Add RPC eth_chainId for querying the current blockchain chain ID

js/src/api/rpc/parity/parity.js

@@ -53,6 +53,11 @@ export default class Parity {
       );
   }
 
+  chainId () {
+    return this._transport
+      .execute('parity_chainId');
+  }
+
   chainStatus () {
     return this._transport
       .execute('parity_chainStatus')

js/src/jsonrpc/interfaces/parity.js

@@ -56,6 +56,16 @@ export default {
     }
   },
 
+  chainId: {
+    desc: 'Returns the current chain ID used for tranaction signing.',
+    params: [],
+    returns: {
+      type: Quantity,
+      desc: 'The current blockchain chain ID',
+      example: '0x1'
+    }
+  },
+
   chainStatus: {
     section: SECTION_NET,
     desc: 'Returns the information on warp sync blocks',

rpc/src/v1/impls/light/parity.rs

@@ -49,6 +49,7 @@ use v1::types::{
 
 /// Parity implementation for light client.
 pub struct ParityClient {
+	client: Arc<LightChainClient>,
 	light_dispatch: Arc<LightDispatcher>,
 	accounts: Arc<AccountProvider>,
 	logger: Arc<RotatingLogger>,
@@ -83,6 +84,7 @@ impl ParityClient {
 			dapps_address,
 			ws_address,
 			eip86_transition: client.eip86_transition(),
+			client: client,
 		}
 	}
 
@@ -320,6 +322,10 @@ impl Parity for ParityClient {
 		Err(errors::light_unimplemented(None))
 	}
 
+	fn chain_id(&self) -> Result<Option<U256>, Error> {
+		Ok(self.client.signing_chain_id().map(U256::from))
+	}
+
 	fn chain(&self) -> Result<String, Error> {
 		Ok(self.settings.chain.clone())
 	}

rpc/src/v1/impls/parity.rs

@@ -200,6 +200,10 @@ impl<C, M, U> Parity for ParityClient<C, M, U> where
 		Ok(self.settings.chain.clone())
 	}
 
+	fn chain_id(&self) -> Result<Option<U256>, Error> {
+		Ok(self.client.signing_chain_id().map(U256::from))
+	}
+
 	fn chain(&self) -> Result<String, Error> {
 		Ok(self.client.spec_name())
 	}

rpc/src/v1/tests/mocked/parity.rs

@@ -220,6 +220,17 @@ fn rpc_parity_extra_data() {
 	assert_eq!(io.handle_request_sync(request), Some(response.to_owned()));
 }
 
+#[test]
+fn rpc_parity_chain_id() {
+	let deps = Dependencies::new();
+	let io = deps.default_client();
+
+	let request = r#"{"jsonrpc": "2.0", "method": "parity_chainId", "params": [], "id": 1}"#;
+	let response = r#"{"jsonrpc":"2.0","result":null,"id":1}"#;
+
+	assert_eq!(io.handle_request_sync(request), Some(response.to_owned()));
+}
+
 #[test]
 fn rpc_parity_default_extra_data() {
 	use util::misc;

rpc/src/v1/traits/parity.rs

@@ -172,6 +172,12 @@ build_rpc_trait! {
 		#[rpc(name = "parity_mode")]
 		fn mode(&self) -> Result<String, Error>;
 
+		/// Returns the chain ID used for transaction signing at the
+		/// current best block. An empty string is returned if not
+		/// available.
+		#[rpc(name = "parity_chainId")]
+		fn chain_id(&self) -> Result<Option<U256>, Error>;
+
 		/// Get the chain name. Returns one of: "foundation", "kovan", &c. of a filename.
 		#[rpc(name = "parity_chain")]
 		fn chain(&self) -> Result<String, Error>;