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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
}