ethclient: Add EstimateGasAt[Hash] to estimate gas against a specific block

ethclient/ethclient.go

@@ -564,9 +564,13 @@ func (ec *Client) FeeHistory(ctx context.Context, blockCount uint64, lastBlock *
 }
 
 // EstimateGas tries to estimate the gas needed to execute a specific transaction based on
-// the current pending state of the backend blockchain. There is no guarantee that this is
+// the current state of the backend blockchain. There is no guarantee that this is the
-// the true gas limit requirement as other transactions may be added or removed by miners,
+// true gas limit requirement as other transactions may be added or removed by miners, but
-// but it should provide a basis for setting a reasonable default.
+// it should provide a basis for setting a reasonable default.
+//
+// Note that the state used by this method is implementation-defined by the remote RPC
+// server, but it's reasonable to assume that it will either be the pending or latest
+// state.
 func (ec *Client) EstimateGas(ctx context.Context, msg ethereum.CallMsg) (uint64, error) {
 	var hex hexutil.Uint64
 	err := ec.c.CallContext(ctx, &hex, "eth_estimateGas", toCallArg(msg))
@@ -576,6 +580,28 @@ func (ec *Client) EstimateGas(ctx context.Context, msg ethereum.CallMsg) (uint64
 	return uint64(hex), nil
 }
 
+// EstimateGasAt is almost the same as EstimateGas except that it selects the block height
+// instead of using the remote RPC's default state for gas estimation.
+func (ec *Client) EstimateGasAt(ctx context.Context, msg ethereum.CallMsg, blockNumber *big.Int) (uint64, error) {
+	var hex hexutil.Uint64
+	err := ec.c.CallContext(ctx, &hex, "eth_estimateGas", toCallArg(msg), toBlockNumArg(blockNumber))
+	if err != nil {
+		return 0, err
+	}
+	return uint64(hex), nil
+}
+
+// EstimateGasAtHash is almost the same as EstimateGas except that it selects the block
+// hash instead of using the remote RPC's default state for gas estimation.
+func (ec *Client) EstimateGasAtHash(ctx context.Context, msg ethereum.CallMsg, blockHash common.Hash) (uint64, error) {
+	var hex hexutil.Uint64
+	err := ec.c.CallContext(ctx, &hex, "eth_estimateGas", toCallArg(msg), rpc.BlockNumberOrHashWithHash(blockHash, false))
+	if err != nil {
+		return 0, err
+	}
+	return uint64(hex), nil
+}
+
 // SendTransaction injects a signed transaction into the pending pool for execution.
 //
 // If the transaction was a contract creation use the TransactionReceipt method to get the

ethclient/ethclient_test.go

@@ -643,6 +643,33 @@ func testAtFunctions(t *testing.T, client *rpc.Client) {
 	if !bytes.Equal(code, penCode) {
 		t.Fatalf("unexpected code: %v %v", code, penCode)
 	}
+	// Use HeaderByNumber to get a header for EstimateGasAt and EstimateGasAtHash
+	latestHeader, err := ec.HeaderByNumber(context.Background(), nil)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	// EstimateGasAt
+	msg := ethereum.CallMsg{
+		From:  testAddr,
+		To:    &common.Address{},
+		Gas:   21000,
+		Value: big.NewInt(1),
+	}
+	gas, err := ec.EstimateGasAt(context.Background(), msg, latestHeader.Number)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if gas != 21000 {
+		t.Fatalf("unexpected gas limit: %v", gas)
+	}
+	// EstimateGasAtHash
+	gas, err = ec.EstimateGasAtHash(context.Background(), msg, latestHeader.Hash())
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if gas != 21000 {
+		t.Fatalf("unexpected gas limit: %v", gas)
+	}
 }
 
 func testTransactionSender(t *testing.T, client *rpc.Client) {