dhcp: tighten up the exported interface by removing some cruft.

Notably, some of the helpers for implementing Conns are internal now.

dhcp/conn.go

@@ -16,6 +16,7 @@ package dhcp
 
 import (
 	"errors"
+	"io"
 	"net"
 	"time"
 
@@ -23,10 +24,55 @@ import (
 )
 
 // defined as a var so tests can override it.
-var dhcpClientPort = 68
+var (
+	dhcpClientPort = 68
+	platformConn   func(string) (Conn, error)
+)
 
-var platformConn func(string) (Conn, error)
+// 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 {
+	io.Closer
+	// 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
+	// SetReadDeadline sets the deadline for future Read calls.
+	// If the deadline is reached, Read will fail with a timeout
+	// (see type Error) instead of blocking.
+	// A zero value for t means Read will not time out.
+	SetReadDeadline(t time.Time) error
+}
+
+// NewConn creates a Conn bound to the given UDP ip:port.
 func NewConn(addr string) (Conn, error) {
 	if platformConn != nil {
 		c, err := platformConn(addr)
@@ -90,8 +136,8 @@ func (c *portableConn) SendDHCP(pkt *Packet, intf *net.Interface) error {
 		return err
 	}
 
-	switch pkt.TxType() {
+	switch pkt.txType() {
-	case TxBroadcast, TxHardwareAddr:
+	case txBroadcast, txHardwareAddr:
 		cm := ipv4.ControlMessage{
 			IfIndex: intf.Index,
 		}
@@ -101,7 +147,7 @@ func (c *portableConn) SendDHCP(pkt *Packet, intf *net.Interface) error {
 		}
 		_, err = c.conn.WriteTo(b, &cm, &addr)
 		return err
-	case TxRelayAddr:
+	case txRelayAddr:
 		// Send to the server port, not the client port.
 		addr := net.UDPAddr{
 			IP:   pkt.RelayAddr,
@@ -109,7 +155,7 @@ func (c *portableConn) SendDHCP(pkt *Packet, intf *net.Interface) error {
 		}
 		_, err = c.conn.WriteTo(b, nil, &addr)
 		return err
-	case TxClientAddr:
+	case txClientAddr:
 		addr := net.UDPAddr{
 			IP:   pkt.ClientAddr,
 			Port: dhcpClientPort,

dhcp/conn_linux.go

@@ -153,19 +153,19 @@ func (c *linuxConn) SendDHCP(pkt *Packet, intf *net.Interface) error {
 		Protocol: 17,
 	}
 
-	switch pkt.TxType() {
+	switch pkt.txType() {
-	case TxBroadcast, TxHardwareAddr:
+	case txBroadcast, txHardwareAddr:
 		hdr.Dst = net.IPv4bcast
 		cm := ipv4.ControlMessage{
 			IfIndex: intf.Index,
 		}
 		return c.conn.WriteTo(&hdr, raw, &cm)
-	case TxRelayAddr:
+	case txRelayAddr:
 		// Send to the server port, not the client port.
 		binary.BigEndian.PutUint16(raw[2:4], 67)
 		hdr.Dst = pkt.RelayAddr
 		return c.conn.WriteTo(&hdr, raw, nil)
-	case TxClientAddr:
+	case txClientAddr:
 		hdr.Dst = pkt.ClientAddr
 		return c.conn.WriteTo(&hdr, raw, nil)
 	default:

dhcp/options.go

@@ -68,22 +68,15 @@ func (o Options) Unmarshal(bs []byte) error {
 // Marshal returns the wire encoding of o.
 func (o Options) Marshal() ([]byte, error) {
 	var ret bytes.Buffer
-	if err := o.MarshalTo(&ret); err != nil {
+	opts, err := o.marshalLimited(&ret, 0, false)
+	if err != nil {
 		return nil, err
 	}
-	return ret.Bytes(), nil
-}
-
-// MarshalTo serializes o into w.
-func (o Options) MarshalTo(w io.Writer) error {
-	opts, err := o.marshalLimited(w, 0, false)
-	if err != nil {
-		return err
-	}
 	if len(opts) > 0 {
-		return errors.New("some options not written, but no limit was given (please file a bug)")
+		return nil, errors.New("some options not written, but no limit was given (please file a bug)")
 	}
-	return nil
+
+	return ret.Bytes(), nil
 }
 
 // Copy returns a shallow copy of o.

dhcp/packet.go

@@ -12,7 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// Package dhcp implements parsing and serialization of DHCP packets.
 package dhcp
 
 import (
@@ -83,23 +82,22 @@ type Packet struct {
 	Options Options
 }
 
-// TxType determines how the Packet should be sent on the wire, based
+// decides how to send Packet on the wire, based on its field values.
-// on its field values.
 //
 // This implements the transmission decision process in section 4.1 of
 // RFC 2131.
-func (p *Packet) TxType() TxType {
+func (p *Packet) txType() txType {
 	switch {
 	case p.RelayAddr != nil && p.RelayAddr.IsGlobalUnicast():
-		return TxRelayAddr
+		return txRelayAddr
 	case p.Type == MsgNack:
-		return TxBroadcast
+		return txBroadcast
 	case p.ClientAddr != nil && (p.ClientAddr.IsGlobalUnicast() || p.ClientAddr.IsLoopback()):
-		return TxClientAddr
+		return txClientAddr
 	case p.Broadcast:
-		return TxBroadcast
+		return txBroadcast
 	default:
-		return TxHardwareAddr
+		return txHardwareAddr
 	}
 }
 
@@ -227,9 +225,13 @@ func (p *Packet) Marshal() ([]byte, error) {
 	}
 
 	ret.Write(magic)
-	if err := opts.MarshalTo(ret); err != nil {
+	leftover, err := opts.marshalLimited(ret, 0, false)
+	if err != nil {
 		return nil, err
 	}
+	if len(leftover) > 0 {
+		return nil, errors.New("some options not written, but no limit was given (please file a bug)")
+	}
 
 	return ret.Bytes(), nil
 }

dhcp/server.go

@@ -1,64 +0,0 @@
-// 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 "go.universe.tf/netboot/dhcp"
-
-import (
-	"io"
-	"net"
-	"time"
-)
-
-// 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 {
-	io.Closer
-	// 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
-	// SetReadDeadline sets the deadline for future Read calls.
-	// If the deadline is reached, Read will fail with a timeout
-	// (see type Error) instead of blocking.
-	// A zero value for t means Read will not time out.
-	SetReadDeadline(t time.Time) error
-}