vmcommon

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Published: Apr 10, 2022 License: GPL-3.0 Imports: 10 Imported by: 6

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elrond-vm-common

Common structs between VM and node

Documentation

Index

Constants

View Source
const (
	// MetadataUpgradeable is the bit for upgradable flag
	MetadataUpgradeable = 1
	// MetadataReadable is the bit for readable flag
	MetadataReadable = 4
)

Const group for the first byte of the metadata

View Source
const (
	// MetadataPayable is the bit for payable flag
	MetadataPayable = 2
	// MetadataPayableBySC is the bit for payable flag
	MetadataPayableBySC = 4
)

Const group for the second byte of the metadata

View Source
const MaxLengthForValueToOptTransfer = 32

MaxLengthForValueToOptTransfer defines the maximum length for value to optimize cross shard transfer

View Source
const NumInitCharactersForScAddress = 10

NumInitCharactersForScAddress numbers of characters for smart contract address identifier

View Source
const ShardIdentiferLen = 2

ShardIdentiferLen number of characters for shard identifier in an address

View Source
const VMTypeLen = 2

VMTypeLen number of characters with VMType identifier in an address, these are the last 2 characters from the initial identifier

Variables

View Source
var ErrSubtractionOverflow = errors.New("uint64 subtraction overflowed")

ErrSubtractionOverflow signals that uint64 subtraction overflowed

View Source
var SystemAccountAddress = bytes.Repeat([]byte{255}, 32)

SystemAccountAddress is the hard-coded address in which we save global settings on all shards

Functions

func IsAllowedToSaveUnderKey

func IsAllowedToSaveUnderKey(key []byte) bool

IsAllowedToSaveUnderKey returns if saving key-value in data tries under given key is allowed

func IsEmptyAddress

func IsEmptyAddress(address []byte) bool

IsEmptyAddress returns whether an address is empty

func IsMetachainIdentifier

func IsMetachainIdentifier(identifier []byte) bool

IsMetachainIdentifier verifies if the identifier is of type metachain

func IsSmartContractAddress

func IsSmartContractAddress(rcvAddress []byte) bool

IsSmartContractAddress verifies if a set address is of type smart contract

func IsSmartContractOnMetachain

func IsSmartContractOnMetachain(identifier []byte, rcvAddress []byte) bool

IsSmartContractOnMetachain verifies if an address is smart contract on metachain

func IsSystemAccountAddress

func IsSystemAccountAddress(address []byte) bool

IsSystemAccountAddress returns true if given address is system account address

func SafeSubUint64

func SafeSubUint64(a, b uint64) (uint64, error)

SafeSubUint64 performs subtraction on uint64 and returns an error if it overflows

Types

type AcceptPayableHandler

type AcceptPayableHandler interface {
	SetPayableHandler(payableHandler PayableHandler) error
	IsInterfaceNil() bool
}

AcceptPayableHandler defines the methods to accept a payable handler through a set function

type AccountDataHandler

type AccountDataHandler interface {
	RetrieveValue(key []byte) ([]byte, error)
	SaveKeyValue(key []byte, value []byte) error
	IsInterfaceNil() bool
}

AccountDataHandler models what how to manipulate data held by a SC account

type AccountHandler

type AccountHandler interface {
	AddressBytes() []byte
	IncreaseNonce(nonce uint64)
	GetNonce() uint64
	IsInterfaceNil() bool
}

AccountHandler models a state account, which can journalize and revert It knows about code and data, as data structures not hashes

type AccountsAdapter

type AccountsAdapter interface {
	GetExistingAccount(address []byte) (AccountHandler, error)
	LoadAccount(address []byte) (AccountHandler, error)
	SaveAccount(account AccountHandler) error
	RemoveAccount(address []byte) error
	Commit() ([]byte, error)
	JournalLen() int
	RevertToSnapshot(snapshot int) error
	GetCode(codeHash []byte) []byte

	RootHash() ([]byte, error)
	RecreateTrie(rootHash []byte) error
	IsInterfaceNil() bool
}

AccountsAdapter is used for the structure that manages the accounts on top of a trie.PatriciaMerkleTrie implementation

type BaseOperationCost

type BaseOperationCost struct {
	StorePerByte      uint64
	ReleasePerByte    uint64
	DataCopyPerByte   uint64
	PersistPerByte    uint64
	CompilePerByte    uint64
	AoTPreparePerByte uint64
}

BaseOperationCost defines cost for base operation cost

type BlockchainHook

type BlockchainHook interface {
	// NewAddress yields the address of a new SC account, when one such account is created.
	// The result should only depend on the creator address and nonce.
	// Returning an empty address lets the VM decide what the new address should be.
	NewAddress(creatorAddress []byte, creatorNonce uint64, vmType []byte) ([]byte, error)

	// GetStorageData should yield the storage value for a certain account and index.
	// Should return an empty byte array if the key is missing from the account storage,
	// or if account does not exist.
	GetStorageData(accountAddress []byte, index []byte) ([]byte, error)

	// GetBlockhash returns the hash of the block with the asked nonce if available
	GetBlockhash(nonce uint64) ([]byte, error)

	// LastNonce returns the nonce from from the last committed block
	LastNonce() uint64

	// LastRound returns the round from the last committed block
	LastRound() uint64

	// LastTimeStamp returns the timeStamp from the last committed block
	LastTimeStamp() uint64

	// LastRandomSeed returns the random seed from the last committed block
	LastRandomSeed() []byte

	// LastEpoch returns the epoch from the last committed block
	LastEpoch() uint32

	// GetStateRootHash returns the state root hash from the last committed block
	GetStateRootHash() []byte

	// CurrentNonce returns the nonce from the current block
	CurrentNonce() uint64

	// CurrentRound returns the round from the current block
	CurrentRound() uint64

	// CurrentTimeStamp return the timestamp from the current block
	CurrentTimeStamp() uint64

	// CurrentRandomSeed returns the random seed from the current header
	CurrentRandomSeed() []byte

	// CurrentEpoch returns the current epoch
	CurrentEpoch() uint32

	// ProcessBuiltInFunction will process the builtIn function for the created input
	ProcessBuiltInFunction(input *ContractCallInput) (*VMOutput, error)

	// GetBuiltinFunctionNames returns the names of protocol built-in functions
	GetBuiltinFunctionNames() FunctionNames

	// GetAllState returns the full state of the account, all the key-value saved
	GetAllState(address []byte) (map[string][]byte, error)

	// GetUserAccount returns a user account
	GetUserAccount(address []byte) (UserAccountHandler, error)

	// GetCode returns the code for the given account
	GetCode(UserAccountHandler) []byte

	// GetShardOfAddress returns the shard ID of a given address
	GetShardOfAddress(address []byte) uint32

	// IsSmartContract returns whether the address points to a smart contract
	IsSmartContract(address []byte) bool

	// IsPayable checks weather the provided address can receive ERD or not
	IsPayable(sndAddress []byte, recvAddress []byte) (bool, error)

	// SaveCompiledCode saves to cache and storage the compiled code
	SaveCompiledCode(codeHash []byte, code []byte)

	// GetCompiledCode returns the compiled code if it finds in the cache or storage
	GetCompiledCode(codeHash []byte) (bool, []byte)

	// ClearCompiledCodes clears the cache and storage of compiled codes
	ClearCompiledCodes()

	// GetESDTToken loads the ESDT digital token for the given key
	GetESDTToken(address []byte, tokenID []byte, nonce uint64) (*esdt.ESDigitalToken, error)

	// GetSnapshot gets the number of entries in the journal as a snapshot id
	GetSnapshot() int

	// RevertToSnapshot reverts snaphots up to the specified one
	RevertToSnapshot(snapshot int) error

	// IsInterfaceNil returns true if there is no value under the interface
	IsInterfaceNil() bool
}

BlockchainHook is the interface for VM blockchain callbacks

type BuiltInCost

type BuiltInCost struct {
	ChangeOwnerAddress       uint64
	ClaimDeveloperRewards    uint64
	SaveUserName             uint64
	SaveKeyValue             uint64
	ESDTTransfer             uint64
	ESDTBurn                 uint64
	ESDTLocalMint            uint64
	ESDTLocalBurn            uint64
	ESDTNFTCreate            uint64
	ESDTNFTAddQuantity       uint64
	ESDTNFTBurn              uint64
	ESDTNFTTransfer          uint64
	ESDTNFTChangeCreateOwner uint64
	ESDTNFTMultiTransfer     uint64
	ESDTNFTAddURI            uint64
	ESDTNFTUpdateAttributes  uint64
}

BuiltInCost defines cost for built-in methods

type BuiltInFunctionContainer

type BuiltInFunctionContainer interface {
	Get(key string) (BuiltinFunction, error)
	Add(key string, function BuiltinFunction) error
	Replace(key string, function BuiltinFunction) error
	Remove(key string)
	Len() int
	Keys() map[string]struct{}
	IsInterfaceNil() bool
}

BuiltInFunctionContainer defines the methods for the built-in protocol container

type BuiltinFunction

type BuiltinFunction interface {
	ProcessBuiltinFunction(acntSnd, acntDst UserAccountHandler, vmInput *ContractCallInput) (*VMOutput, error)
	SetNewGasConfig(gasCost *GasCost)
	IsActive() bool
	IsInterfaceNil() bool
}

BuiltinFunction defines the methods for the built-in protocol smart contract functions

type CallArgsParser

type CallArgsParser interface {
	ParseData(data string) (string, [][]byte, error)
	IsInterfaceNil() bool
}

CallArgsParser will handle parsing transaction data to function and arguments

type CodeMetadata

type CodeMetadata struct {
	Payable     bool
	PayableBySC bool
	Upgradeable bool
	Readable    bool
}

CodeMetadata represents smart contract code metadata

func CodeMetadataFromBytes

func CodeMetadataFromBytes(bytes []byte) CodeMetadata

CodeMetadataFromBytes creates a metadata object from bytes

func (*CodeMetadata) ToBytes

func (metadata *CodeMetadata) ToBytes() []byte

ToBytes converts the metadata to bytes

type ContractCallInput

type ContractCallInput struct {
	VMInput

	// RecipientAddr is the smart contract public key, "to".
	RecipientAddr []byte

	// Function is the name of the smart contract function that will be called.
	// The function must be public
	Function string

	// AllowInitFunction specifies whether calling the initialization method of
	// the smart contract is allowed or not
	AllowInitFunction bool
}

ContractCallInput VM input when calling a function from an existing contract

type ContractCreateInput

type ContractCreateInput struct {
	VMInput

	// ContractCode is the code of the contract being created, assembled into a byte array.
	ContractCode []byte

	// ContractCodeMetadata is the code metadata of the contract being created.
	ContractCodeMetadata []byte
}

ContractCreateInput VM input when creating a new contract. Here we have no RecipientAddr because the address (PK) of the created account will be provided by the vmcommon. We also do not need to specify a Function field, because on creation `init` is always called.

type Coordinator

type Coordinator interface {
	NumberOfShards() uint32
	ComputeId(address []byte) uint32
	SelfId() uint32
	SameShard(firstAddress, secondAddress []byte) bool
	CommunicationIdentifier(destShardID uint32) string
	IsInterfaceNil() bool
}

Coordinator defines what a shard state coordinator should hold

type CryptoHook

type CryptoHook interface {
	// Sha256 cryptographic function
	Sha256(data []byte) ([]byte, error)

	// Keccak256 cryptographic function
	Keccak256(data []byte) ([]byte, error)

	// Ripemd160 cryptographic function
	Ripemd160(data []byte) ([]byte, error)

	// Ecrecover calculates the corresponding Ethereum address for the public key which created the given signature
	// https://ewasm.readthedocs.io/en/mkdocs/system_contracts/
	Ecrecover(hash []byte, recoveryID []byte, r []byte, s []byte) ([]byte, error)

	// IsInterfaceNil returns true if there is no value under the interface
	IsInterfaceNil() bool
}

CryptoHook interface for VM krypto functions

type ESDTGlobalSettingsHandler

type ESDTGlobalSettingsHandler interface {
	IsPaused(token []byte) bool
	IsLimitedTransfer(tokenKey []byte) bool
	IsInterfaceNil() bool
}

ESDTGlobalSettingsHandler provides global settings functions for an ESDT token

type ESDTNFTStorageHandler

type ESDTNFTStorageHandler interface {
	SaveESDTNFTToken(senderAddress []byte, acnt UserAccountHandler, esdtTokenKey []byte, nonce uint64, esdtData *esdt.ESDigitalToken, isCreation bool, isReturnWithError bool) ([]byte, error)
	GetESDTNFTTokenOnSender(acnt UserAccountHandler, esdtTokenKey []byte, nonce uint64) (*esdt.ESDigitalToken, error)
	GetESDTNFTTokenOnDestination(acnt UserAccountHandler, esdtTokenKey []byte, nonce uint64) (*esdt.ESDigitalToken, bool, error)
	WasAlreadySentToDestinationShardAndUpdateState(tickerID []byte, nonce uint64, dstAddress []byte) (bool, error)
	SaveNFTMetaDataToSystemAccount(tx data.TransactionHandler) error
	IsInterfaceNil() bool
}

ESDTNFTStorageHandler will handle the storage for the nft metadata

type ESDTRoleHandler

type ESDTRoleHandler interface {
	CheckAllowedToExecute(account UserAccountHandler, tokenID []byte, action []byte) error
	IsInterfaceNil() bool
}

ESDTRoleHandler provides IsAllowedToExecute function for an ESDT

type ESDTTransfer

type ESDTTransfer struct {
	// ESDTValue is the value (amount of tokens) transferred by the transaction.
	// Before reaching the VM this value is subtracted from sender balance (CallerAddr)
	// and to added to the smart contract balance.
	// It is often, but not always zero in SC calls.
	ESDTValue *big.Int

	// ESDTTokenName is the name of the token which was transferred by the transaction to the SC
	ESDTTokenName []byte

	// ESDTTokenType is the type of the transferred token
	ESDTTokenType uint32

	// ESDTTokenNonce is the nonce for the given NFT token
	ESDTTokenNonce uint64
}

ESDTTransfer defines the structure for and ESDT / NFT transfer

type ESDTTransferParser

type ESDTTransferParser interface {
	ParseESDTTransfers(sndAddr []byte, rcvAddr []byte, function string, args [][]byte) (*ParsedESDTTransfers, error)
	IsInterfaceNil() bool
}

ESDTTransferParser can parse single and multi ESDT / NFT transfers

type EpochNotifier

type EpochNotifier interface {
	RegisterNotifyHandler(handler EpochSubscriberHandler)
	IsInterfaceNil() bool
}

EpochNotifier can notify upon an epoch change and provide the current epoch

type EpochSubscriberHandler

type EpochSubscriberHandler interface {
	EpochConfirmed(epoch uint32, timestamp uint64)
	IsInterfaceNil() bool
}

EpochSubscriberHandler defines the behavior of a component that can be notified if a new epoch was confirmed

type FunctionNames

type FunctionNames = map[string]struct{}

FunctionNames (alias) is a map of function names

type GasCost

type GasCost struct {
	BaseOperationCost BaseOperationCost
	BuiltInCost       BuiltInCost
}

GasCost holds all the needed gas costs for system smart contracts

type LogEntry

type LogEntry struct {
	Identifier []byte
	Address    []byte
	Topics     [][]byte
	Data       []byte
}

LogEntry represents an entry in the contract execution log. TODO: document all fields.

type Marshalizer

type Marshalizer interface {
	Marshal(obj interface{}) ([]byte, error)
	Unmarshal(obj interface{}, buff []byte) error
	IsInterfaceNil() bool
}

Marshalizer defines the 2 basic operations: serialize (marshal) and deserialize (unmarshal)

type OutputAccount

type OutputAccount struct {
	// Address is the public key of the account.
	Address []byte

	// Nonce is the new account nonce.
	Nonce uint64

	// Balance is the account balance after running a SC.
	// Only used for some tests now, please ignore. Might be removed in the future.
	Balance *big.Int

	// StorageUpdates is a map containing pointers to StorageUpdate structs,
	// indexed with strings produced by `string(StorageUpdate.Offset)`, for fast
	// access by the Offset of the StorageUpdate. These StorageUpdate structs
	// will be processed by the Node to modify the storage of the SmartContract.
	// Please note that it is likely that not all existing account storage keys
	// show up here.
	StorageUpdates map[string]*StorageUpdate

	// Code is the assembled code of a smart contract account.
	// This field will be populated when a new SC must be created after the transaction.
	Code []byte

	// CodeMetadata is the metadata of the code
	// Like "Code", this field will be populated when a new SC must be created after the transaction.
	CodeMetadata []byte

	// CodeDeployerAddress will be populated in case of contract deployment or upgrade (both direct and indirect)
	CodeDeployerAddress []byte

	// BalanceDelta is by how much the balance should change following the SC execution.
	// A negative value indicates that balance should decrease.
	BalanceDelta *big.Int

	// OutputTransfers represents the cross shard calls for this account
	OutputTransfers []OutputTransfer

	// GasUsed will be populated if the contract was called in the same shard
	GasUsed uint64
}

OutputAccount shows the state of an account after contract execution. It can be an existing account or a new account created by the transaction. Note: the current implementation might also return unmodified accounts.

func (*OutputAccount) MergeOutputAccounts

func (o *OutputAccount) MergeOutputAccounts(outAcc *OutputAccount)

MergeOutputAccounts merges the given account into the current one

func (*OutputAccount) MergeStorageUpdates

func (o *OutputAccount) MergeStorageUpdates(outAcc *OutputAccount)

MergeStorageUpdates will copy all the storage updates from the given output account

type OutputTransfer

type OutputTransfer struct {
	// Value to be transferred
	Value *big.Int
	// GasLimit to used for the call
	GasLimit uint64
	// GasLocked holds the amount of gas to be kept aside for the eventual callback execution
	GasLocked uint64
	// Data to be used in cross call
	Data []byte
	// CallType is set if it is a smart contract invocation
	CallType vm.CallType
	// SenderAddress is the actual sender for the given output transfer, this is needed when
	// contract A calls contract B and contract B does the transfers
	SenderAddress []byte
}

OutputTransfer contains the fields needed to create transfers to another shard

type ParsedESDTTransfers

type ParsedESDTTransfers struct {
	ESDTTransfers []*ESDTTransfer
	RcvAddr       []byte
	CallFunction  string
	CallArgs      [][]byte
}

ParsedESDTTransfers defines the struct for the parsed esdt transfers

type PayableHandler

type PayableHandler interface {
	IsPayable(sndAddress, rcvAddress []byte) (bool, error)
	IsInterfaceNil() bool
}

PayableHandler provides IsPayable function which returns if an account is payable or not

type ReturnCode

type ReturnCode int

ReturnCode is an enum with the possible error codes returned by the VM

const (
	// Ok is returned when execution was completed normally.
	Ok ReturnCode = 0

	// FunctionNotFound is returned when the input specifies a function name that does not exist or is not public.
	FunctionNotFound ReturnCode = 1

	// FunctionWrongSignature is returned when the wrong number of arguments is provided.
	FunctionWrongSignature ReturnCode = 2

	// ContractNotFound is returned when the called contract does not exist.
	ContractNotFound ReturnCode = 3

	// UserError is returned for various execution errors.
	UserError ReturnCode = 4

	// OutOfGas is returned when VM execution runs out of gas.
	OutOfGas ReturnCode = 5

	// AccountCollision is returned when created account already exists.
	AccountCollision ReturnCode = 6

	// OutOfFunds is returned when the caller (sender) runs out of funds.
	OutOfFunds ReturnCode = 7

	// CallStackOverFlow is returned when stack overflow occurs.
	CallStackOverFlow ReturnCode = 8

	// ContractInvalid is returned when the contract is invalid.
	ContractInvalid ReturnCode = 9

	// ExecutionFailed is returned when the execution of the specified function has failed.
	ExecutionFailed ReturnCode = 10

	// UpgradeFailed is returned when the upgrade of the contract has failed
	UpgradeFailed ReturnCode = 11

	// SimulateFailed is returned when tx simulation fails execution
	SimulateFailed ReturnCode = 12
)

func (ReturnCode) String

func (rc ReturnCode) String() string

type SimpleESDTNFTStorageHandler

type SimpleESDTNFTStorageHandler interface {
	GetESDTNFTTokenOnDestination(accnt UserAccountHandler, esdtTokenKey []byte, nonce uint64) (*esdt.ESDigitalToken, bool, error)
	SaveNFTMetaDataToSystemAccount(tx data.TransactionHandler) error
	IsInterfaceNil() bool
}

SimpleESDTNFTStorageHandler will handle get of ESDT data and save metadata to system acc

type StorageUpdate

type StorageUpdate struct {
	// Offset is the storage key.
	Offset []byte

	// Data is the new storage value.
	// Zero indicates missing data for the key (or even a missing key),
	// therefore a value of zero here indicates that
	// the storage map entry with the given key can be deleted.
	Data []byte

	// Written represents that this storage was change and needs to be persisted
	// into the chain
	Written bool
}

StorageUpdate represents a change in the account storage (insert, update or delete) Note: current implementation might also return unmodified storage entries.

type UserAccountHandler

type UserAccountHandler interface {
	GetCodeMetadata() []byte
	GetCodeHash() []byte
	GetRootHash() []byte
	AccountDataHandler() AccountDataHandler
	AddToBalance(value *big.Int) error
	GetBalance() *big.Int
	ClaimDeveloperRewards([]byte) (*big.Int, error)
	GetDeveloperReward() *big.Int
	ChangeOwnerAddress([]byte, []byte) error
	SetOwnerAddress([]byte)
	GetOwnerAddress() []byte
	SetUserName(userName []byte)
	GetUserName() []byte
	AccountHandler
}

UserAccountHandler models a user account, which can journalize account's data with some extra features like balance, developer rewards, owner

type VMExecutionHandler

type VMExecutionHandler interface {
	closing.Closer

	// RunSmartContractCreate computes how a smart contract creation should be performed
	RunSmartContractCreate(input *ContractCreateInput) (*VMOutput, error)

	// RunSmartContractCall computes the result of a smart contract call and how the system must change after the execution
	RunSmartContractCall(input *ContractCallInput) (*VMOutput, error)

	// GasScheduleChange sets a new gas schedule for the VM
	GasScheduleChange(newGasSchedule map[string]map[string]uint64)

	// GetVersion returns the version of the VM instance
	GetVersion() string

	// IsInterfaceNil returns true if there is no value under the interface
	IsInterfaceNil() bool
}

VMExecutionHandler interface for any Elrond VM endpoint

type VMInput

type VMInput struct {
	// CallerAddr is the public key of the wallet initiating the transaction, "from".
	CallerAddr []byte

	// Arguments are the call parameters to the smart contract function call
	// For contract creation, these are the parameters to the @init function.
	// For contract call, these are the parameters to the function referenced in ContractCallInput.Function.
	// If the number of arguments does not match the function arity,
	// the transaction will return FunctionWrongSignature ReturnCode.
	Arguments [][]byte

	// CallValue is the eGLD value (amount of tokens) transferred by the transaction.
	// Before reaching the VM this value is subtracted from sender balance (CallerAddr)
	// and to added to the smart contract balance.
	// It is often, but not always zero in SC calls.
	CallValue *big.Int

	// CallType is the type of SmartContract call
	// Based on this value, the VM is informed of whether the call is direct,
	// asynchronous, or asynchronous callback.
	CallType vm.CallType

	// GasPrice multiplied by the gas burned by the transaction yields the transaction fee.
	// A larger GasPrice will incentivize block proposers to include the transaction in a block sooner,
	// but will cost the sender more.
	// The total fee should be GasPrice x (GasProvided - VMOutput.GasRemaining - VMOutput.GasRefund).
	// Note: the order of operations on the sender balance is:
	// 1. subtract GasPrice x GasProvided
	// 2. call VM, which will subtract CallValue if enough funds remain
	// 3. reimburse GasPrice x (VMOutput.GasRemaining + VMOutput.GasRefund)
	GasPrice uint64

	// GasProvided is the maximum gas allowed for the smart contract execution.
	// If the transaction consumes more gas than this value, it will immediately terminate
	// and return OutOfGas ReturnCode.
	// The sender will not be charged based on GasProvided, only on the gas burned,
	// so it doesn't cost the sender more to have a higher gas limit.
	GasProvided uint64

	// GasLocked is the amount of gas that must be kept unused during the current
	// call, because it will be used later for a callback. This field is only
	// used during asynchronous calls.
	GasLocked uint64

	// OriginalTxHash
	OriginalTxHash []byte

	// CurrentTxHash
	CurrentTxHash []byte

	// PrevTxHash
	PrevTxHash []byte

	// ESDTTransfers
	ESDTTransfers []*ESDTTransfer

	// ReturnCallAfterError
	ReturnCallAfterError bool
}

VMInput contains the common fields between the 2 types of SC call.

type VMOutput

type VMOutput struct {
	// ReturnData is the function call returned result.
	// This value does not influence the account state in any way.
	// The value should be accessible in a UI.
	// ReturnData is part of the transaction receipt.
	ReturnData [][]byte

	// ReturnCode is the function call error code.
	// If it is not `Ok`, the transaction failed in some way - gas is, however, consumed anyway.
	// This value does not influence the account state in any way.
	// The value should be accessible to a UI.
	// ReturnCode is part of the transaction receipt.
	ReturnCode ReturnCode

	// ReturnMessage is a message set by the SmartContract, destined for the
	// caller
	ReturnMessage string

	// GasRemaining = VMInput.GasProvided - gas used.
	// It is necessary to compute how much to charge the sender for the transaction.
	GasRemaining uint64

	// GasRefund is how much gas the sender earned during the transaction.
	// Certain operations, like freeing up storage, actually return gas instead of consuming it.
	// Based on GasRefund, the sender could in principle be rewarded instead of taxed.
	GasRefund *big.Int

	// OutputAccounts contains data about all accounts changed as a result of the
	// Transaction. It is a map containing pointers to OutputAccount structs,
	// indexed with strings produced by `string(OutputAccount.Address)`, for fast
	// access by the Address of the OutputAccount.
	// This information tells the Node how to update the account data.
	// It can contain new accounts or existing changed accounts.
	// Note: the current implementation might also retrieve accounts that were not changed.
	OutputAccounts map[string]*OutputAccount

	// DeletedAccounts is a list of public keys of accounts that need to be deleted
	// as a result of the transaction.
	DeletedAccounts [][]byte

	// TouchedAccounts is a list of public keys of accounts that were somehow involved in the VM execution.
	// TODO: investigate what we need to to about these.
	TouchedAccounts [][]byte

	// Logs is a list of event data logged by the vmcommon.
	// Smart contracts can choose to log certain events programatically.
	// There are 3 main use cases for events and logs:
	// 1. smart contract return values for the user interface;
	// 2. asynchronous triggers with data;
	// 3. a cheaper form of storage (e.g. storing historical data that can be rendered by the frontend).
	// The logs should be accessible to the UI.
	// The logs are part of the transaction receipt.
	Logs []*LogEntry
}

VMOutput is the return data and final account state after a SC execution.

func (*VMOutput) GetFirstReturnData

func (vmOutput *VMOutput) GetFirstReturnData(asType vm.ReturnDataKind) (interface{}, error)

GetFirstReturnData is a helper function that returns the first ReturnData of VMOutput, interpreted as specified.

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