Handler middlewares (#1019)

Co-authored-by: Will Browne <wbrowne@users.noreply.github.com>

backend/conversion.go

@@ -5,8 +5,8 @@ import (
 )
 
 const (
- // EndpointConvertObject friendly name for the convert object endpoint/handler.
- EndpointConvertObject Endpoint = "convertObject"
+ // EndpointConvertObjects friendly name for the convert objects endpoint/handler.
+ EndpointConvertObjects Endpoint = "convertObjects"
 )
 
 // ConversionHandler is an EXPERIMENTAL service that allows converting objects between versions

backend/conversion_adapter.go

@@ -64,7 +64,7 @@ func (a *conversionSDKAdapter) convertQueryDataRequest(ctx context.Context, requ
 }
 
 func (a *conversionSDKAdapter) ConvertObjects(ctx context.Context, req *pluginv2.ConversionRequest) (*pluginv2.ConversionResponse, error) {
- ctx = setupContext(ctx, EndpointConvertObject)
+ ctx = setupContext(ctx, EndpointConvertObjects)
  parsedReq := FromProto().ConversionRequest(req)
 
  resp := &ConversionResponse{}

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 +1,181 @@
+package backend
+
+import (
+ "context"
+ "errors"
+ "slices"
+)
+
+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 {
+ middlewares []HandlerMiddleware
+ finalHandler 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{
+ middlewares: middlewares,
+ finalHandler: finalHandler,
+ }, nil
+}
+
+func (h *MiddlewareHandler) setupContext(ctx context.Context, pluginCtx PluginContext, endpoint Endpoint) context.Context {
+ ctx = initErrorSource(ctx)
+ ctx = WithEndpoint(ctx, endpoint)
+ ctx = WithPluginContext(ctx, pluginCtx)
+ ctx = WithGrafanaConfig(ctx, pluginCtx.GrafanaConfig)
+ ctx = WithUser(ctx, pluginCtx.User)
+ ctx = WithUserAgent(ctx, pluginCtx.UserAgent)
+ return ctx
+}
+
+func (h *MiddlewareHandler) QueryData(ctx context.Context, req *QueryDataRequest) (*QueryDataResponse, error) {
+ if req == nil {
+ return nil, errNilRequest
+ }
+
+ ctx = h.setupContext(ctx, req.PluginContext, EndpointQueryData)
+ handler := handlerFromMiddlewares(h.middlewares, h.finalHandler)
+ return 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
+ }
+
+ ctx = h.setupContext(ctx, req.PluginContext, EndpointCallResource)
+ handler := handlerFromMiddlewares(h.middlewares, h.finalHandler)
+ return handler.CallResource(ctx, req, sender)
+}
+
+func (h MiddlewareHandler) CollectMetrics(ctx context.Context, req *CollectMetricsRequest) (*CollectMetricsResult, error) {
+ if req == nil {
+ return nil, errNilRequest
+ }
+
+ ctx = h.setupContext(ctx, req.PluginContext, EndpointCollectMetrics)
+ handler := handlerFromMiddlewares(h.middlewares, h.finalHandler)
+ return handler.CollectMetrics(ctx, req)
+}
+
+func (h MiddlewareHandler) CheckHealth(ctx context.Context, req *CheckHealthRequest) (*CheckHealthResult, error) {
+ if req == nil {
+ return nil, errNilRequest
+ }
+
+ ctx = h.setupContext(ctx, req.PluginContext, EndpointCheckHealth)
+ handler := handlerFromMiddlewares(h.middlewares, h.finalHandler)
+ return handler.CheckHealth(ctx, req)
+}
+
+func (h MiddlewareHandler) SubscribeStream(ctx context.Context, req *SubscribeStreamRequest) (*SubscribeStreamResponse, error) {
+ if req == nil {
+ return nil, errNilRequest
+ }
+
+ ctx = h.setupContext(ctx, req.PluginContext, EndpointSubscribeStream)
+ handler := handlerFromMiddlewares(h.middlewares, h.finalHandler)
+ return handler.SubscribeStream(ctx, req)
+}
+
+func (h MiddlewareHandler) PublishStream(ctx context.Context, req *PublishStreamRequest) (*PublishStreamResponse, error) {
+ if req == nil {
+ return nil, errNilRequest
+ }
+
+ ctx = h.setupContext(ctx, req.PluginContext, EndpointPublishStream)
+ handler := handlerFromMiddlewares(h.middlewares, h.finalHandler)
+ return 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")
+ }
+
+ ctx = h.setupContext(ctx, req.PluginContext, EndpointRunStream)
+ handler := handlerFromMiddlewares(h.middlewares, h.finalHandler)
+ return handler.RunStream(ctx, req, sender)
+}
+
+func (h MiddlewareHandler) ValidateAdmission(ctx context.Context, req *AdmissionRequest) (*ValidationResponse, error) {
+ if req == nil {
+ return nil, errNilRequest
+ }
+
+ ctx = h.setupContext(ctx, req.PluginContext, EndpointValidateAdmission)
+ handler := handlerFromMiddlewares(h.middlewares, h.finalHandler)
+ return handler.ValidateAdmission(ctx, req)
+}
+
+func (h MiddlewareHandler) MutateAdmission(ctx context.Context, req *AdmissionRequest) (*MutationResponse, error) {
+ if req == nil {
+ return nil, errNilRequest
+ }
+
+ ctx = h.setupContext(ctx, req.PluginContext, EndpointMutateAdmission)
+ handler := handlerFromMiddlewares(h.middlewares, h.finalHandler)
+ return handler.MutateAdmission(ctx, req)
+}
+
+func (h MiddlewareHandler) ConvertObjects(ctx context.Context, req *ConversionRequest) (*ConversionResponse, error) {
+ if req == nil {
+ return nil, errNilRequest
+ }
+
+ ctx = h.setupContext(ctx, req.PluginContext, EndpointConvertObjects)
+ handler := handlerFromMiddlewares(h.middlewares, h.finalHandler)
+ return handler.ConvertObjects(ctx, req)
+}
+
+func handlerFromMiddlewares(middlewares []HandlerMiddleware, finalHandler Handler) Handler {
+ if len(middlewares) == 0 {
+ return finalHandler
+ }
+
+ clonedMws := slices.Clone(middlewares)
+ slices.Reverse(clonedMws)
+ next := finalHandler
+
+ for _, m := range clonedMws {
+ next = m.CreateHandlerMiddleware(next)
+ }
+
+ return next
+}