otel.go

package main

import (
	"context"
	"errors"
	"fmt"
	"time"

	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp"
	"go.opentelemetry.io/otel/exporters/stdout/stdoutmetric"
	"go.opentelemetry.io/otel/exporters/stdout/stdouttrace"
	"go.opentelemetry.io/otel/propagation"
	"go.opentelemetry.io/otel/sdk/metric"
	"go.opentelemetry.io/otel/sdk/trace"
)

// 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 createOtelExporter(exporterType string) (trace.SpanExporter, error) {
	var exporter trace.SpanExporter
	var err error
	switch exporterType {
	case "otlp":
		var opts []otlptracehttp.Option
		/*
		 * We're not using https, but if we were, could switch on it here
		 *	if !withSecure() {
		 *	  opts = []otlptracehttp.Option{otlptracehttp.WithInsecure()}
		 *	}
		 */
		exporter, err = otlptrace.New(
			context.Background(),
			otlptracehttp.NewClient(opts...),
		)
	case "stdout":
		exporter, err = stdouttrace.New(stdouttrace.WithPrettyPrint())
	default:
		return nil, fmt.Errorf("unrecognized exporter type %s", exporterType)
	}
	return exporter, err
}

func newTraceProvider() (*trace.TracerProvider, error) {
	// Swap this to "stdout" to get traces written to console
	traceExporter, err := createOtelExporter("otlp")
	if err != nil {
		return nil, err
	}

	traceProvider := trace.NewTracerProvider(
		trace.WithBatcher(traceExporter,
			// Default is 5s. Set to 1s for demonstrative purposes.
			trace.WithBatchTimeout(time.Second)),
	)
	return traceProvider, nil
}

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

	meterProvider := metric.NewMeterProvider(
		metric.WithReader(metric.NewPeriodicReader(metricExporter,
			// Default is 1m. Set to 3s for demonstrative purposes.
			metric.WithInterval(3*time.Second))),
	)
	return meterProvider, nil
}