// 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"