#814 Add Transport Layer: AWS Lambda

transport/awslambda/doc.go

@@ -0,0 +1,2 @@
+// Package awslambda provides an AWS Lambda transport layer.
+package awslambda

transport/awslambda/encode_decode.go

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+package awslambda
+
+import (
+	"context"
+)
+
+// DecodeRequestFunc extracts a user-domain request object from an
+// AWS Lambda payload.
+type DecodeRequestFunc func(context.Context, []byte) (interface{}, error)
+
+// EncodeResponseFunc encodes the passed response object into []byte,
+// ready to be sent as AWS Lambda response.
+type EncodeResponseFunc func(context.Context, interface{}) ([]byte, error)
+
+// ErrorEncoder is responsible for encoding an error.
+type ErrorEncoder func(ctx context.Context, err error) ([]byte, error)

transport/awslambda/handler.go

@@ -0,0 +1,120 @@
+package awslambda
+
+import (
+	"context"
+
+	"github.com/go-kit/kit/endpoint"
+	"github.com/go-kit/kit/log"
+)
+
+// Handler wraps an endpoint.
+type Handler struct {
+	e            endpoint.Endpoint
+	dec          DecodeRequestFunc
+	enc          EncodeResponseFunc
+	before       []HandlerRequestFunc
+	after        []HandlerResponseFunc
+	errorEncoder ErrorEncoder
+	finalizer    []HandlerFinalizerFunc
+	logger       log.Logger
+}
+
+// NewHandler constructs a new handler, which implements
+// the AWS lambda.Handler interface.
+func NewHandler(
+	e endpoint.Endpoint,
+	dec DecodeRequestFunc,
+	enc EncodeResponseFunc,
+	options ...HandlerOption,
+) *Handler {
+	h := &Handler{
+		e:            e,
+		dec:          dec,
+		enc:          enc,
+		logger:       log.NewNopLogger(),
+		errorEncoder: DefaultErrorEncoder,
+	}
+	for _, option := range options {
+		option(h)
+	}
+	return h
+}
+
+// HandlerOption sets an optional parameter for handlers.
+type HandlerOption func(*Handler)
+
+// HandlerBefore functions are executed on the payload byte,
+// before the request is decoded.
+func HandlerBefore(before ...HandlerRequestFunc) HandlerOption {
+	return func(h *Handler) { h.before = append(h.before, before...) }
+}
+
+// HandlerAfter functions are only executed after invoking the endpoint
+// but prior to returning a response.
+func HandlerAfter(after ...HandlerResponseFunc) HandlerOption {
+	return func(h *Handler) { h.after = append(h.after, after...) }
+}
+
+// HandlerErrorLogger is used to log non-terminal errors.
+// By default, no errors are logged.
+func HandlerErrorLogger(logger log.Logger) HandlerOption {
+	return func(h *Handler) { h.logger = logger }
+}
+
+// HandlerErrorEncoder is used to encode errors.
+func HandlerErrorEncoder(ee ErrorEncoder) HandlerOption {
+	return func(h *Handler) { h.errorEncoder = ee }
+}
+
+// HandlerFinalizer sets finalizer which are called at the end of
+// request. By default no finalizer is registered.
+func HandlerFinalizer(f ...HandlerFinalizerFunc) HandlerOption {
+	return func(h *Handler) { h.finalizer = append(h.finalizer, f...) }
+}
+
+// DefaultErrorEncoder defines the default behavior of encoding an error response,
+// where it returns nil, and the error itself.
+func DefaultErrorEncoder(ctx context.Context, err error) ([]byte, error) {
+	return nil, err
+}
+
+// Invoke represents implementation of the AWS lambda.Handler interface.
+func (h *Handler) Invoke(
+	ctx context.Context,
+	payload []byte,
+) (resp []byte, err error) {
+	if len(h.finalizer) > 0 {
+		defer func() {
+			for _, f := range h.finalizer {
+				f(ctx, resp, err)
+			}
+		}()
+	}
+
+	for _, f := range h.before {
+		ctx = f(ctx, payload)
+	}
+
+	request, err := h.dec(ctx, payload)
+	if err != nil {
+		h.logger.Log("err", err)
+		return h.errorEncoder(ctx, err)
+	}
+
+	response, err := h.e(ctx, request)
+	if err != nil {
+		h.logger.Log("err", err)
+		return h.errorEncoder(ctx, err)
+	}
+
+	for _, f := range h.after {
+		ctx = f(ctx, response)
+	}
+
+	if resp, err = h.enc(ctx, response); err != nil {
+		h.logger.Log("err", err)
+		return h.errorEncoder(ctx, err)
+	}
+
+	return resp, err
+}