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snapshot.go
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snapshot.go
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// (c) 2019 Dapper Labs - ALL RIGHTS RESERVED
package protocol
import (
"github.com/onflow/flow-go/model/flow"
)
// Snapshot represents an immutable snapshot of the protocol state
// at a specific block, denoted as the Head block.
// The Snapshot is fork-specific and only accounts for the information contained
// in blocks along this fork up to (including) Head.
// It allows us to read the parameters at the selected block in a deterministic manner.
type Snapshot interface {
// Head returns the latest block at the selected point of the protocol state
// history. It can represent either a finalized or ambiguous block,
// depending on our selection criteria. Either way, it's the block on which
// we should build the next block in the context of the selected state.
Head() (*flow.Header, error)
// Identities returns a list of identities at the selected point of the
// protocol state history. At the beginning of an epoch, this list includes
// identities from the previous epoch that are un-staking during the current
// epoch. At the end of an epoch, this includes identities scheduled to join
// in the next epoch but are not active yet.
//
// It allows us to provide optional upfront filters which can be used by the
// implementation to speed up database lookups.
Identities(selector flow.IdentityFilter) (flow.IdentityList, error)
// Identity attempts to retrieve the node with the given identifier at the
// selected point of the protocol state history. It will error if it doesn't exist.
Identity(nodeID flow.Identifier) (*flow.Identity, error)
// Commit return the sealed execution state commitment at this block.
Commit() (flow.StateCommitment, error)
// Pending returns the IDs of all descendants of the Head block. The IDs
// are ordered such that parents are included before their children. These
// are NOT guaranteed to have been validated by HotStuff.
Pending() ([]flow.Identifier, error)
// Seed returns a deterministic seed for a pseudo random number generator.
// The seed is derived from the source of randomness for the Head block.
// In order to deterministically derive task specific seeds, indices must
// be specified. Refer to module/indices/rand.go for different indices.
// NOTE: not to be confused with the epoch source of randomness!
Seed(indices ...uint32) ([]byte, error)
// Phase returns the epoch phase for the current epoch, as of the Head block.
Phase() (flow.EpochPhase, error)
// Epochs returns a query object enabling querying detailed information about
// various epochs.
//
// For epochs that are in the future w.r.t. the Head block, some of Epoch's
// methods may return errors, since the Epoch Preparation Protocol may be
// in-progress and incomplete for the epoch.
Epochs() EpochQuery
}