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compliance_engine.go
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compliance_engine.go
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package follower
import (
"fmt"
"github.com/rs/zerolog"
"github.com/onflow/flow-go/consensus/hotstuff/model"
"github.com/onflow/flow-go/consensus/hotstuff/tracker"
"github.com/onflow/flow-go/engine"
"github.com/onflow/flow-go/engine/common/fifoqueue"
"github.com/onflow/flow-go/engine/consensus"
"github.com/onflow/flow-go/model/flow"
"github.com/onflow/flow-go/model/messages"
"github.com/onflow/flow-go/module"
"github.com/onflow/flow-go/module/compliance"
"github.com/onflow/flow-go/module/component"
"github.com/onflow/flow-go/module/irrecoverable"
"github.com/onflow/flow-go/module/metrics"
"github.com/onflow/flow-go/network"
"github.com/onflow/flow-go/network/channels"
"github.com/onflow/flow-go/storage"
)
type EngineOption func(*ComplianceEngine)
// WithChannel sets the channel the follower engine will use to receive blocks.
func WithChannel(channel channels.Channel) EngineOption {
return func(e *ComplianceEngine) {
e.channel = channel
}
}
// WithComplianceConfigOpt applies compliance config opt to internal config
func WithComplianceConfigOpt(opt compliance.Opt) EngineOption {
return func(e *ComplianceEngine) {
opt(&e.config)
}
}
// defaultBatchProcessingWorkers number of concurrent workers that process incoming blocks.
const defaultBatchProcessingWorkers = 4
// defaultPendingBlockQueueCapacity maximum capacity of inbound queue for blocks directly received from other nodes.
// Small capacity is suitable here, as there will be hardly any pending blocks during normal operations. If the node
// is so overloaded that it can't keep up with the newest blocks within 10 seconds (processing them with priority),
// it is probably better to fall back on synchronization anyway.
const defaultPendingBlockQueueCapacity = 10
// defaultSyncedBlockQueueCapacity maximum capacity of inbound queue for batches of synced blocks.
// While catching up, we want to be able to buffer a bit larger amount of work.
const defaultSyncedBlockQueueCapacity = 100
// defaultPendingConnectedBlocksChanCapacity capacity of buffered channel that is used to receive pending blocks that form a sequence.
const defaultPendingConnectedBlocksChanCapacity = 100
// ComplianceEngine is the highest level structure that consumes events from other components.
// It's an entry point to the follower engine which follows and maintains the local copy of the protocol state.
// It is a passive (read-only) version of the compliance engine. The compliance engine
// is employed by consensus nodes (active consensus participants) where the
// Follower engine is employed by all other node roles.
// ComplianceEngine is responsible for:
// 1. Consuming events from external sources such as sync engine.
// 2. Splitting incoming batches in batches of connected blocks.
// 3. Providing worker goroutines for concurrent processing of batches of connected blocks.
// 4. Handling of finalization events.
//
// See interface `complianceCore` (this package) for detailed documentation of the algorithm.
// Implements consensus.Compliance interface.
type ComplianceEngine struct {
*component.ComponentManager
log zerolog.Logger
me module.Local
engMetrics module.EngineMetrics
con network.Conduit
config compliance.Config
channel channels.Channel
headers storage.Headers
pendingProposals *fifoqueue.FifoQueue // queue for fresh proposals
syncedBlocks *fifoqueue.FifoQueue // queue for processing inbound batches of synced blocks
blocksAvailableNotifier engine.Notifier // notifies that new blocks are ready to be processed
finalizedBlockTracker *tracker.NewestBlockTracker // tracks the latest finalization block
finalizedBlockNotifier engine.Notifier // notifies when the latest finalized block changes
pendingConnectedBlocksChan chan flow.Slashable[[]*flow.Block]
core complianceCore // performs actual processing of incoming messages.
}
var _ network.MessageProcessor = (*ComplianceEngine)(nil)
var _ consensus.Compliance = (*ComplianceEngine)(nil)
// NewComplianceLayer instantiates th compliance layer for the consensus follower. See
// interface `complianceCore` (this package) for detailed documentation of the algorithm.
func NewComplianceLayer(
log zerolog.Logger,
net network.EngineRegistry,
me module.Local,
engMetrics module.EngineMetrics,
headers storage.Headers,
finalized *flow.Header,
core complianceCore,
config compliance.Config,
opts ...EngineOption,
) (*ComplianceEngine, error) {
// FIFO queue for inbound block proposals
pendingBlocks, err := fifoqueue.NewFifoQueue(defaultPendingBlockQueueCapacity)
if err != nil {
return nil, fmt.Errorf("failed to create queue for inbound blocks: %w", err)
}
// FIFO queue for synced blocks
syncedBlocks, err := fifoqueue.NewFifoQueue(defaultSyncedBlockQueueCapacity)
if err != nil {
return nil, fmt.Errorf("failed to create queue for inbound blocks: %w", err)
}
e := &ComplianceEngine{
log: log.With().Str("engine", "follower").Logger(),
me: me,
engMetrics: engMetrics,
config: config,
channel: channels.ReceiveBlocks,
pendingProposals: pendingBlocks,
syncedBlocks: syncedBlocks,
blocksAvailableNotifier: engine.NewNotifier(),
pendingConnectedBlocksChan: make(chan flow.Slashable[[]*flow.Block], defaultPendingConnectedBlocksChanCapacity),
finalizedBlockTracker: tracker.NewNewestBlockTracker(),
finalizedBlockNotifier: engine.NewNotifier(),
headers: headers,
core: core,
}
e.finalizedBlockTracker.Track(model.BlockFromFlow(finalized))
for _, apply := range opts {
apply(e)
}
con, err := net.Register(e.channel, e)
if err != nil {
return nil, fmt.Errorf("could not register engine to network: %w", err)
}
e.con = con
cmBuilder := component.NewComponentManagerBuilder().
AddWorker(e.finalizationProcessingLoop).
AddWorker(e.processBlocksLoop)
cmBuilder.AddWorker(func(ctx irrecoverable.SignalerContext, ready component.ReadyFunc) {
// start internal component
e.core.Start(ctx)
// wait for it to be ready
<-e.core.Ready()
// report that we are ready to process events
ready()
// wait for shutdown to be commenced
<-ctx.Done()
// wait for core to shut down
<-e.core.Done()
})
for i := 0; i < defaultBatchProcessingWorkers; i++ {
cmBuilder.AddWorker(e.processConnectedBatch)
}
e.ComponentManager = cmBuilder.Build()
return e, nil
}
// OnBlockProposal queues *untrusted* proposals for further processing and notifies the Engine's
// internal workers. This method is intended for fresh proposals received directly from leaders.
// It can ingest synced blocks as well, but is less performant compared to method `OnSyncedBlocks`.
func (e *ComplianceEngine) OnBlockProposal(proposal flow.Slashable[*messages.BlockProposal]) {
e.engMetrics.MessageReceived(metrics.EngineFollower, metrics.MessageBlockProposal)
// queue proposal
if e.pendingProposals.Push(proposal) {
e.blocksAvailableNotifier.Notify()
}
}
// OnSyncedBlocks is an optimized consumer for *untrusted* synced blocks. It is specifically
// efficient for batches of continuously connected blocks (honest nodes supply finalized blocks
// in suitable sequences where possible). Nevertheless, the method tolerates blocks in arbitrary
// order (less efficient), making it robust against byzantine nodes.
func (e *ComplianceEngine) OnSyncedBlocks(blocks flow.Slashable[[]*messages.BlockProposal]) {
e.engMetrics.MessageReceived(metrics.EngineFollower, metrics.MessageSyncedBlocks)
// The synchronization engine feeds the follower with batches of blocks. The field `Slashable.OriginID`
// states which node forwarded the batch to us. Each block contains its proposer and signature.
if e.syncedBlocks.Push(blocks) {
e.blocksAvailableNotifier.Notify()
}
}
// OnFinalizedBlock informs the compliance layer about finalization of a new block. It does not block
// and asynchronously executes the internal pruning logic. We accept inputs out of order, and only act
// on inputs with strictly monotonously increasing views.
//
// Implements the `OnFinalizedBlock` callback from the `hotstuff.FinalizationConsumer`
// CAUTION: the input to this callback is treated as trusted; precautions should be taken that messages
// from external nodes cannot be considered as inputs to this function.
func (e *ComplianceEngine) OnFinalizedBlock(block *model.Block) {
if e.finalizedBlockTracker.Track(block) {
e.finalizedBlockNotifier.Notify()
}
}
// Process processes the given event from the node with the given origin ID in
// a blocking manner. It returns the potential processing error when done.
// This method is intended to be used as a callback by the networking layer,
// notifying us about fresh proposals directly from the consensus leaders.
func (e *ComplianceEngine) Process(channel channels.Channel, originID flow.Identifier, message interface{}) error {
switch msg := message.(type) {
case *messages.BlockProposal:
e.OnBlockProposal(flow.Slashable[*messages.BlockProposal]{
OriginID: originID,
Message: msg,
})
default:
e.log.Warn().Msgf("%v delivered unsupported message %T through %v", originID, message, channel)
}
return nil
}
// processBlocksLoop processes available blocks as they are queued.
// Implements `component.ComponentWorker` signature.
func (e *ComplianceEngine) processBlocksLoop(ctx irrecoverable.SignalerContext, ready component.ReadyFunc) {
ready()
doneSignal := ctx.Done()
newPendingBlockSignal := e.blocksAvailableNotifier.Channel()
for {
select {
case <-doneSignal:
return
case <-newPendingBlockSignal:
err := e.processQueuedBlocks(doneSignal) // no errors expected during normal operations
if err != nil {
ctx.Throw(err)
}
}
}
}
// processQueuedBlocks processes any available messages until the message queue is empty.
// Only returns when all inbound queues are empty (or the engine is terminated).
// Prioritization: In a nutshell, we prioritize the resilience of the happy path over
// performance gains on the recovery path. Details:
// - We prioritize new proposals. Thereby, it becomes much harder for a malicious node
// to overwhelm another node through synchronization messages and drown out new blocks
// for a node that is up-to-date.
// - On the flip side, new proposals are relatively infrequent compared to the load that
// synchronization produces for a node that is catching up. In other words, prioritizing
// the few new proposals first is probably not going to be much of a distraction.
// Proposals too far in the future are dropped (see parameter `SkipNewProposalsThreshold`
// in `compliance.Config`), to prevent memory overflow.
//
// No errors are expected during normal operation. All returned exceptions are potential
// symptoms of internal state corruption and should be fatal.
func (e *ComplianceEngine) processQueuedBlocks(doneSignal <-chan struct{}) error {
for {
select {
case <-doneSignal:
return nil
default:
}
// Priority 1: ingest fresh proposals
msg, ok := e.pendingProposals.Pop()
if ok {
blockMsg := msg.(flow.Slashable[*messages.BlockProposal])
block := blockMsg.Message.Block.ToInternal()
log := e.log.With().
Hex("origin_id", blockMsg.OriginID[:]).
Str("chain_id", block.Header.ChainID.String()).
Uint64("view", block.Header.View).
Uint64("height", block.Header.Height).
Logger()
latestFinalizedView := e.finalizedBlockTracker.NewestBlock().View
e.submitConnectedBatch(log, latestFinalizedView, blockMsg.OriginID, []*flow.Block{block})
e.engMetrics.MessageHandled(metrics.EngineFollower, metrics.MessageBlockProposal)
continue
}
// Priority 2: ingest synced blocks
msg, ok = e.syncedBlocks.Pop()
if !ok {
// when there are no more messages in the queue, back to the processQueuedBlocks to wait
// for the next incoming message to arrive.
return nil
}
batch := msg.(flow.Slashable[[]*messages.BlockProposal])
if len(batch.Message) < 1 {
continue
}
blocks := make([]*flow.Block, 0, len(batch.Message))
for _, block := range batch.Message {
blocks = append(blocks, block.Block.ToInternal())
}
firstBlock := blocks[0].Header
lastBlock := blocks[len(blocks)-1].Header
log := e.log.With().
Hex("origin_id", batch.OriginID[:]).
Str("chain_id", lastBlock.ChainID.String()).
Uint64("first_block_height", firstBlock.Height).
Uint64("first_block_view", firstBlock.View).
Uint64("last_block_height", lastBlock.Height).
Uint64("last_block_view", lastBlock.View).
Int("range_length", len(blocks)).
Logger()
// extract sequences of connected blocks and schedule them for further processing
// we assume the sender has already ordered blocks into connected ranges if possible
latestFinalizedView := e.finalizedBlockTracker.NewestBlock().View
parentID := blocks[0].ID()
indexOfLastConnected := 0
for i, block := range blocks {
if block.Header.ParentID != parentID {
e.submitConnectedBatch(log, latestFinalizedView, batch.OriginID, blocks[indexOfLastConnected:i])
indexOfLastConnected = i
}
parentID = block.Header.ID()
}
e.submitConnectedBatch(log, latestFinalizedView, batch.OriginID, blocks[indexOfLastConnected:])
e.engMetrics.MessageHandled(metrics.EngineFollower, metrics.MessageSyncedBlocks)
}
}
// submitConnectedBatch checks if batch is still pending and submits it via channel for further processing by worker goroutines.
func (e *ComplianceEngine) submitConnectedBatch(log zerolog.Logger, latestFinalizedView uint64, originID flow.Identifier, blocks []*flow.Block) {
if len(blocks) < 1 {
return
}
// if latest block of batch is already finalized we can drop such input.
lastBlock := blocks[len(blocks)-1].Header
if lastBlock.View < latestFinalizedView {
log.Debug().Msgf("dropping range [%d, %d] below finalized view %d", blocks[0].Header.View, lastBlock.View, latestFinalizedView)
return
}
skipNewProposalsThreshold := e.config.GetSkipNewProposalsThreshold()
if lastBlock.View > latestFinalizedView+skipNewProposalsThreshold {
log.Debug().
Uint64("skip_new_proposals_threshold", skipNewProposalsThreshold).
Msgf("dropping range [%d, %d] too far ahead of locally finalized view %d",
blocks[0].Header.View, lastBlock.View, latestFinalizedView)
return
}
log.Debug().Msgf("submitting sub-range with views [%d, %d] for further processing", blocks[0].Header.View, lastBlock.View)
select {
case e.pendingConnectedBlocksChan <- flow.Slashable[[]*flow.Block]{
OriginID: originID,
Message: blocks,
}:
case <-e.ComponentManager.ShutdownSignal():
}
}
// processConnectedBatch is a worker goroutine which concurrently consumes connected batches that will be processed by ComplianceCore.
func (e *ComplianceEngine) processConnectedBatch(ctx irrecoverable.SignalerContext, ready component.ReadyFunc) {
ready()
for {
select {
case <-ctx.Done():
return
case msg := <-e.pendingConnectedBlocksChan:
err := e.core.OnBlockRange(msg.OriginID, msg.Message)
if err != nil {
ctx.Throw(err)
}
}
}
}
// finalizationProcessingLoop is a separate goroutine that performs processing of finalization events.
// Implements `component.ComponentWorker` signature.
func (e *ComplianceEngine) finalizationProcessingLoop(ctx irrecoverable.SignalerContext, ready component.ReadyFunc) {
ready()
doneSignal := ctx.Done()
blockFinalizedSignal := e.finalizedBlockNotifier.Channel()
for {
select {
case <-doneSignal:
return
case <-blockFinalizedSignal:
// retrieve the latest finalized header, so we know the height
finalHeader, err := e.headers.ByBlockID(e.finalizedBlockTracker.NewestBlock().BlockID)
if err != nil { // no expected errors
ctx.Throw(err)
}
e.core.OnFinalizedBlock(finalHeader)
}
}
}