chain-spec: add optional 'fork_id'

'fork_id' is used to uniquely identify forks of the same chain/network
'ChainSpec' trait provides default 'None' implementation, meaning this
chain hasn't been forked.

bin/node-template/node/src/service.rs

@@ -170,7 +170,10 @@ pub fn new_full(mut config: Configuration) -> Result<TaskManager, ServiceError>
 		other: (block_import, grandpa_link, mut telemetry),
 	} = new_partial(&config)?;
 	let genesis_hash = client.block_hash(0).ok().flatten().unwrap_or_default();
-	let chain_prefix = format!("/{}/{}", config.protocol_id().as_ref(), genesis_hash);
+	let chain_prefix = match config.chain_spec.fork_id() {
+		Some(fork_id) => format!("/{}/{}", genesis_hash, fork_id),
+		None => format!("/{}", genesis_hash),
+	};
 
 	if let Some(url) = &config.keystore_remote {
 		match remote_keystore(url) {

bin/node/cli/src/service.rs

@@ -327,7 +327,10 @@ pub fn new_full_base(
 	let shared_voter_state = rpc_setup;
 	let auth_disc_publish_non_global_ips = config.network.allow_non_globals_in_dht;
 	let genesis_hash = client.block_hash(0).ok().flatten().unwrap_or_default();
-	let chain_prefix = format!("/{}/{}", config.protocol_id().as_ref(), genesis_hash);
+	let chain_prefix = match config.chain_spec.fork_id() {
+		Some(fork_id) => format!("/{}/{}", genesis_hash, fork_id),
+		None => format!("/{}", genesis_hash),
+	};
 
 	config.network.extra_sets.push(grandpa::grandpa_peers_set_config(&chain_prefix));
 	let warp_sync = Arc::new(grandpa::warp_proof::NetworkProvider::new(

client/chain-spec/src/lib.rs

@@ -165,6 +165,10 @@ pub trait ChainSpec: BuildStorage + Send + Sync {
 	fn telemetry_endpoints(&self) -> &Option<TelemetryEndpoints>;
 	/// Network protocol id.
 	fn protocol_id(&self) -> Option<&str>;
+	/// Optional network fork identifier. `None` by default.
+	fn fork_id(&self) -> Option<&str> {
+		None
+	}
 	/// Additional loosly-typed properties of the chain.
 	///
 	/// Returns an empty JSON object if 'properties' not defined in config