ethclient, internal/ethapi: add support for EIP-695 (eth_chainId) (#19694)

EIP-695 was written in 2017. Parity and Infura have support for this
method and we should, too.

ethclient/ethclient.go

@@ -61,6 +61,16 @@ func (ec *Client) Close() {
 
 // Blockchain Access
 
+// ChainId retrieves the current chain ID for transaction replay protection.
+func (ec *Client) ChainID(ctx context.Context) (*big.Int, error) {
+	var result hexutil.Big
+	err := ec.c.CallContext(ctx, &result, "eth_chainId")
+	if err != nil {
+		return nil, err
+	}
+	return (*big.Int)(&result), err
+}
+
 // BlockByHash returns the given full block.
 //
 // Note that loading full blocks requires two requests. Use HeaderByHash

ethclient/ethclient_test.go

@@ -319,3 +319,19 @@ func TestTransactionInBlockInterrupted(t *testing.T) {
 		t.Fatal("error should not be nil")
 	}
 }
+
+func TestChainID(t *testing.T) {
+	backend, _ := newTestBackend(t)
+	client, _ := backend.Attach()
+	defer backend.Stop()
+	defer client.Close()
+	ec := NewClient(client)
+
+	id, err := ec.ChainID(context.Background())
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if id == nil || id.Cmp(params.AllEthashProtocolChanges.ChainID) != 0 {
+		t.Fatalf("ChainID returned wrong number: %+v", id)
+	}
+}

internal/ethapi/api.go

@@ -529,6 +529,11 @@ func NewPublicBlockChainAPI(b Backend) *PublicBlockChainAPI {
 	return &PublicBlockChainAPI{b}
 }
 
+// ChainId returns the chainID value for transaction replay protection.
+func (s *PublicBlockChainAPI) ChainId() *hexutil.Big {
+	return (*hexutil.Big)(s.b.ChainConfig().ChainID)
+}
+
 // BlockNumber returns the block number of the chain head.
 func (s *PublicBlockChainAPI) BlockNumber() hexutil.Uint64 {
 	header, _ := s.b.HeaderByNumber(context.Background(), rpc.LatestBlockNumber) // latest header should always be available