First implementation of DHCP server, compiles but not tested yet.

dhcpd/filter_conn.go

@@ -0,0 +1,62 @@
+package dhcpd
+
+import (
+	"net"
+
+	"github.com/joomcode/errorx"
+	"golang.org/x/net/ipv4"
+)
+
+// TODO: on windows, controlmessage does not work, try to find out another way
+// https://github.com/golang/net/blob/master/ipv4/payload.go#L13
+
+type filterConn struct {
+	iface net.Interface
+	conn  *ipv4.PacketConn
+	// cm    *ipv4.ControlMessage
+}
+
+func newFilterConn(iface net.Interface, address string) (*filterConn, error) {
+	c, err := net.ListenPacket("udp4", address)
+	if err != nil {
+		return nil, errorx.Decorate(err, "Couldn't listen to %s on UDP4", address)
+	}
+
+	p := ipv4.NewPacketConn(c)
+	err = p.SetControlMessage(ipv4.FlagInterface, true)
+	if err != nil {
+		c.Close()
+		return nil, errorx.Decorate(err, "Couldn't set control message FlagInterface on connection")
+	}
+
+	return &filterConn{iface: iface, conn: p}, nil
+}
+
+func (f *filterConn) ReadFrom(b []byte) (int, net.Addr, error) {
+	for { // read until we find a suitable packet
+		n, cm, addr, err := f.conn.ReadFrom(b)
+		if err != nil {
+			return 0, addr, errorx.Decorate(err, "Error when reading from socket")
+		}
+		if cm == nil {
+			// no controlmessage was passed, so pass the packet to the caller
+			return n, addr, nil
+		}
+		if cm.IfIndex == f.iface.Index {
+			return n, addr, nil
+		}
+		// packet doesn't match criteria, drop it
+	}
+	return 0, nil, nil
+}
+
+func (f *filterConn) WriteTo(b []byte, addr net.Addr) (int, error) {
+	cm := ipv4.ControlMessage{
+		IfIndex: f.iface.Index,
+	}
+	return f.conn.WriteTo(b, &cm, addr)
+}
+
+func (f *filterConn) Close() error {
+	return f.conn.Close()
+}