cwtch/event/eventmanager.go

184 satır
4.9 KiB
Go

package event
import (
"crypto/rand"
"encoding/json"
"fmt"
"git.openprivacy.ca/openprivacy/log"
"math"
"math/big"
"os"
"runtime"
"strings"
"sync"
)
// Event is the core struct type passed around between various subsystems. Events consist of a type which can be
// filtered on, an event ID for tracing and a map of Fields to string values.
type Event struct {
EventType Type
EventID string
Data map[Field]string
}
// GetRandNumber is a helper function which returns a random integer, this is
// currently mostly used to generate message IDs
func GetRandNumber() *big.Int {
num, err := rand.Int(rand.Reader, big.NewInt(math.MaxUint32))
// If we can't generate random numbers then panicking is probably
// the best option.
if err != nil {
panic(err.Error())
}
return num
}
// NewEvent creates a new event object with a unique ID and the given type and data.
func NewEvent(eventType Type, data map[Field]string) Event {
return Event{EventType: eventType, EventID: GetRandNumber().String(), Data: data}
}
// NewEventList creates a new event object with a unique ID and the given type and data supplied in a list format and composed into a map of Type:string
func NewEventList(eventType Type, args ...interface{}) Event {
data := map[Field]string{}
for i := 0; i < len(args); i += 2 {
key, kok := args[i].(Field)
val, vok := args[i+1].(string)
if kok && vok {
data[key] = val
} else {
log.Errorf("attempted to send a field that could not be parsed to a string: %v %v", args[i], args[i+1])
}
}
return Event{EventType: eventType, EventID: GetRandNumber().String(), Data: data}
}
// Manager is an Event Bus which allows subsystems to subscribe to certain EventTypes and publish others.
type manager struct {
subscribers map[Type][]Queue
events chan []byte
mapMutex sync.Mutex
chanMutex sync.Mutex
internal chan bool
closed bool
trace bool
}
// Manager is an interface for an event bus
type Manager interface {
Subscribe(Type, Queue)
Publish(Event)
Shutdown()
}
// NewEventManager returns an initialized EventManager
func NewEventManager() Manager {
em := &manager{}
em.initialize()
return em
}
// Initialize sets up the Manager.
func (em *manager) initialize() {
em.subscribers = make(map[Type][]Queue)
em.events = make(chan []byte)
em.internal = make(chan bool)
em.closed = false
_, em.trace = os.LookupEnv("CWTCH_EVENT_SOURCE")
go em.eventBus()
}
// Subscribe takes an eventType and an Channel and associates them in the eventBus. All future events of that type
// will be sent to the eventChannel.
func (em *manager) Subscribe(eventType Type, queue Queue) {
em.mapMutex.Lock()
defer em.mapMutex.Unlock()
for _, sub := range em.subscribers[eventType] {
if sub == queue {
return // don't add the same queue for the same event twice...
}
}
em.subscribers[eventType] = append(em.subscribers[eventType], queue)
}
// Publish takes an Event and sends it to the internal eventBus where it is distributed to all Subscribers
func (em *manager) Publish(event Event) {
em.chanMutex.Lock()
defer em.chanMutex.Unlock()
if event.EventType != "" && !em.closed {
// Debug Events for Tracing, locked behind an environment variable
// for now.
if em.trace {
pc, _, _, _ := runtime.Caller(1)
funcName := runtime.FuncForPC(pc).Name()
lastSlash := strings.LastIndexByte(funcName, '/')
if lastSlash < 0 {
lastSlash = 0
}
lastDot := strings.LastIndexByte(funcName[lastSlash:], '.') + lastSlash
event.Data[Source] = fmt.Sprintf("%v.%v", funcName[:lastDot], funcName[lastDot+1:])
}
// Deep Copy the Event...
eventJSON, err := json.Marshal(event)
if err != nil {
log.Errorf("Error serializing event: %v", event)
}
em.events <- eventJSON
}
}
// eventBus is an internal function that is used to distribute events to all subscribers
func (em *manager) eventBus() {
for {
eventJSON := <-em.events
// In the case on an empty event. Tear down the Queue
if len(eventJSON) == 0 {
log.Errorf("Received zero length event")
break
}
var event Event
err := json.Unmarshal(eventJSON, &event)
if err != nil {
log.Errorf("Error on Deep Copy: %v %v", eventJSON, err)
}
// maps aren't thread safe
em.mapMutex.Lock()
subscribers := em.subscribers[event.EventType]
em.mapMutex.Unlock()
// Send the event to any subscribers to that event type
for _, subscriber := range subscribers {
// Deep Copy for Each Subscriber
var eventCopy Event
err = json.Unmarshal(eventJSON, &eventCopy)
if err != nil {
log.Errorf("error unmarshalling event: %v ", err)
}
subscriber.Publish(eventCopy)
}
}
// We are about to exit the eventbus thread, fire off an event internally
em.internal <- true
}
// Shutdown triggers, and waits for, the internal eventBus goroutine to finish
func (em *manager) Shutdown() {
em.events <- []byte{}
em.chanMutex.Lock()
em.closed = true
em.chanMutex.Unlock()
// wait for eventBus to finish
<-em.internal
close(em.events)
close(em.internal)
}