// 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, ipv4.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 ipv4.PacketConn is used to enable control
// message transmissons.
//
// 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"