[receiver/prometheus] feat: implement Prometheus API

extension/prometheusapiserverextension/Makefile

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+include ../../Makefile.Common

extension/prometheusapiserverextension/README.md

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+# Prometheus API Server Extension
+
+This extension runs as a Web server that loads the remote observers that are registered against it.
+
+No configuration settings are within the extension itself, but settings to enable in a Prometheus receiver component are necessary in order to have data for the API server.
+
+Example:
+```yaml
+extensions:
+  prometheus_api_server:
+```
+
+The full list of settings exposed for this exporter are documented [here](./config.go).

extension/prometheusapiserverextension/config.go

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+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package prometheusapiserverextension // import "github.com/open-telemetry/opentelemetry-collector-contrib/extension/prometheusapiserverextension"
+
+type Config struct{}

extension/prometheusapiserverextension/doc.go

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+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+//go:generate mdatagen metadata.yaml
+
+// Package prometheusuiextension implements an extension that exposes the Prometheus UI for the prometheus receiver.
+package prometheusapiserverextension // import "github.com/open-telemetry/opentelemetry-collector-contrib/extension/prometheusapiserverextension"

extension/prometheusapiserverextension/extension.go

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+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package prometheusapiserverextension // import "github.com/open-telemetry/opentelemetry-collector-contrib/extension/prometheusapiserverextension"
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"net/url"
+	"os"
+	"runtime"
+	"runtime/debug"
+	"time"
+
+	"github.com/go-kit/kit/log"
+	"github.com/go-kit/log/level"
+	"github.com/mwitkow/go-conntrack"
+	"golang.org/x/net/netutil"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"github.com/prometheus/common/route"
+	toolkit_web "github.com/prometheus/exporter-toolkit/web"
+	"github.com/prometheus/prometheus/config"
+	"github.com/prometheus/prometheus/scrape"
+	"github.com/prometheus/prometheus/storage"
+	"github.com/prometheus/prometheus/util/httputil"
+	"github.com/prometheus/prometheus/web"
+	api_v1 "github.com/prometheus/prometheus/web/api/v1"
+	"go.opentelemetry.io/collector/component"
+	"go.opentelemetry.io/collector/config/confighttp"
+	"go.opentelemetry.io/collector/extension"
+	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
+)
+
+type prometheusAPIServerExtension struct {
+	config              *Config
+	host								component.Host
+	settings            extension.CreateSettings
+	ctx                 context.Context
+	httpServer          *http.Server
+	prometheusReceivers map[string]*prometheusReceiver
+}
+
+type prometheusReceiver struct {
+	name             string
+	serverConfig      confighttp.ServerConfig
+	prometheusConfig *config.Config
+	scrapeManager    *scrape.Manager
+	registerer       prometheus.Registerer
+}
+
+// Use same settings as Prometheus web server
+const (
+	maxConnections     = 512
+	readTimeoutMinutes = 10
+)
+
+func (e *prometheusAPIServerExtension) Start(_ context.Context, host component.Host) error {
+	e.ctx = context.Background()
+	e.host = host
+
+	return nil
+}
+
+func (e *prometheusAPIServerExtension) RegisterPrometheusReceiverComponents(receiverName string, serverConfig confighttp.ServerConfig,
+	prometheusConfig *config.Config, scrapeManager *scrape.Manager, registerer prometheus.Registerer) error {
+
+	prometheusReceiver := &prometheusReceiver{
+		name:             receiverName,
+		serverConfig:     serverConfig,
+		prometheusConfig: prometheusConfig,
+		scrapeManager:    scrapeManager,
+		registerer:       registerer,
+	}
+	e.prometheusReceivers[receiverName] = prometheusReceiver
+
+	o := &web.Options{
+		ScrapeManager: prometheusReceiver.scrapeManager,
+		Context:       e.ctx,
+		ListenAddress: serverConfig.Endpoint,
+		ExternalURL: &url.URL{
+			Scheme: "http",
+			Host:   serverConfig.Endpoint,
+			Path:   "",
+		},
+		RoutePrefix: "/",
+		ReadTimeout: time.Minute * readTimeoutMinutes,
+		PageTitle:   "Prometheus Receiver",
+		Flags:          make(map[string]string),
+		MaxConnections: maxConnections,
+		IsAgent:        true,
+		Gatherer:       prometheus.DefaultGatherer,
+		Registerer:     prometheusReceiver.registerer,
+	}
+
+	// Creates the API object in the same way as the Prometheus web package: https://github.com/prometheus/prometheus/blob/6150e1ca0ede508e56414363cc9062ef522db518/web/web.go#L314-L354
+	// Anything not defined by the options above will be nil, such as o.QueryEngine, o.Storage, etc. IsAgent=true, so these being nil is expected by Prometheus.
+	factorySPr := func(_ context.Context) api_v1.ScrapePoolsRetriever { return prometheusReceiver.scrapeManager }
+	factoryTr := func(_ context.Context) api_v1.TargetRetriever { return prometheusReceiver.scrapeManager }
+	factoryAr := func(_ context.Context) api_v1.AlertmanagerRetriever { return nil }
+	FactoryRr := func(_ context.Context) api_v1.RulesRetriever { return nil }
+	var app storage.Appendable
+	logger := log.NewNopLogger()
+
+	apiV1 := api_v1.NewAPI(o.QueryEngine, o.Storage, app, o.ExemplarStorage, factorySPr, factoryTr, factoryAr,
+		func() config.Config {
+			return *prometheusReceiver.prometheusConfig
+		},
+		o.Flags,
+		api_v1.GlobalURLOptions{
+			ListenAddress: o.ListenAddress,
+			Host:          o.ExternalURL.Host,
+			Scheme:        o.ExternalURL.Scheme,
+		},
+		func(f http.HandlerFunc) http.HandlerFunc {
+			return func(w http.ResponseWriter, r *http.Request) {
+				f(w, r)
+			}
+		},
+		o.LocalStorage,
+		o.TSDBDir,
+		o.EnableAdminAPI,
+		logger,
+		FactoryRr,
+		o.RemoteReadSampleLimit,
+		o.RemoteReadConcurrencyLimit,
+		o.RemoteReadBytesInFrame,
+		o.IsAgent,
+		o.CORSOrigin,
+		func() (api_v1.RuntimeInfo, error) {
+			status := api_v1.RuntimeInfo{
+				GoroutineCount: runtime.NumGoroutine(),
+				GOMAXPROCS:     runtime.GOMAXPROCS(0),
+				GOMEMLIMIT:     debug.SetMemoryLimit(-1),
+				GOGC:           os.Getenv("GOGC"),
+				GODEBUG:        os.Getenv("GODEBUG"),
+			}
+
+			return status, nil
+		},
+		nil,
+		o.Gatherer,
+		o.Registerer,
+		nil,
+		o.EnableRemoteWriteReceiver,
+		o.EnableOTLPWriteReceiver,
+	)
+
+	// Create listener and monitor with conntrack in the same way as the Prometheus web package: https://github.com/prometheus/prometheus/blob/6150e1ca0ede508e56414363cc9062ef522db518/web/web.go#L564-L579
+	listener, err := serverConfig.ToListener(e.ctx)
+	if err != nil {
+		return fmt.Errorf("failed to create listener: %s", err.Error())
+	}
+	listener = netutil.LimitListener(listener, o.MaxConnections)
+	listener = conntrack.NewListener(listener,
+		conntrack.TrackWithName("http"),
+		conntrack.TrackWithTracing())
+
+	// Run the API server in the same way as the Prometheus web package: https://github.com/prometheus/prometheus/blob/6150e1ca0ede508e56414363cc9062ef522db518/web/web.go#L582-L630
+	mux := http.NewServeMux()
+	promHandler := promhttp.HandlerFor(o.Gatherer, promhttp.HandlerOpts{Registry: o.Registerer})
+	mux.Handle("/metrics", promHandler)
+
+	// This is the path the web package uses, but the router above with no prefix can also be Registered by apiV1 instead.
+	apiPath := "/api"
+	if o.RoutePrefix != "/" {
+		apiPath = o.RoutePrefix + apiPath
+		level.Info(logger).Log("msg", "Router prefix", "prefix", o.RoutePrefix)
+	}
+	av1 := route.New().
+		WithInstrumentation(setPathWithPrefix(apiPath + "/v1"))
+	apiV1.Register(av1)
+	mux.Handle(apiPath+"/v1/", http.StripPrefix(apiPath+"/v1", av1))
+
+	spanNameFormatter := otelhttp.WithSpanNameFormatter(func(_ string, r *http.Request) string {
+		return fmt.Sprintf("%s %s", r.Method, r.URL.Path)
+	})
+	e.httpServer, err = serverConfig.ToServer(e.ctx, e.host, e.settings.TelemetrySettings, otelhttp.NewHandler(mux, "", spanNameFormatter))
+	if err != nil {
+		return err
+	}
+	webconfig := ""
+
+	go func() {
+		toolkit_web.Serve(listener, e.httpServer, &toolkit_web.FlagConfig{WebConfigFile: &webconfig}, logger)
+	}()
+
+	return nil
+}
+
+func (e *prometheusAPIServerExtension) UpdatePrometheusConfig(receiverName string, prometheusConfig *config.Config) {
+	e.prometheusReceivers[receiverName].prometheusConfig = prometheusConfig
+}
+
+func (e *prometheusAPIServerExtension) Shutdown(ctx context.Context) error {
+	e.httpServer.Shutdown(ctx)
+
+	return nil
+}
+
+func setPathWithPrefix(prefix string) func(handlerName string, handler http.HandlerFunc) http.HandlerFunc {
+	return func(handlerName string, handler http.HandlerFunc) http.HandlerFunc {
+		return func(w http.ResponseWriter, r *http.Request) {
+			handler(w, r.WithContext(httputil.ContextWithPath(r.Context(), prefix+r.URL.Path)))
+		}
+	}
+}