main.go

package main

import (
	"context"
	"fmt"
	"log"
	"net/http"

	"github.com/gorilla/mux"

	"github.com/uptrace/opentelemetry-go-extra/otelgorm"
	"go.opentelemetry.io/contrib/instrumentation/github.com/gorilla/mux/otelmux"
	"go.opentelemetry.io/otel"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace"
	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
	"go.opentelemetry.io/otel/propagation"
	sdktrace "go.opentelemetry.io/otel/sdk/trace"
	oteltrace "go.opentelemetry.io/otel/trace"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
)

var tracer = otel.Tracer("mux-server")
var db *gorm.DB

type User struct {
	ID   int64
	Name string
	Age  int
}

func main() {
	tp := initTracer()
	defer func() {
		if err := tp.Shutdown(context.Background()); err != nil {
			log.Printf("Error shutting down tracer provider: %v", err)
		}
	}()

	initDB()

	r := mux.NewRouter()
	r.Use(otelmux.Middleware("my-server"))
	r.HandleFunc("/users/{id:[0-9]+}", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		vars := mux.Vars(r)
		id := vars["id"]
		name := getUser(r.Context(), id)
		reply := fmt.Sprintf("user %s (id %s)\n", name, id)
		_, _ = w.Write(([]byte)(reply))
	}))
	http.Handle("/", r)

	_ = http.ListenAndServe(":8080", nil)
}

func initTracer() *sdktrace.TracerProvider {
	exporter, err := otlptrace.New(
		context.Background(),
		otlptracegrpc.NewClient(
			otlptracegrpc.WithEndpoint("otlp.nr-data.net:4317"),
			otlptracegrpc.WithHeaders(map[string]string{"api-key": "233dee83a558dd07fa7223cd167fa3b9aef4NRAL"}),
		))
	if err != nil {
		log.Fatal(err)
	}
	tp := sdktrace.NewTracerProvider(
		sdktrace.WithSampler(sdktrace.AlwaysSample()),
		sdktrace.WithBatcher(exporter),
	)
	otel.SetTracerProvider(tp)
	otel.SetTextMapPropagator(propagation.NewCompositeTextMapPropagator(propagation.TraceContext{}, propagation.Baggage{}))
	return tp
}

func initDB() {
	dsn := "root:toor@tcp(127.0.0.1:3306)/foo?charset=utf8mb4&parseTime=True&loc=Local"
	var err error
	db, err = gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		panic("failed to connect database")
	}

	if err := db.Use(otelgorm.NewPlugin()); err != nil {
		panic(err)
	}
}

func getUser(ctx context.Context, id string) string {
	_, span := tracer.Start(ctx, "getUser", oteltrace.WithAttributes(attribute.String("id", id)))
	defer span.End()

	if id == "123" {
		return "otelmux tester"
	}

	user := User{}
	if err := db.WithContext(ctx).Table("tb_users").Where("id = ?", id).First(&user).Error; err != nil {
		return err.Error()
	}
	return fmt.Sprintf("%#v", user)
}