feat: Add go-kit Kafka transport

pkg/transport/kafka/encode_decode.go

@@ -0,0 +1,25 @@
+package kafka
+
+import (
+	"context"
+
+	"github.com/twmb/franz-go/pkg/kgo"
+)
+
+// DecodeRequestFunc extracts a user-domain request object from
+// an Kafka message. It is designed to be used in Kafka Subscribers.
+type DecodeRequestFunc func(ctx context.Context, msg *kgo.Record) (request interface{}, err error)
+
+// EncodeRequestFunc encodes the passed request object into
+// an Kafka message object. It is designed to be used in Kafka Publishers.
+type EncodeRequestFunc func(context.Context, *kgo.Record, interface{}) error
+
+// EncodeResponseFunc encodes the passed response object into
+// a Kafka message object. It is designed to be used in Kafka Subscribers.
+type EncodeResponseFunc func(context.Context, *kgo.Record, interface{}) error
+
+// DecodeResponseFunc extracts a user-domain response object from kafka
+// response object. It's designed to be used in kafka publisher, for publisher-side
+// endpoints. One straightforward DecodeResponseFunc could be something that
+// JSON decodes from the response payload to the concrete response type.
+type DecodeResponseFunc func(context.Context, *kgo.Record) (response interface{}, err error)

pkg/transport/kafka/publisher.go

@@ -0,0 +1,205 @@
+package kafka
+
+import (
+	"context"
+	"encoding/json"
+	"time"
+
+	"github.com/go-kit/kit/endpoint"
+	"github.com/twmb/franz-go/pkg/kgo"
+)
+
+const (
+	defaultPublisherTimeout = 10 * time.Second
+)
+
+// Publisher wraps single Kafka topic for message publishing
+// and implements endpoint.Endpoint.
+type Publisher struct {
+	handler   Handler
+	topic     string
+	enc       EncodeRequestFunc
+	dec       DecodeResponseFunc
+	before    []RequestFunc
+	after     []PublisherResponseFunc
+	deliverer Deliverer
+	timeout   time.Duration
+}
+
+// NewPublisher constructs a new publisher for a single Kafka topic,
+// which implements endpoint.Endpoint.
+func NewPublisher(
+	handler Handler,
+	topic string,
+	enc EncodeRequestFunc,
+	dec DecodeResponseFunc,
+	options ...PublisherOption,
+) *Publisher {
+	p := &Publisher{
+		handler:   handler,
+		topic:     topic,
+		deliverer: SyncDeliverer,
+		enc:       enc,
+		dec:       dec,
+		timeout:   defaultPublisherTimeout,
+	}
+	for _, opt := range options {
+		opt(p)
+	}
+
+	return p
+}
+
+// PublisherOption sets an optional parameter for publishers.
+type PublisherOption func(publisher *Publisher)
+
+// PublisherBefore sets the RequestFuncs that are applied to the outgoing publisher
+// request before it's invoked.
+func PublisherBefore(before ...RequestFunc) PublisherOption {
+	return func(p *Publisher) {
+		p.before = append(p.before, before...)
+	}
+}
+
+// PublisherAfter adds one or more PublisherResponseFuncs, which are applied to the
+// context after successful message publishing.
+// This is useful for context-manipulation operations.
+func PublisherAfter(after ...PublisherResponseFunc) PublisherOption {
+	return func(p *Publisher) {
+		p.after = append(p.after, after...)
+	}
+}
+
+// PublisherDeliverer sets the deliverer function that the Publisher invokes.
+func PublisherDeliverer(deliverer Deliverer) PublisherOption {
+	return func(p *Publisher) { p.deliverer = deliverer }
+}
+
+// PublisherTimeout sets the available timeout for a kafka request.
+func PublisherTimeout(timeout time.Duration) PublisherOption {
+	return func(p *Publisher) { p.timeout = timeout }
+}
+
+// Endpoint returns a usable endpoint that invokes message publishing.
+func (p Publisher) Endpoint() endpoint.Endpoint {
+	return func(ctx context.Context, request interface{}) (interface{}, error) {
+		ctx, cancel := context.WithTimeout(ctx, p.timeout)
+		defer cancel()
+
+		msg := &kgo.Record{
+			Topic: p.topic,
+		}
+
+		if err := p.enc(ctx, msg, request); err != nil {
+			return nil, err
+		}
+
+		for _, f := range p.before {
+			ctx = f(ctx, msg)
+		}
+
+		event, err := p.deliverer(ctx, p, msg)
+		if err != nil {
+			return nil, err
+		}
+
+		for _, f := range p.after {
+			ctx = f(ctx, event)
+		}
+
+		response, err := p.dec(ctx, event)
+		if err != nil {
+			return nil, err
+		}
+
+		return response, nil
+	}
+}
+
+// Deliverer is invoked by the Publisher to publish the specified Message, and to
+// retrieve the appropriate response Event object.
+type Deliverer func(
+	context.Context,
+	Publisher,
+	*kgo.Record,
+) (*kgo.Record, error)
+
+// SyncDeliverer is a deliverer that publishes the specified message
+// and returns the first  object.
+// If the context times out while waiting for a reply, an error will be returned.
+func SyncDeliverer(ctx context.Context, pub Publisher, msg *kgo.Record) (*kgo.Record, error) {
+	results := pub.handler.ProduceSync(ctx, msg)
+
+	if len(results) > 0 && results[0].Err != nil {
+		return nil, results[0].Err
+	}
+
+	return results[0].Record, nil
+}
+
+// AsyncDeliverer delivers the supplied message and
+// returns a nil response.
+//
+// When using this deliverer please ensure that the supplied DecodeResponseFunc and
+// PublisherResponseFunc are able to handle nil-type responses.
+//
+// AsyncDeliverer will produce the message with the context detached due to the fact that actual
+// message producing is called asynchronously (another goroutine) and at that time original context might be
+// already canceled causing the producer to fail. The detached context will include values attached to the original
+// context, but deadline and cancel will be reset. To provide a context for asynchronous deliverer please
+// use AsyncDelivererCtx function instead.
+func AsyncDeliverer(ctx context.Context, pub Publisher, msg *kgo.Record) (*kgo.Record, error) {
+	pub.handler.Produce(detach{ctx: ctx}, msg, nil)
+
+	return nil, nil
+}
+
+// AsyncDelivererCtx delivers the supplied message and
+// returns a nil response.
+//
+// When using this deliverer please ensure that the supplied DecodeResponseFunc and
+// PublisherResponseFunc are able to handle nil-type responses.
+func AsyncDelivererCtx(ctx context.Context, pub Publisher, msg *kgo.Record) (*kgo.Record, error) {
+	pub.handler.Produce(ctx, msg, nil)
+
+	return nil, nil
+}
+
+// EncodeJSONRequest is an EncodeRequestFunc that serializes the request as a
+// JSON object to the Message value.
+// Many services can use it as a sensible default.
+func EncodeJSONRequest(_ context.Context, msg *kgo.Record, request interface{}) error {
+	rawJSON, err := json.Marshal(request)
+	if err != nil {
+		return err
+	}
+
+	msg.Value = rawJSON
+
+	return nil
+}
+
+// Handler is a handler interface to make testing possible.
+// It is highly recommended to use *kafka.Producer as the interface implementation.
+type Handler interface {
+	Produce(ctx context.Context, rec *kgo.Record, fn func(record *kgo.Record, err error))
+	ProduceSync(ctx context.Context, rs ...*kgo.Record) kgo.ProduceResults
+}
+
+type detach struct {
+	ctx context.Context
+}
+
+func (d detach) Deadline() (time.Time, bool) {
+	return time.Time{}, false
+}
+func (d detach) Done() <-chan struct{} {
+	return nil
+}
+func (d detach) Err() error {
+	return nil
+}
+
+func (d detach) Value(key interface{}) interface{} {
+	return d.ctx.Value(key)
+}