binding

Example of implementing a transport including a simple message type, and a transport sender and receiver.

package main

import (
	"context"
	"encoding/json"
	"io"

	"github.com/cloudevents/sdk-go/pkg/binding"
	"github.com/cloudevents/sdk-go/pkg/cloudevents"
	ce "github.com/cloudevents/sdk-go/pkg/cloudevents"
	"github.com/cloudevents/sdk-go/pkg/cloudevents/transport"
)

// ExMessage is a json.RawMessage, a byte slice containing a JSON encoded event.
// It implements binding.StructMessage
//
// Note: a good binding implementation should provide an easy way to convert
// between the Message implementation and the "native" message format.
// In this case it's as simple as:
//
//	native = ExMessage(impl)
//	impl = json.RawMessage(native)
//
// For example in a HTTP binding it should be easy to convert between
// the HTTP binding.Message implementation and net/http.Request and
// Response types.  There are no interfaces for this conversion as it
// requires the use of unknown types.
type ExMessage json.RawMessage

func (m ExMessage) Structured() (string, []byte) {
	return cloudevents.ApplicationCloudEventsJSON, []byte(m)
}

func (m ExMessage) Event() (e cloudevents.Event, err error) {
	err = json.Unmarshal(json.RawMessage(m), &e)
	return e, err
}

func (m ExMessage) Finish(error) error { return nil }

// ExSender sends by writing JSON encoded events to an io.Writer
type ExSender struct{ encoder *json.Encoder }

func NewExSender(w io.Writer) ExSender { return ExSender{json.NewEncoder(w)} }

func (s ExSender) Send(ctx context.Context, m binding.Message) error {
	if f, b := m.Structured(); f == ce.ApplicationCloudEventsJSON {
		// Fast case: Message is already structured JSON.
		return s.encoder.Encode(json.RawMessage(b))
	}
	// Some other message encoding. Decode as generic Event and re-encode.
	if e, err := m.Event(); err != nil {
		return err
	} else if err := s.encoder.Encode(&e); err != nil {
		return err
	}
	return nil
}
func (s ExSender) Close(context.Context) error { return nil }

// ExReceiver receives by reading JSON encoded events from an io.Reader
type ExReceiver struct{ decoder *json.Decoder }

func NewExReceiver(r io.Reader) ExReceiver { return ExReceiver{json.NewDecoder(r)} }

func (r ExReceiver) Receive(context.Context) (binding.Message, error) {
	var rm json.RawMessage
	err := r.decoder.Decode(&rm) // This is just a byte copy.
	return ExMessage(rm), err
}
func (r ExReceiver) Close(context.Context) error { return nil }

// NewExTransport returns a transport.Transport which is implemented by
// an ExSender and an ExReceiver
func NewExTransport(r io.Reader, w io.Writer) transport.Transport {
	return binding.NewTransport(NewExSender(w), NewExReceiver(r))
}

// Example of implementing a transport including a simple message type,
// and a transport sender and receiver.
func main() {}

This example shows how to use a transport in sender, receiver, and intermediary processes.

The sender and receiver use the client.Client API to send and receive messages. the transport. Only the intermediary example actually uses the transport APIs for efficiency and reliability in forwarding events.

package main

import (
	"context"
	"fmt"
	"io"
	"strconv"

	"github.com/cloudevents/sdk-go/pkg/cloudevents"
	"github.com/cloudevents/sdk-go/pkg/cloudevents/client"
)

const count = 3 // Example ends after this many events.

// The sender uses the cloudevents.Client API, not the transport APIs directly.
func runSender(w io.Writer) error {
	c, err := client.New(NewExTransport(nil, w))
	if err != nil {
		return err
	}
	for i := 0; i < count; i++ {
		e := cloudevents.New()
		e.SetType("example.com/event")
		e.SetSource("example.com/source")
		e.SetID(strconv.Itoa(i))
		if err := e.SetData(fmt.Sprintf("hello %d", i)); err != nil {
			return err
		}
		if _, _, err := c.Send(context.TODO(), e); err != nil {
			return err
		}
	}
	return nil
}

// The receiver uses the cloudevents.Client API, not the transport APIs directly.
func runReceiver(r io.Reader) error {
	i := 0
	process := func(e cloudevents.Event) error {
		fmt.Printf("%s\n", e)
		i++
		if i == count {
			return io.EOF
		}
		return nil
	}
	c, err := client.New(NewExTransport(r, nil))
	if err != nil {
		return err
	}
	return c.StartReceiver(context.TODO(), process)
}

// The intermediary receives events and forwards them to another
// process using ExReceiver and ExSender directly.
//
// By forwarding a transport.Message instead of a cloudevents.Event,
// it allows the transports to avoid un-necessary decoding of
// structured events, and to exchange delivery status between reliable
// transports. Even transports using different protocols can ensure
// reliable delivery.
func runIntermediary(r io.Reader, w io.WriteCloser) error {
	defer w.Close()
	for {
		receiver := NewExReceiver(r)
		sender := NewExSender(w)
		for i := 0; i < count; i++ {
			if m, err := receiver.Receive(context.TODO()); err != nil {
				return err
			} else if err := sender.Send(context.TODO(), m); err != nil {
				return err
			}
		}
	}
}

// This example shows how to use a transport in sender, receiver,
// and intermediary processes.
//
// The sender and receiver use the client.Client API to send and
// receive messages.  the transport.  Only the intermediary example
// actually uses the transport APIs for efficiency and reliability in
// forwarding events.
func main() {
	r1, w1 := io.Pipe() // The sender-to-intermediary pipe
	r2, w2 := io.Pipe() // The intermediary-to-receiver pipe

	done := make(chan error)
	go func() { done <- runReceiver(r2) }()
	go func() { done <- runIntermediary(r1, w2) }()
	go func() { done <- runSender(w1) }()
	for i := 0; i < 2; i++ {
		if err := <-done; err != nil && err != io.EOF {
			fmt.Println(err)
		}
	}

}

Output:

Validation: valid
Context Attributes,
  specversion: 0.2
  type: example.com/event
  source: example.com/source
  id: 0
Data,
  "hello 0"

Validation: valid
Context Attributes,
  specversion: 0.2
  type: example.com/event
  source: example.com/source
  id: 1
Data,
  "hello 1"

Validation: valid
Context Attributes,
  specversion: 0.2
  type: example.com/event
  source: example.com/source
  id: 2
Data,
  "hello 2"