text: // Copyright 2013 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 ipv6 implements IP-level socket options for the Internet
  // Protocol version 6.
  //
  // The package provides IP-level socket options that allow
  // manipulation of IPv6 facilities.
  //
  // The IPv6 protocol is defined in RFC 2460.
  // Socket interface extensions are defined in RFC 3493, RFC 3542 and
  // RFC 3678.
  // MLDv1 and MLDv2 are defined in RFC 2710 and RFC 3810.
  // Source-specific multicast is defined in RFC 4607.
  //
  // On Darwin, this package requires OS X Mavericks version 10.9 or
  // above, or equivalent.
  //
  //
  // Unicasting
  //
  // The options for unicasting are available for net.TCPConn,
  // net.UDPConn and net.IPConn which are created as network connections
  // that use the IPv6 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 traffic class field on the IPv6
  // header for each packet.
  //
  //	ln, err := net.Listen("tcp6", "[::]: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 := ipv6.NewConn(c).SetTrafficClass(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
  // IPv6 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.ParseIP("ff02::114")
  //
  // First, an application listens to an appropriate address with an
  // appropriate service port.
  //
  //	c, err := net.ListenPacket("udp6", "[::]: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 IPv6 and Ethernet.
  //
  //	p := ipv6.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(ipv6.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, rcm, src, err := p.ReadFrom(b)
  //		if err != nil {
  //			// error handling
  //		}
  //		if rcm.Dst.IsMulticast() {
  //			if rcm.Dst.Equal(group) {
  //				// joined group, do something
  //			} else {
  //				// unknown group, discard
  //				continue
  //			}
  //		}
  //
  // The application can also send both unicast and multicast packets.
  //
  //		p.SetTrafficClass(0x0)
  //		p.SetHopLimit(16)
  //		if _, err := p.WriteTo(data[:n], nil, src); err != nil {
  //			// error handling
  //		}
  //		dst := &net.UDPAddr{IP: group, Port: 1024}
  //		wcm := ipv6.ControlMessage{TrafficClass: 0xe0, HopLimit: 1}
  //		for _, ifi := range []*net.Interface{en0, en1} {
  //			wcm.IfIndex = ifi.Index
  //			if _, err := p.WriteTo(data[:n], &wcm, dst); err != nil {
  //				// error handling
  //			}
  //		}
  //	}
  //
  //
  // More multicasting
  //
  // An application that uses PacketConn 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("udp6", "[::]:1024")
  //	if err != nil {
  //		// error handling
  //	}
  //	defer c.Close()
  //	p := ipv6.NewPacketConn(c)
  //	if err := p.JoinGroup(en0, &net.UDPAddr{IP: net.ParseIP("ff02::1:114")}); err != nil {
  //		// error handling
  //	}
  //	if err := p.JoinGroup(en0, &net.UDPAddr{IP: net.ParseIP("ff02::2:114")}); err != nil {
  //		// error handling
  //	}
  //	if err := p.JoinGroup(en1, &net.UDPAddr{IP: net.ParseIP("ff02::2:114")}); 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("udp6", "[ff02::]:1024")
  //	if err != nil {
  //		// error handling
  //	}
  //	defer c1.Close()
  //	c2, err := net.ListenPacket("udp6", "[ff02::]:1024")
  //	if err != nil {
  //		// error handling
  //	}
  //	defer c2.Close()
  //	p1 := ipv6.NewPacketConn(c1)
  //	if err := p1.JoinGroup(en0, &net.UDPAddr{IP: net.ParseIP("ff02::114")}); err != nil {
  //		// error handling
  //	}
  //	p2 := ipv6.NewPacketConn(c2)
  //	if err := p2.JoinGroup(en0, &net.UDPAddr{IP: net.ParseIP("ff02::114")}); 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.ParseIP("ff02::114")}); err != nil {
  //		// error handling
  //	}
  //	if err := p.JoinGroup(en0, &net.UDPAddr{IP: net.ParseIP("ff01::114")}); err != nil {
  //		// error handling
  //	}
  //
  //
  // Source-specific multicasting
  //
  // An application that uses PacketConn on MLDv2 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.ParseIP("ff32::8000:9")}
  //	ssmsource := net.UDPAddr{IP: net.ParseIP("fe80::cafe")}
  //	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.ParseIP("fe80::dead")}
  //	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 MLDv2 unsupported platform uses
  // JoinSourceSpecificGroup and LeaveSourceSpecificGroup.
  // In general the platform tries to fall back to conversations using
  // MLDv1 and starts to listen to multicast traffic.
  // In the fallback case, ExcludeSourceSpecificGroup and
  // IncludeSourceSpecificGroup may return an error.
  package ipv6 // import "golang.org/x/net/ipv6"
  
  // BUG(mikio): This package is not implemented on NaCl and Plan 9.
  