interface.go

package lnwallet

import (
	"errors"
	"fmt"
	"sync"

	"github.com/btcsuite/btcd/btcec"
	"github.com/btcsuite/btcd/chaincfg/chainhash"
	"github.com/btcsuite/btcd/wire"
	"github.com/btcsuite/btcutil"
)

// AddressType is an enum-like type which denotes the possible address types
// WalletController supports.
type AddressType uint8

const (
	// WitnessPubKey represents a p2wkh address.
	WitnessPubKey AddressType = iota

	// NestedWitnessPubKey represents a p2sh output which is itself a
	// nested p2wkh output.
	NestedWitnessPubKey

	// UnknownAddressType represents an output with an unknown or non-standard
	// script.
	UnknownAddressType
)

var (
	// DefaultPublicPassphrase is the default public passphrase used for the
	// wallet.
	DefaultPublicPassphrase = []byte("public")

	// DefaultPrivatePassphrase is the default private passphrase used for
	// the wallet.
	DefaultPrivatePassphrase = []byte("hello")

	// ErrDoubleSpend is returned from PublishTransaction in case the
	// tx being published is spending an output spent by a conflicting
	// transaction.
	ErrDoubleSpend = errors.New("Transaction rejected: output already spent")

	// ErrNotMine is an error denoting that a WalletController instance is
	// unable to spend a specified output.
	ErrNotMine = errors.New("the passed output doesn't belong to the wallet")
)

// Utxo is an unspent output denoted by its outpoint, and output value of the
// original output.
type Utxo struct {
	AddressType   AddressType
	Value         btcutil.Amount
	PkScript      []byte
	RedeemScript  []byte
	WitnessScript []byte
	wire.OutPoint
}

// TransactionDetail describes a transaction with either inputs which belong to
// the wallet, or has outputs that pay to the wallet.
type TransactionDetail struct {
	// Hash is the transaction hash of the transaction.
	Hash chainhash.Hash

	// Value is the net value of this transaction (in satoshis) from the
	// PoV of the wallet. If this transaction purely spends from the
	// wallet's funds, then this value will be negative. Similarly, if this
	// transaction credits the wallet, then this value will be positive.
	Value btcutil.Amount

	// NumConfirmations is the number of confirmations this transaction
	// has. If the transaction is unconfirmed, then this value will be
	// zero.
	NumConfirmations int32

	// BlockHeight is the hash of the block which includes this
	// transaction. Unconfirmed transactions will have a nil value for this
	// field.
	BlockHash *chainhash.Hash

	// BlockHeight is the height of the block including this transaction.
	// Unconfirmed transaction will show a height of zero.
	BlockHeight int32

	// Timestamp is the unix timestamp of the block including this
	// transaction. If the transaction is unconfirmed, then this will be a
	// timestamp of txn creation.
	Timestamp int64

	// TotalFees is the total fee in satoshis paid by this transaction.
	TotalFees int64

	// DestAddresses are the destinations for a transaction
	DestAddresses []btcutil.Address
}

// TransactionSubscription is an interface which describes an object capable of
// receiving notifications of new transaction related to the underlying wallet.
// TODO(roasbeef): add balance updates?
type TransactionSubscription interface {
	// ConfirmedTransactions returns a channel which will be sent on as new
	// relevant transactions are confirmed.
	ConfirmedTransactions() chan *TransactionDetail

	// UnconfirmedTransactions returns a channel which will be sent on as
	// new relevant transactions are seen within the network.
	UnconfirmedTransactions() chan *TransactionDetail

	// Cancel finalizes the subscription, cleaning up any resources
	// allocated.
	Cancel()
}

// WalletController defines an abstract interface for controlling a local Pure
// Go wallet, a local or remote wallet via an RPC mechanism, or possibly even
// a daemon assisted hardware wallet. This interface serves the purpose of
// allowing LightningWallet to be seamlessly compatible with several wallets
// such as: uspv, btcwallet, Bitcoin Core, Electrum, etc. This interface then
// serves as a "base wallet", with Lightning Network awareness taking place at
// a "higher" level of abstraction. Essentially, an overlay wallet.
// Implementors of this interface must closely adhere to the documented
// behavior of all interface methods in order to ensure identical behavior
// across all concrete implementations.
type WalletController interface {
	// FetchInputInfo queries for the WalletController's knowledge of the
	// passed outpoint. If the base wallet determines this output is under
	// its control, then the original txout should be returned. Otherwise,
	// a non-nil error value of ErrNotMine should be returned instead.
	FetchInputInfo(prevOut *wire.OutPoint) (*wire.TxOut, error)

	// ConfirmedBalance returns the sum of all the wallet's unspent outputs
	// that have at least confs confirmations. If confs is set to zero,
	// then all unspent outputs, including those currently in the mempool
	// will be included in the final sum.
	//
	// NOTE: Only witness outputs should be included in the computation of
	// the total spendable balance of the wallet. We require this as only
	// witness inputs can be used for funding channels.
	ConfirmedBalance(confs int32) (btcutil.Amount, error)

	// NewAddress returns the next external or internal address for the
	// wallet dictated by the value of the `change` parameter. If change is
	// true, then an internal address should be used, otherwise an external
	// address should be returned. The type of address returned is dictated
	// by the wallet's capabilities, and may be of type: p2sh, p2wkh,
	// p2wsh, etc.
	NewAddress(addrType AddressType, change bool) (btcutil.Address, error)

	// IsOurAddress checks if the passed address belongs to this wallet
	IsOurAddress(a btcutil.Address) bool

	// SendOutputs funds, signs, and broadcasts a Bitcoin transaction paying
	// out to the specified outputs. In the case the wallet has insufficient
	// funds, or the outputs are non-standard, an error should be returned.
	// This method also takes the target fee expressed in sat/kw that should
	// be used when crafting the transaction.
	SendOutputs(outputs []*wire.TxOut,
		feeRate SatPerKWeight) (*wire.MsgTx, error)

	// ListUnspentWitness returns all unspent outputs which are version 0
	// witness programs. The 'minconfirms' and 'maxconfirms' parameters
	// indicate the minimum and maximum number of confirmations an output
	// needs in order to be returned by this method. Passing -1 as
	// 'minconfirms' indicates that even unconfirmed outputs should be
	// returned. Using MaxInt32 as 'maxconfirms' implies returning all
	// outputs with at least 'minconfirms'.
	ListUnspentWitness(minconfirms, maxconfirms int32) ([]*Utxo, error)

	// ListTransactionDetails returns a list of all transactions which are
	// relevant to the wallet.
	ListTransactionDetails() ([]*TransactionDetail, error)

	// LockOutpoint marks an outpoint as locked meaning it will no longer
	// be deemed as eligible for coin selection. Locking outputs are
	// utilized in order to avoid race conditions when selecting inputs for
	// usage when funding a channel.
	LockOutpoint(o wire.OutPoint)

	// UnlockOutpoint unlocks a previously locked output, marking it
	// eligible for coin selection.
	UnlockOutpoint(o wire.OutPoint)

	// PublishTransaction performs cursory validation (dust checks, etc),
	// then finally broadcasts the passed transaction to the Bitcoin network.
	// If the transaction is rejected because it is conflicting with an
	// already known transaction, ErrDoubleSpend is returned. If the
	// transaction is already known (published already), no error will be
	// returned. Other error returned depends on the currently active chain
	// backend.
	PublishTransaction(tx *wire.MsgTx) error

	// SubscribeTransactions returns a TransactionSubscription client which
	// is capable of receiving async notifications as new transactions
	// related to the wallet are seen within the network, or found in
	// blocks.
	//
	// NOTE: a non-nil error should be returned if notifications aren't
	// supported.
	//
	// TODO(roasbeef): make distinct interface?
	SubscribeTransactions() (TransactionSubscription, error)

	// IsSynced returns a boolean indicating if from the PoV of the wallet,
	// it has fully synced to the current best block in the main chain.
	// It also returns an int64 indicating the timestamp of the best block
	// known to the wallet, expressed in Unix epoch time
	IsSynced() (bool, int64, error)

	// Start initializes the wallet, making any necessary connections,
	// starting up required goroutines etc.
	Start() error

	// Stop signals the wallet for shutdown. Shutdown may entail closing
	// any active sockets, database handles, stopping goroutines, etc.
	Stop() error

	// BackEnd returns a name for the wallet's backing chain service,
	// which could be e.g. btcd, bitcoind, neutrino, or another consensus
	// service.
	BackEnd() string
}

// BlockChainIO is a dedicated source which will be used to obtain queries
// related to the current state of the blockchain. The data returned by each of
// the defined methods within this interface should always return the most up
// to date data possible.
//
// TODO(roasbeef): move to diff package perhaps?
// TODO(roasbeef): move publish txn here?
type BlockChainIO interface {
	// GetBestBlock returns the current height and block hash of the valid
	// most-work chain the implementation is aware of.
	GetBestBlock() (*chainhash.Hash, int32, error)

	// GetUtxo attempts to return the passed outpoint if it's still a
	// member of the utxo set. The passed height hint should be the "birth
	// height" of the passed outpoint. The script passed should be the
	// script that the outpoint creates. In the case that the output is in
	// the UTXO set, then the output corresponding to that output is
	// returned.  Otherwise, a non-nil error will be returned.
	GetUtxo(op *wire.OutPoint, pkScript []byte,
		heightHint uint32) (*wire.TxOut, error)

	// GetBlockHash returns the hash of the block in the best blockchain
	// at the given height.
	GetBlockHash(blockHeight int64) (*chainhash.Hash, error)

	// GetBlock returns the block in the main chain identified by the given
	// hash.
	GetBlock(blockHash *chainhash.Hash) (*wire.MsgBlock, error)
}

// Signer represents an abstract object capable of generating raw signatures as
// well as full complete input scripts given a valid SignDescriptor and
// transaction. This interface fully abstracts away signing paving the way for
// Signer implementations such as hardware wallets, hardware tokens, HSM's, or
// simply a regular wallet.
type Signer interface {
	// SignOutputRaw generates a signature for the passed transaction
	// according to the data within the passed SignDescriptor.
	//
	// NOTE: The resulting signature should be void of a sighash byte.
	SignOutputRaw(tx *wire.MsgTx, signDesc *SignDescriptor) ([]byte, error)

	// ComputeInputScript generates a complete InputIndex for the passed
	// transaction with the signature as defined within the passed
	// SignDescriptor. This method should be capable of generating the
	// proper input script for both regular p2wkh output and p2wkh outputs
	// nested within a regular p2sh output.
	//
	// NOTE: This method will ignore any tweak parameters set within the
	// passed SignDescriptor as it assumes a set of typical script
	// templates (p2wkh, np2wkh, etc).
	ComputeInputScript(tx *wire.MsgTx, signDesc *SignDescriptor) (*InputScript, error)
}

// MessageSigner represents an abstract object capable of signing arbitrary
// messages. The capabilities of this interface are used to sign announcements
// to the network, or just arbitrary messages that leverage the wallet's keys
// to attest to some message.
type MessageSigner interface {
	// SignMessage attempts to sign a target message with the private key
	// that corresponds to the passed public key. If the target private key
	// is unable to be found, then an error will be returned. The actual
	// digest signed is the double SHA-256 of the passed message.
	SignMessage(pubKey *btcec.PublicKey, msg []byte) (*btcec.Signature, error)
}

// PreimageCache is an interface that represents a global cache for preimages.
// We'll utilize this cache to communicate the discovery of new preimages
// across sub-systems.
type PreimageCache interface {
	// LookupPreimage attempts to look up a preimage according to its hash.
	// If found, the preimage is returned along with true for the second
	// argument. Otherwise, it'll return false.
	LookupPreimage(hash []byte) ([]byte, bool)

	// AddPreimage attempts to add a new preimage to the global cache. If
	// successful a nil error will be returned.
	AddPreimage(preimage []byte) error
}

// WalletDriver represents a "driver" for a particular concrete
// WalletController implementation. A driver is identified by a globally unique
// string identifier along with a 'New()' method which is responsible for
// initializing a particular WalletController concrete implementation.
type WalletDriver struct {
	// WalletType is a string which uniquely identifies the
	// WalletController that this driver, drives.
	WalletType string

	// New creates a new instance of a concrete WalletController
	// implementation given a variadic set up arguments. The function takes
	// a variadic number of interface parameters in order to provide
	// initialization flexibility, thereby accommodating several potential
	// WalletController implementations.
	New func(args ...interface{}) (WalletController, error)

	// BackEnds returns a list of available chain service drivers for the
	// wallet driver. This could be e.g. bitcoind, btcd, neutrino, etc.
	BackEnds func() []string
}

var (
	wallets     = make(map[string]*WalletDriver)
	registerMtx sync.Mutex
)

// RegisteredWallets returns a slice of all currently registered notifiers.
//
// NOTE: This function is safe for concurrent access.
func RegisteredWallets() []*WalletDriver {
	registerMtx.Lock()
	defer registerMtx.Unlock()

	registeredWallets := make([]*WalletDriver, 0, len(wallets))
	for _, wallet := range wallets {
		registeredWallets = append(registeredWallets, wallet)
	}

	return registeredWallets
}

// RegisterWallet registers a WalletDriver which is capable of driving a
// concrete WalletController interface. In the case that this driver has
// already been registered, an error is returned.
//
// NOTE: This function is safe for concurrent access.
func RegisterWallet(driver *WalletDriver) error {
	registerMtx.Lock()
	defer registerMtx.Unlock()

	if _, ok := wallets[driver.WalletType]; ok {
		return fmt.Errorf("wallet already registered")
	}

	wallets[driver.WalletType] = driver

	return nil
}

// SupportedWallets returns a slice of strings that represents the wallet
// drivers that have been registered and are therefore supported.
//
// NOTE: This function is safe for concurrent access.
func SupportedWallets() []string {
	registerMtx.Lock()
	defer registerMtx.Unlock()

	supportedWallets := make([]string, 0, len(wallets))
	for walletName := range wallets {
		supportedWallets = append(supportedWallets, walletName)
	}

	return supportedWallets
}