Golang types.UnlockConditions類代碼示例

// SubmitBlock takes a solved block and submits it to the blockchain.
// SubmitBlock should not be called with a lock.
func (m *Miner) SubmitBlock(b types.Block) error {
	// Give the block to the consensus set.
	err := m.cs.AcceptBlock(b)
	// Add the miner to the blocks list if the only problem is that it's stale.
	if err == modules.ErrNonExtendingBlock {
		m.mu.Lock()
		m.blocksFound = append(m.blocksFound, b.ID())
		m.mu.Unlock()
	}
	if err != nil {
		m.tpool.PurgeTransactionPool()
		m.log.Println("ERROR: an invalid block was submitted:", err)
		return err
	}
	m.mu.Lock()
	defer m.mu.Unlock()

	// Grab a new address for the miner. Call may fail if the wallet is locked
	// or if the wallet addresses have been exhausted.
	m.blocksFound = append(m.blocksFound, b.ID())
	var uc types.UnlockConditions
	uc, err = m.wallet.NextAddress()
	if err == nil { // Only update the address if there was no error.
		m.address = uc.UnlockHash()
	}
	return err
}

// managedSubmitBlock takes a solved block and submits it to the blockchain.
// managedSubmitBlock should not be called with a lock.
func (m *Miner) managedSubmitBlock(b types.Block) error {
	// Give the block to the consensus set.
	err := m.cs.AcceptBlock(b)
	// Add the miner to the blocks list if the only problem is that it's stale.
	if err == modules.ErrNonExtendingBlock {
		m.mu.Lock()
		m.persist.BlocksFound = append(m.persist.BlocksFound, b.ID())
		m.mu.Unlock()
		m.log.Println("Mined a stale block - block appears valid but does not extend the blockchain")
		return err
	}
	if err == modules.ErrBlockUnsolved {
		m.log.Println("Mined an unsolved block - header submission appears to be incorrect")
		return err
	}
	if err != nil {
		m.tpool.PurgeTransactionPool()
		m.log.Critical("ERROR: an invalid block was submitted:", err)
		return err
	}
	m.mu.Lock()
	defer m.mu.Unlock()

	// Grab a new address for the miner. Call may fail if the wallet is locked
	// or if the wallet addresses have been exhausted.
	m.persist.BlocksFound = append(m.persist.BlocksFound, b.ID())
	var uc types.UnlockConditions
	uc, err = m.wallet.NextAddress()
	if err != nil {
		return err
	}
	m.persist.Address = uc.UnlockHash()
	return m.saveSync()
}

// considerContract checks that the provided transaction matches the host's
// terms, and doesn't contain any flagrant errors.
func (h *Host) considerContract(txn types.Transaction, renterKey types.SiaPublicKey) error {
	// Check that there is only one file contract.
	// TODO: check that the txn is empty except for the contract?
	if len(txn.FileContracts) != 1 {
		return errors.New("transaction should have only one file contract")
	}
	// convenience variables
	fc := txn.FileContracts[0]
	duration := fc.WindowStart - h.blockHeight
	voidAddress := types.UnlockHash{}

	// check contract fields for sanity and acceptability
	switch {
	case fc.FileSize != 0:
		return errors.New("initial file size must be 0")

	case fc.WindowStart <= h.blockHeight:
		return errors.New("window start cannot be in the past")

	case duration < h.MinDuration || duration > h.MaxDuration:
		return errors.New("duration is out of bounds")

	case fc.WindowEnd <= fc.WindowStart:
		return errors.New("window cannot end before it starts")

	case fc.WindowEnd-fc.WindowStart < h.WindowSize:
		return errors.New("challenge window is not large enough")

	case fc.FileMerkleRoot != crypto.Hash{}:
		return errors.New("bad file contract Merkle root")

	case fc.Payout.IsZero():
		return errors.New("bad file contract payout")

	case len(fc.ValidProofOutputs) != 2:
		return errors.New("bad file contract valid proof outputs")

	case len(fc.MissedProofOutputs) != 2:
		return errors.New("bad file contract missed proof outputs")

	case !fc.ValidProofOutputs[1].Value.IsZero(), !fc.MissedProofOutputs[1].Value.IsZero():
		return errors.New("file contract collateral is not zero")

	case fc.ValidProofOutputs[1].UnlockHash != h.UnlockHash:
		return errors.New("file contract valid proof output not sent to host")
	case fc.MissedProofOutputs[1].UnlockHash != voidAddress:
		return errors.New("file contract missed proof output not sent to void")
	}

	// check unlock hash
	uc := types.UnlockConditions{
		PublicKeys:         []types.SiaPublicKey{renterKey, h.publicKey},
		SignaturesRequired: 2,
	}
	if fc.UnlockHash != uc.UnlockHash() {
		return errors.New("bad file contract unlock hash")
	}

	return nil
}

// verifyKeysSiag_1_0 is a copy-pasted version of the verifyKeys method
// from siag 1.0.
func verifyKeysSiag_1_0(uc types.UnlockConditions, folder string, keyname string) error {
	keysRequired := uc.SignaturesRequired
	totalKeys := uint64(len(uc.PublicKeys))
	loadedKeys := make([]KeyPairSiag_1_0, totalKeys)
	for i := 0; i < len(loadedKeys); i++ {
		err := encoding.ReadFile(filepath.Join(folder, keyname+"_Key"+strconv.Itoa(i)+".siakey"), &loadedKeys[i])
		if err != nil {
			return err
		}
	}
	for _, loadedKey := range loadedKeys {
		if loadedKey.UnlockConditions.UnlockHash() != uc.UnlockHash() {
			return errors.New("ErrCorruptedKey")
		}
	}
	txn := types.Transaction{
		SiafundInputs: []types.SiafundInput{
			types.SiafundInput{
				UnlockConditions: loadedKeys[0].UnlockConditions,
			},
		},
	}
	var i uint64
	for i != totalKeys {
		if i+keysRequired > totalKeys {
			i = totalKeys - keysRequired
		}
		var j uint64
		for j < keysRequired {
			txn.TransactionSignatures = append(txn.TransactionSignatures, types.TransactionSignature{
				PublicKeyIndex: i,
				CoveredFields:  types.CoveredFields{WholeTransaction: true},
			})
			sigHash := txn.SigHash(int(j))
			sig, err := crypto.SignHash(sigHash, loadedKeys[i].SecretKey)
			if err != nil {
				return err
			}
			txn.TransactionSignatures[j].Signature = sig[:]
			i++
			j++
		}
		err := txn.StandaloneValid(0)
		if err != nil {
			return err
		}
		txn.TransactionSignatures = nil
	}
	return nil
}

// submitBlock takes a solved block and submits it to the blockchain.
// submitBlock should not be called with a lock.
func (m *Miner) SubmitBlock(b types.Block) error {
	// Give the block to the consensus set.
	err := m.cs.AcceptBlock(b)
	if err != nil {
		m.tpool.PurgeTransactionPool()
		m.log.Println("ERROR: an invalid block was submitted:", err)
		return err
	}
	lockID := m.mu.Lock()
	defer m.mu.Unlock(lockID)

	// Grab a new address for the miner. Call may fail if the wallet is locked
	// or if the wallet addresses have been exhausted.
	m.blocksFound = append(m.blocksFound, b.ID())
	var uc types.UnlockConditions
	uc, err = m.wallet.NextAddress()
	if err == nil { // Special case: only update the address if there was no error.
		m.address = uc.UnlockHash()
	}
	return err
}

func TestReviseContract(t *testing.T) {
	if testing.Short() {
		t.SkipNow()
	}
	t.Parallel()
	ct, err := newContractorTester("TestReviseContract")
	if err != nil {
		t.Fatal(err)
	}

	// get an address
	ourAddr, err := ct.wallet.NextAddress()
	if err != nil {
		t.Fatal(err)
	}

	// generate keys
	sk, pk, err := crypto.GenerateKeyPair()
	if err != nil {
		t.Fatal(err)
	}
	renterPubKey := types.SiaPublicKey{
		Algorithm: types.SignatureEd25519,
		Key:       pk[:],
	}

	uc := types.UnlockConditions{
		PublicKeys:         []types.SiaPublicKey{renterPubKey, renterPubKey},
		SignaturesRequired: 1,
	}

	// create file contract
	payout := types.NewCurrency64(1e16)

	fc := types.FileContract{
		FileSize:       0,
		FileMerkleRoot: crypto.Hash{}, // no proof possible without data
		WindowStart:    100,
		WindowEnd:      1000,
		Payout:         payout,
		UnlockHash:     uc.UnlockHash(),
		RevisionNumber: 0,
	}
	// outputs need account for tax
	fc.ValidProofOutputs = []types.SiacoinOutput{
		{Value: types.PostTax(ct.contractor.blockHeight, payout), UnlockHash: ourAddr.UnlockHash()},
		{Value: types.ZeroCurrency, UnlockHash: types.UnlockHash{}}, // no collateral
	}
	fc.MissedProofOutputs = []types.SiacoinOutput{
		// same as above
		fc.ValidProofOutputs[0],
		// goes to the void, not the hostdb
		{Value: types.ZeroCurrency, UnlockHash: types.UnlockHash{}},
	}

	txnBuilder := ct.wallet.StartTransaction()
	err = txnBuilder.FundSiacoins(fc.Payout)
	if err != nil {
		t.Fatal(err)
	}
	txnBuilder.AddFileContract(fc)
	signedTxnSet, err := txnBuilder.Sign(true)
	if err != nil {
		t.Fatal(err)
	}

	// submit contract
	err = ct.tpool.AcceptTransactionSet(signedTxnSet)
	if err != nil {
		t.Fatal(err)
	}

	// create revision
	fcid := signedTxnSet[len(signedTxnSet)-1].FileContractID(0)
	rev := types.FileContractRevision{
		ParentID:              fcid,
		UnlockConditions:      uc,
		NewFileSize:           10,
		NewWindowStart:        100,
		NewWindowEnd:          1000,
		NewRevisionNumber:     1,
		NewValidProofOutputs:  fc.ValidProofOutputs,
		NewMissedProofOutputs: fc.MissedProofOutputs,
	}

	// create transaction containing the revision
	signedTxn := types.Transaction{
		FileContractRevisions: []types.FileContractRevision{rev},
		TransactionSignatures: []types.TransactionSignature{{
			ParentID:       crypto.Hash(fcid),
			CoveredFields:  types.CoveredFields{FileContractRevisions: []uint64{0}},
			PublicKeyIndex: 0, // hostdb key is always first -- see negotiateContract
		}},
	}

	// sign the transaction
	encodedSig, err := crypto.SignHash(signedTxn.SigHash(0), sk)
	if err != nil {
		t.Fatal(err)
	}
//.........這裏部分代碼省略.........

// testFileContractRevision creates and revises a file contract on the
// blockchain.
func (cst *consensusSetTester) testFileContractRevision() {
	// COMPATv0.4.0 - Step the block height up past the hardfork amount. This
	// code stops nondeterministic failures when producing storage proofs that
	// is related to buggy old code.
	for cst.cs.dbBlockHeight() <= 10 {
		_, err := cst.miner.AddBlock()
		if err != nil {
			panic(err)
		}
	}

	// Create a file (as a bytes.Buffer) that will be used for the file
	// contract.
	filesize := uint64(4e3)
	file := randFile(filesize)
	merkleRoot, err := crypto.ReaderMerkleRoot(file)
	if err != nil {
		panic(err)
	}
	file.Seek(0, 0)

	// Create a spendable unlock hash for the file contract.
	sk, pk, err := crypto.GenerateKeyPair()
	if err != nil {
		panic(err)
	}
	uc := types.UnlockConditions{
		PublicKeys: []types.SiaPublicKey{{
			Algorithm: types.SignatureEd25519,
			Key:       pk[:],
		}},
		SignaturesRequired: 1,
	}

	// Create a file contract that will be revised.
	validProofDest := randAddress()
	payout := types.NewCurrency64(400e6)
	fc := types.FileContract{
		FileSize:       filesize,
		FileMerkleRoot: crypto.Hash{},
		WindowStart:    cst.cs.dbBlockHeight() + 2,
		WindowEnd:      cst.cs.dbBlockHeight() + 3,
		Payout:         payout,
		ValidProofOutputs: []types.SiacoinOutput{{
			UnlockHash: validProofDest,
			Value:      types.PostTax(cst.cs.dbBlockHeight(), payout),
		}},
		MissedProofOutputs: []types.SiacoinOutput{{
			UnlockHash: types.UnlockHash{},
			Value:      types.PostTax(cst.cs.dbBlockHeight(), payout),
		}},
		UnlockHash: uc.UnlockHash(),
	}

	// Submit a transaction with the file contract.
	txnBuilder := cst.wallet.StartTransaction()
	err = txnBuilder.FundSiacoins(payout)
	if err != nil {
		panic(err)
	}
	fcIndex := txnBuilder.AddFileContract(fc)
	txnSet, err := txnBuilder.Sign(true)
	if err != nil {
		panic(err)
	}
	err = cst.tpool.AcceptTransactionSet(txnSet)
	if err != nil {
		panic(err)
	}
	_, err = cst.miner.AddBlock()
	if err != nil {
		panic(err)
	}

	// Submit a revision for the file contract.
	ti := len(txnSet) - 1
	fcid := txnSet[ti].FileContractID(fcIndex)
	fcr := types.FileContractRevision{
		ParentID:          fcid,
		UnlockConditions:  uc,
		NewRevisionNumber: 69292,

		NewFileSize:           filesize,
		NewFileMerkleRoot:     merkleRoot,
		NewWindowStart:        cst.cs.dbBlockHeight() + 1,
		NewWindowEnd:          cst.cs.dbBlockHeight() + 2,
		NewValidProofOutputs:  fc.ValidProofOutputs,
		NewMissedProofOutputs: fc.MissedProofOutputs,
		NewUnlockHash:         uc.UnlockHash(),
	}
	ts := types.TransactionSignature{
		ParentID:       crypto.Hash(fcid),
		CoveredFields:  types.CoveredFields{WholeTransaction: true},
		PublicKeyIndex: 0,
	}
	txn := types.Transaction{
		FileContractRevisions: []types.FileContractRevision{fcr},
		TransactionSignatures: []types.TransactionSignature{ts},
//.........這裏部分代碼省略.........

// negotiateContract establishes a connection to a host and negotiates an
// initial file contract according to the terms of the host.
func negotiateContract(conn net.Conn, addr modules.NetAddress, fc types.FileContract, txnBuilder transactionBuilder, tpool transactionPool) (hostContract, error) {
	// allow 30 seconds for negotiation
	conn.SetDeadline(time.Now().Add(30 * time.Second))

	// read host key
	var hostPublicKey types.SiaPublicKey
	if err := encoding.ReadObject(conn, &hostPublicKey, 256); err != nil {
		return hostContract{}, errors.New("couldn't read host's public key: " + err.Error())
	}

	// create our key
	ourSK, ourPK, err := crypto.GenerateKeyPair()
	if err != nil {
		return hostContract{}, errors.New("failed to generate keypair: " + err.Error())
	}
	ourPublicKey := types.SiaPublicKey{
		Algorithm: types.SignatureEd25519,
		Key:       ourPK[:],
	}

	// send our public key
	if err := encoding.WriteObject(conn, ourPublicKey); err != nil {
		return hostContract{}, errors.New("couldn't send our public key: " + err.Error())
	}

	// create unlock conditions
	uc := types.UnlockConditions{
		PublicKeys:         []types.SiaPublicKey{ourPublicKey, hostPublicKey},
		SignaturesRequired: 2,
	}

	// add UnlockHash to file contract
	fc.UnlockHash = uc.UnlockHash()

	// build transaction containing fc
	err = txnBuilder.FundSiacoins(fc.Payout)
	if err != nil {
		return hostContract{}, err
	}
	txnBuilder.AddFileContract(fc)
	txn, parents := txnBuilder.View()
	txnSet := append(parents, txn)

	// calculate contract ID
	fcid := txn.FileContractID(0) // TODO: is it actually 0?

	// send txn
	if err := encoding.WriteObject(conn, txnSet); err != nil {
		return hostContract{}, errors.New("couldn't send our proposed contract: " + err.Error())
	}

	// read back acceptance
	var response string
	if err := encoding.ReadObject(conn, &response, 128); err != nil {
		return hostContract{}, errors.New("couldn't read the host's response to our proposed contract: " + err.Error())
	}
	if response != modules.AcceptResponse {
		return hostContract{}, errors.New("host rejected proposed contract: " + response)
	}

	// read back txn with host collateral.
	var hostTxnSet []types.Transaction
	if err := encoding.ReadObject(conn, &hostTxnSet, types.BlockSizeLimit); err != nil {
		return hostContract{}, errors.New("couldn't read the host's updated contract: " + err.Error())
	}

	// check that txn is okay. For now, no collateral will be added, so the
	// transaction sets should be identical.
	if len(hostTxnSet) != len(txnSet) {
		return hostContract{}, errors.New("host sent bad collateral transaction")
	}
	for i := range hostTxnSet {
		if hostTxnSet[i].ID() != txnSet[i].ID() {
			return hostContract{}, errors.New("host sent bad collateral transaction")
		}
	}

	// sign the txn and resend
	// NOTE: for now, we are assuming that the transaction has not changed
	// since we sent it. Otherwise, the txnBuilder would have to be updated
	// with whatever fields were added by the host.
	signedTxnSet, err := txnBuilder.Sign(true)
	if err != nil {
		return hostContract{}, err
	}
	if err := encoding.WriteObject(conn, signedTxnSet); err != nil {
		return hostContract{}, errors.New("couldn't send the contract signed by us: " + err.Error())
	}

	// read signed txn from host
	var signedHostTxnSet []types.Transaction
	if err := encoding.ReadObject(conn, &signedHostTxnSet, types.BlockSizeLimit); err != nil {
		return hostContract{}, errors.New("couldn't read the contract signed by the host: " + err.Error())
	}

	// submit to blockchain
	err = tpool.AcceptTransactionSet(signedHostTxnSet)
	if err == modules.ErrDuplicateTransactionSet {
//.........這裏部分代碼省略.........

// generateKeys generates a set of keys and saves them to disk.
func generateKeys(requiredKeys int, totalKeys int, folder string, keyname string) (types.UnlockConditions, error) {
	// Check that the inputs have sane values.
	if requiredKeys < 1 {
		return types.UnlockConditions{}, ErrInsecureAddress
	}
	if totalKeys < requiredKeys {
		return types.UnlockConditions{}, ErrUnspendableAddress
	}

	// Generate 'TotalKeys', filling out everything except the unlock
	// conditions.
	keys := make([]KeyPair, totalKeys)
	pubKeys := make([]crypto.PublicKey, totalKeys)
	for i := range keys {
		var err error
		keys[i].Header = FileHeader
		keys[i].Version = FileVersion
		keys[i].Index = i
		keys[i].SecretKey, pubKeys[i], err = crypto.GenerateSignatureKeys()
		if err != nil {
			return types.UnlockConditions{}, err
		}
	}

	// Generate the unlock conditions and add them to each KeyPair object. This
	// must be done second because the keypairs can't be given unlock
	// conditions until the PublicKeys have all been added.
	unlockConditions := types.UnlockConditions{
		Timelock:           0,
		SignaturesRequired: uint64(requiredKeys),
	}
	for i := range keys {
		unlockConditions.PublicKeys = append(unlockConditions.PublicKeys, types.SiaPublicKey{
			Algorithm: types.SignatureEd25519,
			Key:       pubKeys[i][:],
		})
	}
	for i := range keys {
		keys[i].UnlockConditions = unlockConditions
	}

	// Save the KeyPairs to disk.
	if folder != "" {
		err := os.MkdirAll(folder, 0700)
		if err != nil {
			return types.UnlockConditions{}, err
		}
	}
	for i, key := range keys {
		keyFilename := filepath.Join(folder, keyname+"_Key"+strconv.Itoa(i)+FileExtension)
		_, err := os.Stat(keyFilename)
		if !os.IsNotExist(err) {
			if err != nil {
				return types.UnlockConditions{}, err
			}
			return types.UnlockConditions{}, ErrOverwrite
		}
		err = encoding.WriteFile(keyFilename, key)
		if err != nil {
			return types.UnlockConditions{}, err
		}
	}

	return unlockConditions, nil
}

// verifyKeys checks a set of keys on disk to see that they can spend funds
// sent to their address.
func verifyKeys(uc types.UnlockConditions, folder string, keyname string) error {
	keysRequired := uc.SignaturesRequired
	totalKeys := uint64(len(uc.PublicKeys))

	// Load the keys from disk back into memory, then verify that the keys on
	// disk are able to sign outputs in transactions.
	loadedKeys := make([]KeyPair, totalKeys)
	for i := 0; i < len(loadedKeys); i++ {
		err := encoding.ReadFile(filepath.Join(folder, keyname+"_Key"+strconv.Itoa(i)+FileExtension), &loadedKeys[i])
		if err != nil {
			return err
		}
		if loadedKeys[i].Header != FileHeader {
			return ErrUnknownHeader
		}
		if loadedKeys[i].Version != FileVersion {
			return ErrUnknownVersion
		}
	}

	// Check that the keys can be used to spend transactions.
	for _, loadedKey := range loadedKeys {
		if loadedKey.UnlockConditions.UnlockHash() != uc.UnlockHash() {
			return ErrCorruptedKey
		}
	}
	// Create a transaction for the keys to sign.
	txn := types.Transaction{
		SiafundInputs: []types.SiafundInput{
			types.SiafundInput{
				UnlockConditions: loadedKeys[0].UnlockConditions,
			},
		},
	}
	// Loop through and sign the transaction multiple times. All keys will be
	// used at least once by the time the loop terminates.
	var i uint64
	for i != totalKeys {
		// i tracks which key is next to be used. If i + RequiredKeys results
		// in going out-of-bounds, reduce i so that the last key will be used
		// for the final signature.
		if i+keysRequired > totalKeys {
			i = totalKeys - keysRequired
		}
		var j uint64
		for j < keysRequired {
			txn.TransactionSignatures = append(txn.TransactionSignatures, types.TransactionSignature{
				PublicKeyIndex: i,
				CoveredFields:  types.CoveredFields{WholeTransaction: true},
			})
			sigHash := txn.SigHash(int(j))
			sig, err := crypto.SignHash(sigHash, loadedKeys[i].SecretKey)
			if err != nil {
				return err
			}
			txn.TransactionSignatures[j].Signature = sig[:]
			i++
			j++
		}
		// Check that the signature is valid.
		err := txn.StandaloneValid(0)
		if err != nil {
			return err
		}
		// Delete all of the signatures for the next iteration.
		txn.TransactionSignatures = nil
	}
	return nil
}

// considerContract checks that the provided transaction matches the host's
// terms, and doesn't contain any flagrant errors.
func (h *Host) considerContract(txn types.Transaction, renterKey types.SiaPublicKey, filesize uint64, merkleRoot crypto.Hash) error {
	// Check that there is only one file contract.
	if len(txn.FileContracts) != 1 {
		return errors.New("transaction should have only one file contract")
	}

	// convenience variables
	fc := txn.FileContracts[0]
	duration := fc.WindowStart - h.blockHeight
	minPayment := types.NewCurrency64(filesize).Mul(types.NewCurrency64(uint64(duration))).Mul(h.settings.Price)
	expectedOutputSum := types.PostTax(h.blockHeight, fc.Payout)

	// check contract fields for sanity and acceptability
	switch {
	// Check for legal filesize and content.
	case fc.FileSize != filesize:
		return errors.New("bad initial file size")
	case fc.FileSize >= uint64(h.spaceRemaining):
		return ErrHostCapacity
	case fc.FileMerkleRoot != merkleRoot:
		return errors.New("bad file contract Merkle root")

	// Check for legal duration and proof window.
	case fc.WindowStart <= h.blockHeight:
		return errors.New("window start cannot be in the past")
	case duration < h.settings.MinDuration || duration > h.settings.MaxDuration:
		return errors.New("duration is out of bounds")
	case fc.WindowEnd <= fc.WindowStart:
		return errors.New("window cannot end before it starts")
	case fc.WindowEnd-fc.WindowStart < h.settings.WindowSize:
		return errors.New("challenge window is not large enough")

	// Check for legal payout.
	case fc.Payout.IsZero():
		return errors.New("bad file contract payout")
	case len(fc.ValidProofOutputs) != 2:
		return errors.New("bad file contract valid proof outputs")
	case len(fc.MissedProofOutputs) != 2:
		return errors.New("bad file contract missed proof outputs")
	case fc.ValidProofOutputs[0].Value.Add(fc.ValidProofOutputs[1].Value).Cmp(expectedOutputSum) != 0,
		fc.MissedProofOutputs[0].Value.Add(fc.MissedProofOutputs[1].Value).Cmp(expectedOutputSum) != 0:
		return errors.New("file contract outputs do not sum to original payout")
	case fc.ValidProofOutputs[1].UnlockHash != h.settings.UnlockHash:
		return errors.New("file contract valid proof output not sent to host")
	case fc.ValidProofOutputs[1].Value.Cmp(minPayment) < 0:
		return ErrLowPayment
	case fc.MissedProofOutputs[0].Value.Cmp(fc.ValidProofOutputs[0].Value) != 0:
		return errors.New("file contract missed renter payout does not match valid payout")
	case fc.MissedProofOutputs[1].UnlockHash != (types.UnlockHash{}):
		return errors.New("file contract missed proof output not sent to void")
	}

	// check unlock hash
	uc := types.UnlockConditions{
		PublicKeys:         []types.SiaPublicKey{renterKey, h.publicKey},
		SignaturesRequired: 2,
	}
	if fc.UnlockHash != uc.UnlockHash() {
		return errors.New("bad file contract unlock hash")
	}

	return nil
}

// FormContract forms a contract with a host and submits the contract
// transaction to tpool.
func FormContract(params ContractParams, txnBuilder transactionBuilder, tpool transactionPool) (modules.RenterContract, error) {
	// extract vars from params, for convenience
	host, filesize, startHeight, endHeight, refundAddress := params.Host, params.Filesize, params.StartHeight, params.EndHeight, params.RefundAddress

	// create our key
	ourSK, ourPK, err := crypto.GenerateKeyPair()
	if err != nil {
		return modules.RenterContract{}, err
	}
	ourPublicKey := types.SiaPublicKey{
		Algorithm: types.SignatureEd25519,
		Key:       ourPK[:],
	}
	// create unlock conditions
	uc := types.UnlockConditions{
		PublicKeys:         []types.SiaPublicKey{ourPublicKey, host.PublicKey},
		SignaturesRequired: 2,
	}

	// calculate cost to renter and cost to host
	// TODO: clarify/abstract this math
	storageAllocation := host.StoragePrice.Mul64(filesize).Mul64(uint64(endHeight - startHeight))
	hostCollateral := host.Collateral.Mul64(filesize).Mul64(uint64(endHeight - startHeight))
	if hostCollateral.Cmp(host.MaxCollateral) > 0 {
		// TODO: if we have to cap the collateral, it probably means we shouldn't be using this host
		// (ok within a factor of 2)
		hostCollateral = host.MaxCollateral
	}
	hostPayout := hostCollateral.Add(host.ContractPrice)
	payout := storageAllocation.Add(hostPayout).Mul64(10406).Div64(10000) // renter pays for siafund fee
	renterCost := payout.Sub(hostCollateral)

	// check for negative currency
	if types.PostTax(startHeight, payout).Cmp(hostPayout) < 0 {
		return modules.RenterContract{}, errors.New("payout smaller than host payout")
	}

	// create file contract
	fc := types.FileContract{
		FileSize:       0,
		FileMerkleRoot: crypto.Hash{}, // no proof possible without data
		WindowStart:    endHeight,
		WindowEnd:      endHeight + host.WindowSize,
		Payout:         payout,
		UnlockHash:     uc.UnlockHash(),
		RevisionNumber: 0,
		ValidProofOutputs: []types.SiacoinOutput{
			// outputs need to account for tax
			{Value: types.PostTax(startHeight, payout).Sub(hostPayout), UnlockHash: refundAddress},
			// collateral is returned to host
			{Value: hostPayout, UnlockHash: host.UnlockHash},
		},
		MissedProofOutputs: []types.SiacoinOutput{
			// same as above
			{Value: types.PostTax(startHeight, payout).Sub(hostPayout), UnlockHash: refundAddress},
			// same as above
			{Value: hostPayout, UnlockHash: host.UnlockHash},
			// once we start doing revisions, we'll move some coins to the host and some to the void
			{Value: types.ZeroCurrency, UnlockHash: types.UnlockHash{}},
		},
	}

	// calculate transaction fee
	_, maxFee := tpool.FeeEstimation()
	fee := maxFee.Mul64(estTxnSize)

	// build transaction containing fc
	err = txnBuilder.FundSiacoins(renterCost.Add(fee))
	if err != nil {
		return modules.RenterContract{}, err
	}
	txnBuilder.AddFileContract(fc)

	// add miner fee
	txnBuilder.AddMinerFee(fee)

	// create initial transaction set
	txn, parentTxns := txnBuilder.View()
	txnSet := append(parentTxns, txn)

	// initiate connection
	conn, err := net.DialTimeout("tcp", string(host.NetAddress), 15*time.Second)
	if err != nil {
		return modules.RenterContract{}, err
	}
	defer func() { _ = conn.Close() }()

	// allot time for sending RPC ID + verifySettings
	extendDeadline(conn, modules.NegotiateSettingsTime)
	if err = encoding.WriteObject(conn, modules.RPCFormContract); err != nil {
		return modules.RenterContract{}, err
	}

	// verify the host's settings and confirm its identity
	host, err = verifySettings(conn, host)
	if err != nil {
		return modules.RenterContract{}, err
	}
//.........這裏部分代碼省略.........