminate once `sender` is closed. The loop may also terminate in case of errors while fetching blocks
+/// or decoding events (pallet events, contract event decoding errors are sent over the channel).
+pub async fn listen_contract_events(
+    conn: &Connection,
+    contracts: &[&ContractInstance],
+    sender: UnboundedSender<Result<ContractEvent>>,
+) -> Result<()> {
+    let mut block_subscription = conn.as_client().blocks().subscribe_finalized().await?;
+
+    while let Some(block) = block_subscription.next().await {
+        if sender.is_closed() {
+            break;
+        }
+
+        let block = block?;
+
+        for event in block.events().await?.iter() {
+            let event = event?;
+
+            if let Some(event) =
+                event.as_event::<crate::api::contracts::events::ContractEmitted>()?
+            {
+                if let Some(contract) = contracts
+                    .iter()
+                    .find(|contract| contract.address() == &event.contract)
+                {
+                    let data = zero_prefixed(&event.data);
+                    let event = contract
+                        .transcoder
+                        .decode_contract_event(&mut data.as_slice());
+
+                    sender.unbounded_send(
+                        event.and_then(|event| build_event(contract.address().clone(), event)),
+                    )?;
+                }
+            }
+        }
+    }
+
+    Ok(())
+}
+
+/// The contract transcoder assumes there is an extra byte (that it discards) indicating the size of the data. However,
+/// data arriving through the subscription as used in this file don't have this extra byte. This function adds it.
+fn zero_prefixed(data: &[u8]) -> Vec<u8> {
+    let mut result = vec![0];
+    result.extend_from_slice(data);
+    result
+}
+
+fn build_event(address: AccountId, event_data: Value) -> Result<ContractEvent> {
+    match event_data {
+        Value::Map(map) => Ok(ContractEvent {
+            contract: address,
+            name: map.ident(),
+            data: map
+                .iter()
+                .map(|(key, value)| (key.to_string(), value.clone()))
+                .collect(),
+        }),
+        _ => bail!("Contract event data is not a map"),
+    }
+}

aleph-client/src/contract/mod.rs

@@ -43,6 +43,7 @@
 //! ```
 
 mod convertible_value;
+pub mod event;
 
 use std::fmt::{Debug, Formatter};