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topics.go
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topics.go
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// Copyright 2021 Nitric Technologies Pty Ltd.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package topics
import (
"context"
"fmt"
"slices"
"sync"
"github.com/nitrictech/nitric/core/pkg/help"
topicspb "github.com/nitrictech/nitric/core/pkg/proto/topics/v1"
"github.com/nitrictech/nitric/core/pkg/workers"
"golang.org/x/sync/errgroup"
)
type TopicName = string
type WorkerConnection = workers.WorkerRequestBroker[*topicspb.ServerMessage, *topicspb.ClientMessage]
type SubscriptionRequestHandler interface {
topicspb.SubscriberServer
HandleRequest(request *topicspb.ServerMessage) (*topicspb.ClientMessage, error)
WorkerCount() int
}
type SubscriberManager struct {
subscriberMap map[TopicName][]*WorkerConnection
lock sync.RWMutex
}
func (s *SubscriberManager) registerSubscriber(subscriber *WorkerConnection, registrationRequest *topicspb.RegistrationRequest) error {
s.lock.Lock()
defer s.lock.Unlock()
topicName := registrationRequest.GetTopicName()
if _, exists := s.subscriberMap[topicName]; !exists {
s.subscriberMap[topicName] = make([]*WorkerConnection, 0, 1)
}
s.subscriberMap[topicName] = append(s.subscriberMap[topicName], subscriber)
return nil
}
func (s *SubscriberManager) unregisterSubscriber(topicName string, subscriber *WorkerConnection) {
s.lock.Lock()
defer s.lock.Unlock()
s.subscriberMap[topicName] = slices.DeleteFunc[[]*WorkerConnection](s.subscriberMap[topicName], func(wc *WorkerConnection) bool {
return wc == subscriber
})
if len(s.subscriberMap[topicName]) == 0 {
delete(s.subscriberMap, topicName)
}
}
func (s *SubscriberManager) WorkerCount() int {
s.lock.RLock()
defer s.lock.RUnlock()
var count int
for _, subscribers := range s.subscriberMap {
count += len(subscribers)
}
return count
}
// Subscribe allows the local nitric server to register new subscribers
//
// called by Nitric applications wishing to subscribe to a topic.
// the stream establishes communication between that subscriber and this server
func (s *SubscriberManager) Subscribe(subscriberConnectionStream topicspb.Subscriber_SubscribeServer) error {
// The client MUST send registration request on the stream as its first message
initialRequest, err := subscriberConnectionStream.Recv()
if err != nil {
return err
}
registrationRequest := initialRequest.GetRegistrationRequest()
if registrationRequest == nil {
return fmt.Errorf("request received from unregistered subscriber, initial request must be a registration request. %s", help.BugInNitricHelpText())
}
subscriber := workers.NewWorkerRequestBroker[*topicspb.ServerMessage, *topicspb.ClientMessage](subscriberConnectionStream)
if err := s.registerSubscriber(subscriber, registrationRequest); err != nil {
return err
}
defer s.unregisterSubscriber(registrationRequest.GetTopicName(), subscriber)
// send acknowledgement of registration
err = subscriberConnectionStream.Send(&topicspb.ServerMessage{
Content: &topicspb.ServerMessage_RegistrationResponse{
RegistrationResponse: &topicspb.RegistrationResponse{},
},
})
if err != nil {
return err
}
err = subscriber.Run()
if err != nil {
return fmt.Errorf("subscriber connection broker encountered and error: %w", err)
}
return nil
}
// findMatchingSubscriber returns the subscribers for a given topic, or an error if none are found
func (s *SubscriberManager) findMatchingSubscriber(topicName string) ([]*WorkerConnection, error) {
s.lock.RLock()
defer s.lock.RUnlock()
workers, ok := s.subscriberMap[topicName]
if !ok || len(workers) == 0 {
return nil, fmt.Errorf("no workers registered for topic subscription: %s", topicName)
}
return workers, nil
}
// ForwardRequestToSubscribers forwards an event to all subscribers for a given topic
// returns a slice of errors encountered while forwarding the event
func ForwardRequestToSubscribers(subscribers []*WorkerConnection, request *topicspb.ServerMessage) (bool, error) {
success := true
errs, _ := errgroup.WithContext(context.Background())
for _, subscriber := range subscribers {
footLongSub := subscriber
errs.Go(func() error {
resp, err := footLongSub.Send(request)
if err != nil {
return err
} else if !(*resp).GetMessageResponse().GetSuccess() {
success = false
}
return nil
})
}
err := errs.Wait()
if err != nil {
return false, fmt.Errorf("errors occurred handling subscription %v", errs)
}
return success, nil
}
func (s *SubscriberManager) HandleRequest(request *topicspb.ServerMessage) (*topicspb.ClientMessage, error) {
if request.Id == "" {
request.Id = workers.GenerateUniqueId()
}
messageRequest := request.GetMessageRequest()
if messageRequest == nil {
return nil, fmt.Errorf("invalid request, expected message request. %s", help.BugInNitricHelpText())
}
topicName := messageRequest.GetTopicName()
subscribers, err := s.findMatchingSubscriber(topicName)
if err != nil {
return nil, err
}
success, err := ForwardRequestToSubscribers(subscribers, request)
if err != nil {
return nil, err
}
// Compute units support multiple subscribers for a single topic.
//
// This makes topics are a unique case where the worker's response isn't directly returned.
// instead we return a response indicating success or failure of all subscribers.
//
// Since subscription workers should always be idempotent, this ensures a failure in any subscriber
// will trigger a retry of the event processing.
return &topicspb.ClientMessage{
Content: &topicspb.ClientMessage_MessageResponse{
MessageResponse: &topicspb.MessageResponse{
Success: success,
},
},
}, nil
}
func New() *SubscriberManager {
return &SubscriberManager{
subscriberMap: make(map[string][]*WorkerConnection),
lock: sync.RWMutex{},
}
}