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publisher.go
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package streams
import (
"context"
"time"
"github.com/alexandria-oss/streams/codec"
)
// PublisherConfig is the Publisher configuration.
type PublisherConfig struct {
IdentifierFactory IdentifierFactory
Codec codec.Codec
}
// A Publisher is a high-level component which writes Event(s) into topics (streams).
// Depending on the underlying Writer, publish routines will write Event(s) in batches or one-by-one.
type Publisher struct {
writer Writer
eventReg EventRegistry
idFactory IdentifierFactory
codec codec.Codec
}
func newPublisherDefaults() PublisherConfig {
return PublisherConfig{
IdentifierFactory: NewUUID,
Codec: codec.JSON{},
}
}
// NewPublisher allocates a new Publisher instance ready to be used. Specify options to customize default
// configurations.
func NewPublisher(w Writer, eventReg EventRegistry, options ...PublisherOption) Publisher {
cfg := newPublisherDefaults()
for _, opt := range options {
opt.apply(&cfg)
}
return Publisher{
writer: w,
eventReg: eventReg,
idFactory: cfg.IdentifierFactory,
codec: cfg.Codec,
}
}
// builds a Message out from an Event.
func (p Publisher) newMessage(event Event) (Message, error) {
msgID, err := p.idFactory()
if err != nil {
return Message{}, err
}
topic, err := p.eventReg.GetEventTopic(event)
if err != nil {
return Message{}, err
}
encodedMsg, err := p.codec.Encode(event)
if err != nil {
return Message{}, err
}
return Message{
ID: msgID,
StreamName: topic,
StreamKey: event.GetKey(),
Headers: event.GetHeaders(), // might require to merge maps here if we want to use `streams` internal headers.
ContentType: p.codec.ApplicationType(),
Data: encodedMsg,
Time: time.Now().UTC(),
}, nil
}
// builds a Message out from an Event with specified topic.
func (p Publisher) newMessageWithTopic(topic string, event Event) (Message, error) {
msgID, err := p.idFactory()
if err != nil {
return Message{}, err
}
encodedMsg, err := p.codec.Encode(event)
if err != nil {
return Message{}, err
}
return Message{
ID: msgID,
StreamName: topic,
StreamKey: event.GetKey(),
Headers: event.GetHeaders(), // might require to merge maps here if we want to use `streams` internal headers.
ContentType: p.codec.ApplicationType(),
Data: encodedMsg,
Time: time.Now().UTC(),
}, nil
}
// Publish writes Event(s) into a topic specified on each Event.
func (p Publisher) Publish(ctx context.Context, events ...Event) error {
msgBuf := make([]Message, 0, len(events))
for _, ev := range events {
msg, err := p.newMessage(ev)
if err != nil {
return err
}
msgBuf = append(msgBuf, msg)
}
return p.writer.Write(ctx, msgBuf)
}
// PublishToTopic writes Event(s) into a specific topic.
func (p Publisher) PublishToTopic(ctx context.Context, topic string, events ...Event) error {
msgBuf := make([]Message, 0, len(events))
for _, ev := range events {
msg, err := p.newMessageWithTopic(topic, ev)
if err != nil {
return err
}
msgBuf = append(msgBuf, msg)
}
return p.writer.Write(ctx, msgBuf)
}