net/discovery: File persistence for AddrCache

Cargo.toml

@@ -1272,6 +1272,7 @@ serde = { version = "1.0.214", default-features = false }
 serde-big-array = { version = "0.3.2" }
 serde_derive = { version = "1.0.117" }
 serde_json = { version = "1.0.132", default-features = false }
+serde_with = { version = "3.12.0", default-features = false, features = ["macros", "hex"]}
 serde_yaml = { version = "0.9" }
 sha1 = { version = "0.10.6" }
 sha2 = { version = "0.10.7", default-features = false }

prdoc/pr_8839.prdoc

@@ -0,0 +1,20 @@
+title: net/discovery: File persistence for AddrCache
+
+doc:
+  - audience: [ Node Dev, Node Operator ]
+    description: |
+      Introduce file persistence for `AddrCache`. Upon authority-discovery worker
+      startup, the worker tries to read a persisted cache from file, if not found
+      or if deserialization would fail (it should not with this PR, but might
+      in future if we were to change the JSON format) an empty cache is used.
+
+      For every time the in-memory cache is changed, the file is persisted to file,
+      by serializing the AddrCache to JSON. 
+
+      The writing to disc is done using a new helper `ThrottlingAsyncFileWriter`
+      which "throttles" consecutive writes and only uses the last one, plus writing
+      is done in a background thread, as to not block worker execution.
+
+crates:
+  - name: sc-authority-discovery
+    bump: patch

substrate/client/authority-discovery/Cargo.toml

@@ -30,6 +30,9 @@ rand = { workspace = true, default-features = true }
 sc-client-api = { workspace = true, default-features = true }
 sc-network = { workspace = true, default-features = true }
 sc-network-types = { workspace = true, default-features = true }
+serde_json.workspace = true
+serde_with.workspace = true
+serde.workspace = true
 sp-api = { workspace = true, default-features = true }
 sp-authority-discovery = { workspace = true, default-features = true }
 sp-blockchain = { workspace = true, default-features = true }
@@ -39,6 +42,8 @@ sp-runtime = { workspace = true, default-features = true }
 thiserror = { workspace = true }
 
 [dev-dependencies]
+hex.workspace = true
+tempfile.workspace = true
 quickcheck = { workspace = true }
 sp-tracing = { workspace = true, default-features = true }
 substrate-test-runtime-client = { workspace = true }

substrate/client/authority-discovery/src/error.rs

@@ -52,6 +52,9 @@ pub enum Error {
 	#[error("Failed to encode or decode scale payload.")]
 	EncodingDecodingScale(#[from] codec::Error),
 
+	#[error("Failed to encode or decode AddrCache.")]
+	EncodingDecodingAddrCache(String),
+
 	#[error("Failed to parse a libp2p multi address.")]
 	ParsingMultiaddress(#[from] sc_network::multiaddr::ParseError),
 

substrate/client/authority-discovery/src/worker.rs

@@ -19,19 +19,20 @@
 use crate::{
 	error::{Error, Result},
 	interval::ExpIncInterval,
+	worker::addr_cache::create_addr_cache,
 	ServicetoWorkerMsg, WorkerConfig,
 };
 
 use std::{
 	collections::{HashMap, HashSet},
 	marker::PhantomData,
+	path::PathBuf,
 	sync::Arc,
 	time::{Duration, Instant, SystemTime, UNIX_EPOCH},
 };
 
 use futures::{channel::mpsc, future, stream::Fuse, FutureExt, Stream, StreamExt};
 
-use addr_cache::AddrCache;
 use codec::{Decode, Encode};
 use ip_network::IpNetwork;
 use linked_hash_set::LinkedHashSet;
@@ -69,6 +70,7 @@ mod schema {
 pub mod tests;
 
 const LOG_TARGET: &str = "sub-authority-discovery";
+const ADDR_CACHE_PERSISTENCE_PATH: &str = "authority_discovery_addr_cache.json";
 
 /// Maximum number of addresses cached per authority. Additional addresses are discarded.
 const MAX_ADDRESSES_PER_AUTHORITY: usize = 16;
@@ -261,7 +263,9 @@ where
 		let publish_if_changed_interval =
 			ExpIncInterval::new(config.keystore_refresh_interval, config.keystore_refresh_interval);
 
-		let addr_cache = AddrCache::new();
+		// Load contents of persisted cache from file, if it exists, and is valid. Create a new one
+		// otherwise, and install a callback to persist it on change.
+		let addr_cache = create_addr_cache(PathBuf::from(ADDR_CACHE_PERSISTENCE_PATH));
 
 		let metrics = match prometheus_registry {
 			Some(registry) => match Metrics::register(&registry) {