Add a Conn type for sending and receiving DHCP packets.

dhcp/packet.go

@@ -83,6 +83,26 @@ type Packet struct {
 	Options Options
 }
 
+// TxType determines how the Packet should be sent on the wire, based
+// on its field values.
+//
+// This implements the transmission decision process in section 4.1 of
+// RFC 2131.
+func (p *Packet) TxType() TxType {
+	switch {
+	case p.RelayAddr != nil && p.RelayAddr.IsGlobalUnicast():
+		return TxRelayAddr
+	case p.Type == MsgNack:
+		return TxBroadcast
+	case p.ClientAddr != nil && p.ClientAddr.IsGlobalUnicast():
+		return TxClientAddr
+	case p.Broadcast:
+		return TxBroadcast
+	default:
+		return TxHardwareAddr
+	}
+}
+
 // DebugString prints the contents of a DHCP packet for human consumption.
 func (p *Packet) DebugString() string {
 	var b bytes.Buffer

dhcp/server.go

@@ -0,0 +1,54 @@
+// Copyright 2016 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package dhcp
+
+import "net"
+
+// TxType describes how a Packet should be sent on the wire.
+type TxType int
+
+// The various transmission strategies described in RFC 2131. "MUST",
+// "MUST NOT", "SHOULD" and "MAY" are as specified in RFC 2119.
+const (
+	// Packet MUST be broadcast.
+	TxBroadcast TxType = iota
+	// Packet MUST be unicasted to port 67 of RelayAddr
+	TxRelayAddr
+	// Packet MUST be unicasted to port 68 of ClientAddr
+	TxClientAddr
+	// Packet SHOULD be unicasted to port 68 of YourAddr, with the
+	// link-layer destination explicitly set to HardwareAddr. You MUST
+	// NOT rely on ARP resolution to discover the link-layer
+	// destination address.
+	//
+	// Conn implementations that cannot explicitly set the link-layer
+	// destination address MAY instead broadcast the packet.
+	TxHardwareAddr
+)
+
+// Conn is a DHCP-oriented packet socket.
+//
+// Multiple goroutines may invoke methods on a Conn simultaneously.
+type Conn interface {
+	// RecvDHCP reads a Packet from the connection. It returns the
+	// packet and the interface it was received on, which may be nil
+	// if interface information cannot be obtained.
+	RecvDHCP() (pkt *Packet, intf *net.Interface, err error)
+	// SendDHCP sends pkt. The precise transmission mechanism depends
+	// on pkt.TxType(). intf should be the net.Interface returned by
+	// RecvDHCP if responding to a DHCP client, or the interface for
+	// which configuration is desired if acting as a client.
+	SendDHCP(pkt *Packet, intf *net.Interface) error
+}