otel.go

package main

import (
	"context"
	"errors"

	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/exporters/prometheus"
	stdout "go.opentelemetry.io/otel/exporters/stdout/stdouttrace"
	"go.opentelemetry.io/otel/propagation"
	"go.opentelemetry.io/otel/sdk/metric"
	"go.opentelemetry.io/otel/sdk/resource"
	"go.opentelemetry.io/otel/sdk/trace"
	semconv "go.opentelemetry.io/otel/semconv/v1.4.0"
)

// setupOTelSDK bootstraps the OpenTelemetry pipeline.
// If it does not return an error, make sure to call shutdown for proper cleanup.
func setupOTelSDK(ctx context.Context) (shutdown func(context.Context) error, err error) {
	var shutdownFuncs []func(context.Context) error

	// shutdown calls cleanup functions registered via shutdownFuncs.
	// The errors from the calls are joined.
	// Each registered cleanup will be invoked once.
	shutdown = func(ctx context.Context) error {
		var err error
		for _, fn := range shutdownFuncs {
			err = errors.Join(err, fn(ctx))
		}
		shutdownFuncs = nil
		return err
	}

	// handleErr calls shutdown for cleanup and makes sure that all errors are returned.
	handleErr := func(inErr error) {
		err = errors.Join(inErr, shutdown(ctx))
	}

	// Set up propagator.
	prop := newPropagator()
	otel.SetTextMapPropagator(prop)

	// Set up trace provider.
	tracerProvider, err := newTraceProvider()
	if err != nil {
		handleErr(err)
		return
	}
	shutdownFuncs = append(shutdownFuncs, tracerProvider.Shutdown)
	otel.SetTracerProvider(tracerProvider)

	// Set up meter provider.
	meterProvider, err := newMeterProvider()
	if err != nil {
		handleErr(err)
		return
	}
	shutdownFuncs = append(shutdownFuncs, meterProvider.Shutdown)
	otel.SetMeterProvider(meterProvider)

	return
}

func newPropagator() propagation.TextMapPropagator {
	return propagation.NewCompositeTextMapPropagator(
		propagation.TraceContext{},
		propagation.Baggage{},
	)
}

func newTraceProvider() (*trace.TracerProvider, error) {
	// exporter, err := otlptracehttp.New(context.Background())
	exporter, err := stdout.New(stdout.WithPrettyPrint())
	if err != nil {
		panic(err)
	}

	tp := trace.NewTracerProvider(
		trace.WithSampler(trace.AlwaysSample()),
		trace.WithResource(resource.NewWithAttributes(semconv.SchemaURL,
			semconv.ServiceNameKey.String("services"),
		)),
		trace.WithBatcher(exporter),
	)
	return tp, nil
}

func newMeterProvider() (*metric.MeterProvider, error) {
	metricExporter, err := prometheus.New()
	if err != nil {
		return nil, err
	}

	meterProvider := metric.NewMeterProvider(metric.WithReader(metricExporter))
	return meterProvider, nil
}