ethclient: add CallContractAtHash (ethereum#24355)

* add CallContractAtHash to ethclient

* add docstring and test

* optimize test

* ethclient: nits

Co-authored-by: Péter Szilágyi <peterke@gmail.com>

ethclient/ethclient.go

@@ -456,6 +456,17 @@ func (ec *Client) CallContract(ctx context.Context, msg ethereum.CallMsg, blockN
 	return hex, nil
 }
 
+// CallContractAtHash is almost the same as CallContract except that it selects
+// the block by block hash instead of block height.
+func (ec *Client) CallContractAtHash(ctx context.Context, msg ethereum.CallMsg, blockHash common.Hash) ([]byte, error) {
+	var hex hexutil.Bytes
+	err := ec.c.CallContext(ctx, &hex, "eth_call", toCallArg(msg), rpc.BlockNumberOrHashWithHash(blockHash, false))
+	if err != nil {
+		return nil, err
+	}
+	return hex, nil
+}
+
 // PendingCallContract executes a message call transaction using the EVM.
 // The state seen by the contract call is the pending state.
 func (ec *Client) PendingCallContract(ctx context.Context, msg ethereum.CallMsg) ([]byte, error) {

ethclient/ethclient_test.go

@@ -285,6 +285,9 @@ func TestEthClient(t *testing.T) {
 		"CallContract": {
 			func(t *testing.T) { testCallContract(t, client) },
 		},
+		"CallContractAtHash": {
+			func(t *testing.T) { testCallContractAtHash(t, client) },
+		},
 		"AtFunctions": {
 			func(t *testing.T) { testAtFunctions(t, client) },
 		},
@@ -507,6 +510,33 @@ func testStatusFunctions(t *testing.T, client *rpc.Client) {
 	}
 }
 
+func testCallContractAtHash(t *testing.T, client *rpc.Client) {
+	ec := NewClient(client)
+
+	// EstimateGas
+	msg := ethereum.CallMsg{
+		From:  testAddr,
+		To:    &common.Address{},
+		Gas:   21000,
+		Value: big.NewInt(1),
+	}
+	gas, err := ec.EstimateGas(context.Background(), msg)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if gas != 21000 {
+		t.Fatalf("unexpected gas price: %v", gas)
+	}
+	block, err := ec.HeaderByNumber(context.Background(), big.NewInt(1))
+	if err != nil {
+		t.Fatalf("BlockByNumber error: %v", err)
+	}
+	// CallContract
+	if _, err := ec.CallContractAtHash(context.Background(), msg, block.Hash()); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
 func testCallContract(t *testing.T, client *rpc.Client) {
 	ec := NewClient(client)