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engine.go
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engine.go
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package requester
import (
"fmt"
"math"
"math/rand"
"time"
"github.com/rs/zerolog"
"github.com/vmihailenco/msgpack"
"github.com/onflow/flow-go/engine"
"github.com/onflow/flow-go/model/flow"
"github.com/onflow/flow-go/model/flow/filter"
"github.com/onflow/flow-go/model/messages"
"github.com/onflow/flow-go/module"
"github.com/onflow/flow-go/module/metrics"
"github.com/onflow/flow-go/network"
"github.com/onflow/flow-go/state/protocol"
"github.com/onflow/flow-go/utils/logging"
)
// HandleFunc is a function provided to the requester engine to handle an entity
// once it has been retrieved from a provider. The function should be non-blocking
// and errors should be handled internally within the function.
type HandleFunc func(originID flow.Identifier, entity flow.Entity)
// CreateFunc is a function that creates a `flow.Entity` with an underlying type
// so that we can properly decode entities transmitted over the network.
type CreateFunc func() flow.Entity
// Engine is a generic requester engine, handling the requesting of entities
// on the flow network. It is the `request` part of the request-reply
// pattern provided by the pair of generic exchange engines.
type Engine struct {
unit *engine.Unit
log zerolog.Logger
cfg Config
metrics module.EngineMetrics
me module.Local
state protocol.State
con network.Conduit
channel network.Channel
selector flow.IdentityFilter
create CreateFunc
handle HandleFunc
items map[flow.Identifier]*Item
requests map[uint64]*messages.EntityRequest
}
// New creates a new requester engine, operating on the provided network channel, and requesting entities from a node
// within the set obtained by applying the provided selector filter. The options allow customization of the parameters
// related to the batch and retry logic.
func New(log zerolog.Logger, metrics module.EngineMetrics, net module.Network, me module.Local, state protocol.State,
channel network.Channel, selector flow.IdentityFilter, create CreateFunc, options ...OptionFunc) (*Engine, error) {
// initialize the default config
cfg := Config{
BatchThreshold: 32,
BatchInterval: time.Second,
RetryInitial: 4 * time.Second,
RetryFunction: RetryGeometric(2),
RetryMaximum: 2 * time.Minute,
RetryAttempts: math.MaxUint32,
}
// apply the custom option parameters
for _, option := range options {
option(&cfg)
}
// check validity of retry function
interval := cfg.RetryFunction(time.Second)
if interval < time.Second {
return nil, fmt.Errorf("invalid retry function (interval must always increase)")
}
// check validity of maximum interval
if cfg.RetryMaximum < cfg.RetryInitial {
return nil, fmt.Errorf("invalid retry maximum (must not be smaller than initial interval)")
}
// make sure we don't send requests from self or unstaked nodes
selector = filter.And(
selector,
filter.HasStake(true),
filter.Not(filter.Ejected),
filter.Not(filter.HasNodeID(me.NodeID())),
)
// initialize the propagation engine with its dependencies
e := &Engine{
unit: engine.NewUnit(),
log: log.With().Str("engine", "requester").Logger(),
cfg: cfg,
metrics: metrics,
me: me,
state: state,
channel: channel,
selector: selector,
create: create,
handle: nil,
items: make(map[flow.Identifier]*Item), // holds all pending items
requests: make(map[uint64]*messages.EntityRequest), // holds all sent requests
}
// register the engine with the network layer and store the conduit
con, err := net.Register(network.Channel(channel), e)
if err != nil {
return nil, fmt.Errorf("could not register engine: %w", err)
}
e.con = con
return e, nil
}
// WithHandle sets the handle function of the requester, which is how it processes
// returned entities. The engine can not be started without setting the handle
// function. It is done in a separate call so that the requester can be injected
// into engines upon construction, and then provide a handle function to the
// requester from that engine itself.
func (e *Engine) WithHandle(handle HandleFunc) *Engine {
e.handle = handle
return e
}
// Ready returns a ready channel that is closed once the engine has fully
// started. For consensus engine, this is true once the underlying consensus
// algorithm has started.
func (e *Engine) Ready() <-chan struct{} {
if e.handle == nil {
panic("must initialize requester engine with handler")
}
e.unit.Launch(e.poll)
return e.unit.Ready()
}
// Done returns a done channel that is closed once the engine has fully stopped.
// For the consensus engine, we wait for hotstuff to finish.
func (e *Engine) Done() <-chan struct{} {
return e.unit.Done()
}
// SubmitLocal submits an message originating on the local node.
func (e *Engine) SubmitLocal(message interface{}) {
e.Submit(e.me.NodeID(), message)
}
// Submit submits the given message from the node with the given origin ID
// for processing in a non-blocking manner. It returns instantly and logs
// a potential processing error internally when done.
func (e *Engine) Submit(originID flow.Identifier, message interface{}) {
e.unit.Launch(func() {
err := e.Process(originID, message)
if err != nil {
engine.LogError(e.log, err)
}
})
}
// ProcessLocal processes an message originating on the local node.
func (e *Engine) ProcessLocal(message interface{}) error {
return e.Process(e.me.NodeID(), message)
}
// Process processes the given message from the node with the given origin ID in
// a blocking manner. It returns the potential processing error when done.
func (e *Engine) Process(originID flow.Identifier, message interface{}) error {
return e.unit.Do(func() error {
return e.process(originID, message)
})
}
// EntityByID adds an entity to the list of entities to be requested from the
// provider. It is idempotent, meaning that adding the same entity to the
// requester engine multiple times has no effect, unless the item has
// expired due to too many requests and has thus been deleted from the
// list. The provided selector will be applied to the set of valid providers on top
// of the global selector injected upon construction. It allows for finer-grained
// control over which subset of providers to request a given entity from, such as
// selection of a collection cluster. Use `filter.Any` if no additional selection
// is required. Checks integrity of response to make sure that we got entity that we were requesting.
func (e *Engine) EntityByID(entityID flow.Identifier, selector flow.IdentityFilter) {
e.addEntityRequest(entityID, selector, true)
}
// Query will request data through the request engine backing the interface.
//The additional selector will be applied to the subset
// of valid providers for the data and allows finer-grained control
// over which providers to request data from. Doesn't perform integrity check
// can be used to get entities without knowing their ID.
func (e *Engine) Query(key flow.Identifier, selector flow.IdentityFilter) {
e.addEntityRequest(key, selector, false)
}
func (e *Engine) addEntityRequest(entityID flow.Identifier, selector flow.IdentityFilter, checkIntegrity bool) {
e.unit.Lock()
defer e.unit.Unlock()
// check if we already have an item for this entity
_, duplicate := e.items[entityID]
if duplicate {
return
}
// otherwise, add a new item to the list
item := &Item{
EntityID: entityID,
NumAttempts: 0,
LastRequested: time.Time{},
RetryAfter: e.cfg.RetryInitial,
ExtraSelector: selector,
checkIntegrity: checkIntegrity,
}
e.items[entityID] = item
}
// Force will force the requester engine to dispatch all currently
// valid batch requests.
func (e *Engine) Force() {
count := uint(0)
for {
dispatched, err := e.dispatchRequest()
if err != nil {
e.log.Error().Err(err).Msg("could not dispatch requests")
return
}
if !dispatched {
e.log.Debug().Uint("requests", count).Msg("forced request dispatch")
return
}
count++
}
}
func (e *Engine) poll() {
ticker := time.NewTicker(e.cfg.BatchInterval)
PollLoop:
for {
select {
case <-e.unit.Quit():
break PollLoop
case <-ticker.C:
dispatched, err := e.dispatchRequest()
if err != nil {
e.log.Error().Err(err).Msg("could not dispatch requests")
continue PollLoop
}
if dispatched {
e.log.Debug().Uint("requests", 1).Msg("regular request dispatch")
}
}
}
ticker.Stop()
}
func (e *Engine) dispatchRequest() (bool, error) {
e.unit.Lock()
defer e.unit.Unlock()
// get the current top-level set of valid providers
providers, err := e.state.Final().Identities(e.selector)
if err != nil {
return false, fmt.Errorf("could not get providers: %w", err)
}
// go through each item and decide if it should be requested again
now := time.Now().UTC()
var providerID flow.Identifier
var entityIDs []flow.Identifier
for entityID, item := range e.items {
// if the item should not be requested yet, ignore
cutoff := item.LastRequested.Add(item.RetryAfter)
if cutoff.After(now) {
continue
}
// if the item reached maximum amount of retries, drop
if item.NumAttempts >= e.cfg.RetryAttempts {
delete(e.items, entityID)
continue
}
// if the provider has already been chosen, check if this item
// can be requested from the same provider; otherwise skip it
// for now, so it will be part of the next batch request
if providerID != flow.ZeroID {
overlap := providers.Filter(filter.And(
filter.HasNodeID(providerID),
item.ExtraSelector,
))
if len(overlap) == 0 {
continue
}
}
// if no provider has been chosen yet, choose from restricted set
// NOTE: a single item can not permanently block requests going
// out when no providers are available for it, because the map
// iteration is random and will skip the item most of the times
// when other items are available
if providerID == flow.ZeroID {
providers = providers.Filter(item.ExtraSelector)
if len(providers) == 0 {
return false, fmt.Errorf("no valid providers available")
}
providerID = providers.Sample(1)[0].NodeID
}
// add item to list and set retry parameters
// NOTE: we add the retry interval to the last requested timestamp,
// rather than using the current timestamp, in order to conserve a
// more even distribution of timestamps over time, which should lead
// to a more even distribution of entities over batch requests
entityIDs = append(entityIDs, entityID)
item.NumAttempts++
item.LastRequested = now
item.RetryAfter = e.cfg.RetryFunction(item.RetryAfter)
// make sure the interval is within parameters
if item.RetryAfter < e.cfg.RetryInitial {
item.RetryAfter = e.cfg.RetryInitial
}
if item.RetryAfter > e.cfg.RetryMaximum {
item.RetryAfter = e.cfg.RetryMaximum
}
// if we reached the maximum size for a batch, bail
if uint(len(entityIDs)) >= e.cfg.BatchThreshold {
break
}
}
// if there are no items to request, return
if len(entityIDs) == 0 {
return false, nil
}
// create a batch request, send it and store it for reference
req := &messages.EntityRequest{
Nonce: rand.Uint64(),
EntityIDs: entityIDs,
}
err = e.con.Unicast(req, providerID)
if err != nil {
return true, fmt.Errorf("could not send request: %w", err)
}
e.requests[req.Nonce] = req
// NOTE: we forget about requests after the expiry of the shortest retry time
// from the entities in the list; this means that we purge requests aggressively.
// However, most requests should be responded to on the first attempt and clearing
// these up only removes the ability to instantly retry upon partial responses, so
// it won't affect much.
go func() {
<-time.After(e.cfg.RetryInitial)
e.unit.Lock()
defer e.unit.Unlock()
delete(e.requests, req.Nonce)
}()
e.metrics.MessageSent(e.channel.String(), metrics.MessageEntityRequest)
return true, nil
}
// process processes events for the propagation engine on the consensus node.
func (e *Engine) process(originID flow.Identifier, message interface{}) error {
e.metrics.MessageReceived(e.channel.String(), metrics.MessageEntityResponse)
defer e.metrics.MessageHandled(e.channel.String(), metrics.MessageEntityResponse)
e.unit.Lock()
defer e.unit.Unlock()
switch msg := message.(type) {
case *messages.EntityResponse:
return e.onEntityResponse(originID, msg)
default:
return engine.NewInvalidInputErrorf("invalid message type (%T)", message)
}
}
func (e *Engine) onEntityResponse(originID flow.Identifier, res *messages.EntityResponse) error {
// check that the response comes from a valid provider
providers, err := e.state.Final().Identities(filter.And(
e.selector,
filter.HasNodeID(originID),
))
if err != nil {
return fmt.Errorf("could not get providers: %w", err)
}
if len(providers) == 0 {
return engine.NewInvalidInputErrorf("invalid provider origin (%x)", originID)
}
// build a list of needed entities; if not available, process anyway,
// but in that case we can't re-queue missing items
needed := make(map[flow.Identifier]struct{})
req, exists := e.requests[res.Nonce]
if exists {
delete(e.requests, req.Nonce)
for _, entityID := range req.EntityIDs {
needed[entityID] = struct{}{}
}
}
// ensure the response is correctly formed
if len(res.Blobs) != len(res.EntityIDs) {
return engine.NewInvalidInputErrorf("invalid response with %d blobs, %d IDs", len(res.Blobs), len(res.EntityIDs))
}
// process each entity in the response
// NOTE: this requires engines to be somewhat idempotent, which is a good
// thing, as it increases the robustness of their code
for i := 0; i < len(res.Blobs); i++ {
blob := res.Blobs[i]
entityID := res.EntityIDs[i]
// the entity might already have been returned in another response
item, exists := e.items[entityID]
if !exists {
continue
}
// create the entity with underlying concrete type and decode blob
entity := e.create()
err := msgpack.Unmarshal(blob, &entity)
if err != nil {
return fmt.Errorf("could not decode entity: %w", err)
}
if item.checkIntegrity {
actualEntityID := entity.ID()
// validate that we got correct entity, exactly what we were expecting
if entityID != actualEntityID {
e.log.Error().
Hex("origin", logging.ID(originID)).
Hex("stated_entity_id", logging.ID(entityID)).
Hex("provided_entity", logging.ID(actualEntityID)).
Msg("provided entity does not match stated ID")
continue
}
}
// remove from needed items and pending items
delete(needed, entityID)
delete(e.items, entityID)
// process the entity
go e.handle(originID, entity)
}
// requeue requested entities that have not been delivered in the response
// NOTE: this logic allows a provider to send back an empty response to
// indicate that none of the requested entities are available, thus allowing
// the requester engine to immediately request them from another provider
for entityID := range needed {
// it's possible the item is unavailable, if it was already received
// in another response
item, exists := e.items[entityID]
if !exists {
// the entity could have been received in another request
continue
}
// we set the timestamp to zero, so that the item will be included
// in the next batch regardless of retry interval
item.LastRequested = time.Time{}
}
return nil
}