chainselection

package
v0.46.1 Latest Latest
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 Go to latest Published: May 14, 2026 License: Apache-2.0 Imports: 19 Imported by: 0

Documentation

Overview

Package chainselection implements multi-peer chain selection. It tracks the tip reported by each connected peer and, for Shelley-family headers, uses the Praos select view projected from the observed header: longer chain first, then the reference implementation's equal-length opcert/VRF tiebreaker when it is armed.

Genesis selection mode can be enabled at startup to prefer observed density during bootstrap before automatically falling back to Praos once the local tip is close enough to the best observed peer tip.

ChainSelector is the top-level type. It consumes PeerTipUpdateEvent events from chainsync, compares peer tips against the local tip, and emits ChainSwitchEvent on the EventBus when the selected peer changes. The node's Run loop listens for those events and repoints the active chainsync stream at the new best peer.

This package does not perform any block validation; it only selects which peer's chain to follow. Validation happens downstream in the ledger package after blocks are fetched from the selected peer.

Index

Constants

View Source 
const (
	PeerTipUpdateEventType  event.EventType = "chainselection.peer_tip_update"
	PeerActivityEventType   event.EventType = "chainselection.peer_activity"
	PeerRollbackEventType   event.EventType = "chainselection.peer_rollback"
	ChainSwitchEventType    event.EventType = "chainselection.chain_switch"
	ChainSelectionEventType event.EventType = "chainselection.selection"
	PeerEvictedEventType    event.EventType = "chainselection.peer_evicted"
)
View Source 
const (

	// DefaultMaxTrackedPeers is the maximum number of peers tracked by
	// the ChainSelector. When a new peer is added and the limit is reached,
	// the least-recently-updated peer is evicted. This bounds memory usage
	// and CPU cost of chain selection, preventing Sybil-based resource
	// exhaustion.
	DefaultMaxTrackedPeers = 200
)
View Source 
const VRFOutputSize = 64

VRFOutputSize is the expected size of a VRF output in bytes.

Variables

This section is empty.

Functions

func GenesisWindowSlotsForParams added in v0.37.0 

func GenesisWindowSlotsForParams(
	securityParam uint64,
	activeSlotsCoeff float64,
) uint64

GenesisWindowSlotsForParams returns the Genesis density window in slots. Shelley-style networks use 3k/f, where k is the security parameter and f is the active slot coefficient.

func GetVRFOutput 

func GetVRFOutput(header ledger.BlockHeader) []byte

GetVRFOutput extracts the VRF output from a block header. Returns nil if the header type is not supported or doesn't contain VRF data.

The VRF output is used for tie-breaking in chain selection when two chains have equal block numbers and equal density. The chain with the LOWER VRF output (lexicographically) wins.

func PreferPraosCandidate added in v0.46.0 

func PreferPraosCandidate(
	ours, cand PraosTiebreakerView,
) bool

PreferPraosCandidate mirrors ouroboros-consensus' preferCandidate cfg ours cand for equal-length Praos chains.

Types

type ChainComparisonResult 

type ChainComparisonResult int

ChainComparisonResult indicates the result of comparing two chains. 

const (
	ChainEqual             ChainComparisonResult = 0
	ChainABetter           ChainComparisonResult = 1
	ChainBBetter           ChainComparisonResult = -1
	ChainComparisonUnknown ChainComparisonResult = 2
)

func ComparePraosTips added in v0.46.0 

func ComparePraosTips(
	tipA, tipB ochainsync.Tip,
	viewA, viewB PraosTiebreakerView,
) ChainComparisonResult

ComparePraosTips compares two Praos-era tips using cardano-node's equal-length tiebreaker shape:

  1. Higher block number wins.
  2. At equal block number, prefer a candidate with the same issuer and slot only when it has a higher opcert issue number.
  3. Otherwise compare the tip VRF only when the era's VRF tiebreaker flavor is armed. Conway restricts this to tips at most 5 slots apart.

If neither reference implementation rule applies, this returns ChainEqual so callers keep the incumbent.

func CompareVRFOutputs 

func CompareVRFOutputs(vrfA, vrfB []byte) ChainComparisonResult

CompareVRFOutputs compares two VRF outputs for chain selection tie-breaking. Returns:

  • ChainABetter (1) if vrfA is lower (A wins)
  • ChainBBetter (-1) if vrfB is lower (B wins)
  • ChainEqual (0) if equal, either is nil, or either has invalid length

Per Ouroboros Praos: the chain with the LOWER VRF output wins the tie-break. Both outputs must be exactly VRFOutputSize (64) bytes; outputs of any other length are treated the same as nil to prevent truncated values from winning.

type ChainSelectionEvent 

type ChainSelectionEvent struct {
	BestConnectionId ouroboros.ConnectionId
	BestTip          ochainsync.Tip
	PeerCount        int
	SwitchOccurred   bool
}

ChainSelectionEvent is published when chain selection evaluation completes.

type ChainSelector 

type ChainSelector struct {
	// contains filtered or unexported fields
}

ChainSelector tracks chain tips from multiple peers and selects the best chain using the active mode's comparison rules.

func NewChainSelector 

func NewChainSelector(cfg ChainSelectorConfig) *ChainSelector

NewChainSelector creates a new ChainSelector with the given configuration.

func (*ChainSelector) EvaluateAndSwitch 

func (cs *ChainSelector) EvaluateAndSwitch() bool

EvaluateAndSwitch evaluates all peer tips and switches to the best chain if it differs from the current best. Returns true if a switch occurred.

func (*ChainSelector) GenesisWindowSlots added in v0.37.0 

func (cs *ChainSelector) GenesisWindowSlots() uint64

GenesisWindowSlots returns the slot window used for Genesis density checks.

func (*ChainSelector) GetAllPeerTips 

func (cs *ChainSelector) GetAllPeerTips() map[ouroboros.ConnectionId]*PeerChainTip

GetAllPeerTips returns a deep copy of all tracked peer tips.

func (*ChainSelector) GetBestPeer 

func (cs *ChainSelector) GetBestPeer() *ouroboros.ConnectionId

GetBestPeer returns the connection ID of the peer with the best chain, or nil if no suitable peer is available.

func (*ChainSelector) GetPeerTip 

func (cs *ChainSelector) GetPeerTip(
	connId ouroboros.ConnectionId,
) *PeerChainTip

GetPeerTip returns a deep copy of the chain tip for a specific peer. Returns nil if the peer is not tracked.

func (*ChainSelector) HandlePeerActivityEvent added in v0.27.7 

func (cs *ChainSelector) HandlePeerActivityEvent(evt event.Event)

HandlePeerActivityEvent refreshes a peer's liveness on non-tip protocol activity such as keepalive responses.

func (*ChainSelector) HandlePeerTipUpdateEvent 

func (cs *ChainSelector) HandlePeerTipUpdateEvent(evt event.Event)

HandlePeerTipUpdateEvent handles PeerTipUpdateEvent from the event bus.

func (*ChainSelector) PeerCount 

func (cs *ChainSelector) PeerCount() int

PeerCount returns the number of peers being tracked.

func (*ChainSelector) RemovePeer 

func (cs *ChainSelector) RemovePeer(connId ouroboros.ConnectionId)

RemovePeer removes a peer from tracking.

func (*ChainSelector) SelectBestChain 

func (cs *ChainSelector) SelectBestChain() *ouroboros.ConnectionId

SelectBestChain evaluates all peer tips and returns the connection ID of the peer with the best chain.

func (*ChainSelector) SelectionMode added in v0.37.0 

func (cs *ChainSelector) SelectionMode() SelectionMode

SelectionMode returns the selector's current mode.

func (*ChainSelector) SetLocalTip 

func (cs *ChainSelector) SetLocalTip(tip ochainsync.Tip)

SetLocalTip updates the local chain tip for comparison.

func (*ChainSelector) SetSecurityParam 

func (cs *ChainSelector) SetSecurityParam(k uint64)

SetSecurityParam updates the security parameter (k) dynamically. This allows the selector to use protocol parameters for density-based comparison.

func (*ChainSelector) Start 

func (cs *ChainSelector) Start(ctx context.Context) error

Start begins the chain selector's background evaluation loop and subscribes to relevant events.

func (*ChainSelector) Stop 

func (cs *ChainSelector) Stop()

Stop stops the chain selector.

func (*ChainSelector) TouchPeerActivity added in v0.27.7 

func (cs *ChainSelector) TouchPeerActivity(connId ouroboros.ConnectionId)

func (*ChainSelector) UpdatePeerTip 

func (cs *ChainSelector) UpdatePeerTip(
	connId ouroboros.ConnectionId,
	tip ochainsync.Tip,
	vrfOutput []byte,
) bool

UpdatePeerTip updates the chain tip for a specific peer and triggers evaluation if needed. The vrfOutput parameter is the VRF output from the tip block header, used for tie-breaking when chains have equal block number and slot.

Returns true if the tip was accepted, false if it was rejected as implausible. A tip is considered implausible if it claims a block number more than securityParam (k) blocks ahead of a reference point. For known peers, the reference is the peer's own previous tip; for new peers, the reference is the best known peer tip. This avoids rejecting legitimate peers during sync (where the local tip is far behind).

type ChainSelectorConfig 

type ChainSelectorConfig struct {
	Logger             *slog.Logger
	EventBus           *event.EventBus
	EvaluationInterval time.Duration
	StaleTipThreshold  time.Duration
	SecurityParam      uint64
	GenesisMode        bool
	GenesisWindowSlots uint64
	ConnectionLive     func(ouroboros.ConnectionId) bool
	ConnectionEligible func(ouroboros.ConnectionId) bool
	ConnectionPriority func(ouroboros.ConnectionId) int
	MaxTrackedPeers    int // 0 means use DefaultMaxTrackedPeers
	// BlockfetchLatency returns the EWMA first-block latency for a
	// connection and whether any samples exist. Used only to choose a
	// peer when two peers advertise the exact same selected block.
	BlockfetchLatency func(ouroboros.ConnectionId) (time.Duration, bool)
}

ChainSelectorConfig holds configuration for the ChainSelector.

type ChainSwitchEvent 

type ChainSwitchEvent struct {
	PreviousConnectionId ouroboros.ConnectionId
	NewConnectionId      ouroboros.ConnectionId
	NewTip               ochainsync.Tip
	PreviousTip          ochainsync.Tip
	ComparisonResult     ChainComparisonResult
	BlockDifference      int64
}

ChainSwitchEvent is published when the chain selector decides to switch to a different peer's chain.

Fields:

  • PreviousConnectionId: The connection ID of the peer we were following.
  • NewConnectionId: The connection ID of the peer we are now following.
  • NewTip: The chain tip of the new peer.
  • PreviousTip: The chain tip of the previous peer at the time of the switch.
  • ComparisonResult: Why the new chain is better than the previous chain.
  • BlockDifference: NewTip.BlockNumber - PreviousTip.BlockNumber.

type PeerActivityEvent added in v0.27.7 

type PeerActivityEvent struct {
	ConnectionId ouroboros.ConnectionId
}

PeerActivityEvent is published when a peer has recent protocol activity (for example, a keepalive response) without a tip change. This refreshes selector liveness for healthy but temporarily quiet peers.

type PeerChainTip 

type PeerChainTip struct {
	ConnectionId ouroboros.ConnectionId
	Tip          ochainsync.Tip
	ObservedTip  ochainsync.Tip
	VRFOutput    []byte // VRF output from tip block for tie-breaking
	PraosView    PraosTiebreakerView
	LastUpdated  time.Time
	// contains filtered or unexported fields
}

PeerChainTip tracks the chain tip reported by a specific peer.

func NewPeerChainTip 

func NewPeerChainTip(
	connId ouroboros.ConnectionId,
	tip ochainsync.Tip,
	vrfOutput []byte,
) *PeerChainTip

NewPeerChainTip creates a new PeerChainTip with the given connection ID, tip, and VRF output.

func (*PeerChainTip) ApplyRollback added in v0.37.0 

func (p *PeerChainTip) ApplyRollback(
	point ocommon.Point,
	tip ochainsync.Tip,
)

ApplyRollback trims observed history at the rollback point and refreshes the peer tip to the chainsync tip reported with the rollback.

func (*PeerChainTip) IsStale 

func (p *PeerChainTip) IsStale(threshold time.Duration) bool

IsStale returns true if the peer's tip hasn't been updated within the given duration.

func (*PeerChainTip) SelectionTip added in v0.27.7 

func (p *PeerChainTip) SelectionTip() ochainsync.Tip

SelectionTip returns the best locally observed frontier for this peer. When available, prefer the latest block the peer has actually delivered to us over its remote advertised tip. This avoids switching to peers whose far-end tip is high while their chainsync cursor is still lagging.

func (*PeerChainTip) Touch added in v0.27.7 

func (p *PeerChainTip) Touch()

Touch marks the peer as recently active without changing its advertised tip.

func (*PeerChainTip) UpdateTip 

func (p *PeerChainTip) UpdateTip(tip ochainsync.Tip, vrfOutput []byte)

UpdateTip updates the peer's chain tip, VRF output, and last updated timestamp.

func (*PeerChainTip) UpdateTipWithObserved added in v0.27.7 

func (p *PeerChainTip) UpdateTipWithObserved(
	tip ochainsync.Tip,
	observedTip ochainsync.Tip,
	vrfOutput []byte,
)

UpdateTipWithObserved updates both the remote advertised tip and the latest locally observed frontier for the peer.

func (*PeerChainTip) UpdateTipWithObservedPraosView added in v0.46.0 

func (p *PeerChainTip) UpdateTipWithObservedPraosView(
	tip ochainsync.Tip,
	observedTip ochainsync.Tip,
	vrfOutput []byte,
	praosView PraosTiebreakerView,
)

UpdateTipWithObservedPraosView updates the remote advertised tip, the latest locally observed frontier, the VRF output, and the Praos tiebreaker view for the peer. Callers must provide a PraosTiebreakerView derived from observedTip and the supplied vrfOutput when that VRF output participates in the view. The view is stored as supplied; this method does not validate consistency, so an inconsistent view can make later chain-selection comparisons incorrect.

type PeerEvictedEvent added in v0.22.0 

type PeerEvictedEvent struct {
	ConnectionId ouroboros.ConnectionId
}

PeerEvictedEvent is published when a tracked peer is evicted from the chain selector to make room for a new peer. Subscribers (e.g. connection manager) can use this to close the evicted peer's connection.

type PeerRollbackEvent added in v0.37.0 

type PeerRollbackEvent struct {
	ConnectionId ouroboros.ConnectionId
	Point        ocommon.Point
	Tip          ochainsync.Tip
}

PeerRollbackEvent is published when an ingress-eligible chainsync peer reports a rollback. Point is the rollback point; Tip is the peer's current chainsync tip after the rollback.

type PeerTipUpdateEvent 

type PeerTipUpdateEvent struct {
	ConnectionId ouroboros.ConnectionId
	Tip          ochainsync.Tip
	ObservedTip  ochainsync.Tip
	VRFOutput    []byte // VRF output from observed block header for tie-breaking
	PraosView    PraosTiebreakerView
}

PeerTipUpdateEvent is published when a peer's chain tip is updated via chainsync roll forward.

type PraosTiebreakerConfig added in v0.46.0 

type PraosTiebreakerConfig struct {
	Flavor          PraosTiebreakerFlavor
	MaxSlotDistance uint64
}

PraosTiebreakerConfig is the chain-order config projected from the current Shelley-family block config. The reference implementation uses unrestricted VRF before Conway and restricted VRF with max distance 5 from Conway onward.

func PraosTiebreakerConfigBeforeConway added in v0.46.0 

func PraosTiebreakerConfigBeforeConway() PraosTiebreakerConfig

func PraosTiebreakerConfigConway added in v0.46.0 

func PraosTiebreakerConfigConway() PraosTiebreakerConfig

func PraosTiebreakerConfigUnknown added in v0.46.0 

func PraosTiebreakerConfigUnknown() PraosTiebreakerConfig

type PraosTiebreakerFlavor added in v0.46.0 

type PraosTiebreakerFlavor uint8

PraosTiebreakerFlavor matches ouroboros-consensus' VRFTiebreakerFlavor. 

const (
	PraosTiebreakerUnknown PraosTiebreakerFlavor = iota
	PraosTiebreakerUnrestricted
	PraosTiebreakerRestricted
)

type PraosTiebreakerView added in v0.46.0 

type PraosTiebreakerView struct {
	Slot             uint64
	Issuer           []byte
	IssueNo          uint64
	TieBreakVRF      []byte
	TiebreakerConfig PraosTiebreakerConfig
	// contains filtered or unexported fields
}

PraosTiebreakerView mirrors ouroboros-consensus' PraosTiebreakerView for equal-length chain selection.

func GetPraosTiebreakerView added in v0.46.0 

func GetPraosTiebreakerView(
	header ledger.BlockHeader,
) (PraosTiebreakerView, bool)

GetPraosTiebreakerView extracts the Praos select-view fields from a Shelley-family header.

func PraosTiebreakerViewFromTip added in v0.46.0 

func PraosTiebreakerViewFromTip(
	tip ochainsync.Tip,
	vrfOutput []byte,
	config PraosTiebreakerConfig,
) PraosTiebreakerView

PraosTiebreakerViewFromTip builds a partial view when only a chainsync tip and VRF are available. The issuer/opcert rule cannot be applied to partial views.

type SelectionMode added in v0.37.0 

type SelectionMode uint8

SelectionMode describes the chain-selection strategy currently in use. 

const (
	SelectionModePraos SelectionMode = iota
	SelectionModeGenesis
)

func (SelectionMode) String added in v0.37.0 

func (m SelectionMode) String() string

Source Files

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