246 lines
9.4 KiB
Go
246 lines
9.4 KiB
Go
// Copyright 2023 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package gasestimator
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import (
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"context"
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"errors"
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"fmt"
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"math"
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"math/big"
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"github.com/ethereum/go-ethereum/common"
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"github.com/ethereum/go-ethereum/core"
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"github.com/ethereum/go-ethereum/core/state"
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"github.com/ethereum/go-ethereum/core/types"
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"github.com/ethereum/go-ethereum/core/vm"
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"github.com/ethereum/go-ethereum/log"
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"github.com/ethereum/go-ethereum/params"
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)
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// Options are the contextual parameters to execute the requested call.
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//
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// Whilst it would be possible to pass a blockchain object that aggregates all
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// these together, it would be excessively hard to test. Splitting the parts out
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// allows testing without needing a proper live chain.
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type Options struct {
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Config *params.ChainConfig // Chain configuration for hard fork selection
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Chain core.ChainContext // Chain context to access past block hashes
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Header *types.Header // Header defining the block context to execute in
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State *state.StateDB // Pre-state on top of which to estimate the gas
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ErrorRatio float64 // Allowed overestimation ratio for faster estimation termination
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}
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// Estimate returns the lowest possible gas limit that allows the transaction to
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// run successfully with the provided context options. It returns an error if the
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// transaction would always revert, or if there are unexpected failures.
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func Estimate(ctx context.Context, call *core.Message, opts *Options, gasCap uint64) (uint64, []byte, error) {
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// Binary search the gas limit, as it may need to be higher than the amount used
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var (
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lo uint64 // lowest-known gas limit where tx execution fails
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hi uint64 // lowest-known gas limit where tx execution succeeds
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)
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// Determine the highest gas limit can be used during the estimation.
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hi = opts.Header.GasLimit
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if call.GasLimit >= params.TxGas {
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hi = call.GasLimit
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}
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// Normalize the max fee per gas the call is willing to spend.
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var feeCap *big.Int
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if call.GasFeeCap != nil {
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feeCap = call.GasFeeCap
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} else if call.GasPrice != nil {
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feeCap = call.GasPrice
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} else {
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feeCap = common.Big0
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}
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// Recap the highest gas limit with account's available balance.
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if feeCap.BitLen() != 0 {
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balance := opts.State.GetBalance(call.From).ToBig()
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available := balance
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if call.Value != nil {
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if call.Value.Cmp(available) >= 0 {
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return 0, nil, core.ErrInsufficientFundsForTransfer
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}
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available.Sub(available, call.Value)
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}
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if opts.Config.IsCancun(opts.Header.Number, opts.Header.Time) && len(call.BlobHashes) > 0 {
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blobGasPerBlob := new(big.Int).SetInt64(params.BlobTxBlobGasPerBlob)
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blobBalanceUsage := new(big.Int).SetInt64(int64(len(call.BlobHashes)))
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blobBalanceUsage.Mul(blobBalanceUsage, blobGasPerBlob)
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blobBalanceUsage.Mul(blobBalanceUsage, call.BlobGasFeeCap)
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if blobBalanceUsage.Cmp(available) >= 0 {
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return 0, nil, core.ErrInsufficientFunds
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}
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available.Sub(available, blobBalanceUsage)
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}
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allowance := new(big.Int).Div(available, feeCap)
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// If the allowance is larger than maximum uint64, skip checking
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if allowance.IsUint64() && hi > allowance.Uint64() {
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transfer := call.Value
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if transfer == nil {
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transfer = new(big.Int)
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}
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log.Debug("Gas estimation capped by limited funds", "original", hi, "balance", balance,
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"sent", transfer, "maxFeePerGas", feeCap, "fundable", allowance)
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hi = allowance.Uint64()
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}
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}
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// Recap the highest gas allowance with specified gascap.
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if gasCap != 0 && hi > gasCap {
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log.Debug("Caller gas above allowance, capping", "requested", hi, "cap", gasCap)
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hi = gasCap
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}
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// If the transaction is a plain value transfer, short circuit estimation and
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// directly try 21000. Returning 21000 without any execution is dangerous as
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// some tx field combos might bump the price up even for plain transfers (e.g.
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// unused access list items). Ever so slightly wasteful, but safer overall.
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if len(call.Data) == 0 {
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if call.To != nil && opts.State.GetCodeSize(*call.To) == 0 {
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failed, _, err := execute(ctx, call, opts, params.TxGas)
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if !failed && err == nil {
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return params.TxGas, nil, nil
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}
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}
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}
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// We first execute the transaction at the highest allowable gas limit, since if this fails we
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// can return error immediately.
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failed, result, err := execute(ctx, call, opts, hi)
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if err != nil {
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return 0, nil, err
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}
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if failed {
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if result != nil && !errors.Is(result.Err, vm.ErrOutOfGas) {
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return 0, result.Revert(), result.Err
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}
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return 0, nil, fmt.Errorf("gas required exceeds allowance (%d)", hi)
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}
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// For almost any transaction, the gas consumed by the unconstrained execution
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// above lower-bounds the gas limit required for it to succeed. One exception
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// is those that explicitly check gas remaining in order to execute within a
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// given limit, but we probably don't want to return the lowest possible gas
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// limit for these cases anyway.
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lo = result.UsedGas - 1
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// There's a fairly high chance for the transaction to execute successfully
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// with gasLimit set to the first execution's usedGas + gasRefund. Explicitly
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// check that gas amount and use as a limit for the binary search.
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optimisticGasLimit := (result.UsedGas + result.RefundedGas + params.CallStipend) * 64 / 63
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if optimisticGasLimit < hi {
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failed, _, err = execute(ctx, call, opts, optimisticGasLimit)
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if err != nil {
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// This should not happen under normal conditions since if we make it this far the
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// transaction had run without error at least once before.
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log.Error("Execution error in estimate gas", "err", err)
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return 0, nil, err
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}
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if failed {
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lo = optimisticGasLimit
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} else {
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hi = optimisticGasLimit
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}
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}
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// Binary search for the smallest gas limit that allows the tx to execute successfully.
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for lo+1 < hi {
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if opts.ErrorRatio > 0 {
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// It is a bit pointless to return a perfect estimation, as changing
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// network conditions require the caller to bump it up anyway. Since
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// wallets tend to use 20-25% bump, allowing a small approximation
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// error is fine (as long as it's upwards).
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if float64(hi-lo)/float64(hi) < opts.ErrorRatio {
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break
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}
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}
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mid := (hi + lo) / 2
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if mid > lo*2 {
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// Most txs don't need much higher gas limit than their gas used, and most txs don't
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// require near the full block limit of gas, so the selection of where to bisect the
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// range here is skewed to favor the low side.
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mid = lo * 2
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}
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failed, _, err = execute(ctx, call, opts, mid)
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if err != nil {
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// This should not happen under normal conditions since if we make it this far the
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// transaction had run without error at least once before.
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log.Error("Execution error in estimate gas", "err", err)
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return 0, nil, err
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}
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if failed {
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lo = mid
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} else {
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hi = mid
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}
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}
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return hi, nil, nil
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}
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// execute is a helper that executes the transaction under a given gas limit and
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// returns true if the transaction fails for a reason that might be related to
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// not enough gas. A non-nil error means execution failed due to reasons unrelated
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// to the gas limit.
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func execute(ctx context.Context, call *core.Message, opts *Options, gasLimit uint64) (bool, *core.ExecutionResult, error) {
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// Configure the call for this specific execution (and revert the change after)
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defer func(gas uint64) { call.GasLimit = gas }(call.GasLimit)
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call.GasLimit = gasLimit
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// Execute the call and separate execution faults caused by a lack of gas or
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// other non-fixable conditions
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result, err := run(ctx, call, opts)
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if err != nil {
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if errors.Is(err, core.ErrIntrinsicGas) {
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return true, nil, nil // Special case, raise gas limit
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}
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return true, nil, err // Bail out
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}
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return result.Failed(), result, nil
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}
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// run assembles the EVM as defined by the consensus rules and runs the requested
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// call invocation.
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func run(ctx context.Context, call *core.Message, opts *Options) (*core.ExecutionResult, error) {
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// Assemble the call and the call context
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var (
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msgContext = core.NewEVMTxContext(call)
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evmContext = core.NewEVMBlockContext(opts.Header, opts.Chain, nil)
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dirtyState = opts.State.Copy()
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evm = vm.NewEVM(evmContext, msgContext, dirtyState, opts.Config, vm.Config{NoBaseFee: true})
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)
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// Monitor the outer context and interrupt the EVM upon cancellation. To avoid
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// a dangling goroutine until the outer estimation finishes, create an internal
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// context for the lifetime of this method call.
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ctx, cancel := context.WithCancel(ctx)
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defer cancel()
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go func() {
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<-ctx.Done()
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evm.Cancel()
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}()
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// Execute the call, returning a wrapped error or the result
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result, err := core.ApplyMessage(evm, call, new(core.GasPool).AddGas(math.MaxUint64))
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if vmerr := dirtyState.Error(); vmerr != nil {
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return nil, vmerr
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}
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if err != nil {
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return result, fmt.Errorf("failed with %d gas: %w", call.GasLimit, err)
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}
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return result, nil
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}
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