eth,internal: add eth_chainId method to PublicEthereumApi JSONRPC

eth/api.go

@@ -71,6 +71,11 @@ func (api *PublicEthereumAPI) Hashrate() hexutil.Uint64 {
 	return hexutil.Uint64(api.e.Miner().HashRate())
 }
 
+// ChainId is the EIP-155 replay-protection chain id for the current ethereum chain config.
+func (api *PublicEthereumAPI) ChainId() *big.Int {
+	return api.e.chainConfig.ChainId
+}
+
 // PublicMinerAPI provides an API to control the miner.
 // It offers only methods that operate on data that pose no security risk when it is publicly accessible.
 type PublicMinerAPI struct {

internal/web3ext/web3ext.go

@@ -360,6 +360,11 @@ web3._extend({
 	property: 'eth',
 	methods:
 	[
+		new web3._extend.Method({
+			name: 'chainId',
+			call: 'eth_chainId',
+			params: 0
+		}),
 		new web3._extend.Method({
 			name: 'sign',
 			call: 'eth_sign',