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contract.go
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contract.go
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// (c) 2019-2020, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.
package precompile
import (
"fmt"
"math/big"
"github.com/ethereum/go-ethereum/common"
)
const (
selectorLen = 4
)
type RunStatefulPrecompileFunc func(accessibleState PrecompileAccessibleState, caller common.Address, addr common.Address, input []byte, suppliedGas uint64, readOnly bool) (ret []byte, remainingGas uint64, err error)
// PrecompileAccessibleState defines the interface exposed to stateful precompile contracts
type PrecompileAccessibleState interface {
GetStateDB() StateDB
GetBlockContext() BlockContext
NativeAssetCall(caller common.Address, input []byte, suppliedGas uint64, gasGost uint64, readOnly bool) (ret []byte, remainingGas uint64, err error)
}
// BlockContext defines an interface that provides information to a stateful precompile
// about the block that activates the upgrade. The precompile can access this information
// to initialize its state.
type BlockContext interface {
Number() *big.Int
Timestamp() *big.Int
}
// ChainContext defines an interface that provides information to a stateful precompile
// about the chain configuration. The precompile can access this information to initialize
// its state.
type ChainConfig interface {
// Note: None of the existing stateful precompiles currently access chain config information
// in Configure so this interface is empty.
}
// StateDB is the interface for accessing EVM state
type StateDB interface {
GetState(common.Address, common.Hash) common.Hash
SetState(common.Address, common.Hash, common.Hash)
SetCode(common.Address, []byte)
SetNonce(common.Address, uint64)
GetNonce(common.Address) uint64
GetBalance(common.Address) *big.Int
AddBalance(common.Address, *big.Int)
SubBalance(common.Address, *big.Int)
SubBalanceMultiCoin(common.Address, common.Hash, *big.Int)
AddBalanceMultiCoin(common.Address, common.Hash, *big.Int)
GetBalanceMultiCoin(common.Address, common.Hash) *big.Int
CreateAccount(common.Address)
Exist(common.Address) bool
}
// StatefulPrecompiledContract is the interface for executing a precompiled contract
type StatefulPrecompiledContract interface {
// Run executes the precompiled contract.
Run(accessibleState PrecompileAccessibleState, caller common.Address, addr common.Address, input []byte, suppliedGas uint64, readOnly bool) (ret []byte, remainingGas uint64, err error)
}
// statefulPrecompileFunction defines a function implemented by a stateful precompile
type statefulPrecompileFunction struct {
// selector is the 4 byte function selector for this function
// This should be calculated from the function signature using CalculateFunctionSelector
selector []byte
// execute is performed when this function is selected
execute RunStatefulPrecompileFunc
}
// newStatefulPrecompileFunction creates a stateful precompile function with the given arguments
//
//nolint:unused,deadcode
func newStatefulPrecompileFunction(selector []byte, execute RunStatefulPrecompileFunc) *statefulPrecompileFunction {
return &statefulPrecompileFunction{
selector: selector,
execute: execute,
}
}
// statefulPrecompileWithFunctionSelectors implements StatefulPrecompiledContract by using 4 byte function selectors to pass
// off responsibilities to internal execution functions.
// Note: because we only ever read from [functions] there no lock is required to make it thread-safe.
type statefulPrecompileWithFunctionSelectors struct {
fallback *statefulPrecompileFunction
functions map[string]*statefulPrecompileFunction
}
// newStatefulPrecompileWithFunctionSelectors generates new StatefulPrecompile using [functions] as the available functions and [fallback]
// as an optional fallback if there is no input data. Note: the selector of [fallback] will be ignored, so it is required to be left empty.
//
//nolint:unused,deadcode
func newStatefulPrecompileWithFunctionSelectors(fallback *statefulPrecompileFunction, functions []*statefulPrecompileFunction) StatefulPrecompiledContract {
// Ensure that if a fallback is present, it does not have a mistakenly populated function selector.
if fallback != nil && len(fallback.selector) != 0 {
panic(fmt.Errorf("fallback function cannot specify non-zero length function selector"))
}
// Construct the contract and populate [functions].
contract := &statefulPrecompileWithFunctionSelectors{
fallback: fallback,
functions: make(map[string]*statefulPrecompileFunction),
}
for _, function := range functions {
_, exists := contract.functions[string(function.selector)]
if exists {
panic(fmt.Errorf("cannot create stateful precompile with duplicated function selector: %q", function.selector))
}
contract.functions[string(function.selector)] = function
}
return contract
}
// Run selects the function using the 4 byte function selector at the start of the input and executes the underlying function on the
// given arguments.
func (s *statefulPrecompileWithFunctionSelectors) Run(accessibleState PrecompileAccessibleState, caller common.Address, addr common.Address, input []byte, suppliedGas uint64, readOnly bool) (ret []byte, remainingGas uint64, err error) {
// If there is no input data present, call the fallback function if present.
if len(input) == 0 && s.fallback != nil {
return s.fallback.execute(accessibleState, caller, addr, nil, suppliedGas, readOnly)
}
// Otherwise, an unexpected input size will result in an error.
if len(input) < selectorLen {
return nil, suppliedGas, fmt.Errorf("missing function selector to precompile - input length (%d)", len(input))
}
// Use the function selector to grab the correct function
selector := input[:selectorLen]
functionInput := input[selectorLen:]
function, ok := s.functions[string(selector)]
if !ok {
return nil, suppliedGas, fmt.Errorf("invalid function selector %#x", selector)
}
return function.execute(accessibleState, caller, addr, functionInput, suppliedGas, readOnly)
}