Add receiverhelper functions for creating metrics receiver, optionall…

…y adding scrape targets

receiver/receiverhelper/receiver.go

@@ -0,0 +1,265 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//       http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package receiverhelper
+
+import (
+	"context"
+	"time"
+
+	"go.opentelemetry.io/collector/component"
+	"go.opentelemetry.io/collector/component/componenterror"
+	"go.opentelemetry.io/collector/config/configmodels"
+	"go.opentelemetry.io/collector/consumer"
+)
+
+// Start specifies the function invoked when the receiver is being started.
+type Start func(context.Context, component.Host) error
+
+// Shutdown specifies the function invoked when the receiver is being shutdown.
+type Shutdown func(context.Context) error
+
+// Option apply changes to internal options.
+type Option func(*baseReceiver)
+
+// WithStart overrides the default Start function for a receiver.
+// The default shutdown function does nothing and always returns nil.
+func WithStart(start Start) Option {
+	return func(o *baseReceiver) {
+		o.start = start
+	}
+}
+
+// WithShutdown overrides the default Shutdown function for a receiver.
+// The default shutdown function does nothing and always returns nil.
+func WithShutdown(shutdown Shutdown) Option {
+	return func(o *baseReceiver) {
+		o.shutdown = shutdown
+	}
+}
+
+type baseReceiver struct {
+	fullName string
+	start    Start
+	shutdown Shutdown
+}
+
+// Construct the internalOptions from multiple Option.
+func newBaseReceiver(fullName string, options ...Option) baseReceiver {
+	br := baseReceiver{fullName: fullName}
+
+	for _, op := range options {
+		op(&br)
+	}
+
+	return br
+}
+
+// Start the receiver, invoked during service start.
+func (br *baseReceiver) Start(ctx context.Context, host component.Host) error {
+	if br.start != nil {
+		return br.start(ctx, host)
+	}
+	return nil
+}
+
+// Shutdown the receiver, invoked during service shutdown.
+func (br *baseReceiver) Shutdown(ctx context.Context) error {
+	if br.shutdown != nil {
+		return br.shutdown(ctx)
+	}
+	return nil
+}
+
+// MetricOption apply changes to internal options.
+type MetricOption func(*metricsReceiver)
+
+// WithBaseOptions applies any base options to a metrics receiver.
+func WithBaseOptions(options ...Option) MetricOption {
+	return func(o *metricsReceiver) {
+		for _, option := range options {
+			option(&o.baseReceiver)
+		}
+	}
+}
+
+// WithDefaultCollectionInterval overrides the default collection
+// interval (1 minute) that will be applied to all scrapers if not
+// overridden by the individual scraper.
+func WithDefaultCollectionInterval(defaultCollectionInterval time.Duration) MetricOption {
+	return func(o *metricsReceiver) {
+		o.defaultCollectionInterval = defaultCollectionInterval
+	}
+}
+
+// AddScraper configures the provided scrape function to be called with
+// the specified options, and at the specified collection interval (one
+// minute by default).
+//
+// Observability information will be reported, and the scraped metrics
+// will be passed to the next consumer.
+func AddScraper(cfg ScraperConfig, scrape Scrape, options ...ScraperOption) MetricOption {
+	return func(o *metricsReceiver) {
+		o.scrapers = append(o.scrapers, newScraper(cfg, scrape, options...))
+	}
+}
+
+type metricsReceiver struct {
+	baseReceiver
+	defaultCollectionInterval time.Duration
+	nextConsumer              consumer.MetricsConsumer
+
+	scrapers []*scraper
+	done     chan struct{}
+}
+
+// NewMetricReceiver creates a Receiver with the configured options.
+func NewMetricReceiver(config configmodels.Receiver, nextConsumer consumer.MetricsConsumer, options ...MetricOption) (component.Receiver, error) {
+	if nextConsumer == nil {
+		return nil, componenterror.ErrNilNextConsumer
+	}
+
+	mr := &metricsReceiver{
+		baseReceiver:              newBaseReceiver(config.Name()),
+		defaultCollectionInterval: time.Minute,
+		nextConsumer:              nextConsumer,
+		done:                      make(chan struct{}),
+	}
+
+	for _, op := range options {
+		op(mr)
+	}
+
+	// wrap the start function with a call to initialize scrapers
+	// and start scraping
+	start := mr.start
+	mr.start = func(ctx context.Context, host component.Host) error {
+		if start != nil {
+			if err := start(ctx, host); err != nil {
+				return err
+			}
+		}
+
+		if err := mr.initializeScrapers(ctx); err != nil {
+			return err
+		}
+
+		mr.startScraping()
+		return nil
+	}
+
+	// wrap the shutdown function with a call to close scrapers
+	// and stop scraping
+	shutdown := mr.shutdown
+	mr.shutdown = func(ctx context.Context) error {
+		mr.stopScraping()
+
+		var errors []error
+
+		if err := mr.closeScrapers(ctx); err != nil {
+			errors = append(errors, err)
+		}
+
+		if shutdown != nil {
+			if err := shutdown(ctx); err != nil {
+				errors = append(errors, err)
+			}
+		}
+
+		return componenterror.CombineErrors(errors)
+	}
+
+	return mr, nil
+}
+
+// initializeScrapers initializes all the scrapers
+func (mr *metricsReceiver) initializeScrapers(ctx context.Context) error {
+	for _, scraper := range mr.scrapers {
+		if scraper.initialize == nil {
+			continue
+		}
+
+		if err := scraper.initialize(ctx); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// startScraping initiates a ticker that calls Scrape based on the configured
+// collection interval.
+func (mr *metricsReceiver) startScraping() {
+	// TODO1: use one ticker for each set of scrapers that have the same collection interval.
+	// TODO2: consider allowing different "Scrape" functions to be configured, i.e. functions
+	//        that return MetricsSlice or ResourceMetricsSlice (similar to the existing Scraper
+	//        & ResourceScraper interfaces in the host metrics receiver). That will allow data
+	//        from multiple scrapers (that have the same collection interval) to be batched.
+
+	for i := 0; i < len(mr.scrapers); i++ {
+		scraper := mr.scrapers[i]
+		go func() {
+			collectionInterval := mr.defaultCollectionInterval
+			if scraper.cfg.CollectionInterval() != 0 {
+				collectionInterval = scraper.cfg.CollectionInterval()
+			}
+
+			ticker := time.NewTicker(collectionInterval)
+			defer ticker.Stop()
+
+			for {
+				select {
+				case <-ticker.C:
+					mr.scrapeAndReport(context.Background(), scraper)
+				case <-mr.done:
+					return
+				}
+			}
+		}()
+	}
+}
+
+// scrapeAndReport calls the Scrape function of the provided Scraper, records
+// observability information, and passes the scraped metrics to the next component.
+func (mr *metricsReceiver) scrapeAndReport(ctx context.Context, scraper *scraper) {
+	// TODO: Add observability metrics support
+	metrics, err := scraper.scrape(ctx)
+	if err != nil {
+		return
+	}
+
+	mr.nextConsumer.ConsumeMetrics(ctx, metrics)
+}
+
+// stopScraping stops the ticker
+func (mr *metricsReceiver) stopScraping() {
+	close(mr.done)
+}
+
+// closeScrapers closes all the scrapers
+func (mr *metricsReceiver) closeScrapers(ctx context.Context) error {
+	var errors []error
+
+	for _, scraper := range mr.scrapers {
+		if scraper.close == nil {
+			continue
+		}
+
+		if err := scraper.close(ctx); err != nil {
+			errors = append(errors, err)
+		}
+	}
+
+	return componenterror.CombineErrors(errors)
+}