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package services
import (
"context"
"encoding/json"
"errors"
"fmt"
"net/http"
"sync"
"time"
"go.opentelemetry.io/otel/metric"
semconv "go.opentelemetry.io/otel/semconv/v1.18.0"
"go.opentelemetry.io/otel/trace"
"github.com/NdoleStudio/httpsms/pkg/events"
"github.com/NdoleStudio/httpsms/pkg/telemetry"
cloudevents "github.com/cloudevents/sdk-go/v2"
"github.com/palantir/stacktrace"
)
// EventDispatcher dispatches a new event
type EventDispatcher struct {
logger telemetry.Logger
tracer telemetry.Tracer
listeners map[string][]events.EventListener
meter metric.Float64Histogram
queue PushQueue
queueConfig PushQueueConfig
}
// NewEventDispatcher creates a new EventDispatcher
func NewEventDispatcher(
logger telemetry.Logger,
tracer telemetry.Tracer,
meter metric.Float64Histogram,
queue PushQueue,
queueConfig PushQueueConfig,
) (dispatcher *EventDispatcher) {
return &EventDispatcher{
logger: logger,
tracer: tracer,
meter: meter,
listeners: make(map[string][]events.EventListener),
queue: queue,
queueConfig: queueConfig,
}
}
// DispatchSync dispatches a new event
func (dispatcher *EventDispatcher) DispatchSync(ctx context.Context, event cloudevents.Event) error {
ctx, span := dispatcher.tracer.Start(ctx)
defer span.End()
if err := event.Validate(); err != nil {
msg := fmt.Sprintf("cannot dispatch event with ID [%s] and type [%s] because it is invalid", event.ID(), event.Type())
return dispatcher.tracer.WrapErrorSpan(span, stacktrace.Propagate(err, msg))
}
dispatcher.Publish(ctx, event)
return nil
}
// DispatchWithTimeout dispatches an event with a timeout
func (dispatcher *EventDispatcher) DispatchWithTimeout(ctx context.Context, event cloudevents.Event, timeout time.Duration) (queueID string, err error) {
ctx, span := dispatcher.tracer.Start(ctx)
defer span.End()
if err = event.Validate(); err != nil {
msg := fmt.Sprintf("cannot dispatch event with ID [%s] and type [%s] because it is invalid", event.ID(), event.Type())
return queueID, dispatcher.tracer.WrapErrorSpan(span, stacktrace.Propagate(err, msg))
}
task, err := dispatcher.createCloudTask(event)
if err != nil {
msg := fmt.Sprintf("cannot create cloud task for event [%s] with id [%s]", event.Type(), event.ID())
return queueID, dispatcher.tracer.WrapErrorSpan(span, stacktrace.Propagate(err, msg))
}
if queueID, err = dispatcher.enqueue(ctx, event, task, timeout); err != nil {
msg := fmt.Sprintf("cannot enqueue event with ID [%s] and type [%s]", event.ID(), event.Type())
return queueID, dispatcher.tracer.WrapErrorSpan(span, stacktrace.Propagate(err, msg))
}
return queueID, nil
}
func (dispatcher *EventDispatcher) enqueue(ctx context.Context, event cloudevents.Event, task *PushQueueTask, timeout time.Duration) (string, error) {
ctx, span, ctxLogger := dispatcher.tracer.StartWithLogger(ctx, dispatcher.logger)
defer span.End()
queueID, err := dispatcher.queue.Enqueue(ctx, task, timeout)
if errors.Is(err, context.DeadlineExceeded) {
msg := fmt.Sprintf("cannot enqueue event with ID [%s] and type [%s] to [%T]", event.ID(), event.Type(), dispatcher.queue)
ctxLogger.Warn(stacktrace.Propagate(err, msg))
queueID, err = fmt.Sprintf("local-%s", event.ID()), nil
time.AfterFunc(timeout, func() {
dispatcher.Publish(ctx, event)
})
}
return queueID, err
}
// Dispatch a new event by adding it to the queue to be processed async
func (dispatcher *EventDispatcher) Dispatch(ctx context.Context, event cloudevents.Event) error {
ctx, span := dispatcher.tracer.Start(ctx)
defer span.End()
_, err := dispatcher.DispatchWithTimeout(ctx, event, time.Nanosecond*1)
return err
}
// Subscribe a listener to an event
func (dispatcher *EventDispatcher) Subscribe(eventType string, listener events.EventListener) {
if _, ok := dispatcher.listeners[eventType]; !ok {
dispatcher.listeners[eventType] = []events.EventListener{}
}
dispatcher.listeners[eventType] = append(dispatcher.listeners[eventType], listener)
}
// Publish an event to subscribers
func (dispatcher *EventDispatcher) Publish(ctx context.Context, event cloudevents.Event) {
ctx, span, ctxLogger := dispatcher.tracer.StartWithLogger(ctx, dispatcher.logger)
defer span.End()
dispatcher.addCloudEventAttributes(span, event)
start := time.Now()
subscribers, ok := dispatcher.listeners[event.Type()]
if !ok {
ctxLogger.Info(fmt.Sprintf("no listener is configured for event type [%s] with id [%s]", event.Type(), event.ID()))
return
}
var wg sync.WaitGroup
for _, sub := range subscribers {
wg.Add(1)
go func(ctx context.Context, sub events.EventListener) {
if err := sub(ctx, event); err != nil {
msg := fmt.Sprintf("subscriber [%T] cannot handle event [%s]", sub, event.Type())
ctxLogger.Error(stacktrace.Propagate(err, msg))
}
wg.Done()
}(ctx, sub)
}
wg.Wait()
dispatcher.meter.Record(
ctx,
float64(time.Since(start).Milliseconds()),
metric.WithAttributes(
semconv.CloudeventsEventType(event.Type()),
semconv.CloudeventsEventSpecVersion(event.SpecVersion()),
),
)
}
func (dispatcher *EventDispatcher) addCloudEventAttributes(span trace.Span, event cloudevents.Event) {
span.SetAttributes(
semconv.CloudeventsEventType(event.Type()),
semconv.CloudeventsEventID(event.ID()),
semconv.CloudeventsEventSource(event.Source()),
semconv.CloudeventsEventSpecVersion(event.SpecVersion()),
)
}
func (dispatcher *EventDispatcher) createCloudTask(event cloudevents.Event) (*PushQueueTask, error) {
eventContent, err := json.Marshal(event)
if err != nil {
return nil, stacktrace.Propagate(err, fmt.Sprintf("cannot marshall [%T] with ID [%s]", event, event.ID()))
}
return &PushQueueTask{
Method: http.MethodPost,
URL: dispatcher.queueConfig.ConsumerEndpoint,
Body: eventContent,
Headers: map[string]string{
"x-api-key": dispatcher.queueConfig.UserAPIKey,
},
}, nil
}