ethclient.go

// (c) 2019-2020, Ava Labs, Inc.
//
// This file is a derived work, based on the go-ethereum library whose original
// notices appear below.
//
// It is distributed under a license compatible with the licensing terms of the
// original code from which it is derived.
//
// Much love to the original authors for their work.
// **********
// Copyright 2016 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

// Package ethclient provides a client for the Ethereum RPC API.
package ethclient

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"math/big"

	"github.com/ava-labs/avalanchego/ids"
	"github.com/ava-labs/coreth/accounts/abi/bind"
	"github.com/ava-labs/coreth/core/types"
	"github.com/ava-labs/coreth/interfaces"
	"github.com/ava-labs/coreth/rpc"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/hexutil"
)

// Verify that Client implements required interfaces
var (
	_ bind.AcceptedContractCaller = (*client)(nil)
	_ bind.ContractBackend        = (*client)(nil)
	_ bind.ContractFilterer       = (*client)(nil)
	_ bind.ContractTransactor     = (*client)(nil)
	_ bind.DeployBackend          = (*client)(nil)

	_ interfaces.ChainReader            = (*client)(nil)
	_ interfaces.ChainStateReader       = (*client)(nil)
	_ interfaces.TransactionReader      = (*client)(nil)
	_ interfaces.TransactionSender      = (*client)(nil)
	_ interfaces.ContractCaller         = (*client)(nil)
	_ interfaces.GasEstimator           = (*client)(nil)
	_ interfaces.GasPricer              = (*client)(nil)
	_ interfaces.LogFilterer            = (*client)(nil)
	_ interfaces.AcceptedStateReader    = (*client)(nil)
	_ interfaces.AcceptedContractCaller = (*client)(nil)

	_ Client = (*client)(nil)
)

// Client defines interface for typed wrappers for the Ethereum RPC API.
type Client interface {
	Close()
	ChainID(context.Context) (*big.Int, error)
	BlockByHash(context.Context, common.Hash) (*types.Block, error)
	BlockByNumber(context.Context, *big.Int) (*types.Block, error)
	BlockNumber(context.Context) (uint64, error)
	HeaderByHash(context.Context, common.Hash) (*types.Header, error)
	HeaderByNumber(context.Context, *big.Int) (*types.Header, error)
	TransactionByHash(context.Context, common.Hash) (tx *types.Transaction, isPending bool, err error)
	TransactionSender(context.Context, *types.Transaction, common.Hash, uint) (common.Address, error)
	TransactionCount(context.Context, common.Hash) (uint, error)
	TransactionInBlock(context.Context, common.Hash, uint) (*types.Transaction, error)
	TransactionReceipt(context.Context, common.Hash) (*types.Receipt, error)
	SyncProgress(ctx context.Context) error
	SubscribeNewAcceptedTransactions(context.Context, chan<- *common.Hash) (interfaces.Subscription, error)
	SubscribeNewPendingTransactions(context.Context, chan<- *common.Hash) (interfaces.Subscription, error)
	SubscribeNewHead(context.Context, chan<- *types.Header) (interfaces.Subscription, error)
	NetworkID(context.Context) (*big.Int, error)
	BalanceAt(context.Context, common.Address, *big.Int) (*big.Int, error)
	AssetBalanceAt(context.Context, common.Address, ids.ID, *big.Int) (*big.Int, error)
	StorageAt(context.Context, common.Address, common.Hash, *big.Int) ([]byte, error)
	CodeAt(context.Context, common.Address, *big.Int) ([]byte, error)
	NonceAt(context.Context, common.Address, *big.Int) (uint64, error)
	FilterLogs(context.Context, interfaces.FilterQuery) ([]types.Log, error)
	SubscribeFilterLogs(context.Context, interfaces.FilterQuery, chan<- types.Log) (interfaces.Subscription, error)
	AcceptedCodeAt(context.Context, common.Address) ([]byte, error)
	AcceptedNonceAt(context.Context, common.Address) (uint64, error)
	AcceptedCallContract(context.Context, interfaces.CallMsg) ([]byte, error)
	CallContract(context.Context, interfaces.CallMsg, *big.Int) ([]byte, error)
	CallContractAtHash(ctx context.Context, msg interfaces.CallMsg, blockHash common.Hash) ([]byte, error)
	SuggestGasPrice(context.Context) (*big.Int, error)
	SuggestGasTipCap(context.Context) (*big.Int, error)
	FeeHistory(ctx context.Context, blockCount uint64, lastBlock *big.Int, rewardPercentiles []float64) (*interfaces.FeeHistory, error)
	EstimateGas(context.Context, interfaces.CallMsg) (uint64, error)
	EstimateBaseFee(context.Context) (*big.Int, error)
	SendTransaction(context.Context, *types.Transaction) error
}

// client defines implementation for typed wrappers for the Ethereum RPC API.
type client struct {
	c *rpc.Client
}

// Dial connects a client to the given URL.
func Dial(rawurl string) (Client, error) {
	return DialContext(context.Background(), rawurl)
}

func DialContext(ctx context.Context, rawurl string) (Client, error) {
	c, err := rpc.DialContext(ctx, rawurl)
	if err != nil {
		return nil, err
	}
	return NewClient(c), nil
}

// NewClient creates a client that uses the given RPC client.
func NewClient(c *rpc.Client) Client {
	return &client{c}
}

func (ec *client) Close() {
	ec.c.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
// if you don't need all transactions or uncle headers.
func (ec *client) BlockByHash(ctx context.Context, hash common.Hash) (*types.Block, error) {
	return ec.getBlock(ctx, "eth_getBlockByHash", hash, true)
}

// BlockByNumber returns a block from the current canonical chain. If number is nil, the
// latest known block is returned.
//
// Note that loading full blocks requires two requests. Use HeaderByNumber
// if you don't need all transactions or uncle headers.
func (ec *client) BlockByNumber(ctx context.Context, number *big.Int) (*types.Block, error) {
	return ec.getBlock(ctx, "eth_getBlockByNumber", ToBlockNumArg(number), true)
}

// BlockNumber returns the most recent block number
func (ec *client) BlockNumber(ctx context.Context) (uint64, error) {
	var result hexutil.Uint64
	err := ec.c.CallContext(ctx, &result, "eth_blockNumber")
	return uint64(result), err
}

type rpcBlock struct {
	Hash           common.Hash      `json:"hash"`
	Transactions   []rpcTransaction `json:"transactions"`
	UncleHashes    []common.Hash    `json:"uncles"`
	Version        uint32           `json:"version"`
	BlockExtraData *hexutil.Bytes   `json:"blockExtraData"`
}

func (ec *client) getBlock(ctx context.Context, method string, args ...interface{}) (*types.Block, error) {
	var raw json.RawMessage
	err := ec.c.CallContext(ctx, &raw, method, args...)
	if err != nil {
		return nil, err
	} else if len(raw) == 0 {
		return nil, interfaces.NotFound
	}
	// Decode header and transactions.
	var head *types.Header
	var body rpcBlock
	if err := json.Unmarshal(raw, &head); err != nil {
		return nil, err
	}
	if err := json.Unmarshal(raw, &body); err != nil {
		return nil, err
	}
	// Quick-verify transaction and uncle lists. This mostly helps with debugging the server.
	if head.UncleHash == types.EmptyUncleHash && len(body.UncleHashes) > 0 {
		return nil, fmt.Errorf("server returned non-empty uncle list but block header indicates no uncles")
	}
	if head.UncleHash != types.EmptyUncleHash && len(body.UncleHashes) == 0 {
		return nil, fmt.Errorf("server returned empty uncle list but block header indicates uncles")
	}
	if head.TxHash == types.EmptyRootHash && len(body.Transactions) > 0 {
		return nil, fmt.Errorf("server returned non-empty transaction list but block header indicates no transactions")
	}
	if head.TxHash != types.EmptyRootHash && len(body.Transactions) == 0 {
		return nil, fmt.Errorf("server returned empty transaction list but block header indicates transactions")
	}
	// Load uncles because they are not included in the block response.
	var uncles []*types.Header
	if len(body.UncleHashes) > 0 {
		uncles = make([]*types.Header, len(body.UncleHashes))
		reqs := make([]rpc.BatchElem, len(body.UncleHashes))
		for i := range reqs {
			reqs[i] = rpc.BatchElem{
				Method: "eth_getUncleByBlockHashAndIndex",
				Args:   []interface{}{body.Hash, hexutil.EncodeUint64(uint64(i))},
				Result: &uncles[i],
			}
		}
		if err := ec.c.BatchCallContext(ctx, reqs); err != nil {
			return nil, err
		}
		for i := range reqs {
			if reqs[i].Error != nil {
				return nil, reqs[i].Error
			}
			if uncles[i] == nil {
				return nil, fmt.Errorf("got null header for uncle %d of block %x", i, body.Hash[:])
			}
		}
	}
	// Fill the sender cache of transactions in the block.
	txs := make([]*types.Transaction, len(body.Transactions))
	for i, tx := range body.Transactions {
		if tx.From != nil {
			setSenderFromServer(tx.tx, *tx.From, body.Hash)
		}
		txs[i] = tx.tx
	}
	return types.NewBlockWithHeader(head).WithBody(txs, uncles, body.Version, (*[]byte)(body.BlockExtraData)), nil
}

// HeaderByHash returns the block header with the given hash.
func (ec *client) HeaderByHash(ctx context.Context, hash common.Hash) (*types.Header, error) {
	var head *types.Header
	err := ec.c.CallContext(ctx, &head, "eth_getBlockByHash", hash, false)
	if err == nil && head == nil {
		err = interfaces.NotFound
	}
	return head, err
}

// HeaderByNumber returns a block header from the current canonical chain. If number is
// nil, the latest known header is returned.
func (ec *client) HeaderByNumber(ctx context.Context, number *big.Int) (*types.Header, error) {
	var head *types.Header
	err := ec.c.CallContext(ctx, &head, "eth_getBlockByNumber", ToBlockNumArg(number), false)
	if err == nil && head == nil {
		err = interfaces.NotFound
	}
	return head, err
}

type rpcTransaction struct {
	tx *types.Transaction
	txExtraInfo
}

type txExtraInfo struct {
	BlockNumber *string         `json:"blockNumber,omitempty"`
	BlockHash   *common.Hash    `json:"blockHash,omitempty"`
	From        *common.Address `json:"from,omitempty"`
}

func (tx *rpcTransaction) UnmarshalJSON(msg []byte) error {
	if err := json.Unmarshal(msg, &tx.tx); err != nil {
		return err
	}
	return json.Unmarshal(msg, &tx.txExtraInfo)
}

// TransactionByHash returns the transaction with the given hash.
func (ec *client) TransactionByHash(ctx context.Context, hash common.Hash) (tx *types.Transaction, isPending bool, err error) {
	var json *rpcTransaction
	err = ec.c.CallContext(ctx, &json, "eth_getTransactionByHash", hash)
	if err != nil {
		return nil, false, err
	} else if json == nil {
		return nil, false, interfaces.NotFound
	} else if _, r, _ := json.tx.RawSignatureValues(); r == nil {
		return nil, false, fmt.Errorf("server returned transaction without signature")
	}
	if json.From != nil && json.BlockHash != nil {
		setSenderFromServer(json.tx, *json.From, *json.BlockHash)
	}
	return json.tx, json.BlockNumber == nil, nil
}

// TransactionSender returns the sender address of the given transaction. The transaction
// must be known to the remote node and included in the blockchain at the given block and
// index. The sender is the one derived by the protocol at the time of inclusion.
//
// There is a fast-path for transactions retrieved by TransactionByHash and
// TransactionInBlock. Getting their sender address can be done without an RPC interaction.
func (ec *client) TransactionSender(ctx context.Context, tx *types.Transaction, block common.Hash, index uint) (common.Address, error) {
	// Try to load the address from the cache.
	sender, err := types.Sender(&senderFromServer{blockhash: block}, tx)
	if err == nil {
		return sender, nil
	}

	// It was not found in cache, ask the server.
	var meta struct {
		Hash common.Hash
		From common.Address
	}
	if err = ec.c.CallContext(ctx, &meta, "eth_getTransactionByBlockHashAndIndex", block, hexutil.Uint64(index)); err != nil {
		return common.Address{}, err
	}
	if meta.Hash == (common.Hash{}) || meta.Hash != tx.Hash() {
		return common.Address{}, errors.New("wrong inclusion block/index")
	}
	return meta.From, nil
}

// TransactionCount returns the total number of transactions in the given block.
func (ec *client) TransactionCount(ctx context.Context, blockHash common.Hash) (uint, error) {
	var num hexutil.Uint
	err := ec.c.CallContext(ctx, &num, "eth_getBlockTransactionCountByHash", blockHash)
	return uint(num), err
}

// TransactionInBlock returns a single transaction at index in the given block.
func (ec *client) TransactionInBlock(ctx context.Context, blockHash common.Hash, index uint) (*types.Transaction, error) {
	var json *rpcTransaction
	err := ec.c.CallContext(ctx, &json, "eth_getTransactionByBlockHashAndIndex", blockHash, hexutil.Uint64(index))
	if err != nil {
		return nil, err
	}
	if json == nil {
		return nil, interfaces.NotFound
	} else if _, r, _ := json.tx.RawSignatureValues(); r == nil {
		return nil, fmt.Errorf("server returned transaction without signature")
	}
	if json.From != nil && json.BlockHash != nil {
		setSenderFromServer(json.tx, *json.From, *json.BlockHash)
	}
	return json.tx, err
}

// TransactionReceipt returns the receipt of a transaction by transaction hash.
// Note that the receipt is not available for pending transactions.
func (ec *client) TransactionReceipt(ctx context.Context, txHash common.Hash) (*types.Receipt, error) {
	var r *types.Receipt
	err := ec.c.CallContext(ctx, &r, "eth_getTransactionReceipt", txHash)
	if err == nil {
		if r == nil {
			return nil, interfaces.NotFound
		}
	}
	return r, err
}

// SyncProgress retrieves the current progress of the sync algorithm. If there's
// no sync currently running, it returns nil.
func (ec *client) SyncProgress(ctx context.Context) error {
	var (
		raw     json.RawMessage
		syncing bool
	)

	if err := ec.c.CallContext(ctx, &raw, "eth_syncing"); err != nil {
		return err
	}
	// If not syncing, the response will be 'false'. To detect this
	// we unmarshal into a boolean and return nil on success.
	// If the chain is syncing, the engine will not forward the
	// request to the chain and a non-nil err will be returned.
	return json.Unmarshal(raw, &syncing)
}

// SubscribeNewAcceptedTransactions subscribes to notifications about the accepted transaction hashes on the given channel.
func (ec *client) SubscribeNewAcceptedTransactions(ctx context.Context, ch chan<- *common.Hash) (interfaces.Subscription, error) {
	return ec.c.EthSubscribe(ctx, ch, "newAcceptedTransactions")
}

// SubscribeNewAcceptedTransactions subscribes to notifications about the accepted transaction hashes on the given channel.
func (ec *client) SubscribeNewPendingTransactions(ctx context.Context, ch chan<- *common.Hash) (interfaces.Subscription, error) {
	return ec.c.EthSubscribe(ctx, ch, "newPendingTransactions")
}

// SubscribeNewHead subscribes to notifications about the current blockchain head
// on the given channel.
func (ec *client) SubscribeNewHead(ctx context.Context, ch chan<- *types.Header) (interfaces.Subscription, error) {
	return ec.c.EthSubscribe(ctx, ch, "newHeads")
}

// State Access

// NetworkID returns the network ID (also known as the chain ID) for this chain.
func (ec *client) NetworkID(ctx context.Context) (*big.Int, error) {
	version := new(big.Int)
	var ver string
	if err := ec.c.CallContext(ctx, &ver, "net_version"); err != nil {
		return nil, err
	}
	if _, ok := version.SetString(ver, 10); !ok {
		return nil, fmt.Errorf("invalid net_version result %q", ver)
	}
	return version, nil
}

// BalanceAt returns the wei balance of the given account.
// The block number can be nil, in which case the balance is taken from the latest known block.
func (ec *client) BalanceAt(ctx context.Context, account common.Address, blockNumber *big.Int) (*big.Int, error) {
	var result hexutil.Big
	err := ec.c.CallContext(ctx, &result, "eth_getBalance", account, ToBlockNumArg(blockNumber))
	return (*big.Int)(&result), err
}

// AssetBalanceAt returns the [assetID] balance of the given account
// The block number can be nil, in which case the balance is taken from the latest known block.
func (ec *client) AssetBalanceAt(ctx context.Context, account common.Address, assetID ids.ID, blockNumber *big.Int) (*big.Int, error) {
	var result hexutil.Big
	err := ec.c.CallContext(ctx, &result, "eth_getAssetBalance", account, ToBlockNumArg(blockNumber), assetID)
	return (*big.Int)(&result), err
}

// StorageAt returns the value of key in the contract storage of the given account.
// The block number can be nil, in which case the value is taken from the latest known block.
func (ec *client) StorageAt(ctx context.Context, account common.Address, key common.Hash, blockNumber *big.Int) ([]byte, error) {
	var result hexutil.Bytes
	err := ec.c.CallContext(ctx, &result, "eth_getStorageAt", account, key, ToBlockNumArg(blockNumber))
	return result, err
}

// CodeAt returns the contract code of the given account.
// The block number can be nil, in which case the code is taken from the latest known block.
func (ec *client) CodeAt(ctx context.Context, account common.Address, blockNumber *big.Int) ([]byte, error) {
	var result hexutil.Bytes
	err := ec.c.CallContext(ctx, &result, "eth_getCode", account, ToBlockNumArg(blockNumber))
	return result, err
}

// NonceAt returns the account nonce of the given account.
// The block number can be nil, in which case the nonce is taken from the latest known block.
func (ec *client) NonceAt(ctx context.Context, account common.Address, blockNumber *big.Int) (uint64, error) {
	var result hexutil.Uint64
	err := ec.c.CallContext(ctx, &result, "eth_getTransactionCount", account, ToBlockNumArg(blockNumber))
	return uint64(result), err
}

// Filters

// FilterLogs executes a filter query.
func (ec *client) FilterLogs(ctx context.Context, q interfaces.FilterQuery) ([]types.Log, error) {
	var result []types.Log
	arg, err := toFilterArg(q)
	if err != nil {
		return nil, err
	}
	err = ec.c.CallContext(ctx, &result, "eth_getLogs", arg)
	return result, err
}

// SubscribeFilterLogs subscribes to the results of a streaming filter query.
func (ec *client) SubscribeFilterLogs(ctx context.Context, q interfaces.FilterQuery, ch chan<- types.Log) (interfaces.Subscription, error) {
	arg, err := toFilterArg(q)
	if err != nil {
		return nil, err
	}
	return ec.c.EthSubscribe(ctx, ch, "logs", arg)
}

func toFilterArg(q interfaces.FilterQuery) (interface{}, error) {
	arg := map[string]interface{}{
		"address": q.Addresses,
		"topics":  q.Topics,
	}
	if q.BlockHash != nil {
		arg["blockHash"] = *q.BlockHash
		if q.FromBlock != nil || q.ToBlock != nil {
			return nil, fmt.Errorf("cannot specify both BlockHash and FromBlock/ToBlock")
		}
	} else {
		if q.FromBlock == nil {
			arg["fromBlock"] = "0x0"
		} else {
			arg["fromBlock"] = ToBlockNumArg(q.FromBlock)
		}
		arg["toBlock"] = ToBlockNumArg(q.ToBlock)
	}
	return arg, nil
}

// AcceptedCodeAt returns the contract code of the given account in the accepted state.
func (ec *client) AcceptedCodeAt(ctx context.Context, account common.Address) ([]byte, error) {
	return ec.CodeAt(ctx, account, nil)
}

// AcceptedNonceAt returns the account nonce of the given account in the accepted state.
// This is the nonce that should be used for the next transaction.
func (ec *client) AcceptedNonceAt(ctx context.Context, account common.Address) (uint64, error) {
	return ec.NonceAt(ctx, account, nil)
}

// AcceptedCallContract executes a message call transaction in the accepted
// state.
func (ec *client) AcceptedCallContract(ctx context.Context, msg interfaces.CallMsg) ([]byte, error) {
	return ec.CallContract(ctx, msg, nil)
}

// Contract Calling

// CallContract executes a message call transaction, which is directly executed in the VM
// of the node, but never mined into the blockchain.
//
// blockNumber selects the block height at which the call runs. It can be nil, in which
// case the code is taken from the latest known block. Note that state from very old
// blocks might not be available.
func (ec *client) CallContract(ctx context.Context, msg interfaces.CallMsg, blockNumber *big.Int) ([]byte, error) {
	var hex hexutil.Bytes
	err := ec.c.CallContext(ctx, &hex, "eth_call", toCallArg(msg), ToBlockNumArg(blockNumber))
	if err != nil {
		return nil, err
	}
	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 interfaces.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
}

// SuggestGasPrice retrieves the currently suggested gas price to allow a timely
// execution of a transaction.
func (ec *client) SuggestGasPrice(ctx context.Context) (*big.Int, error) {
	var hex hexutil.Big
	if err := ec.c.CallContext(ctx, &hex, "eth_gasPrice"); err != nil {
		return nil, err
	}
	return (*big.Int)(&hex), nil
}

// SuggestGasTipCap retrieves the currently suggested gas tip cap after 1559 to
// allow a timely execution of a transaction.
func (ec *client) SuggestGasTipCap(ctx context.Context) (*big.Int, error) {
	var hex hexutil.Big
	if err := ec.c.CallContext(ctx, &hex, "eth_maxPriorityFeePerGas"); err != nil {
		return nil, err
	}
	return (*big.Int)(&hex), nil
}

type feeHistoryResultMarshaling struct {
	OldestBlock  *hexutil.Big     `json:"oldestBlock"`
	Reward       [][]*hexutil.Big `json:"reward,omitempty"`
	BaseFee      []*hexutil.Big   `json:"baseFeePerGas,omitempty"`
	GasUsedRatio []float64        `json:"gasUsedRatio"`
}

// FeeHistory retrieves the fee market history.
func (ec *client) FeeHistory(ctx context.Context, blockCount uint64, lastBlock *big.Int, rewardPercentiles []float64) (*interfaces.FeeHistory, error) {
	var res feeHistoryResultMarshaling
	if err := ec.c.CallContext(ctx, &res, "eth_feeHistory", hexutil.Uint(blockCount), ToBlockNumArg(lastBlock), rewardPercentiles); err != nil {
		return nil, err
	}
	reward := make([][]*big.Int, len(res.Reward))
	for i, r := range res.Reward {
		reward[i] = make([]*big.Int, len(r))
		for j, r := range r {
			reward[i][j] = (*big.Int)(r)
		}
	}
	baseFee := make([]*big.Int, len(res.BaseFee))
	for i, b := range res.BaseFee {
		baseFee[i] = (*big.Int)(b)
	}
	return &interfaces.FeeHistory{
		OldestBlock:  (*big.Int)(res.OldestBlock),
		Reward:       reward,
		BaseFee:      baseFee,
		GasUsedRatio: res.GasUsedRatio,
	}, nil
}

// 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.
func (ec *client) EstimateGas(ctx context.Context, msg interfaces.CallMsg) (uint64, error) {
	var hex hexutil.Uint64
	err := ec.c.CallContext(ctx, &hex, "eth_estimateGas", toCallArg(msg))
	if err != nil {
		return 0, err
	}
	return uint64(hex), nil
}

// EstimateBaseFee tries to estimate the base fee for the next block if it were created
// immediately. There is no guarantee that this will be the base fee used in the next block
// or that the next base fee will be higher or lower than the returned value.
func (ec *client) EstimateBaseFee(ctx context.Context) (*big.Int, error) {
	var hex hexutil.Big
	err := ec.c.CallContext(ctx, &hex, "eth_baseFee")
	if err != nil {
		return nil, err
	}
	return (*big.Int)(&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
// contract address after the transaction has been mined.
func (ec *client) SendTransaction(ctx context.Context, tx *types.Transaction) error {
	data, err := tx.MarshalBinary()
	if err != nil {
		return err
	}
	return ec.c.CallContext(ctx, nil, "eth_sendRawTransaction", hexutil.Encode(data))
}

func ToBlockNumArg(number *big.Int) string {
	// The Ethereum implementation uses a different mapping from
	// negative numbers to special strings (latest, pending) then is
	// used on its server side. See rpc/types.go for the comparison.
	// In Coreth, latest, pending, and accepted are all treated the same
	// therefore, if [number] is nil or a negative number in [-3, -1]
	// we want the latest accepted block
	if number == nil {
		return "latest"
	}
	low := big.NewInt(-3)
	high := big.NewInt(-1)
	if number.Cmp(low) >= 0 && number.Cmp(high) <= 0 {
		return "latest"
	}
	return hexutil.EncodeBig(number)
}

func toCallArg(msg interfaces.CallMsg) interface{} {
	arg := map[string]interface{}{
		"from": msg.From,
		"to":   msg.To,
	}
	if len(msg.Data) > 0 {
		arg["data"] = hexutil.Bytes(msg.Data)
	}
	if msg.Value != nil {
		arg["value"] = (*hexutil.Big)(msg.Value)
	}
	if msg.Gas != 0 {
		arg["gas"] = hexutil.Uint64(msg.Gas)
	}
	if msg.GasPrice != nil {
		arg["gasPrice"] = (*hexutil.Big)(msg.GasPrice)
	}
	return arg
}