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