ethclient: add EstimateGasAt[Hash] functions ethereum#27508 (#1396)

Author: gzliudan

ethclient/ethclient.go

@@ -646,9 +646,13 @@ 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 true gas limit requirement as other transactions may be added or removed by miners,
-// but it should provide a basis for setting a reasonable default.
+// the current state of the backend blockchain. There is no guarantee that this is the
+// true gas limit requirement as other transactions may be added or removed by miners, but
+// 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))
@@ -658,6 +662,28 @@ func (ec *Client) EstimateGas(ctx context.Context, msg ethereum.CallMsg) (uint64
 	return uint64(hex), nil
 }
 
+// EstimateGasAtBlock 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) EstimateGasAtBlock(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
+}
+
+// EstimateGasAtBlockHash 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) EstimateGasAtBlockHash(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