go-net-dhcp — a small, dependency-free DHCPv4 server library in pure Go, no cgo

go-net-dhcp is a pure-Go (no cgo) DHCPv4 server library. It implements the RFC 2131 / 2132 wire format (Parse a DISCOVER/REQUEST, BuildReply an OFFER / ACK / NAK), a stateless platform-agnostic decision core (Decide), and a real Linux UDP/67 server bound to a single kernel interface via SO_BINDTODEVICE. It targets the "one subnet, hand out a lease per known MAC" case — a host that owns a bridge / VLAN and needs to answer DHCP for the guests it spawns on it, without running an external dnsmasq. You supply a Source that resolves a client MAC into a Lease; the library never persists anything itself. The wire codec is hand-rolled, so the core module has zero third-party dependencies; the optional Prometheus adapter lives in its own sub-package.

Wire codec ready

RFC 2131 / 2132 parse + build — Parse decodes a DISCOVER/REQUEST (BOOTP header + magic cookie + TLV options), BuildReply emits an OFFER / ACK / NAK. Strict on framing, tolerant of unknown option codes, hand-rolled so the core has zero third-party dependencies.

Decision core ready

Decide(pkt, opts) runs the stateless state machine — DISCOVER→OFFER, REQUEST→ACK, mismatched requested-IP→NAK, unknown MAC / other message types→drop. Build-tag-free and portable, so it is unit-tested on every platform without a socket.

Linux UDP/67 server ready

LinuxServer binds UDP/67 to one kernel interface via SO_BINDTODEVICE + SO_BROADCAST + SO_REUSEADDR and replies by broadcast. The socket path is covered without root through injectable syscall seams, so every error branch runs in CI.

Cross-platform surface ready

A build stub on non-Linux plus a socket-free StubServer that drives the Source → Lease pipeline. Callers compile and test the integration surface on darwin / windows / *bsd; the real bind only ships on Linux.

Optional metrics ready

Pass any Metrics implementation in Options; a nil sink discards everything. A ready-made Prometheus adapter (dhcpv4_packets_total{outcome} + dhcpv4_handle_duration_seconds) lives in the prom sub-package so the core library keeps no Prometheus dependency.

Coverage & 6 arches ready

100% test coverage including error branches (socket paths via syscall seams, no root), gofmt + go vet clean, green across all six 64-bit Go arches (amd64, arm64, riscv64, loong64, ppc64le, s390x).

ready capability complete (exit criteria met, nothing material left)
active in progress (substantial work shipped, not yet finished)
planned not started yet (or downstream by design)

Pure Go, cgo disabled, so it cross-compiles and embeds anywhere. A hand-rolled RFC 2131 / 2132 wire codec keeps the core dependency-free; the socket path is covered without root via injectable syscall seams; metrics are optional and the Prometheus adapter is quarantined in the prom sub-package. Part of the github.com/go-net-dhcp organization.