latexgrambot: inline LaTeX bot for Telegram in Go

Renders LaTeX expressions into PNG pictures, PDF documents and native
Telegram rich text messages, entirely locally with TeX Live and poppler.

- Chat mode with /image, /pdf, /rich plus per-user preamble and DPI
- Inline mode delivering picture, PDF and rich text results
- Broad default package set preloaded into a TeX format at image build
- MongoDB persistence: settings, users, groups, render statistics
- Private S3-compatible bucket with short-lived presigned URLs
- OpenTelemetry traces over OTLP
- Kubernetes manifests and Argo CD application, Docker Compose, GitHub
  Actions CI, BSD 3-Clause license

internal/telemetry/telemetry.go

@@ -0,0 +1,65 @@
+// Package telemetry wires the OpenTelemetry SDK to an OTLP collector
+// (OTEL_EXPORTER_OTLP_ENDPOINT). With no endpoint configured the global
+// tracer provider stays a no-op.
+package telemetry
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
+	"go.opentelemetry.io/otel/propagation"
+	"go.opentelemetry.io/otel/sdk/resource"
+	sdktrace "go.opentelemetry.io/otel/sdk/trace"
+)
+
+// Setup installs the global tracer provider backed by the OTLP collector.
+// The returned shutdown flushes pending spans; call it on process exit.
+func Setup(ctx context.Context) (shutdown func(context.Context) error, err error) {
+	endpoint := strings.TrimSpace(os.Getenv("OTEL_EXPORTER_OTLP_ENDPOINT"))
+	if endpoint == "" {
+		otel.SetTracerProvider(sdktrace.NewTracerProvider())
+		return func(context.Context) error { return nil }, nil
+	}
+	insecure, parseErr := strconv.ParseBool(getenv("OTEL_EXPORTER_OTLP_INSECURE", "true"))
+	if parseErr != nil {
+		return nil, fmt.Errorf("invalid OTEL_EXPORTER_OTLP_INSECURE: %w", parseErr)
+	}
+	options := []otlptracegrpc.Option{otlptracegrpc.WithEndpoint(endpoint)}
+	if insecure {
+		options = append(options, otlptracegrpc.WithInsecure())
+	}
+	exporter, err := otlptracegrpc.New(ctx, options...)
+	if err != nil {
+		return nil, fmt.Errorf("create OTLP exporter: %w", err)
+	}
+	res, err := resource.New(ctx,
+		resource.WithFromEnv(),
+		resource.WithAttributes(attribute.String("service.name", getenv("OTEL_SERVICE_NAME", "latexgrambot"))),
+	)
+	if err != nil {
+		return nil, fmt.Errorf("create resource: %w", err)
+	}
+	provider := sdktrace.NewTracerProvider(
+		sdktrace.WithBatcher(exporter),
+		sdktrace.WithResource(res),
+	)
+	otel.SetTracerProvider(provider)
+	otel.SetTextMapPropagator(propagation.NewCompositeTextMapPropagator(
+		propagation.TraceContext{},
+		propagation.Baggage{},
+	))
+	return provider.Shutdown, nil
+}
+
+func getenv(key, fallback string) string {
+	if value := strings.TrimSpace(os.Getenv(key)); value != "" {
+		return value
+	}
+	return fallback
+}