plugeth/eth/gasestimator/gasestimator.go

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