Handler middlewares

backend/handler.go

@@ -0,0 +1,70 @@
+package backend
+
+import "context"
+
+// Handler interface for all handlers.
+type Handler interface {
+	QueryDataHandler
+	CheckHealthHandler
+	CallResourceHandler
+	CollectMetricsHandler
+	StreamHandler
+	AdmissionHandler
+	ConversionHandler
+}
+
+var _ = Handler(&BaseHandler{})
+
+// BaseHandler base handler provides a base implementation of Handler interface
+// passing the request down the chain to next Handler.
+// This allows handlers to avoid implementing the full Handler interface.
+type BaseHandler struct {
+	next Handler
+}
+
+// NewBaseHandler creates a new BaseHandler.
+func NewBaseHandler(next Handler) BaseHandler {
+	return BaseHandler{
+		next: next,
+	}
+}
+
+func (m BaseHandler) QueryData(ctx context.Context, req *QueryDataRequest) (*QueryDataResponse, error) {
+	return m.next.QueryData(ctx, req)
+}
+
+func (m BaseHandler) CallResource(ctx context.Context, req *CallResourceRequest, sender CallResourceResponseSender) error {
+	return m.next.CallResource(ctx, req, sender)
+}
+
+func (m BaseHandler) CheckHealth(ctx context.Context, req *CheckHealthRequest) (*CheckHealthResult, error) {
+	return m.next.CheckHealth(ctx, req)
+}
+
+func (m BaseHandler) CollectMetrics(ctx context.Context, req *CollectMetricsRequest) (*CollectMetricsResult, error) {
+	return m.next.CollectMetrics(ctx, req)
+}
+
+func (m BaseHandler) SubscribeStream(ctx context.Context, req *SubscribeStreamRequest) (*SubscribeStreamResponse, error) {
+	return m.next.SubscribeStream(ctx, req)
+}
+
+func (m BaseHandler) PublishStream(ctx context.Context, req *PublishStreamRequest) (*PublishStreamResponse, error) {
+	return m.next.PublishStream(ctx, req)
+}
+
+func (m BaseHandler) RunStream(ctx context.Context, req *RunStreamRequest, sender *StreamSender) error {
+	return m.next.RunStream(ctx, req, sender)
+}
+
+func (m BaseHandler) ValidateAdmission(ctx context.Context, req *AdmissionRequest) (*ValidationResponse, error) {
+	return m.next.ValidateAdmission(ctx, req)
+}
+
+func (m *BaseHandler) MutateAdmission(ctx context.Context, req *AdmissionRequest) (*MutationResponse, error) {
+	return m.next.MutateAdmission(ctx, req)
+}
+
+func (m *BaseHandler) ConvertObjects(ctx context.Context, req *ConversionRequest) (*ConversionResponse, error) {
+	return m.next.ConvertObjects(ctx, req)
+}

backend/handler_middleware.go

@@ -0,0 +1,158 @@
+package backend
+
+import (
+	"context"
+	"errors"
+)
+
+var (
+	errNilRequest = errors.New("req cannot be nil")
+	errNilSender  = errors.New("sender cannot be nil")
+)
+
+// HandlerMiddleware is an interface representing the ability to create a middleware
+// that implements the Handler interface.
+type HandlerMiddleware interface {
+	// CreateHandlerMiddleware creates a new Handler by decorating next Handler.
+	CreateHandlerMiddleware(next Handler) Handler
+}
+
+// The HandlerMiddlewareFunc type is an adapter to allow the use of ordinary
+// functions as HandlerMiddleware's. If f is a function with the appropriate
+// signature, HandlerMiddlewareFunc(f) is a HandlerMiddleware that calls f.
+type HandlerMiddlewareFunc func(next Handler) Handler
+
+// CreateHandlerMiddleware implements the HandlerMiddleware interface.
+func (fn HandlerMiddlewareFunc) CreateHandlerMiddleware(next Handler) Handler {
+	return fn(next)
+}
+
+// MiddlewareHandler decorates a Handler with HandlerMiddleware's.
+type MiddlewareHandler struct {
+	handler Handler
+}
+
+// HandlerFromMiddlewares creates a new MiddlewareHandler implementing Handler that decorates finalHandler with middlewares.
+func HandlerFromMiddlewares(finalHandler Handler, middlewares ...HandlerMiddleware) (*MiddlewareHandler, error) {
+	if finalHandler == nil {
+		return nil, errors.New("finalHandler cannot be nil")
+	}
+
+	return &MiddlewareHandler{
+		handler: handlerFromMiddlewares(middlewares, finalHandler),
+	}, nil
+}
+
+func (h *MiddlewareHandler) QueryData(ctx context.Context, req *QueryDataRequest) (*QueryDataResponse, error) {
+	if req == nil {
+		return nil, errNilRequest
+	}
+
+	return h.handler.QueryData(ctx, req)
+}
+
+func (h MiddlewareHandler) CallResource(ctx context.Context, req *CallResourceRequest, sender CallResourceResponseSender) error {
+	if req == nil {
+		return errNilRequest
+	}
+
+	if sender == nil {
+		return errNilSender
+	}
+
+	return h.handler.CallResource(ctx, req, sender)
+}
+
+func (h MiddlewareHandler) CollectMetrics(ctx context.Context, req *CollectMetricsRequest) (*CollectMetricsResult, error) {
+	if req == nil {
+		return nil, errNilRequest
+	}
+
+	return h.handler.CollectMetrics(ctx, req)
+}
+
+func (h MiddlewareHandler) CheckHealth(ctx context.Context, req *CheckHealthRequest) (*CheckHealthResult, error) {
+	if req == nil {
+		return nil, errNilRequest
+	}
+
+	return h.handler.CheckHealth(ctx, req)
+}
+
+func (h MiddlewareHandler) SubscribeStream(ctx context.Context, req *SubscribeStreamRequest) (*SubscribeStreamResponse, error) {
+	if req == nil {
+		return nil, errNilRequest
+	}
+
+	return h.handler.SubscribeStream(ctx, req)
+}
+
+func (h MiddlewareHandler) PublishStream(ctx context.Context, req *PublishStreamRequest) (*PublishStreamResponse, error) {
+	if req == nil {
+		return nil, errNilRequest
+	}
+
+	return h.handler.PublishStream(ctx, req)
+}
+
+func (h MiddlewareHandler) RunStream(ctx context.Context, req *RunStreamRequest, sender *StreamSender) error {
+	if req == nil {
+		return errNilRequest
+	}
+
+	if sender == nil {
+		return errors.New("sender cannot be nil")
+	}
+
+	return h.handler.RunStream(ctx, req, sender)
+}
+
+func (h MiddlewareHandler) ValidateAdmission(ctx context.Context, req *AdmissionRequest) (*ValidationResponse, error) {
+	if req == nil {
+		return nil, errNilRequest
+	}
+
+	return h.handler.ValidateAdmission(ctx, req)
+}
+
+func (h MiddlewareHandler) MutateAdmission(ctx context.Context, req *AdmissionRequest) (*MutationResponse, error) {
+	if req == nil {
+		return nil, errNilRequest
+	}
+
+	return h.handler.MutateAdmission(ctx, req)
+}
+
+func (h MiddlewareHandler) ConvertObjects(ctx context.Context, req *ConversionRequest) (*ConversionResponse, error) {
+	if req == nil {
+		return nil, errNilRequest
+	}
+
+	return h.handler.ConvertObjects(ctx, req)
+}
+
+func handlerFromMiddlewares(middlewares []HandlerMiddleware, finalHandler Handler) Handler {
+	if len(middlewares) == 0 {
+		return finalHandler
+	}
+
+	reversed := reverseMiddlewares(middlewares)
+	next := finalHandler
+
+	for _, m := range reversed {
+		next = m.CreateHandlerMiddleware(next)
+	}
+
+	return next
+}
+
+func reverseMiddlewares(middlewares []HandlerMiddleware) []HandlerMiddleware {
+	reversed := make([]HandlerMiddleware, len(middlewares))
+	copy(reversed, middlewares)
+
+	for i, j := 0, len(reversed)-1; i < j; i, j = i+1, j-1 {
+		reversed[i], reversed[j] = reversed[j], reversed[i]
+	}
+
+	return reversed
+}