github.com/nebulouslabs/sia@v1.3.7/modules/host/storageobligations.go

package host

// storageobligations.go is responsible for managing the storage obligations
// within the host - making sure that any file contracts, transaction
// dependencies, file contract revisions, and storage proofs are making it into
// the blockchain in a reasonable time.
//
// NOTE: Currently, the code partially supports changing the storage proof
// window in file contract revisions, however the action item code will not
// handle it correctly. Until the action item code is improved (to also handle
// byzantine situations where the renter submits prior revisions), the host
// should not support changing the storage proof window, especially to further
// in the future.

// TODO: Need to queue the action item for checking on the submission status of
// the file contract revision. Also need to make sure that multiple actions are
// being taken if needed.

// TODO: Make sure that the origin tranasction set is not submitted to the
// transaction pool before addSO is called - if it is, there will be a
// duplicate transaction error, and then the storage obligation will return an
// error, which is bad. Well, or perhas we just need to have better logic
// handling.

// TODO: Need to make sure that 'revision confirmed' is actually looking only
// at the most recent revision (I think it is...)

// TODO: Make sure that not too many action items are being created.

// TODO: The ProofConstructed and NegotiationHeight fields of storageObligation
// are not set or used.

import (
	"encoding/binary"
	"encoding/json"
	"errors"
	"strconv"

	"github.com/NebulousLabs/Sia/build"
	"github.com/NebulousLabs/Sia/crypto"
	"github.com/NebulousLabs/Sia/encoding"
	"github.com/NebulousLabs/Sia/modules"
	"github.com/NebulousLabs/Sia/types"

	"github.com/coreos/bbolt"
)

const (
	obligationUnresolved storageObligationStatus = iota // Indicatees that an unitialized value was used.
	obligationRejected                                  // Indicates that the obligation never got started, no revenue gained or lost.
	obligationSucceeded                                 // Indicates that the obligation was completed, revenues were gained.
	obligationFailed                                    // Indicates that the obligation failed, revenues and collateral were lost.
)

var (
	// errDuplicateStorageObligation is returned when the storage obligation
	// database already has a storage obligation with the provided file
	// contract. This error should only happen in the event of a developer
	// mistake.
	errDuplicateStorageObligation = errors.New("storage obligation has a file contract which conflicts with an existing storage obligation")

	// errInsaneFileContractOutputCounts is returned when a file contract has
	// the wrong number of outputs for either the valid or missed payouts.
	errInsaneFileContractOutputCounts = errors.New("file contract has incorrect number of outputs for the valid or missed payouts")

	// errInsaneFileContractRevisionOutputCounts is returned when a file
	// contract has the wrong number of outputs for either the valid or missed
	// payouts.
	errInsaneFileContractRevisionOutputCounts = errors.New("file contract revision has incorrect number of outputs for the valid or missed payouts")

	// errInsaneOriginSetFileContract is returned is the final transaction of
	// the origin transaction set of a storage obligation does not have a file
	// contract in the final transaction - there should be a file contract
	// associated with every storage obligation.
	errInsaneOriginSetFileContract = errors.New("origin transaction set of storage obligation should have one file contract in the final transaction")

	// errInsaneOriginSetSize is returned if the origin transaction set of a
	// storage obligation is empty - there should be a file contract associated
	// with every storage obligation.
	errInsaneOriginSetSize = errors.New("origin transaction set of storage obligation is size zero")

	// errInsaneRevisionSetRevisionCount is returned if the final transaction
	// in the revision transaction set of a storage obligation has more or less
	// than one file contract revision.
	errInsaneRevisionSetRevisionCount = errors.New("revision transaction set of storage obligation should have one file contract revision in the final transaction")

	// errInsaneStorageObligationRevision is returned if there is an attempted
	// storage obligation revision which does not have sensical inputs.
	errInsaneStorageObligationRevision = errors.New("revision to storage obligation does not make sense")

	// errInsaneStorageObligationRevisionData is returned if there is an
	// attempted storage obligation revision which does not have sensical
	// inputs.
	errInsaneStorageObligationRevisionData = errors.New("revision to storage obligation has insane data")

	// errNoBuffer is returned if there is an attempted storage obligation that
	// needs to have the storage proof submitted in less than
	// revisionSubmissionBuffer blocks.
	errNoBuffer = errors.New("file contract rejected because storage proof window is too close")

	// errNoStorageObligation is returned if the requested storage obligation
	// is not found in the database.
	errNoStorageObligation = errors.New("storage obligation not found in database")

	// errObligationUnlocked is returned when a storage obligation is being
	// removed from lock, but is already unlocked.
	errObligationUnlocked = errors.New("storage obligation is unlocked, and should not be getting unlocked")
)

type storageObligationStatus uint64

// storageObligation contains all of the metadata related to a file contract
// and the storage contained by the file contract.
type storageObligation struct {
	// Storage obligations are broken up into ordered atomic sectors that are
	// exactly 4MiB each. By saving the roots of each sector, storage proofs
	// and modifications to the data can be made inexpensively by making use of
	// the merkletree.CachedTree. Sectors can be appended, modified, or deleted
	// and the host can recompute the Merkle root of the whole file without
	// much computational or I/O expense.
	SectorRoots []crypto.Hash

	// Variables about the file contract that enforces the storage obligation.
	// The origin an revision transaction are stored as a set, where the set
	// contains potentially unconfirmed transactions.
	ContractCost             types.Currency
	LockedCollateral         types.Currency
	PotentialDownloadRevenue types.Currency
	PotentialStorageRevenue  types.Currency
	PotentialUploadRevenue   types.Currency
	RiskedCollateral         types.Currency
	TransactionFeesAdded     types.Currency

	// The negotiation height specifies the block height at which the file
	// contract was negotiated. If the origin transaction set is not accepted
	// onto the blockchain quickly enough, the contract is pruned from the
	// host. The origin and revision transaction set contain the contracts +
	// revisions as well as all parent transactions. The parents are necessary
	// because after a restart the transaction pool may be emptied out.
	NegotiationHeight      types.BlockHeight
	OriginTransactionSet   []types.Transaction
	RevisionTransactionSet []types.Transaction

	// Variables indicating whether the critical transactions in a storage
	// obligation have been confirmed on the blockchain.
	ObligationStatus    storageObligationStatus
	OriginConfirmed     bool
	ProofConfirmed      bool
	ProofConstructed    bool
	RevisionConfirmed   bool
	RevisionConstructed bool
}

func (i storageObligationStatus) String() string {
	if i == 0 {
		return "obligationUnresolved"
	}
	if i == 1 {
		return "obligationRejected"
	}
	if i == 2 {
		return "obligationSucceeded"
	}
	if i == 3 {
		return "obligationFailed"
	}
	return "storageObligationStatus(" + strconv.FormatInt(int64(i), 10) + ")"
}

// getStorageObligation fetches a storage obligation from the database tx.
func getStorageObligation(tx *bolt.Tx, soid types.FileContractID) (so storageObligation, err error) {
	soBytes := tx.Bucket(bucketStorageObligations).Get(soid[:])
	if soBytes == nil {
		return storageObligation{}, errNoStorageObligation
	}
	err = json.Unmarshal(soBytes, &so)
	if err != nil {
		return storageObligation{}, err
	}
	return so, nil
}

// putStorageObligation places a storage obligation into the database,
// overwriting the existing storage obligation if there is one.
func putStorageObligation(tx *bolt.Tx, so storageObligation) error {
	soBytes, err := json.Marshal(so)
	if err != nil {
		return err
	}
	soid := so.id()
	return tx.Bucket(bucketStorageObligations).Put(soid[:], soBytes)
}

// expiration returns the height at which the storage obligation expires.
func (so storageObligation) expiration() types.BlockHeight {
	if len(so.RevisionTransactionSet) > 0 {
		return so.RevisionTransactionSet[len(so.RevisionTransactionSet)-1].FileContractRevisions[0].NewWindowStart
	}
	return so.OriginTransactionSet[len(so.OriginTransactionSet)-1].FileContracts[0].WindowStart
}

// fileSize returns the size of the data protected by the obligation.
func (so storageObligation) fileSize() uint64 {
	if len(so.RevisionTransactionSet) > 0 {
		return so.RevisionTransactionSet[len(so.RevisionTransactionSet)-1].FileContractRevisions[0].NewFileSize
	}
	return so.OriginTransactionSet[len(so.OriginTransactionSet)-1].FileContracts[0].FileSize
}

// id returns the id of the storage obligation, which is definied by the file
// contract id of the file contract that governs the storage contract.
func (so storageObligation) id() types.FileContractID {
	return so.OriginTransactionSet[len(so.OriginTransactionSet)-1].FileContractID(0)
}

// isSane checks that required assumptions about the storage obligation are
// correct.
func (so storageObligation) isSane() error {
	// There should be an origin transaction set.
	if len(so.OriginTransactionSet) == 0 {
		build.Critical("origin transaction set is empty")
		return errInsaneOriginSetSize
	}

	// The final transaction of the origin transaction set should have one file
	// contract.
	final := len(so.OriginTransactionSet) - 1
	fcCount := len(so.OriginTransactionSet[final].FileContracts)
	if fcCount != 1 {
		build.Critical("wrong number of file contracts associated with storage obligation:", fcCount)
		return errInsaneOriginSetFileContract
	}

	// The file contract in the final transaction of the origin transaction set
	// should have two valid proof outputs and two missed proof outputs.
	lenVPOs := len(so.OriginTransactionSet[final].FileContracts[0].ValidProofOutputs)
	lenMPOs := len(so.OriginTransactionSet[final].FileContracts[0].MissedProofOutputs)
	if lenVPOs != 2 || lenMPOs != 2 {
		build.Critical("file contract has wrong number of VPOs and MPOs, expecting 2 each:", lenVPOs, lenMPOs)
		return errInsaneFileContractOutputCounts
	}

	// If there is a revision transaction set, there should be one file
	// contract revision in the final transaction.
	if len(so.RevisionTransactionSet) > 0 {
		final = len(so.OriginTransactionSet) - 1
		fcrCount := len(so.OriginTransactionSet[final].FileContractRevisions)
		if fcrCount != 1 {
			build.Critical("wrong number of file contract revisions in final transaction of revision transaction set:", fcrCount)
			return errInsaneRevisionSetRevisionCount
		}

		// The file contract revision in the final transaction of the revision
		// transaction set should have two valid proof outputs and two missed
		// proof outputs.
		lenVPOs = len(so.RevisionTransactionSet[final].FileContractRevisions[0].NewValidProofOutputs)
		lenMPOs = len(so.RevisionTransactionSet[final].FileContractRevisions[0].NewMissedProofOutputs)
		if lenVPOs != 2 || lenMPOs != 2 {
			build.Critical("file contract has wrong number of VPOs and MPOs, expecting 2 each:", lenVPOs, lenMPOs)
			return errInsaneFileContractRevisionOutputCounts
		}
	}
	return nil
}

// merkleRoot returns the file merkle root of a storage obligation.
func (so storageObligation) merkleRoot() crypto.Hash {
	if len(so.RevisionTransactionSet) > 0 {
		return so.RevisionTransactionSet[len(so.RevisionTransactionSet)-1].FileContractRevisions[0].NewFileMerkleRoot
	}
	return so.OriginTransactionSet[len(so.OriginTransactionSet)-1].FileContracts[0].FileMerkleRoot
}

// payous returns the set of valid payouts and missed payouts that represent
// the latest revision for the storage obligation.
func (so storageObligation) payouts() (valid []types.SiacoinOutput, missed []types.SiacoinOutput) {
	valid = make([]types.SiacoinOutput, 2)
	missed = make([]types.SiacoinOutput, 2)
	if len(so.RevisionTransactionSet) > 0 {
		copy(valid, so.RevisionTransactionSet[len(so.RevisionTransactionSet)-1].FileContractRevisions[0].NewValidProofOutputs)
		copy(missed, so.RevisionTransactionSet[len(so.RevisionTransactionSet)-1].FileContractRevisions[0].NewMissedProofOutputs)
		return
	}
	copy(valid, so.OriginTransactionSet[len(so.OriginTransactionSet)-1].FileContracts[0].ValidProofOutputs)
	copy(missed, so.OriginTransactionSet[len(so.OriginTransactionSet)-1].FileContracts[0].MissedProofOutputs)
	return
}

// proofDeadline returns the height by which the storage proof must be
// submitted.
func (so storageObligation) proofDeadline() types.BlockHeight {
	if len(so.RevisionTransactionSet) > 0 {
		return so.RevisionTransactionSet[len(so.RevisionTransactionSet)-1].FileContractRevisions[0].NewWindowEnd
	}
	return so.OriginTransactionSet[len(so.OriginTransactionSet)-1].FileContracts[0].WindowEnd
}

// value returns the value of fulfilling the storage obligation to the host.
func (so storageObligation) value() types.Currency {
	return so.ContractCost.Add(so.PotentialDownloadRevenue).Add(so.PotentialStorageRevenue).Add(so.PotentialUploadRevenue).Add(so.RiskedCollateral)
}

// queueActionItem adds an action item to the host at the input height so that
// the host knows to perform maintenance on the associated storage obligation
// when that height is reached.
func (h *Host) queueActionItem(height types.BlockHeight, id types.FileContractID) error {
	// Sanity check - action item should be at a higher height than the current
	// block height.
	if height <= h.blockHeight {
		h.log.Println("action item queued improperly")
	}
	return h.db.Update(func(tx *bolt.Tx) error {
		// Translate the height into a byte slice.
		heightBytes := make([]byte, 8)
		binary.BigEndian.PutUint64(heightBytes, uint64(height))

		// Get the list of action items already at this height and extend it.
		bai := tx.Bucket(bucketActionItems)
		existingItems := bai.Get(heightBytes)
		var extendedItems = make([]byte, len(existingItems), len(existingItems)+len(id[:]))
		copy(extendedItems, existingItems)
		extendedItems = append(extendedItems, id[:]...)
		return bai.Put(heightBytes, extendedItems)
	})
}

// managedAddStorageObligation adds a storage obligation to the host. Because
// this operation can return errors, the transactions should not be submitted to
// the blockchain until after this function has indicated success. All of the
// sectors that are present in the storage obligation should already be on disk,
// which means that addStorageObligation should be exclusively called when
// creating a new, empty file contract or when renewing an existing file
// contract.
func (h *Host) managedAddStorageObligation(so storageObligation) error {
	var soid types.FileContractID
	err := func() error {
		h.mu.Lock()
		defer h.mu.Unlock()

		// Sanity check - obligation should be under lock while being added.
		soid = so.id()
		_, exists := h.lockedStorageObligations[soid]
		if !exists {
			h.log.Critical("addStorageObligation called with an obligation that is not locked")
		}
		// Sanity check - There needs to be enough time left on the file contract
		// for the host to safely submit the file contract revision.
		if h.blockHeight+revisionSubmissionBuffer >= so.expiration() {
			h.log.Critical("submission window was not verified before trying to submit a storage obligation")
			return errNoBuffer
		}
		// Sanity check - the resubmission timeout needs to be smaller than storage
		// proof window.
		if so.expiration()+resubmissionTimeout >= so.proofDeadline() {
			h.log.Critical("host is misconfigured - the storage proof window needs to be long enough to resubmit if needed")
			return errors.New("fill me in")
		}

		// Add the storage obligation information to the database.
		err := h.db.Update(func(tx *bolt.Tx) error {
			// Sanity check - a storage obligation using the same file contract id
			// should not already exist. This situation can happen if the
			// transaction pool ejects a file contract and then a new one is
			// created. Though the file contract will have the same terms, some
			// other conditions might cause problems. The check for duplicate file
			// contract ids should happen during the negotiation phase, and not
			// during the 'addStorageObligation' phase.
			bso := tx.Bucket(bucketStorageObligations)

			// If the storage obligation already has sectors, it means that the
			// file contract is being renewed, and that the sector should be
			// re-added with a new expiration height. If there is an error at any
			// point, all of the sectors should be removed.
			if len(so.SectorRoots) != 0 {
				err := h.AddSectorBatch(so.SectorRoots)
				if err != nil {
					return err
				}
			}

			// Add the storage obligation to the database.
			soBytes, err := json.Marshal(so)
			if err != nil {
				return err
			}
			return bso.Put(soid[:], soBytes)
		})
		if err != nil {
			return err
		}

		// Update the host financial metrics with regards to this storage
		// obligation.
		h.financialMetrics.ContractCount++
		h.financialMetrics.PotentialContractCompensation = h.financialMetrics.PotentialContractCompensation.Add(so.ContractCost)
		h.financialMetrics.LockedStorageCollateral = h.financialMetrics.LockedStorageCollateral.Add(so.LockedCollateral)
		h.financialMetrics.PotentialStorageRevenue = h.financialMetrics.PotentialStorageRevenue.Add(so.PotentialStorageRevenue)
		h.financialMetrics.PotentialDownloadBandwidthRevenue = h.financialMetrics.PotentialDownloadBandwidthRevenue.Add(so.PotentialDownloadRevenue)
		h.financialMetrics.PotentialUploadBandwidthRevenue = h.financialMetrics.PotentialUploadBandwidthRevenue.Add(so.PotentialUploadRevenue)
		h.financialMetrics.RiskedStorageCollateral = h.financialMetrics.RiskedStorageCollateral.Add(so.RiskedCollateral)
		h.financialMetrics.TransactionFeeExpenses = h.financialMetrics.TransactionFeeExpenses.Add(so.TransactionFeesAdded)
		return nil
	}()
	if err != nil {
		return err
	}

	// Check that the transaction is fully valid and submit it to the
	// transaction pool.
	err = h.tpool.AcceptTransactionSet(so.OriginTransactionSet)
	if err != nil {
		h.log.Println("Failed to add storage obligation, transaction set was not accepted:", err)
		return err
	}

	// Queue the action items.
	h.mu.Lock()
	defer h.mu.Unlock()

	// The file contract was already submitted to the blockchain, need to check
	// after the resubmission timeout that it was submitted successfully.
	err1 := h.queueActionItem(h.blockHeight+resubmissionTimeout, soid)
	err2 := h.queueActionItem(h.blockHeight+resubmissionTimeout*2, soid) // Paranoia
	// Queue an action item to submit the file contract revision - if there is
	// never a file contract revision, the handling of this action item will be
	// a no-op.
	err3 := h.queueActionItem(so.expiration()-revisionSubmissionBuffer, soid)
	err4 := h.queueActionItem(so.expiration()-revisionSubmissionBuffer+resubmissionTimeout, soid) // Paranoia
	// The storage proof should be submitted
	err5 := h.queueActionItem(so.expiration()+resubmissionTimeout, soid)
	err6 := h.queueActionItem(so.expiration()+resubmissionTimeout*2, soid) // Paranoia
	err = composeErrors(err1, err2, err3, err4, err5, err6)
	if err != nil {
		h.log.Println("Error with transaction set, redacting obligation, id", so.id())
		return composeErrors(err, h.removeStorageObligation(so, obligationRejected))
	}
	return nil
}

// modifyStorageObligation will take an updated storage obligation along with a
// list of sector changes and update the database to account for all of it. The
// sector modifications are only used to update the sector database, they will
// not be used to modify the storage obligation (most importantly, this means
// that sectorRoots needs to be updated by the calling function). Virtual
// sectors will be removed the number of times that they are listed, to remove
// multiple instances of the same virtual sector, the virtural sector will need
// to appear in 'sectorsRemoved' multiple times. Same with 'sectorsGained'.
func (h *Host) modifyStorageObligation(so storageObligation, sectorsRemoved []crypto.Hash, sectorsGained []crypto.Hash, gainedSectorData [][]byte) error {
	// Sanity check - obligation should be under lock while being modified.
	soid := so.id()
	_, exists := h.lockedStorageObligations[soid]
	if !exists {
		h.log.Critical("modifyStorageObligation called with an obligation that is not locked")
	}
	// Sanity check - there needs to be enough time to submit the file contract
	// revision to the blockchain.
	if so.expiration()-revisionSubmissionBuffer <= h.blockHeight {
		return errNoBuffer
	}
	// Sanity check - sectorsGained and gainedSectorData need to have the same length.
	if len(sectorsGained) != len(gainedSectorData) {
		h.log.Critical("modifying a revision with garbage sector data", len(sectorsGained), len(gainedSectorData))
		return errInsaneStorageObligationRevision
	}
	// Sanity check - all of the sector data should be modules.SectorSize
	for _, data := range gainedSectorData {
		if uint64(len(data)) != modules.SectorSize {
			h.log.Critical("modifying a revision with garbase sector sizes", len(data))
			return errInsaneStorageObligationRevision
		}
	}

	// Note, for safe error handling, the operation order should be: add
	// sectors, update database, remove sectors. If the adding or update fails,
	// the added sectors should be removed and the storage obligation shoud be
	// considered invalid. If the removing fails, this is okay, it's ignored
	// and left to consistency checks and user actions to fix (will reduce host
	// capacity, but will not inhibit the host's ability to submit storage
	// proofs)
	var i int
	var err error
	for i = range sectorsGained {
		err = h.AddSector(sectorsGained[i], gainedSectorData[i])
		if err != nil {
			break
		}
	}
	if err != nil {
		// Because there was an error, all of the sectors that got added need
		// to be reverted.
		for j := 0; j < i; j++ {
			// Error is not checked because there's nothing useful that can be
			// done about an error.
			_ = h.RemoveSector(sectorsGained[j])
		}
		return err
	}
	// Update the database to contain the new storage obligation.
	var oldSO storageObligation
	err = h.db.Update(func(tx *bolt.Tx) error {
		// Get the old storage obligation as a reference to know how to upate
		// the host financial stats.
		oldSO, err = getStorageObligation(tx, soid)
		if err != nil {
			return err
		}

		// Store the new storage obligation to replace the old one.
		return putStorageObligation(tx, so)
	})
	if err != nil {
		// Because there was an error, all of the sectors that got added need
		// to be reverted.
		for i := range sectorsGained {
			// Error is not checked because there's nothing useful that can be
			// done about an error.
			_ = h.RemoveSector(sectorsGained[i])
		}
		return err
	}
	// Call removeSector for all of the sectors that have been removed.
	for k := range sectorsRemoved {
		// Error is not checkeed because there's nothing useful that can be
		// done about an error. Failing to remove a sector is not a terrible
		// place to be, especially if the host can run consistency checks.
		_ = h.RemoveSector(sectorsRemoved[k])
	}

	// Update the financial information for the storage obligation - apply the
	// new values.
	h.financialMetrics.PotentialContractCompensation = h.financialMetrics.PotentialContractCompensation.Add(so.ContractCost)
	h.financialMetrics.LockedStorageCollateral = h.financialMetrics.LockedStorageCollateral.Add(so.LockedCollateral)
	h.financialMetrics.PotentialStorageRevenue = h.financialMetrics.PotentialStorageRevenue.Add(so.PotentialStorageRevenue)
	h.financialMetrics.PotentialDownloadBandwidthRevenue = h.financialMetrics.PotentialDownloadBandwidthRevenue.Add(so.PotentialDownloadRevenue)
	h.financialMetrics.PotentialUploadBandwidthRevenue = h.financialMetrics.PotentialUploadBandwidthRevenue.Add(so.PotentialUploadRevenue)
	h.financialMetrics.RiskedStorageCollateral = h.financialMetrics.RiskedStorageCollateral.Add(so.RiskedCollateral)
	h.financialMetrics.TransactionFeeExpenses = h.financialMetrics.TransactionFeeExpenses.Add(so.TransactionFeesAdded)

	// Update the financial information for the storage obligation - remove the
	// old values.
	h.financialMetrics.PotentialContractCompensation = h.financialMetrics.PotentialContractCompensation.Sub(oldSO.ContractCost)
	h.financialMetrics.LockedStorageCollateral = h.financialMetrics.LockedStorageCollateral.Sub(oldSO.LockedCollateral)
	h.financialMetrics.PotentialStorageRevenue = h.financialMetrics.PotentialStorageRevenue.Sub(oldSO.PotentialStorageRevenue)
	h.financialMetrics.PotentialDownloadBandwidthRevenue = h.financialMetrics.PotentialDownloadBandwidthRevenue.Sub(oldSO.PotentialDownloadRevenue)
	h.financialMetrics.PotentialUploadBandwidthRevenue = h.financialMetrics.PotentialUploadBandwidthRevenue.Sub(oldSO.PotentialUploadRevenue)
	h.financialMetrics.RiskedStorageCollateral = h.financialMetrics.RiskedStorageCollateral.Sub(oldSO.RiskedCollateral)
	h.financialMetrics.TransactionFeeExpenses = h.financialMetrics.TransactionFeeExpenses.Sub(oldSO.TransactionFeesAdded)
	return nil
}

// removeStorageObligation will remove a storage obligation from the host,
// either due to failure or success.
func (h *Host) removeStorageObligation(so storageObligation, sos storageObligationStatus) error {
	// Error is not checked, we want to call remove on every sector even if
	// there are problems - disk health information will be updated.
	_ = h.RemoveSectorBatch(so.SectorRoots)

	// Update the host revenue metrics based on the status of the obligation.
	if sos == obligationUnresolved {
		h.log.Critical("storage obligation 'unresolved' during call to removeStorageObligation, id", so.id())
	}
	if sos == obligationRejected {
		if h.financialMetrics.TransactionFeeExpenses.Cmp(so.TransactionFeesAdded) >= 0 {
			h.financialMetrics.TransactionFeeExpenses = h.financialMetrics.TransactionFeeExpenses.Sub(so.TransactionFeesAdded)

			// Remove the obligation statistics as potential risk and income.
			h.log.Printf("Rejecting storage obligation expiring at block %v, current height is %v. Potential revenue is %v.\n", so.expiration(), h.blockHeight, h.financialMetrics.PotentialContractCompensation.Add(h.financialMetrics.PotentialStorageRevenue).Add(h.financialMetrics.PotentialDownloadBandwidthRevenue).Add(h.financialMetrics.PotentialUploadBandwidthRevenue))
			h.financialMetrics.PotentialContractCompensation = h.financialMetrics.PotentialContractCompensation.Sub(so.ContractCost)
			h.financialMetrics.LockedStorageCollateral = h.financialMetrics.LockedStorageCollateral.Sub(so.LockedCollateral)
			h.financialMetrics.PotentialStorageRevenue = h.financialMetrics.PotentialStorageRevenue.Sub(so.PotentialStorageRevenue)
			h.financialMetrics.PotentialDownloadBandwidthRevenue = h.financialMetrics.PotentialDownloadBandwidthRevenue.Sub(so.PotentialDownloadRevenue)
			h.financialMetrics.PotentialUploadBandwidthRevenue = h.financialMetrics.PotentialUploadBandwidthRevenue.Sub(so.PotentialUploadRevenue)
			h.financialMetrics.RiskedStorageCollateral = h.financialMetrics.RiskedStorageCollateral.Sub(so.RiskedCollateral)
		}
	}
	if sos == obligationSucceeded {
		// Empty obligations don't submit a storage proof. The revenue for an empty
		// storage obligation should equal the contract cost of the obligation
		revenue := so.ContractCost.Add(so.PotentialStorageRevenue).Add(so.PotentialDownloadRevenue).Add(so.PotentialUploadRevenue)
		if len(so.SectorRoots) == 0 {
			h.log.Printf("No need to submit a storage proof for empty contract. Revenue is %v.\n", revenue)
		} else {
			h.log.Printf("Successfully submitted a storage proof. Revenue is %v.\n", revenue)
		}

		// Remove the obligation statistics as potential risk and income.
		h.financialMetrics.PotentialContractCompensation = h.financialMetrics.PotentialContractCompensation.Sub(so.ContractCost)
		h.financialMetrics.LockedStorageCollateral = h.financialMetrics.LockedStorageCollateral.Sub(so.LockedCollateral)
		h.financialMetrics.PotentialStorageRevenue = h.financialMetrics.PotentialStorageRevenue.Sub(so.PotentialStorageRevenue)
		h.financialMetrics.PotentialDownloadBandwidthRevenue = h.financialMetrics.PotentialDownloadBandwidthRevenue.Sub(so.PotentialDownloadRevenue)
		h.financialMetrics.PotentialUploadBandwidthRevenue = h.financialMetrics.PotentialUploadBandwidthRevenue.Sub(so.PotentialUploadRevenue)
		h.financialMetrics.RiskedStorageCollateral = h.financialMetrics.RiskedStorageCollateral.Sub(so.RiskedCollateral)

		// Add the obligation statistics as actual income.
		h.financialMetrics.ContractCompensation = h.financialMetrics.ContractCompensation.Add(so.ContractCost)
		h.financialMetrics.StorageRevenue = h.financialMetrics.StorageRevenue.Add(so.PotentialStorageRevenue)
		h.financialMetrics.DownloadBandwidthRevenue = h.financialMetrics.DownloadBandwidthRevenue.Add(so.PotentialDownloadRevenue)
		h.financialMetrics.UploadBandwidthRevenue = h.financialMetrics.UploadBandwidthRevenue.Add(so.PotentialUploadRevenue)
	}
	if sos == obligationFailed {
		// Remove the obligation statistics as potential risk and income.
		h.log.Printf("Missed storage proof. Revenue would have been %v.\n", so.ContractCost.Add(so.PotentialStorageRevenue).Add(so.PotentialDownloadRevenue).Add(so.PotentialUploadRevenue))
		h.financialMetrics.PotentialContractCompensation = h.financialMetrics.PotentialContractCompensation.Sub(so.ContractCost)
		h.financialMetrics.LockedStorageCollateral = h.financialMetrics.LockedStorageCollateral.Sub(so.LockedCollateral)
		h.financialMetrics.PotentialStorageRevenue = h.financialMetrics.PotentialStorageRevenue.Sub(so.PotentialStorageRevenue)
		h.financialMetrics.PotentialDownloadBandwidthRevenue = h.financialMetrics.PotentialDownloadBandwidthRevenue.Sub(so.PotentialDownloadRevenue)
		h.financialMetrics.PotentialUploadBandwidthRevenue = h.financialMetrics.PotentialUploadBandwidthRevenue.Sub(so.PotentialUploadRevenue)
		h.financialMetrics.RiskedStorageCollateral = h.financialMetrics.RiskedStorageCollateral.Sub(so.RiskedCollateral)

		// Add the obligation statistics as loss.
		h.financialMetrics.LostStorageCollateral = h.financialMetrics.LostStorageCollateral.Add(so.RiskedCollateral)
		h.financialMetrics.LostRevenue = h.financialMetrics.LostRevenue.Add(so.ContractCost).Add(so.PotentialStorageRevenue).Add(so.PotentialDownloadRevenue).Add(so.PotentialUploadRevenue)
	}

	// Update the storage obligation to be finalized but still in-database. The
	// obligation status is updated so that the user can see how the obligation
	// ended up, and the sector roots are removed because they are large
	// objects with little purpose once storage proofs are no longer needed.
	h.financialMetrics.ContractCount--
	so.ObligationStatus = sos
	so.SectorRoots = nil
	return h.db.Update(func(tx *bolt.Tx) error {
		return putStorageObligation(tx, so)
	})
}

// threadedHandleActionItem will look at a storage obligation and determine
// which action is necessary for the storage obligation to succeed.
func (h *Host) threadedHandleActionItem(soid types.FileContractID) {
	err := h.tg.Add()
	if err != nil {
		return
	}
	defer h.tg.Done()

	// Lock the storage obligation in question.
	h.managedLockStorageObligation(soid)
	defer func() {
		h.managedUnlockStorageObligation(soid)
	}()

	// Fetch the storage obligation associated with the storage obligation id.
	var so storageObligation
	h.mu.RLock()
	blockHeight := h.blockHeight
	err = h.db.View(func(tx *bolt.Tx) error {
		so, err = getStorageObligation(tx, soid)
		return err
	})
	h.mu.RUnlock()
	if err != nil {
		h.log.Println("Could not get storage obligation:", err)
		return
	}

	// Check whether the storage obligation has already been completed.
	if so.ObligationStatus != obligationUnresolved {
		// Storage obligation has already been completed, skip action item.
		return
	}

	// Check whether the file contract has been seen. If not, resubmit and
	// queue another action item. Check for death. (signature should have a
	// kill height)
	if !so.OriginConfirmed {
		// Submit the transaction set again, try to get the transaction
		// confirmed.
		err := h.tpool.AcceptTransactionSet(so.OriginTransactionSet)
		if err != nil {
			h.log.Debugln("Could not get origin transaction set accepted", err)

			// Check if the transaction is invalid with the current consensus set.
			// If so, the transaction is highly unlikely to ever be confirmed, and
			// the storage obligation should be removed. This check should come
			// after logging the errror so that the function can quit.
			//
			// TODO: If the host or tpool is behind consensus, might be difficult
			// to have certainty about the issue. If some but not all of the
			// parents are confirmed, might be some difficulty.
			_, t := err.(modules.ConsensusConflict)
			if t {
				h.log.Println("Consensus conflict on the origin transaction set, id", so.id())
				h.mu.Lock()
				err = h.removeStorageObligation(so, obligationRejected)
				h.mu.Unlock()
				if err != nil {
					h.log.Println("Error removing storage obligation:", err)
				}
				return
			}
		}

		// Queue another action item to check the status of the transaction.
		h.mu.Lock()
		err = h.queueActionItem(h.blockHeight+resubmissionTimeout, so.id())
		h.mu.Unlock()
		if err != nil {
			h.log.Println("Error queuing action item:", err)
		}
	}

	// Check if the file contract revision is ready for submission. Check for death.
	if !so.RevisionConfirmed && len(so.RevisionTransactionSet) > 0 && blockHeight >= so.expiration()-revisionSubmissionBuffer {
		// Sanity check - there should be a file contract revision.
		rtsLen := len(so.RevisionTransactionSet)
		if rtsLen < 1 || len(so.RevisionTransactionSet[rtsLen-1].FileContractRevisions) != 1 {
			h.log.Critical("transaction revision marked as unconfirmed, yet there is no transaction revision")
			return
		}

		// Check if the revision has failed to submit correctly.
		if blockHeight > so.expiration() {
			// TODO: Check this error.
			//
			// TODO: this is not quite right, because a previous revision may
			// be confirmed, and the origin transaction may be confirmed, which
			// would confuse the revenue stuff a bit. Might happen frequently
			// due to the dynamic fee pool.
			h.log.Println("Full time has elapsed, but the revision transaction could not be submitted to consensus, id", so.id())
			h.mu.Lock()
			h.removeStorageObligation(so, obligationRejected)
			h.mu.Unlock()
			return
		}

		// Queue another action item to check the status of the transaction.
		h.mu.Lock()
		err := h.queueActionItem(blockHeight+resubmissionTimeout, so.id())
		h.mu.Unlock()
		if err != nil {
			h.log.Println("Error queuing action item:", err)
		}

		// Add a miner fee to the transaction and submit it to the blockchain.
		revisionTxnIndex := len(so.RevisionTransactionSet) - 1
		revisionParents := so.RevisionTransactionSet[:revisionTxnIndex]
		revisionTxn := so.RevisionTransactionSet[revisionTxnIndex]
		builder, err := h.wallet.RegisterTransaction(revisionTxn, revisionParents)
		if err != nil {
			h.log.Println("Error registering transaction:", err)
			return
		}
		_, feeRecommendation := h.tpool.FeeEstimation()
		if so.value().Div64(2).Cmp(feeRecommendation) < 0 {
			// There's no sense submitting the revision if the fee is more than
			// half of the anticipated revenue - fee market went up
			// unexpectedly, and the money that the renter paid to cover the
			// fees is no longer enough.
			builder.Drop()
			return
		}
		txnSize := uint64(len(encoding.MarshalAll(so.RevisionTransactionSet)) + 300)
		requiredFee := feeRecommendation.Mul64(txnSize)
		err = builder.FundSiacoins(requiredFee)
		if err != nil {
			h.log.Println("Error funding transaction fees", err)
			builder.Drop()
		}
		builder.AddMinerFee(requiredFee)
		if err != nil {
			h.log.Println("Error adding miner fees", err)
			builder.Drop()
		}
		feeAddedRevisionTransactionSet, err := builder.Sign(true)
		if err != nil {
			h.log.Println("Error signing transaction", err)
			builder.Drop()
		}
		err = h.tpool.AcceptTransactionSet(feeAddedRevisionTransactionSet)
		if err != nil {
			h.log.Println("Error submitting transaction to transaction pool", err)
			builder.Drop()
		}
		so.TransactionFeesAdded = so.TransactionFeesAdded.Add(requiredFee)
		// return
	}

	// Check whether a storage proof is ready to be provided, and whether it
	// has been accepted. Check for death.
	if !so.ProofConfirmed && blockHeight >= so.expiration()+resubmissionTimeout {
		h.log.Debugln("Host is attempting a storage proof for", so.id())

		// If the obligation has no sector roots, we can remove the obligation and not
		// submit a storage proof. The host payout for a failed empty contract
		// includes the contract cost and locked collateral.
		if len(so.SectorRoots) == 0 {
			h.log.Debugln("storage proof not submitted for empty contract, id", so.id())
			h.mu.Lock()
			err := h.removeStorageObligation(so, obligationSucceeded)
			h.mu.Unlock()
			if err != nil {
				h.log.Println("Error removing storage obligation:", err)
			}
			return
		}
		// If the window has closed, the host has failed and the obligation can
		// be removed.
		if so.proofDeadline() < blockHeight {
			h.log.Debugln("storage proof not confirmed by deadline, id", so.id())
			h.mu.Lock()
			err := h.removeStorageObligation(so, obligationFailed)
			h.mu.Unlock()
			if err != nil {
				h.log.Println("Error removing storage obligation:", err)
			}
			return
		}
		// Get the index of the segment, and the index of the sector containing
		// the segment.
		segmentIndex, err := h.cs.StorageProofSegment(so.id())
		if err != nil {
			h.log.Debugln("Host got an error when fetching a storage proof segment:", err)
			return
		}
		sectorIndex := segmentIndex / (modules.SectorSize / crypto.SegmentSize)
		// Pull the corresponding sector into memory.
		sectorRoot := so.SectorRoots[sectorIndex]
		sectorBytes, err := h.ReadSector(sectorRoot)
		if err != nil {
			h.log.Debugln(err)
			return
		}

		// Build the storage proof for just the sector.
		sectorSegment := segmentIndex % (modules.SectorSize / crypto.SegmentSize)
		base, cachedHashSet := crypto.MerkleProof(sectorBytes, sectorSegment)

		// Using the sector, build a cached root.
		log2SectorSize := uint64(0)
		for 1<<log2SectorSize < (modules.SectorSize / crypto.SegmentSize) {
			log2SectorSize++
		}
		ct := crypto.NewCachedTree(log2SectorSize)
		ct.SetIndex(segmentIndex)
		for _, root := range so.SectorRoots {
			ct.Push(root)
		}
		hashSet := ct.Prove(base, cachedHashSet)
		sp := types.StorageProof{
			ParentID: so.id(),
			HashSet:  hashSet,
		}
		copy(sp.Segment[:], base)

		// Create and build the transaction with the storage proof.
		builder, err := h.wallet.StartTransaction()
		if err != nil {
			h.log.Println("Failed to start transaction:", err)
			return
		}
		_, feeRecommendation := h.tpool.FeeEstimation()
		if so.value().Cmp(feeRecommendation) < 0 {
			// There's no sense submitting the storage proof if the fee is more
			// than the anticipated revenue.
			h.log.Debugln("Host not submitting storage proof due to a value that does not sufficiently exceed the fee cost")
			builder.Drop()
			return
		}
		txnSize := uint64(len(encoding.Marshal(sp)) + 300)
		requiredFee := feeRecommendation.Mul64(txnSize)
		err = builder.FundSiacoins(requiredFee)
		if err != nil {
			h.log.Println("Host error when funding a storage proof transaction fee:", err)
			builder.Drop()
			return
		}
		builder.AddMinerFee(requiredFee)
		builder.AddStorageProof(sp)
		storageProofSet, err := builder.Sign(true)
		if err != nil {
			h.log.Println("Host error when signing the storage proof transaction:", err)
			builder.Drop()
			return
		}
		err = h.tpool.AcceptTransactionSet(storageProofSet)
		if err != nil {
			h.log.Println("Host unable to submit storage proof transaction to transaction pool:", err)
			builder.Drop()
			return
		}
		so.TransactionFeesAdded = so.TransactionFeesAdded.Add(requiredFee)

		// Queue another action item to check whether the storage proof
		// got confirmed.
		h.mu.Lock()
		err = h.queueActionItem(so.proofDeadline(), so.id())
		h.mu.Unlock()
		if err != nil {
			h.log.Println("Error queuing action item:", err)
		}
	}

	// Save the storage obligation to account for any fee changes.
	err = h.db.Update(func(tx *bolt.Tx) error {
		soBytes, err := json.Marshal(so)
		if err != nil {
			return err
		}
		return tx.Bucket(bucketStorageObligations).Put(soid[:], soBytes)
	})
	if err != nil {
		h.log.Println("Error updating the storage obligations", err)
	}

	// Check if all items have succeeded with the required confirmations. Report
	// success, delete the obligation.
	if so.ProofConfirmed && blockHeight >= so.proofDeadline() {
		h.log.Println("file contract complete, id", so.id())
		h.mu.Lock()
		h.removeStorageObligation(so, obligationSucceeded)
		h.mu.Unlock()
	}
}

// StorageObligations fetches the set of storage obligations in the host and
// returns metadata on them.
func (h *Host) StorageObligations() (sos []modules.StorageObligation) {
	h.mu.RLock()
	defer h.mu.RUnlock()

	err := h.db.View(func(tx *bolt.Tx) error {
		b := tx.Bucket(bucketStorageObligations)
		err := b.ForEach(func(idBytes, soBytes []byte) error {
			var so storageObligation
			err := json.Unmarshal(soBytes, &so)
			if err != nil {
				return build.ExtendErr("unable to unmarshal storage obligation:", err)
			}
			mso := modules.StorageObligation{
				ContractCost:             so.ContractCost,
				DataSize:                 so.fileSize(),
				LockedCollateral:         so.LockedCollateral,
				ObligationId:             so.id(),
				PotentialDownloadRevenue: so.PotentialDownloadRevenue,
				PotentialStorageRevenue:  so.PotentialStorageRevenue,
				PotentialUploadRevenue:   so.PotentialUploadRevenue,
				RiskedCollateral:         so.RiskedCollateral,
				SectorRootsCount:         uint64(len(so.SectorRoots)),
				TransactionFeesAdded:     so.TransactionFeesAdded,

				ExpirationHeight:  so.expiration(),
				NegotiationHeight: so.NegotiationHeight,
				ProofDeadLine:     so.proofDeadline(),

				ObligationStatus:    so.ObligationStatus.String(),
				OriginConfirmed:     so.OriginConfirmed,
				ProofConfirmed:      so.ProofConfirmed,
				ProofConstructed:    so.ProofConstructed,
				RevisionConfirmed:   so.RevisionConfirmed,
				RevisionConstructed: so.RevisionConstructed,
			}
			sos = append(sos, mso)
			return nil
		})
		if err != nil {
			return build.ExtendErr("ForEach failed to get next storage obligation:", err)
		}
		return nil
	})
	if err != nil {
		h.log.Println(build.ExtendErr("database failed to provide storage obligations:", err))
	}

	return sos
}