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// Copyright 2009 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.

// UDP for Plan 9

package net

import (

        "errors"

        "os"

        "time"

)

// UDPConn is the implementation of the Conn and PacketConn

// interfaces for UDP network connections.

type UDPConn struct {

        plan9Conn

}

// SetDeadline implements the Conn SetDeadline method.

func (c *UDPConn) SetDeadline(t time.Time) error {

        return os.EPLAN9

}

// SetReadDeadline implements the Conn SetReadDeadline method.

func (c *UDPConn) SetReadDeadline(t time.Time) error {

        return os.EPLAN9

}

// SetWriteDeadline implements the Conn SetWriteDeadline method.

func (c *UDPConn) SetWriteDeadline(t time.Time) error {

        return os.EPLAN9

}

// UDP-specific methods.

// ReadFromUDP reads a UDP packet from c, copying the payload into b.

// It returns the number of bytes copied into b and the return address

// that was on the packet.

//

// ReadFromUDP can be made to time out and return an error with Timeout() == true

// after a fixed time limit; see SetDeadline and SetReadDeadline.

func (c *UDPConn) ReadFromUDP(b []byte) (n int, addr *UDPAddr, err error) {

        if !c.ok() {

                return 0, nil, os.EINVAL

        }

        if c.data == nil {

                c.data, err = os.OpenFile(c.dir+"/data", os.O_RDWR, 0)

                if err != nil {

                        return 0, nil, err

                }

        }

        buf := make([]byte, udpHeaderSize+len(b))

        m, err := c.data.Read(buf)

        if err != nil {

                return

        }

        if m < udpHeaderSize {

                return 0, nil, errors.New("short read reading UDP header")

        }

        buf = buf[:m]

        h, buf := unmarshalUDPHeader(buf)

        n = copy(b, buf)

        return n, &UDPAddr{h.raddr, int(h.rport)}, nil

}

// ReadFrom implements the PacketConn ReadFrom method.

func (c *UDPConn) ReadFrom(b []byte) (n int, addr Addr, err error) {

        if !c.ok() {

                return 0, nil, os.EINVAL

        }

        return c.ReadFromUDP(b)

}

// WriteToUDP writes a UDP packet to addr via c, copying the payload from b.

//

// WriteToUDP can be made to time out and return

// an error with Timeout() == true after a fixed time limit;

// see SetDeadline and SetWriteDeadline.

// On packet-oriented connections, write timeouts are rare.

func (c *UDPConn) WriteToUDP(b []byte, addr *UDPAddr) (n int, err error) {

        if !c.ok() {

                return 0, os.EINVAL

        }

        if c.data == nil {

                c.data, err = os.OpenFile(c.dir+"/data", os.O_RDWR, 0)

                if err != nil {

                        return 0, err

                }

        }

        h := new(udpHeader)

        h.raddr = addr.IP.To16()

        h.laddr = c.laddr.(*UDPAddr).IP.To16()

        h.ifcaddr = IPv6zero // ignored (receive only)

        h.rport = uint16(addr.Port)

        h.lport = uint16(c.laddr.(*UDPAddr).Port)

        buf := make([]byte, udpHeaderSize+len(b))

        i := copy(buf, h.Bytes())

        copy(buf[i:], b)

        return c.data.Write(buf)

}

// WriteTo implements the PacketConn WriteTo method.

func (c *UDPConn) WriteTo(b []byte, addr Addr) (n int, err error) {

        if !c.ok() {

                return 0, os.EINVAL

        }

        a, ok := addr.(*UDPAddr)

        if !ok {

                return 0, &OpError{"write", c.dir, addr, os.EINVAL}

        }

        return c.WriteToUDP(b, a)

}

// DialUDP connects to the remote address raddr on the network net,

// which must be "udp", "udp4", or "udp6".  If laddr is not nil, it is used

// as the local address for the connection.

func DialUDP(net string, laddr, raddr *UDPAddr) (c *UDPConn, err error) {

        switch net {

        case "udp", "udp4", "udp6":

        default:

                return nil, UnknownNetworkError(net)

        }

        if raddr == nil {

                return nil, &OpError{"dial", net, nil, errMissingAddress}

        }

        c1, err := dialPlan9(net, laddr, raddr)

        if err != nil {

                return

        }

        return &UDPConn{*c1}, nil

}

const udpHeaderSize = 16*3 + 2*2

type udpHeader struct {

        raddr, laddr, ifcaddr IP

        rport, lport          uint16

}

func (h *udpHeader) Bytes() []byte {

        b := make([]byte, udpHeaderSize)

        i := 0

        i += copy(b[i:i+16], h.raddr)

        i += copy(b[i:i+16], h.laddr)

        i += copy(b[i:i+16], h.ifcaddr)

        b[i], b[i+1], i = byte(h.rport>>8), byte(h.rport), i+2

        b[i], b[i+1], i = byte(h.lport>>8), byte(h.lport), i+2

        return b

}

func unmarshalUDPHeader(b []byte) (*udpHeader, []byte) {

        h := new(udpHeader)

        h.raddr, b = IP(b[:16]), b[16:]

        h.laddr, b = IP(b[:16]), b[16:]

        h.ifcaddr, b = IP(b[:16]), b[16:]

        h.rport, b = uint16(b[0])<<8|uint16(b[1]), b[2:]

        h.lport, b = uint16(b[0])<<8|uint16(b[1]), b[2:]

        return h, b

}

// ListenUDP listens for incoming UDP packets addressed to the

// local address laddr.  The returned connection c's ReadFrom

// and WriteTo methods can be used to receive and send UDP

// packets with per-packet addressing.

func ListenUDP(net string, laddr *UDPAddr) (c *UDPConn, err error) {

        switch net {

        case "udp", "udp4", "udp6":

        default:

                return nil, UnknownNetworkError(net)

        }

        if laddr == nil {

                return nil, &OpError{"listen", net, nil, errMissingAddress}

        }

        l, err := listenPlan9(net, laddr)

        if err != nil {

                return

        }

        _, err = l.ctl.WriteString("headers")

        if err != nil {

                return

        }

        return &UDPConn{*l.plan9Conn()}, nil

}

// ListenMulticastUDP listens for incoming multicast UDP packets

// addressed to the group address gaddr on ifi, which specifies

// the interface to join.  ListenMulticastUDP uses default

// multicast interface if ifi is nil.

func ListenMulticastUDP(net string, ifi *Interface, gaddr *UDPAddr) (*UDPConn, error) {

        return nil, os.EPLAN9

}