basic UDP server bound to an interface

server/BUILD.bazel

@@ -0,0 +1,15 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "server",
+    srcs = [
+        "ifi.go",
+        "server.go",
+    ],
+    importpath = "git.wntrmute.dev/kyle/kdhcp/server",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//config",
+        "//log",
+    ],
+)

server/ifi.go

@@ -0,0 +1,39 @@
+package server
+
+import (
+	"net"
+	"syscall"
+)
+
+func BindInterface(ip net.IP, port int, dev string) (net.PacketConn, error) {
+	if port == 0 {
+		port = 67
+	}
+
+	udpAddr := &net.UDPAddr{
+		IP:   ip,
+		Port: port,
+	}
+
+	conn, err := net.ListenUDP("udp4", udpAddr)
+	if err != nil {
+		return nil, err
+	}
+
+	sysconn, err := conn.SyscallConn()
+	if err != nil {
+		conn.Close()
+		return nil, err
+	}
+
+	sysconn.Control(func(fd uintptr) {
+		err = syscall.BindToDevice(int(fd), dev)
+	})
+
+	if err != nil {
+		conn.Close()
+		return nil, err
+	}
+
+	return conn, nil
+}

server/server.go

@@ -0,0 +1,76 @@
+package server
+
+import (
+	"errors"
+	"net"
+
+	"git.wntrmute.dev/kyle/kdhcp/config"
+	"git.wntrmute.dev/kyle/kdhcp/log"
+)
+
+const (
+	MaxPacketSize = 512
+)
+
+type Server struct {
+	Conn   net.PacketConn
+	Config *config.Config
+}
+
+func (s *Server) Close() error {
+	return s.Conn.Close()
+}
+
+func (s *Server) Bind() (err error) {
+	s.Conn, err = BindInterface(s.Config.IP, s.Config.Port, s.Config.Interface)
+	return err
+}
+
+func (s *Server) ReadFrom() ([]byte, net.Addr, error) {
+	b := make([]byte, MaxPacketSize)
+	n, addr, err := s.Conn.ReadFrom(b)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	b = b[:n]
+	return b, addr, nil
+}
+
+func (s *Server) WriteTo(b []byte, addr net.Addr) error {
+	return errors.New("server: not implemented")
+}
+
+func (s *Server) AcceptPacket() error {
+	packet, addr, err := s.ReadFrom()
+	if err != nil {
+		return err
+	}
+
+	log.Debugf("accepted %d byte packet from %s", len(packet), addr)
+	return nil
+}
+
+func (s *Server) Listen() {
+	for {
+		if err := s.AcceptPacket(); err != nil {
+			log.Errf("server: error reading packet: %s", err)
+			continue
+		}
+	}
+}
+
+func New(cfg *config.Config) (*Server, error) {
+	srv := &Server{
+		Config: cfg,
+	}
+
+	err := srv.Bind()
+	if err != nil {
+		return nil, err
+	}
+
+	log.Infof("server: bound to %s:%s", cfg.Interface, srv.Conn.LocalAddr())
+
+	return srv, nil
+}