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event.go
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event.go
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package handler
import (
"fmt"
"github.com/onflow/cadence"
jsoncdc "github.com/onflow/cadence/encoding/json"
"github.com/onflow/flow-go/fvm/errors"
"github.com/onflow/flow-go/fvm/systemcontracts"
"github.com/onflow/flow-go/model/flow"
)
// EventHandler collect events, separates out service events, and enforces event size limits
type EventHandler struct {
chain flow.Chain
eventCollectionEnabled bool
serviceEventCollectionEnabled bool
eventCollectionByteSizeLimit uint64
eventCollection *EventCollection
}
// NewEventHandler constructs a new EventHandler
func NewEventHandler(chain flow.Chain,
eventCollectionEnabled bool,
serviceEventCollectionEnabled bool,
eventCollectionByteSizeLimit uint64) *EventHandler {
return &EventHandler{
chain: chain,
eventCollectionEnabled: eventCollectionEnabled,
serviceEventCollectionEnabled: serviceEventCollectionEnabled,
eventCollectionByteSizeLimit: eventCollectionByteSizeLimit,
eventCollection: NewEventCollection(),
}
}
func (h *EventHandler) EventCollection() *EventCollection {
return h.eventCollection
}
func (h *EventHandler) EmitEvent(event cadence.Event,
txID flow.Identifier,
txIndex uint32,
payer flow.Address) error {
if !h.eventCollectionEnabled {
return nil
}
payload, err := jsoncdc.Encode(event)
if err != nil {
return errors.NewEncodingFailuref("failed to json encode a cadence event: %w", err)
}
payloadSize := uint64(len(payload))
// skip limit if payer is service account
if payer != h.chain.ServiceAddress() {
if h.eventCollection.TotalByteSize()+payloadSize > h.eventCollectionByteSizeLimit {
return errors.NewEventLimitExceededError(h.eventCollection.TotalByteSize()+payloadSize, h.eventCollectionByteSizeLimit)
}
}
flowEvent := flow.Event{
Type: flow.EventType(event.EventType.ID()),
TransactionID: txID,
TransactionIndex: txIndex,
EventIndex: h.eventCollection.eventCounter,
Payload: payload,
}
if h.serviceEventCollectionEnabled {
ok, err := IsServiceEvent(event, h.chain.ChainID())
if err != nil {
return fmt.Errorf("unable to check service event: %w", err)
}
if ok {
h.eventCollection.AppendServiceEvent(flowEvent, payloadSize)
}
// we don't return and append the service event into event collection as well.
}
h.eventCollection.AppendEvent(flowEvent, payloadSize)
return nil
}
func (h *EventHandler) Events() []flow.Event {
return h.eventCollection.events
}
func (h *EventHandler) ServiceEvents() []flow.Event {
return h.eventCollection.serviceEvents
}
type EventCollection struct {
events flow.EventsList
serviceEvents flow.EventsList
totalByteSize uint64
eventCounter uint32
}
func NewEventCollection() *EventCollection {
return &EventCollection{
events: make([]flow.Event, 0, 10),
serviceEvents: make([]flow.Event, 0, 10),
totalByteSize: uint64(0),
eventCounter: uint32(0),
}
}
func (e *EventCollection) Child() *EventCollection {
res := NewEventCollection()
res.eventCounter = e.eventCounter
return res
}
// Merge merges another event collection into this event collection
func (e *EventCollection) Merge(other *EventCollection) {
e.events = append(e.events, other.events...)
e.serviceEvents = append(e.serviceEvents, other.serviceEvents...)
e.totalByteSize = e.totalByteSize + other.totalByteSize
e.eventCounter = e.eventCounter + other.eventCounter
}
func (e *EventCollection) Events() []flow.Event {
return e.events
}
func (e *EventCollection) AppendEvent(event flow.Event, size uint64) {
e.events = append(e.events, event)
e.totalByteSize += size
e.eventCounter++
}
func (e *EventCollection) ServiceEvents() []flow.Event {
return e.serviceEvents
}
func (e *EventCollection) AppendServiceEvent(event flow.Event, size uint64) {
e.serviceEvents = append(e.serviceEvents, event)
e.totalByteSize += size
e.eventCounter++
}
func (e *EventCollection) TotalByteSize() uint64 {
return e.totalByteSize
}
// IsServiceEvent determines whether or not an emitted Cadence event is considered
// a service event for the given chain.
func IsServiceEvent(event cadence.Event, chain flow.ChainID) (bool, error) {
// retrieve the service event information for this chain
events, err := systemcontracts.ServiceEventsForChain(chain)
if err != nil {
return false, fmt.Errorf("unknown system contracts for chain (%s): %w", chain.String(), err)
}
eventType := flow.EventType(event.EventType.ID())
for _, serviceEvent := range events.All() {
if serviceEvent.EventType() == eventType {
return true, nil
}
}
return false, nil
}