Metrics

Metrics are an optional hook. The core library depends on nothing third-party; if you want Prometheus, you opt in via a separate sub-package.

The Metrics interface

type Metrics interface {
    RecordPacket(outcome string)         // one call per inbound packet
    RecordHandleDuration(seconds float64) // parse+decide+send latency
}

Pass any implementation as Options.Metrics. A nil value is replaced by a no-op sink, so metrics cost nothing until you ask for them. The outcome is one of the exported constants:

Constant	Value	Meaning
OutcomeOffer	offer	sent an OFFER
OutcomeAck	ack	sent an ACK
OutcomeNak	nak	sent a NAK
OutcomeDropParseErr	drop_parse_err	malformed wire packet
OutcomeDropUnknownMAC	drop_unknown_mac	Source.Resolve returned false
OutcomeDropDecideErr	drop_decide_err	lease validation / build failed
OutcomeDropUnsupported	drop_unsupported	message type we don't answer
OutcomeSendErr	send_err	wire-side write failed

The Prometheus adapter

import (
    "github.com/go-net-dhcp/dhcp"
    dhcpprom "github.com/go-net-dhcp/dhcp/prom"
    "github.com/prometheus/client_golang/prometheus"
)

m, err := dhcpprom.New(prometheus.DefaultRegisterer)
if err != nil {
    // a collector with the same name is already registered
}
opts.Metrics = m

prom.New registers two collectors (bounded cardinality — no per-MAC labels):

• dhcpv4_packets_total{outcome} — a counter, labelled by the outcomes above;
• dhcpv4_handle_duration_seconds — a histogram of per-packet latency.

Because this lives in github.com/go-net-dhcp/dhcp/prom, importing the core dhcp package never pulls in the Prometheus client. Bring your own Metrics implementation just as easily — the interface is two methods.