The contract represents a contract in the Ethereum state database. Contains the contract code and calls the parameters.
structure
// ContractRef is a reference to the contract's backing object
type ContractRef interface {
Address() common.Address
}
// AccountRef implements ContractRef.
//
// Account references are used during EVM initialisation and
// it's primary use is to fetch addresses. Removing this object
// proves difficult because of the cached jump destinations which
// are fetched from the parent contract (i.e. the caller), which
// is a ContractRef.
type AccountRef common.Address
// Address casts AccountRef to a Address
func (ar AccountRef) Address() common.Address { return (common.Address)(ar) }
// Contract represents an ethereum contract in the state database. It contains
// the the contract code, calling arguments. Contract implements ContractRef
type Contract struct {
// CallerAddress is the result of the caller which initialised this
// contract. However when the "call method" is delegated this value
// needs to be initialised to that of the caller's caller.
CallerAddress common.Address
caller ContractRef
self ContractRef
jumpdests destinations // result of JUMPDEST analysis.
Code []byte
CodeHash common.Hash
CodeAddr *common.Address
Input []byte
Gas uint64
value *big.Int
Args []byte
DelegateCall bool
}structure
// NewContract returns a new contract environment for the execution of EVM.
func NewContract(caller ContractRef, object ContractRef, value *big.Int, gas uint64) *Contract {
c := &Contract{CallerAddress: caller.Address(), caller: caller, self: object, Args: nil}
if parent, ok := caller.(*Contract); ok {
// Reuse JUMPDEST analysis from parent context if available.
// If the caller is a contract, it means that the contract called us. Jumpdests set to jumper's jumpdests
c.jumpdests = parent.jumpdests
} else {
c.jumpdests = make(destinations)
}
// Gas should be a pointer so it can safely be reduced through the run
// This pointer will be off the state transition
c.Gas = gas
// ensures a value is set
c.value = value
return c
}AsDelegate sets the contract as a delegate call and returns the current contract (for chained calls)
// AsDelegate sets the contract to be a delegate call and returns the current
// contract (for chaining calls)
func (c *Contract) AsDelegate() *Contract {
c.DelegateCall = true
// NOTE: caller must, at all times be a contract. It should never happen
// that caller is something other than a Contract.
parent := c.caller.(*Contract)
c.CallerAddress = parent.CallerAddress
c.value = parent.value
return c
}GetOp is used to get the next hop instruction
// GetOp returns the n'th element in the contract's byte array
func (c *Contract) GetOp(n uint64) OpCode {
return OpCode(c.GetByte(n))
}
// GetByte returns the n'th byte in the contract's byte array
func (c *Contract) GetByte(n uint64) byte {
if n < uint64(len(c.Code)) {
return c.Code[n]
}
return 0
}
// Caller returns the caller of the contract.
//
// Caller will recursively call caller when the contract is a delegate
// call, including that of caller's caller.
func (c *Contract) Caller() common.Address {
return c.CallerAddress
}UseGas uses Gas。
// UseGas attempts the use gas and subtracts it and returns true on success
func (c *Contract) UseGas(gas uint64) (ok bool) {
if c.Gas < gas {
return false
}
c.Gas -= gas
return true
}
// Address returns the contracts address
func (c *Contract) Address() common.Address {
return c.self.Address()
}
// Value returns the contracts value (sent to it from it's caller)
func (c *Contract) Value() *big.Int {
return c.value
}SetCode ，SetCallCode set the code
// SetCode sets the code to the contract
func (self *Contract) SetCode(hash common.Hash, code []byte) {
self.Code = code
self.CodeHash = hash
}
// SetCallCode sets the code of the contract and address of the backing data
// object
func (self *Contract) SetCallCode(addr *common.Address, hash common.Hash, code []byte) {
self.Code = code
self.CodeHash = hash
self.CodeAddr = addr
}structure
// Context provides the EVM with auxiliary information. Once provided
// it shouldn't be modified.
type Context struct {
// CanTransfer returns whether the account contains
// sufficient ether to transfer the value
CanTransfer CanTransferFunc
// Transfer transfers ether from one account to the other
Transfer TransferFunc
// GetHash returns the hash corresponding to n
GetHash GetHashFunc
// Message information
Origin common.Address // Provides information for ORIGIN
GasPrice *big.Int // Provides information for GASPRICE
// Block information
Coinbase common.Address // Provides information for COINBASE
GasLimit *big.Int // Provides information for GASLIMIT
BlockNumber *big.Int // Provides information for NUMBER
Time *big.Int // Provides information for TIME
Difficulty *big.Int // Provides information for DIFFICULTY
}
// EVM is the Ethereum Virtual Machine base object and provides
// the necessary tools to run a contract on the given state with
// the provided context. It should be noted that any error
// generated through any of the calls should be considered a
// revert-state-and-consume-all-gas operation, no checks on
// specific errors should ever be performed. The interpreter makes
// sure that any errors generated are to be considered faulty code.
// The EVM should never be reused and is not thread safe.
type EVM struct {
// Context provides auxiliary blockchain related information
Context
// StateDB gives access to the underlying state
StateDB StateDB
// Depth is the current call stack
depth int
// chainConfig contains information about the current chain
chainConfig *params.ChainConfig
// chain rules contains the chain rules for the current epoch
chainRules params.Rules
// virtual machine configuration options used to initialise the
// evm.
vmConfig Config
// global (to this context) ethereum virtual machine
// used throughout the execution of the tx.
interpreter *Interpreter
// abort is used to abort the EVM calling operations
// NOTE: must be set atomically
abort int32
}constructor
// NewEVM retutrns a new EVM . The returned EVM is not thread safe and should
// only ever be used *once*.
func NewEVM(ctx Context, statedb StateDB, chainConfig *params.ChainConfig, vmConfig Config) *EVM {
evm := &EVM{
Context: ctx,
StateDB: statedb,
vmConfig: vmConfig,
chainConfig: chainConfig,
chainRules: chainConfig.Rules(ctx.BlockNumber),
}
evm.interpreter = NewInterpreter(evm, vmConfig)
return evm
}
// Cancel cancels any running EVM operation. This may be called concurrently and
// it's safe to be called multiple times.
func (evm *EVM) Cancel() {
atomic.StoreInt32(&evm.abort, 1)
}The contract creation Create will create a new contract.
// Create creates a new contract using code as deployment code.
func (evm *EVM) Create(caller ContractRef, code []byte, gas uint64, value *big.Int) (ret []byte, contractAddr common.Address, leftOverGas uint64, err error) {
// Depth check execution. Fail if we're trying to execute above the
// limit.
if evm.depth > int(params.CallCreateDepth) {
return nil, common.Address{}, gas, ErrDepth
}
if !evm.CanTransfer(evm.StateDB, caller.Address(), value) {
return nil, common.Address{}, gas, ErrInsufficientBalance
}
// Ensure there's no existing contract already at the designated address
nonce := evm.StateDB.GetNonce(caller.Address())
evm.StateDB.SetNonce(caller.Address(), nonce+1)
contractAddr = crypto.CreateAddress(caller.Address(), nonce)
contractHash := evm.StateDB.GetCodeHash(contractAddr)
if evm.StateDB.GetNonce(contractAddr) != 0 || (contractHash != (common.Hash{}) && contractHash != emptyCodeHash) { // if already existed
return nil, common.Address{}, 0, ErrContractAddressCollision
}
// Create a new account on the state
snapshot := evm.StateDB.Snapshot() // Create a snapshot of StateDB for rollback
evm.StateDB.CreateAccount(contractAddr)
if evm.ChainConfig().IsEIP158(evm.BlockNumber) {
evm.StateDB.SetNonce(contractAddr, 1) // first
}
evm.Transfer(evm.StateDB, caller.Address(), contractAddr, value) // transfer money to contract
// initialise a new contract and set the code that is to be used by the
// E The contract is a scoped evmironment for this execution context
// only.
contract := NewContract(caller, AccountRef(contractAddr), value, gas)
contract.SetCallCode(&contractAddr, crypto.Keccak256Hash(code), code)
if evm.vmConfig.NoRecursion && evm.depth > 0 {
return nil, contractAddr, gas, nil
}
ret, err = run(evm, snapshot, contract, nil) // initialization code
// check whether the max code size has been exceeded
maxCodeSizeExceeded := evm.ChainConfig().IsEIP158(evm.BlockNumber) && len(ret) > params.MaxCodeSize
// if the contract creation ran successfully and no errors were returned
// calculate the gas required to store the code. If the code could not
// be stored due to not enough gas set an error and let it be handled
// by the error checking condition below.
if err == nil && !maxCodeSizeExceeded {
createDataGas := uint64(len(ret)) * params.CreateDataGas
if contract.UseGas(createDataGas) {
evm.StateDB.SetCode(contractAddr, ret)
} else {
err = ErrCodeStoreOutOfGas
}
}
// When an error was returned by the EVM or when setting the creation code
// above we revert to the snapshot and consume any gas remaining. Additionally
// when we're in homestead this also counts for code storage gas errors.
if maxCodeSizeExceeded || (err != nil && (evm.ChainConfig().IsHomestead(evm.BlockNumber) || err != ErrCodeStoreOutOfGas)) {
evm.StateDB.RevertToSnapshot(snapshot)
if err != errExecutionReverted {
contract.UseGas(contract.Gas)
}
}
// Assign err if contract code size exceeds the max while the err is still empty.
if maxCodeSizeExceeded && err == nil {
err = errMaxCodeSizeExceeded
}
return ret, contractAddr, contract.Gas, err
}Call method, whether we transfer or execute code that will call to this contract, the contract while the inside of the call instruction will be executed here.
// Call executes the contract associated with the addr with the given input as
// parameters. It also handles any necessary value transfer required and takes
// the necessary steps to create accounts and reverses the state in case of an
// execution error or failed value transfer.
func (evm *EVM) Call(caller ContractRef, addr common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, leftOverGas uint64, err error) {
if evm.vmConfig.NoRecursion && evm.depth > 0 {
return nil, gas, nil
}
// Fail if we're trying to execute above the call depth limit
// call depth up to 1024, recursion impossible
if evm.depth > int(params.CallCreateDepth) {
return nil, gas, ErrDepth
}
// Fail if we're trying to transfer more than the available balance
if !evm.Context.CanTransfer(evm.StateDB, caller.Address(), value) {
return nil, gas, ErrInsufficientBalance
}
var (
to = AccountRef(addr)
snapshot = evm.StateDB.Snapshot()
)
if !evm.StateDB.Exist(addr) { // contract does not exists
// If the address does not exist, check if it is a native go contract, the native go contract is
// inside the contracts.go
precompiles := PrecompiledContractsHomestead
if evm.ChainConfig().IsByzantium(evm.BlockNumber) {
precompiles = PrecompiledContractsByzantium
}
if precompiles[addr] == nil && evm.ChainConfig().IsEIP158(evm.BlockNumber) && value.Sign() == 0 {
// If it is not the specified contract address, and the value of value is 0, then it returns to normal, and this call does not consume Gas.
return nil, gas, nil
}
// Responsible for creating addr in local state
evm.StateDB.CreateAccount(addr)
}
// Perform transfer
evm.Transfer(evm.StateDB, caller.Address(), to.Address(), value)
// initialise a new contract and set the code that is to be used by the
// E The contract is a scoped environment for this execution context
// only.
contract := NewContract(caller, to, value, gas)
contract.SetCallCode(&addr, evm.StateDB.GetCodeHash(addr), evm.StateDB.GetCode(addr))
ret, err = run(evm, snapshot, contract, input)
// When an error was returned by the EVM or when setting the creation code
// above we revert to the snapshot and consume any gas remaining. Additionally
// when we're in homestead this also counts for code storage gas errors.
if err != nil {
evm.StateDB.RevertToSnapshot(snapshot)
if err != errExecutionReverted {
// If it is an error triggered by the revert command, because ICO generally sets a limit on the number of people or funds
// These restrictions are likely to be triggered when you snap up, causing a lot of money to be drawn. at this time
// You can't set the lower GasPrice and GasLimit. Because it is fast.
// Then don't use all the remaining Gas, but only the Gas that is executed using the code
// Otherwise it will be taken away by GasLimit *GasPrice, which is quite a lot.
contract.UseGas(contract.Gas)
}
}
return ret, contract.Gas, err
}The remaining three functions, CallCode, DelegateCall, and StaticCall, cannot be called externally and can only be triggered by Opcode.
CallCode
// CallCode differs from Call in the sense that it executes the given address'
// code with the caller as context.
func (evm *EVM) CallCode(caller ContractRef, addr common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, leftOverGas uint64, err error) {
if evm.vmConfig.NoRecursion && evm.depth > 0 {
return nil, gas, nil
}
// Fail if we're trying to execute above the call depth limit
if evm.depth > int(params.CallCreateDepth) {
return nil, gas, ErrDepth
}
// Fail if we're trying to transfer more than the available balance
if !evm.CanTransfer(evm.StateDB, caller.Address(), value) {
return nil, gas, ErrInsufficientBalance
}
var (
snapshot = evm.StateDB.Snapshot()
to = AccountRef(caller.Address()) //This is the most different place. The address of to is changed to the address of the caller and there is no transfer behavior.
)
// initialise a new contract and set the code that is to be used by the
// E The contract is a scoped evmironment for this execution context
// only.
contract := NewContract(caller, to, value, gas)
contract.SetCallCode(&addr, evm.StateDB.GetCodeHash(addr), evm.StateDB.GetCode(addr))
ret, err = run(evm, snapshot, contract, input)
if err != nil {
evm.StateDB.RevertToSnapshot(snapshot)
if err != errExecutionReverted {
contract.UseGas(contract.Gas)
}
}
return ret, contract.Gas, err
}DelegateCall
// DelegateCall differs from CallCode in the sense that it executes the given address'
// code with the caller as context and the caller is set to the caller of the caller.
func (evm *EVM) DelegateCall(caller ContractRef, addr common.Address, input []byte, gas uint64) (ret []byte, leftOverGas uint64, err error) {
if evm.vmConfig.NoRecursion && evm.depth > 0 {
return nil, gas, nil
}
// Fail if we're trying to execute above the call depth limit
if evm.depth > int(params.CallCreateDepth) {
return nil, gas, ErrDepth
}
var (
snapshot = evm.StateDB.Snapshot()
to = AccountRef(caller.Address())
)
// Initialise a new contract and make initialise the delegate values
// Identified as AsDelete()
contract := NewContract(caller, to, nil, gas).AsDelegate()
contract.SetCallCode(&addr, evm.StateDB.GetCodeHash(addr), evm.StateDB.GetCode(addr))
ret, err = run(evm, snapshot, contract, input)
if err != nil {
evm.StateDB.RevertToSnapshot(snapshot)
if err != errExecutionReverted {
contract.UseGas(contract.Gas)
}
}
return ret, contract.Gas, err
}
// StaticCall executes the contract associated with the addr with the given input
// as parameters while disallowing any modifications to the state during the call.
// Opcodes that attempt to perform such modifications will result in exceptions
// instead of performing the modifications.
func (evm *EVM) StaticCall(caller ContractRef, addr common.Address, input []byte, gas uint64) (ret []byte, leftOverGas uint64, err error) {
if evm.vmConfig.NoRecursion && evm.depth > 0 {
return nil, gas, nil
}
// Fail if we're trying to execute above the call depth limit
if evm.depth > int(params.CallCreateDepth) {
return nil, gas, ErrDepth
}
// Make sure the readonly is only set if we aren't in readonly yet
// this makes also sure that the readonly flag isn't removed for
// child calls.
if !evm.interpreter.readOnly {
evm.interpreter.readOnly = true
defer func() { evm.interpreter.readOnly = false }()
}
var (
to = AccountRef(addr)
snapshot = evm.StateDB.Snapshot()
)
// Initialise a new contract and set the code that is to be used by the
// EVM. The contract is a scoped environment for this execution context
// only.
contract := NewContract(caller, to, new(big.Int), gas)
contract.SetCallCode(&addr, evm.StateDB.GetCodeHash(addr), evm.StateDB.GetCode(addr))
// When an error was returned by the EVM or when setting the creation code
// above we revert to the snapshot and consume any gas remaining. Additionally
// when we're in Homestead this also counts for code storage gas errors.
ret, err = run(evm, snapshot, contract, input)
if err != nil {
evm.StateDB.RevertToSnapshot(snapshot)
if err != errExecutionReverted {
contract.UseGas(contract.Gas)
}
}
return ret, contract.Gas, err
}