http-handler.go

// general http handler
func httpHandler(w http.ResponseWriter, r *http.Request) {
	// get tracer provider from otel package and inject ctx to tracer
	tracer := otel.GetTracerProvider().Tracer("httpHandler")
	ctx, span := tracer.Start(r.Context(), "httpHandler")
	defer span.End()

	// create http client with transport for inject trace signal to http header automatically
	client := &http.Client{
		Transport: otelhttp.NewTransport(nil),
	}
	// create http request with context for inject trace signal to http header in request
	request, err := http.NewRequestWithContext(ctx, http.MethodGet, "http://echo:8081", nil)
	if err != nil {
		// if error should set status to span
		span.RecordError(err)
		span.SetStatus(codes.Error, codes.Error.String())

		// write response like general handler
		w.WriteHeader(http.StatusInternalServerError)
		w.Write([]byte("new request error"))

		return
	}

	// use client to call other service
	res, err := client.Do(request)
	if err != nil {
		// if error should set status to span
		span.RecordError(err)
		span.SetStatus(codes.Error, codes.Error.String())

		// write response like general handler
		w.WriteHeader(http.StatusInternalServerError)
		w.Write([]byte("http request error"))

		return
	}

	fmt.Println(res.Status)
	if res.StatusCode != http.StatusOK {
		// if error should set status to span
		span.RecordError(err)
		span.SetStatus(codes.Error, codes.Error.String())

		// write response like general handler
		bb, _ := io.ReadAll(res.Body)
		w.WriteHeader(http.StatusInternalServerError)
		w.Write(bb)

		return
	}

	w.Write([]byte("ok with tracing"))
}