--- /dev/null
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package ipv4 implements IP-level socket options for the Internet
+// Protocol version 4.
+//
+// The package provides IP-level socket options that allow
+// manipulation of IPv4 facilities.
+//
+// The IPv4 protocol and basic host requirements for IPv4 are defined
+// in RFC 791 and RFC 1122.
+// Host extensions for multicasting and socket interface extensions
+// for multicast source filters are defined in RFC 1112 and RFC 3678.
+// IGMPv1, IGMPv2 and IGMPv3 are defined in RFC 1112, RFC 2236 and RFC
+// 3376.
+// Source-specific multicast is defined in RFC 4607.
+//
+//
+// Unicasting
+//
+// The options for unicasting are available for net.TCPConn,
+// net.UDPConn and net.IPConn which are created as network connections
+// that use the IPv4 transport. When a single TCP connection carrying
+// a data flow of multiple packets needs to indicate the flow is
+// important, Conn is used to set the type-of-service field on the
+// IPv4 header for each packet.
+//
+// ln, err := net.Listen("tcp4", "0.0.0.0:1024")
+// if err != nil {
+// // error handling
+// }
+// defer ln.Close()
+// for {
+// c, err := ln.Accept()
+// if err != nil {
+// // error handling
+// }
+// go func(c net.Conn) {
+// defer c.Close()
+//
+// The outgoing packets will be labeled DiffServ assured forwarding
+// class 1 low drop precedence, known as AF11 packets.
+//
+// if err := ipv4.NewConn(c).SetTOS(0x28); err != nil {
+// // error handling
+// }
+// if _, err := c.Write(data); err != nil {
+// // error handling
+// }
+// }(c)
+// }
+//
+//
+// Multicasting
+//
+// The options for multicasting are available for net.UDPConn and
+// net.IPconn which are created as network connections that use the
+// IPv4 transport. A few network facilities must be prepared before
+// you begin multicasting, at a minimum joining network interfaces and
+// multicast groups.
+//
+// en0, err := net.InterfaceByName("en0")
+// if err != nil {
+// // error handling
+// }
+// en1, err := net.InterfaceByIndex(911)
+// if err != nil {
+// // error handling
+// }
+// group := net.IPv4(224, 0, 0, 250)
+//
+// First, an application listens to an appropriate address with an
+// appropriate service port.
+//
+// c, err := net.ListenPacket("udp4", "0.0.0.0:1024")
+// if err != nil {
+// // error handling
+// }
+// defer c.Close()
+//
+// Second, the application joins multicast groups, starts listening to
+// the groups on the specified network interfaces. Note that the
+// service port for transport layer protocol does not matter with this
+// operation as joining groups affects only network and link layer
+// protocols, such as IPv4 and Ethernet.
+//
+// p := ipv4.NewPacketConn(c)
+// if err := p.JoinGroup(en0, &net.UDPAddr{IP: group}); err != nil {
+// // error handling
+// }
+// if err := p.JoinGroup(en1, &net.UDPAddr{IP: group}); err != nil {
+// // error handling
+// }
+//
+// The application might set per packet control message transmissions
+// between the protocol stack within the kernel. When the application
+// needs a destination address on an incoming packet,
+// SetControlMessage of PacketConn is used to enable control message
+// transmissions.
+//
+// if err := p.SetControlMessage(ipv4.FlagDst, true); err != nil {
+// // error handling
+// }
+//
+// The application could identify whether the received packets are
+// of interest by using the control message that contains the
+// destination address of the received packet.
+//
+// b := make([]byte, 1500)
+// for {
+// n, cm, src, err := p.ReadFrom(b)
+// if err != nil {
+// // error handling
+// }
+// if cm.Dst.IsMulticast() {
+// if cm.Dst.Equal(group) {
+// // joined group, do something
+// } else {
+// // unknown group, discard
+// continue
+// }
+// }
+//
+// The application can also send both unicast and multicast packets.
+//
+// p.SetTOS(0x0)
+// p.SetTTL(16)
+// if _, err := p.WriteTo(data, nil, src); err != nil {
+// // error handling
+// }
+// dst := &net.UDPAddr{IP: group, Port: 1024}
+// for _, ifi := range []*net.Interface{en0, en1} {
+// if err := p.SetMulticastInterface(ifi); err != nil {
+// // error handling
+// }
+// p.SetMulticastTTL(2)
+// if _, err := p.WriteTo(data, nil, dst); err != nil {
+// // error handling
+// }
+// }
+// }
+//
+//
+// More multicasting
+//
+// An application that uses PacketConn or RawConn may join multiple
+// multicast groups. For example, a UDP listener with port 1024 might
+// join two different groups across over two different network
+// interfaces by using:
+//
+// c, err := net.ListenPacket("udp4", "0.0.0.0:1024")
+// if err != nil {
+// // error handling
+// }
+// defer c.Close()
+// p := ipv4.NewPacketConn(c)
+// if err := p.JoinGroup(en0, &net.UDPAddr{IP: net.IPv4(224, 0, 0, 248)}); err != nil {
+// // error handling
+// }
+// if err := p.JoinGroup(en0, &net.UDPAddr{IP: net.IPv4(224, 0, 0, 249)}); err != nil {
+// // error handling
+// }
+// if err := p.JoinGroup(en1, &net.UDPAddr{IP: net.IPv4(224, 0, 0, 249)}); err != nil {
+// // error handling
+// }
+//
+// It is possible for multiple UDP listeners that listen on the same
+// UDP port to join the same multicast group. The net package will
+// provide a socket that listens to a wildcard address with reusable
+// UDP port when an appropriate multicast address prefix is passed to
+// the net.ListenPacket or net.ListenUDP.
+//
+// c1, err := net.ListenPacket("udp4", "224.0.0.0:1024")
+// if err != nil {
+// // error handling
+// }
+// defer c1.Close()
+// c2, err := net.ListenPacket("udp4", "224.0.0.0:1024")
+// if err != nil {
+// // error handling
+// }
+// defer c2.Close()
+// p1 := ipv4.NewPacketConn(c1)
+// if err := p1.JoinGroup(en0, &net.UDPAddr{IP: net.IPv4(224, 0, 0, 248)}); err != nil {
+// // error handling
+// }
+// p2 := ipv4.NewPacketConn(c2)
+// if err := p2.JoinGroup(en0, &net.UDPAddr{IP: net.IPv4(224, 0, 0, 248)}); err != nil {
+// // error handling
+// }
+//
+// Also it is possible for the application to leave or rejoin a
+// multicast group on the network interface.
+//
+// if err := p.LeaveGroup(en0, &net.UDPAddr{IP: net.IPv4(224, 0, 0, 248)}); err != nil {
+// // error handling
+// }
+// if err := p.JoinGroup(en0, &net.UDPAddr{IP: net.IPv4(224, 0, 0, 250)}); err != nil {
+// // error handling
+// }
+//
+//
+// Source-specific multicasting
+//
+// An application that uses PacketConn or RawConn on IGMPv3 supported
+// platform is able to join source-specific multicast groups.
+// The application may use JoinSourceSpecificGroup and
+// LeaveSourceSpecificGroup for the operation known as "include" mode,
+//
+// ssmgroup := net.UDPAddr{IP: net.IPv4(232, 7, 8, 9)}
+// ssmsource := net.UDPAddr{IP: net.IPv4(192, 168, 0, 1)})
+// if err := p.JoinSourceSpecificGroup(en0, &ssmgroup, &ssmsource); err != nil {
+// // error handling
+// }
+// if err := p.LeaveSourceSpecificGroup(en0, &ssmgroup, &ssmsource); err != nil {
+// // error handling
+// }
+//
+// or JoinGroup, ExcludeSourceSpecificGroup,
+// IncludeSourceSpecificGroup and LeaveGroup for the operation known
+// as "exclude" mode.
+//
+// exclsource := net.UDPAddr{IP: net.IPv4(192, 168, 0, 254)}
+// if err := p.JoinGroup(en0, &ssmgroup); err != nil {
+// // error handling
+// }
+// if err := p.ExcludeSourceSpecificGroup(en0, &ssmgroup, &exclsource); err != nil {
+// // error handling
+// }
+// if err := p.LeaveGroup(en0, &ssmgroup); err != nil {
+// // error handling
+// }
+//
+// Note that it depends on each platform implementation what happens
+// when an application which runs on IGMPv3 unsupported platform uses
+// JoinSourceSpecificGroup and LeaveSourceSpecificGroup.
+// In general the platform tries to fall back to conversations using
+// IGMPv1 or IGMPv2 and starts to listen to multicast traffic.
+// In the fallback case, ExcludeSourceSpecificGroup and
+// IncludeSourceSpecificGroup may return an error.
+package ipv4 // import "golang.org/x/net/ipv4"
+
+// BUG(mikio): This package is not implemented on NaCl and Plan 9.
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