component/otelcol/processor: create processor component abstraction

This commit introduces a new package, component/otelcol/processor, which
exposes a generic Flow component implementation which can run
OpenTelemetry Collector processor.

Like grafana#2227 and grafana#2254, it leaves some work unfinished for future PRs:

* A Zap logging adapter needs to be created to correctly process logs
  from OpenTelemetry Collector components.
* Component-specific metrics are currently ignored.
* Component-specific traces are currently ignored.

As of this commit, there are no registered `otelcol.processor.*`
components. Implementations for OpenTelemetry Collector Flow components
will be done in future PRs.

Related to grafana#2213.

component/otelcol/processor/processor.go

@@ -0,0 +1,178 @@
+// Package processor exposes utilities to create a Flow component from
+// OpenTelemetry Collector processors.
+package processor
+
+import (
+	"context"
+	"errors"
+	"os"
+
+	"github.com/grafana/agent/component"
+	"github.com/grafana/agent/component/otelcol"
+	"github.com/grafana/agent/component/otelcol/internal/fanoutconsumer"
+	"github.com/grafana/agent/component/otelcol/internal/lazyconsumer"
+	"github.com/grafana/agent/component/otelcol/internal/scheduler"
+	"github.com/grafana/agent/pkg/build"
+	otelcomponent "go.opentelemetry.io/collector/component"
+	otelconfig "go.opentelemetry.io/collector/config"
+	"go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/trace"
+	"go.uber.org/zap"
+)
+
+// Arguments is an extension of component.Arguments which contains necessary
+// settings for OpenTelemetry Collector processors.
+type Arguments interface {
+	component.Arguments
+
+	// Convert converts the Arguments into an OpenTelemetry Collector processor
+	// configuration.
+	Convert() otelconfig.Processor
+
+	// Extensions returns the set of extensions that the configured component is
+	// allowed to use.
+	Extensions() map[otelconfig.ComponentID]otelcomponent.Extension
+
+	// Exporters returns the set of exporters that are exposed to the configured
+	// component.
+	Exporters() map[otelconfig.DataType]map[otelconfig.ComponentID]otelcomponent.Exporter
+
+	// NextConsumers returns the set of consumers to send data to.
+	NextConsumers() *otelcol.ConsumerArguments
+}
+
+// Processor is a Flow component shim which manages an OpenTelemetry Collector
+// processor component.
+type Processor struct {
+	ctx    context.Context
+	cancel context.CancelFunc
+
+	opts     component.Options
+	factory  otelcomponent.ProcessorFactory
+	consumer *lazyconsumer.Consumer
+
+	sched *scheduler.Scheduler
+}
+
+var (
+	_ component.Component       = (*Processor)(nil)
+	_ component.HealthComponent = (*Processor)(nil)
+)
+
+// New creates a new Flow component which encapsulates an OpenTelemetry
+// Collector processor. args must hold a value of the argument type registered
+// with the Flow component.
+//
+// The registered component must be registered to export the
+// otelcol.ConsumerExports type, otherwise New will panic.
+func New(opts component.Options, f otelcomponent.ProcessorFactory, args Arguments) (*Processor, error) {
+	ctx, cancel := context.WithCancel(context.Background())
+
+	consumer := lazyconsumer.New(ctx)
+
+	// Immediately set our state with our consumer. The exports will never change
+	// throughout the lifetime of our component.
+	//
+	// This will panic if the wrapping component is not registered to export
+	// otelcol.ConsumerExports.
+	opts.OnStateChange(otelcol.ConsumerExports{Input: consumer})
+
+	e := &Processor{
+		ctx:    ctx,
+		cancel: cancel,
+
+		opts:     opts,
+		factory:  f,
+		consumer: consumer,
+
+		sched: scheduler.New(opts.Logger),
+	}
+	if err := e.Update(args); err != nil {
+		return nil, err
+	}
+	return e, nil
+}
+
+// Run starts the Processor component.
+func (e *Processor) Run(ctx context.Context) error {
+	defer e.cancel()
+	return e.sched.Run(ctx)
+}
+
+// Update implements component.Component. It will convert the Arguments into
+// configuration for OpenTelemetry Collector processor configuration and manage
+// the underlying OpenTelemetry Collector processor.
+func (e *Processor) Update(args component.Arguments) error {
+	pargs := args.(Arguments)
+
+	host := scheduler.NewHost(
+		e.opts.Logger,
+		scheduler.WithHostExtensions(pargs.Extensions()),
+		scheduler.WithHostExporters(pargs.Exporters()),
+	)
+
+	settings := otelcomponent.ProcessorCreateSettings{
+		TelemetrySettings: otelcomponent.TelemetrySettings{
+			// TODO(rfratto): create an adapter from zap -> go-kit/log
+			Logger: zap.NewNop(),
+
+			// TODO(rfratto): expose tracing and logging statistics.
+			//
+			// We may want to put off tracing until we have native tracing
+			// instrumentation from Flow, but metrics should come sooner since we're
+			// already set up for supporting component-specific metrics.
+			TracerProvider: trace.NewNoopTracerProvider(),
+			MeterProvider:  metric.NewNoopMeterProvider(),
+		},
+
+		BuildInfo: otelcomponent.BuildInfo{
+			Command:     os.Args[0],
+			Description: "Grafana Agent",
+			Version:     build.Version,
+		},
+	}
+
+	exporterConfig := pargs.Convert()
+
+	var (
+		next        = pargs.NextConsumers()
+		nextTraces  = fanoutconsumer.Traces(next.Traces)
+		nextMetrics = fanoutconsumer.Metrics(next.Metrics)
+		nextLogs    = fanoutconsumer.Logs(next.Logs)
+	)
+
+	// Create instances of the exporter from our factory for each of our
+	// supported telemetry signals.
+	var components []otelcomponent.Component
+
+	tracesProcessor, err := e.factory.CreateTracesProcessor(e.ctx, settings, exporterConfig, nextTraces)
+	if err != nil && !errors.Is(err, otelcomponent.ErrDataTypeIsNotSupported) {
+		return err
+	} else if tracesProcessor != nil {
+		components = append(components, tracesProcessor)
+	}
+
+	metricsProcessor, err := e.factory.CreateMetricsProcessor(e.ctx, settings, exporterConfig, nextMetrics)
+	if err != nil && !errors.Is(err, otelcomponent.ErrDataTypeIsNotSupported) {
+		return err
+	} else if metricsProcessor != nil {
+		components = append(components, metricsProcessor)
+	}
+
+	logsProcessor, err := e.factory.CreateLogsProcessor(e.ctx, settings, exporterConfig, nextLogs)
+	if err != nil && !errors.Is(err, otelcomponent.ErrDataTypeIsNotSupported) {
+		return err
+	} else if logsProcessor != nil {
+		components = append(components, logsProcessor)
+	}
+
+	// Schedule the components to run once our component is running.
+	e.sched.Schedule(host, components...)
+	e.consumer.SetConsumers(tracesProcessor, metricsProcessor, logsProcessor)
+	return nil
+}
+
+// CurrentHealth implements component.HealthComponent.
+func (e *Processor) CurrentHealth() component.Health {
+	return e.sched.CurrentHealth()
+}

component/otelcol/processor/processor_test.go

@@ -0,0 +1,206 @@
+package processor_test
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	"github.com/grafana/agent/component"
+	"github.com/grafana/agent/component/otelcol"
+	"github.com/grafana/agent/component/otelcol/internal/fakeconsumer"
+	"github.com/grafana/agent/component/otelcol/processor"
+	"github.com/grafana/agent/pkg/flow/componenttest"
+	"github.com/grafana/agent/pkg/util"
+	"github.com/stretchr/testify/require"
+	otelcomponent "go.opentelemetry.io/collector/component"
+	otelconfig "go.opentelemetry.io/collector/config"
+	otelconsumer "go.opentelemetry.io/collector/consumer"
+	"go.opentelemetry.io/collector/pdata/ptrace"
+)
+
+func TestProcessor(t *testing.T) {
+	ctx := componenttest.TestContext(t)
+
+	// Create an instance of a fake OpenTelemetry Collector processor which our
+	// Flow component will wrap around. It is expected
+
+	var (
+		consumer otelconsumer.Traces
+
+		waitConsumerTrigger = util.NewWaitTrigger()
+		onTracesConsumer    = func(t otelconsumer.Traces) {
+			consumer = t
+			waitConsumerTrigger.Trigger()
+		}
+
+		waitTracesTrigger = util.NewWaitTrigger()
+		nextConsumer      = &fakeconsumer.Consumer{
+			ConsumeTracesFunc: func(context.Context, ptrace.Traces) error {
+				waitTracesTrigger.Trigger()
+				return nil
+			},
+		}
+
+		// Our fake processor will wait for a consumer to be registered and then
+		// pass along data directly to it.
+		innerProcessor = &fakeProcessor{
+			ConsumeTracesFunc: func(ctx context.Context, td ptrace.Traces) error {
+				require.NoError(t, waitConsumerTrigger.Wait(time.Second), "no next consumer registered")
+				return consumer.ConsumeTraces(ctx, td)
+			},
+		}
+	)
+
+	// Create and start our Flow component. We then wait for it to export a
+	// consumer that we can send data to.
+	te := newTestEnvironment(t, innerProcessor, onTracesConsumer)
+	te.Start(fakeProcessorArgs{
+		Output: &otelcol.ConsumerArguments{
+			Metrics: []otelcol.Consumer{nextConsumer},
+			Logs:    []otelcol.Consumer{nextConsumer},
+			Traces:  []otelcol.Consumer{nextConsumer},
+		},
+	})
+
+	require.NoError(t, te.Controller.WaitExports(1*time.Second), "test component did not generate exports")
+	ce := te.Controller.Exports().(otelcol.ConsumerExports)
+
+	// Create a test set of traces and send it to our consumer in the background.
+	// We then wait for our channel to receive the traces, indicating that
+	// everything was wired up correctly.
+	go func() {
+		var err error
+
+		for {
+			err = ce.Input.ConsumeTraces(ctx, ptrace.NewTraces())
+
+			if errors.Is(err, otelcomponent.ErrDataTypeIsNotSupported) {
+				// Our component may not have been fully initialized yet. Wait a little
+				// bit before trying again.
+				time.Sleep(100 * time.Millisecond)
+				continue
+			}
+
+			require.NoError(t, err)
+			break
+		}
+	}()
+
+	require.NoError(t, waitTracesTrigger.Wait(time.Second), "consumer did not get invoked")
+}
+
+type testEnvironment struct {
+	t *testing.T
+
+	Controller *componenttest.Controller
+}
+
+func newTestEnvironment(
+	t *testing.T,
+	fp otelcomponent.TracesProcessor,
+	onTracesConsumer func(t otelconsumer.Traces),
+) *testEnvironment {
+	t.Helper()
+
+	reg := component.Registration{
+		Name:    "testcomponent",
+		Args:    fakeProcessorArgs{},
+		Exports: otelcol.ConsumerExports{},
+		Build: func(opts component.Options, args component.Arguments) (component.Component, error) {
+			// Create a factory which always returns our instance of fakeExporter
+			// defined above.
+			factory := otelcomponent.NewProcessorFactory(
+				"testcomponent",
+				func() otelconfig.Processor {
+					return fakeProcessorArgs{}.Convert()
+				},
+				otelcomponent.WithTracesProcessor(func(
+					_ context.Context,
+					_ otelcomponent.ProcessorCreateSettings,
+					_ otelconfig.Processor,
+					t otelconsumer.Traces,
+				) (otelcomponent.TracesProcessor, error) {
+
+					onTracesConsumer(t)
+					return fp, nil
+				}, otelcomponent.StabilityLevelUndefined),
+			)
+
+			return processor.New(opts, factory, args.(processor.Arguments))
+		},
+	}
+
+	return &testEnvironment{
+		t:          t,
+		Controller: componenttest.NewControllerFromReg(util.TestLogger(t), reg),
+	}
+}
+
+func (te *testEnvironment) Start(args component.Arguments) {
+	go func() {
+		ctx := componenttest.TestContext(te.t)
+		err := te.Controller.Run(ctx, args)
+		require.NoError(te.t, err, "failed to run component")
+	}()
+}
+
+type fakeProcessorArgs struct {
+	Output *otelcol.ConsumerArguments
+}
+
+var _ processor.Arguments = fakeProcessorArgs{}
+
+func (fa fakeProcessorArgs) Convert() otelconfig.Processor {
+	settings := otelconfig.NewProcessorSettings(otelconfig.NewComponentID("testcomponent"))
+	return &settings
+}
+
+func (fa fakeProcessorArgs) Extensions() map[otelconfig.ComponentID]otelcomponent.Extension {
+	return nil
+}
+
+func (fa fakeProcessorArgs) Exporters() map[otelconfig.DataType]map[otelconfig.ComponentID]otelcomponent.Exporter {
+	return nil
+}
+
+func (fa fakeProcessorArgs) NextConsumers() *otelcol.ConsumerArguments {
+	return fa.Output
+}
+
+type fakeProcessor struct {
+	StartFunc         func(ctx context.Context, host otelcomponent.Host) error
+	ShutdownFunc      func(ctx context.Context) error
+	CapabilitiesFunc  func() otelconsumer.Capabilities
+	ConsumeTracesFunc func(ctx context.Context, td ptrace.Traces) error
+}
+
+var _ otelcomponent.TracesExporter = (*fakeProcessor)(nil)
+
+func (fe *fakeProcessor) Start(ctx context.Context, host otelcomponent.Host) error {
+	if fe.StartFunc != nil {
+		return fe.StartFunc(ctx, host)
+	}
+	return nil
+}
+
+func (fe *fakeProcessor) Shutdown(ctx context.Context) error {
+	if fe.ShutdownFunc != nil {
+		return fe.ShutdownFunc(ctx)
+	}
+	return nil
+}
+
+func (fe *fakeProcessor) Capabilities() otelconsumer.Capabilities {
+	if fe.CapabilitiesFunc != nil {
+		return fe.CapabilitiesFunc()
+	}
+	return otelconsumer.Capabilities{}
+}
+
+func (fe *fakeProcessor) ConsumeTraces(ctx context.Context, td ptrace.Traces) error {
+	if fe.ConsumeTracesFunc != nil {
+		return fe.ConsumeTracesFunc(ctx, td)
+	}
+	return nil
+}

component/otelcol/receiver/receiver.go

@@ -24,7 +24,7 @@ import (
 type Arguments interface {
 	component.Arguments
 
-	// Convert converts the Arguments into an OpenTelemetry Collector exporter
+	// Convert converts the Arguments into an OpenTelemetry Collector receiver
 	// configuration.
 	Convert() otelconfig.Receiver