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subscriber.go
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subscriber.go
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package eventbus
import (
"context"
"fmt"
"reflect"
"strings"
"sync"
"github.com/quarks-tech/protoevent-go/pkg/encoding"
"github.com/quarks-tech/protoevent-go/pkg/event"
)
type Receiver interface {
Receive(ctx context.Context, p Processor) error
}
type Setuper interface {
Setup(ctx context.Context, serviceName string, info ...ServiceInfo) error
}
type Processor func(md *event.Metadata, data []byte) error
type EventDesc struct {
Name string
HandlerType interface{}
Handler eventHandler
}
type ServiceDesc struct {
ServiceName string
Events []EventDesc
Metadata string
}
func (sd ServiceDesc) getEventDesc(name string) (EventDesc, bool) {
for _, ed := range sd.Events {
if ed.Name == name {
return ed, true
}
}
return EventDesc{}, false
}
type eventInfo struct {
handler eventHandler
handlerImpl interface{}
}
type serviceInfo struct {
events map[string]*eventInfo
mdata string
}
type eventHandler func(h interface{}, md *event.Metadata, ctx context.Context, dec func(interface{}) error, inter SubscriberInterceptor) error
type EventHandlerRegistrar interface {
RegisterEventHandler(desc *ServiceDesc, event string, impl interface{})
}
type subscriberOptions struct {
interceptor SubscriberInterceptor
chainInterceptors []SubscriberInterceptor
}
func defaultSubscriberOptions() subscriberOptions {
return subscriberOptions{}
}
type SubscriberOption func(opts *subscriberOptions)
type Subscriber struct {
mux sync.Mutex
name string
opts subscriberOptions
services map[string]*serviceInfo
serve bool
}
func NewSubscriber(name string, opts ...SubscriberOption) *Subscriber {
options := defaultSubscriberOptions()
for _, opt := range opts {
opt(&options)
}
s := &Subscriber{
opts: options,
name: name,
services: make(map[string]*serviceInfo),
}
chainSubscriberInterceptors(s)
return s
}
func (s *Subscriber) RegisterEventHandler(sd *ServiceDesc, eventName string, h interface{}) {
ed, ok := sd.getEventDesc(eventName)
if !ok {
panicf("event not found: %s", eventName)
}
if h != nil {
sht := reflect.TypeOf(ed.HandlerType).Elem()
ht := reflect.TypeOf(h)
if !ht.Implements(sht) {
panicf("Subscriber.RegisterSubscription found the handlerImpl of type %v that does not satisfy %v", ht, sht)
}
}
s.register(sd, ed, h)
}
func (s *Subscriber) register(sd *ServiceDesc, ed EventDesc, h interface{}) {
s.mux.Lock()
defer s.mux.Unlock()
if s.serve {
panicf("Subscriber.RegisterEventHandler after Subscriber.Subscribe for %q", ed.Name)
}
if _, ok := s.services[sd.ServiceName]; !ok {
s.services[sd.ServiceName] = &serviceInfo{
events: make(map[string]*eventInfo),
mdata: sd.Metadata,
}
}
if _, ok := s.services[sd.ServiceName].events[ed.Name]; ok {
panicf("Subscriber.RegisterEventHandler found duplicate service registration for %q", ed.Name)
}
s.services[sd.ServiceName].events[ed.Name] = &eventInfo{
handler: ed.Handler,
handlerImpl: h,
}
}
type ServiceInfo struct {
ServiceName string
Events []string
}
func (s *Subscriber) GetServiceInfo() []ServiceInfo {
sInfos := make([]ServiceInfo, 0, len(s.services))
for sName, service := range s.services {
si := ServiceInfo{
ServiceName: sName,
Events: make([]string, 0, len(service.events)),
}
for eName := range service.events {
si.Events = append(si.Events, eName)
}
sInfos = append(sInfos, si)
}
return sInfos
}
func (s *Subscriber) Subscribe(ctx context.Context, r Receiver) error {
s.mux.Lock()
s.serve = true
s.mux.Unlock()
if setuper, ok := r.(Setuper); ok {
if err := setuper.Setup(ctx, s.name, s.GetServiceInfo()...); err != nil {
return err
}
}
return r.Receive(ctx, s.process)
}
func (s *Subscriber) process(md *event.Metadata, data []byte) error {
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
pos := strings.LastIndex(md.Type, ".")
service := md.Type[:pos]
eventName := md.Type[pos+1:]
srv, knownService := s.services[service]
if !knownService {
return NewUnprocessableEventError(fmt.Errorf("subscription not found: %s", md.Type))
}
ei, ok := srv.events[eventName]
if !ok {
return NewUnprocessableEventError(fmt.Errorf("subscription not found: %s", md.Type))
}
df := func(v interface{}) error {
contentSubtype, valid := event.ContentSubtype(md.DataContentType)
if !valid {
return NewUnprocessableEventError(fmt.Errorf("invalid content type: %s", md.DataContentType))
}
codec, err := encoding.GetCodec(contentSubtype)
if err != nil {
return NewUnprocessableEventError(fmt.Errorf("get codec %s: %w", contentSubtype, err))
}
if err = codec.Unmarshal(data, v); err != nil {
return NewUnprocessableEventError(fmt.Errorf("unmarshalling event data: %w", err))
}
return nil
}
ctx = event.NewIncomingContext(ctx, md)
return ei.handler(ei.handlerImpl, md, ctx, df, s.opts.interceptor)
}
func panicf(format string, a ...interface{}) {
panic(fmt.Sprintf("eventbus: "+format, a...))
}