Method Write

prometheus/metric.go:180–222

(pb *dto.Metric)

}

func (m *withExemplarsMetric) Write(pb *dto.Metric) error {
	if err := m.Metric.Write(pb); err != nil {
		return err
	}

	switch {
	case pb.Counter != nil:
		pb.Counter.Exemplar = m.exemplars[len(m.exemplars)-1]
	case pb.Histogram != nil:
		h := pb.Histogram
		for _, e := range m.exemplars {
			if (h.GetZeroThreshold() != 0 || h.GetZeroCount() != 0 ||
				len(h.PositiveSpan) != 0 || len(h.NegativeSpan) != 0) &&
				e.GetTimestamp() != nil {
				h.Exemplars = append(h.Exemplars, e)
				if len(h.Bucket) == 0 {
					// Don't proceed to classic buckets if there are none.
					continue
				}
			}
			// h.Bucket are sorted by UpperBound.
			i := sort.Search(len(h.Bucket), func(i int) bool {
				return h.Bucket[i].GetUpperBound() >= e.GetValue()
			})
			if i < len(h.Bucket) {
				h.Bucket[i].Exemplar = e
			} else {
				// The +Inf bucket should be explicitly added if there is an exemplar for it, similar to non-const histogram logic in https://github.com/prometheus/client_golang/blob/main/prometheus/histogram.go#L357-L365.
				b := &dto.Bucket{
					CumulativeCount: proto.Uint64(h.GetSampleCount()),
					UpperBound:      proto.Float64(math.Inf(1)),
					Exemplar:        e,
				}
				h.Bucket = append(h.Bucket, b)
			}
		}
	default:
		// TODO(bwplotka): Implement Gauge?
		return errors.New("cannot inject exemplar into Gauge, Summary or Untyped")
	}

	return nil
}

// Exemplar is easier to use, user-facing representation of *dto.Exemplar.
type Exemplar struct {