ModifyResponse modify response body in cb before returning to client, can filter url through urls parameter, does not filter if urls is nil.

NewMetric associates prometheus.Collector based on Metric.Type.

NewPrometheus generates a new set of metrics with a certain subsystem name.

Metric is a definition for the name, description, type, ID, and prometheus.Collector type (i.e.

Prometheus contains the metrics gathered by the instance and its path.

PrometheusPushGateway contains the configuration for pushing to a Prometheus pushgateway (optional).

RequestCounterURLLabelMappingFn is a function which can be supplied to the middleware to control the cardinality of the request counter's "url" label, which might be required in some contexts.