visitor := func(vpc *proxy.VisitPayloadsContext, payloads []*commonpb.Payload) ([]*commonpb.Payload, error) {
for _, p := range payloads {
for _, extPayload := range p.ExternalPayloads {
totalSize += extPayload.SizeBytes
metricsHandler.Histogram(metrics.ExternalPayloadUploadSize.Name(), metrics.Bytes).Record(int64(extPayload.SizeBytes))