dhcpd: imp code, docs

go.mod

@@ -12,6 +12,7 @@ require (
 	github.com/fsnotify/fsnotify v1.4.9
 	github.com/go-ping/ping v0.0.0-20210506233800-ff8be3320020
 	github.com/google/go-cmp v0.5.5
+	github.com/google/gopacket v1.1.19
 	github.com/google/renameio v1.0.1
 	github.com/insomniacslk/dhcp v0.0.0-20210310193751-cfd4d47082c2
 	github.com/kardianos/service v1.2.0

go.sum

@@ -93,6 +93,8 @@ github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
 github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/google/go-github v17.0.0+incompatible/go.mod h1:zLgOLi98H3fifZn+44m+umXrS52loVEgC2AApnigrVQ=
 github.com/google/go-querystring v1.0.0/go.mod h1:odCYkC5MyYFN7vkCjXpyrEuKhc/BUO6wN/zVPAxq5ck=
+github.com/google/gopacket v1.1.19 h1:ves8RnFZPGiFnTS0uPQStjwru6uO6h+nlr9j6fL7kF8=
+github.com/google/gopacket v1.1.19/go.mod h1:iJ8V8n6KS+z2U1A8pUwu8bW5SyEMkXJB8Yo/Vo+TKTo=
 github.com/google/martian v2.1.0+incompatible/go.mod h1:9I4somxYTbIHy5NJKHRl3wXiIaQGbYVAs8BPL6v8lEs=
 github.com/google/pprof v0.0.0-20181206194817-3ea8567a2e57/go.mod h1:zfwlbNMJ+OItoe0UupaVj+oy1omPYYDuagoSzA8v9mc=
 github.com/google/renameio v1.0.1 h1:Lh/jXZmvZxb0BBeSY5VKEfidcbcbenKjZFzM/q0fSeU=
@@ -268,6 +270,7 @@ golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL
 golang.org/x/lint v0.0.0-20180702182130-06c8688daad7/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
 golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
 golang.org/x/lint v0.0.0-20190227174305-5b3e6a55c961/go.mod h1:wehouNa3lNwaWXcvxsM5YxQ5yQlVC4a0KAMCusXpPoU=
+golang.org/x/lint v0.0.0-20200302205851-738671d3881b/go.mod h1:3xt1FjdF8hUf6vQPIChWIBhFzV8gjjsPE/fR3IyQdNY=
 golang.org/x/mod v0.1.1-0.20191105210325-c90efee705ee/go.mod h1:QqPTAvyqsEbceGzBzNggFXnrqF1CaUcvgkdR5Ot7KZg=
 golang.org/x/mod v0.4.2/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
@@ -377,6 +380,7 @@ golang.org/x/tools v0.0.0-20190328211700-ab21143f2384/go.mod h1:LCzVGOaR6xXOjkQ3
 golang.org/x/tools v0.0.0-20190425150028-36563e24a262/go.mod h1:RgjU9mgBXZiqYHBnxXauZ1Gv1EHHAz9KjViQ78xBX0Q=
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.0.0-20191216052735-49a3e744a425/go.mod h1:TB2adYChydJhpapKDTa4BR/hXlZSLoq2Wpct/0txZ28=
+golang.org/x/tools v0.0.0-20200130002326-2f3ba24bd6e7/go.mod h1:TB2adYChydJhpapKDTa4BR/hXlZSLoq2Wpct/0txZ28=
 golang.org/x/tools v0.1.1/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

internal/dhcpd/conn_unix.go

@@ -4,23 +4,24 @@
 package dhcpd
 
 import (
-	"encoding/binary"
 	"fmt"
 	"net"
 	"os"
 	"time"
 
 	"github.com/AdguardTeam/golibs/errors"
 	"github.com/AdguardTeam/golibs/netutil"
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
 	"github.com/insomniacslk/dhcp/dhcpv4"
 	"github.com/insomniacslk/dhcp/dhcpv4/server4"
 	"github.com/mdlayher/ethernet"
 	"github.com/mdlayher/raw"
 )
 
-// dhcpUcastAddr is the combination of MAC and IP addresses for responding to
+// dhcpUnicastAddr is the combination of MAC and IP addresses for responding to
 // the unconfigured host.
-type dhcpUcastAddr struct {
+type dhcpUnicastAddr struct {
 	// raw.Addr is embedded here to make *dhcpUcastAddr a net.Addr without
 	// actually implementing all methods.  It also contains the client's
 	// hardware address.
@@ -79,15 +80,16 @@ func (s *v4Server) newDHCPConn(ifi *net.Interface) (c net.PacketConn, err error)
 	}, nil
 }
 
-// wrapErrs is a helper to wrap the errors from two independent connections.
-func (c *dhcpConn) wrapErrs(action string, uerr, rerr error) (err error) {
+// wrapErrs is a helper to wrap the errors from two independent underlying
+// connections.
+func (c *dhcpConn) wrapErrs(action string, udpConnErr, rawConnErr error) (err error) {
 	switch {
-	case uerr != nil && rerr != nil:
-		return errors.List(fmt.Sprintf("%s both connections", action), uerr, rerr)
-	case uerr != nil:
-		return fmt.Errorf("%s udp connection: %w", action, uerr)
-	case rerr != nil:
-		return fmt.Errorf("%s raw connection: %w", action, rerr)
+	case udpConnErr != nil && rawConnErr != nil:
+		return errors.List(fmt.Sprintf("%s both connections", action), udpConnErr, rawConnErr)
+	case udpConnErr != nil:
+		return fmt.Errorf("%s udp connection: %w", action, udpConnErr)
+	case rawConnErr != nil:
+		return fmt.Errorf("%s raw connection: %w", action, rawConnErr)
 	default:
 		return nil
 	}
@@ -97,7 +99,7 @@ func (c *dhcpConn) wrapErrs(action string, uerr, rerr error) (err error) {
 // connection to write to based on the type of addr.
 func (c *dhcpConn) WriteTo(p []byte, addr net.Addr) (n int, err error) {
 	switch addr := addr.(type) {
-	case *dhcpUcastAddr:
+	case *dhcpUnicastAddr:
 		// Unicast the message to the client's MAC address.  Use the raw
 		// connection.
 		//
@@ -136,9 +138,9 @@ func (c *dhcpConn) ReadFrom(p []byte) (n int, addr net.Addr, err error) {
 }
 
 // unicast wraps respData with required frames and writes it to the peer.
-func (c *dhcpConn) unicast(respData []byte, peer *dhcpUcastAddr) (n int, err error) {
+func (c *dhcpConn) unicast(respData []byte, peer *dhcpUnicastAddr) (n int, err error) {
 	var data []byte
-	data, err = c.buildEtherPacket(respData, peer)
+	data, err = c.buildEtherPkt(respData, peer)
 	if err != nil {
 		return 0, err
 	}
@@ -185,199 +187,47 @@ func (c *dhcpConn) SetWriteDeadline(t time.Time) error {
 	)
 }
 
-// ipv4HdrVals describes the values of IPv4 packet's header as defined in
-// RFC-791 (https://datatracker.ietf.org/doc/html/rfc791#section-3.1).
-type ipv4HdrVals struct {
-	// src is the Source Address field of the header.
-	src net.IP
-
-	// dst is the Destination Address field of the header.
-	dst net.IP
-
-	// fragOffset is the Fragment Offset field of the header.
-	fragOffset uint16
-
-	// totalLen is the Total Length field of the header.
-	totalLen uint16
-
-	// id is the Identification field of the header.
-	id uint16
-
-	// ihl is the Internet Header Length field of the header.
-	ihl uint8
-
-	// tos is the Type of Service field of the header.
-	tos uint8
-
-	// flags is the Flags field of the header.
-	flags uint8
-
-	// ttl is the Time to Live field of the header.
-	ttl uint8
-
-	// proto is the Protocol field of the header.
-	proto uint8
-}
-
-// ipv4Hdr is used to encode the ipv4HdrVals into the underlying byte slice.
-type ipv4Hdr []byte
-
 const (
-	// ipv4Sz is the lowest size of an IPv4 packet.
-	ipv4Sz = 20
-
-	// ipv4FlagDontFrag is the value for flags to avoid rfragmentation of
-	// the packet.
-	//
-	// See https://datatracker.ietf.org/doc/html/rfc791#section-3.1.
-	ipv4FlagDontFrag = 1 << 1
-
-	// ipv4DefaultTTL is the Time to Live values as recommended by RFC-1700
-	// (https://datatracker.ietf.org/doc/html/rfc1700).
+	// ipv4DefaultTTL is the default Time to Live value as recommended by
+	// RFC-1700 (https://datatracker.ietf.org/doc/html/rfc1700) in seconds.
 	ipv4DefaultTTL = 64
 )
 
-// Indexes of IPv4 header's fields in bytes slice representation.
-const (
-	versIHL     = 0
-	tos         = 1
-	totalLen    = 2
-	id          = 4
-	flagsFO     = 6
-	ttl         = 8
-	protocol    = 9
-	checksumOff = 10
-	srcAddr     = 12
-	dstAddr     = 16
-)
-
-// encode writes all the data from i to b.
-func (b ipv4Hdr) encode(i ipv4HdrVals) {
-	b[versIHL] = (4 << 4) | ((i.ihl / 4) & 0xf)
-	b[tos] = i.tos
-	binary.BigEndian.PutUint16(b[totalLen:], i.totalLen)
-	binary.BigEndian.PutUint16(b[id:], i.id)
-	binary.BigEndian.PutUint16(b[flagsFO:], (uint16(i.flags)<<13)|(i.fragOffset>>3))
-	b[ttl] = i.ttl
-	b[protocol] = i.proto
-	copy(b[srcAddr:srcAddr+net.IPv4len], i.src)
-	copy(b[dstAddr:dstAddr+net.IPv4len], i.dst)
-
-	hl := (b[versIHL] & 0x0f) * 4
-	binary.BigEndian.PutUint16(b[checksumOff:], ^checksum(b[:hl], 0))
-}
-
-// udpHdrVals describes the values of UDP header as defined by RFC-768
-// (https://datatracker.ietf.org/doc/html/rfc768).
-type udpHdrVals struct {
-	// srcPort is the Source Port field of the header.
-	srcPort uint16
-
-	// dstPort is the Destination Port field of the header.
-	dstPort uint16
-
-	// length is the Length field of the header.
-	length uint16
-}
-
-// ipv4Hdr is used to encode the udpHdrVals into the underlying byte slice.
-type udpHdr []byte
-
-const (
-	// udpSz is the minimum size of a valid udp packet.
-	udpSz = 8
-
-	// udpProto is udp's transport protocol number.
-	udpProto = 17
-)
-
-// Indexes of UDP header's fields in bytes slice representation.
-const (
-	udpSrcPort  = 0
-	udpDstPort  = 2
-	udpLength   = 4
-	udpChecksum = 6
-)
-
-// encode writes all the data from u to b.
-func (b udpHdr) encode(u udpHdrVals, src, dst net.IP, proto uint8, payload []byte) {
-	binary.BigEndian.PutUint16(b[udpSrcPort:], u.srcPort)
-	binary.BigEndian.PutUint16(b[udpDstPort:], u.dstPort)
-	binary.BigEndian.PutUint16(b[udpLength:], u.length)
-
-	xsum := checksum([]byte(src), 0)
-	for _, buf := range [...][]byte{
-		[]byte(dst),
-		{0, proto},
-		payload,
-		b[udpLength : udpLength+2],
-		b[:udpSz],
-	} {
-		xsum = checksum(buf, xsum)
+func (c *dhcpConn) buildEtherPkt(payload []byte, peer *dhcpUnicastAddr) (pkt []byte, err error) {
+	dhcpPkt := gopacket.NewPacket(payload, layers.LayerTypeDHCPv4, gopacket.DecodeOptions{
+		NoCopy: true,
+	}).Layer(layers.LayerTypeDHCPv4)
+	dhcpLayer, ok := dhcpPkt.(gopacket.SerializableLayer)
+	if !ok {
+		return nil, fmt.Errorf("layer %s is not serializable", dhcpLayer.LayerType())
 	}
 
-	binary.BigEndian.PutUint16(b[udpChecksum:], ^xsum)
-}
-
-// checksum calculates the internet checksum as defined in RFC-1071
-// (https://datatracker.ietf.org/doc/html/rfc1071).
-//
-// The initial checksum must have been calculated on a byte slice of even
-// length.
-func checksum(buf []byte, initial uint16) (c uint16) {
-	v := uint32(initial)
-
-	l := len(buf)
-	if l%2 != 0 {
-		l--
-		v += uint32(buf[l]) << 8
+	udpLayer := &layers.UDP{
+		SrcPort: dhcpv4.ServerPort,
+		DstPort: dhcpv4.ClientPort,
 	}
-
-	for i := 0; i < l; i += 2 {
-		v += (uint32(buf[i]) << 8) + uint32(buf[i+1])
+	ipv4Layer := &layers.IPv4{
+		Version:  uint8(layers.IPProtocolIPv4),
+		Flags:    layers.IPv4DontFragment,
+		TTL:      ipv4DefaultTTL,
+		Protocol: layers.IPProtocolUDP,
+		SrcIP:    c.srcIP,
+		DstIP:    peer.yiaddr,
+	}
+	ethLayer := &layers.Ethernet{
+		SrcMAC:       c.srcMAC,
+		DstMAC:       peer.HardwareAddr,
+		EthernetType: layers.EthernetTypeIPv4,
 	}
 
-	v = uint32(uint16(v)) + uint32(uint16(v>>16))
-
-	return uint16(v + v>>16)
-}
-
-// buildEtherPacket wraps the payload with IPv4, UDP and Ethernet frames.
-func (c *dhcpConn) buildEtherPacket(payload []byte, peer *dhcpUcastAddr) (pkt []byte, err error) {
-	pkt = make([]byte, ipv4Sz+udpSz+len(payload))
-
-	// TODO(e.burkov):  Think about generalizing all the layers marshalling
-	// using interfaces.
-
-	ipLayer := ipv4Hdr(pkt[:ipv4Sz])
-	ipLayer.encode(ipv4HdrVals{
-		ihl:      ipv4Sz,
-		totalLen: uint16(ipv4Sz + udpSz + len(payload)),
-		flags:    ipv4FlagDontFrag,
-		ttl:      ipv4DefaultTTL,
-		proto:    udpProto,
-		src:      c.srcIP,
-		dst:      peer.yiaddr,
-	})
-
-	udpLayer := udpHdr(pkt[ipv4Sz : ipv4Sz+udpSz])
-	udpLayer.encode(udpHdrVals{
-		srcPort: dhcpv4.ServerPort,
-		dstPort: dhcpv4.ClientPort,
-		length:  uint16(udpSz + len(payload)),
-	}, c.srcIP, peer.yiaddr, ipLayer[protocol], payload)
-
-	copy(pkt[ipv4Sz+udpSz:], payload)
-
-	pkt, err = (&ethernet.Frame{
-		Destination: peer.HardwareAddr,
-		Source:      c.srcMAC,
-		EtherType:   ethernet.EtherTypeIPv4,
-		Payload:     pkt,
-	}).MarshalBinary()
+	buf := gopacket.NewSerializeBuffer()
+	err = gopacket.SerializeLayers(buf, gopacket.SerializeOptions{
+		FixLengths:       true,
+		ComputeChecksums: true,
+	}, ethLayer, ipv4Layer, udpLayer, dhcpLayer)
 	if err != nil {
-		return nil, fmt.Errorf("marshaling ethernet frame: %w", err)
+		return nil, fmt.Errorf("serializing layers: %w", err)
 	}
 
-	return pkt, nil
+	return buf.Bytes(), nil
 }

internal/dhcpd/conn_unix_test.go

@@ -46,11 +46,3 @@ func TestDHCPConn_WriteTo_common(t *testing.T) {
 		assert.Zero(t, n)
 	})
 }
-
-// TODO(e.burkov):  Cover network layers' encoders with tests:
-//
-//   ipv4Hdr.encode
-//   udpHdr.encode
-//   checksum
-//   dhcpConn.buildEtherPacket
-//

internal/dhcpd/v4.go

@@ -984,7 +984,7 @@ func (s *v4Server) send(peer net.Addr, conn net.PacketConn, req, resp *dhcpv4.DH
 	case !req.IsBroadcast() && req.ClientHWAddr != nil:
 		// Unicast DHCPOFFER and DHCPACK messages to the client's
 		// hardware address and yiaddr.
-		peer = &dhcpUcastAddr{
+		peer = &dhcpUnicastAddr{
 			Addr:   raw.Addr{HardwareAddr: req.ClientHWAddr},
 			yiaddr: resp.YourIPAddr,
 		}

internal/dhcpd/v4_test.go

@@ -440,7 +440,7 @@ func TestV4Server_Send(t *testing.T) {
 		name: "chaddr",
 		req:  &dhcpv4.DHCPv4{ClientHWAddr: knownMAC},
 		resp: &dhcpv4.DHCPv4{YourIPAddr: knownIP},
-		want: &dhcpUcastAddr{
+		want: &dhcpUnicastAddr{
 			Addr:   raw.Addr{HardwareAddr: knownMAC},
 			yiaddr: knownIP,
 		},