// The MIT License (MIT)
//
// Copyright (c) 2015 xtaci
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

//go:build linux
// +build linux

package kcp

import (
	"net"
	"os"
	"sync/atomic"

	"github.com/pkg/errors"
	"golang.org/x/net/ipv4"
	"golang.org/x/net/ipv6"
)

// readLoop is the optimized version of readLoop for linux utilizing recvmmsg syscall
func (s *UDPSession) readLoop() {
	// default version
	if s.xconn == nil {
		s.defaultReadLoop()
		return
	}

	// x/net version
	var src string
	msgs := make([]ipv4.Message, batchSize)
	for k := range msgs {
		msgs[k].Buffers = [][]byte{make([]byte, mtuLimit)}
	}

	for {
		if count, err := s.xconn.ReadBatch(msgs, 0); err == nil {
			if s.isClosed() {
				return
			}
			for i := 0; i < count; i++ {
				msg := &msgs[i]
				// make sure the packet is from the same source
				if src == "" { // set source address if nil
					src = msg.Addr.String()
				} else if msg.Addr.String() != src {
					atomic.AddUint64(&DefaultSnmp.InErrs, 1)
					continue
				}

				// source and size has validated
				s.packetInput(msg.Buffers[0][:msg.N])
			}
		} else {
			// compatibility issue:
			// for linux kernel<=2.6.32, support for sendmmsg is not available
			// an error of type os.SyscallError will be returned
			if operr, ok := err.(*net.OpError); ok {
				if se, ok := operr.Err.(*os.SyscallError); ok {
					if se.Syscall == "recvmmsg" {
						s.defaultReadLoop()
						return
					}
				}
			}
			s.notifyReadError(errors.WithStack(err))
			return
		}
	}
}

// monitor is the optimized version of monitor for linux utilizing recvmmsg syscall
func (l *Listener) monitor() {
	var xconn batchConn
	if _, ok := l.conn.(*net.UDPConn); ok {
		addr, err := net.ResolveUDPAddr("udp", l.conn.LocalAddr().String())
		if err == nil {
			if addr.IP.To4() != nil {
				xconn = ipv4.NewPacketConn(l.conn)
			} else {
				xconn = ipv6.NewPacketConn(l.conn)
			}
		}
	}

	// default version
	if xconn == nil {
		l.defaultMonitor()
		return
	}

	// x/net version
	msgs := make([]ipv4.Message, batchSize)
	for k := range msgs {
		msgs[k].Buffers = [][]byte{make([]byte, mtuLimit)}
	}

	for {
		if count, err := xconn.ReadBatch(msgs, 0); err == nil {
			for i := 0; i < count; i++ {
				msg := &msgs[i]
				l.packetInput(msg.Buffers[0][:msg.N], msg.Addr)
			}
		} else {
			// compatibility issue:
			// for linux kernel<=2.6.32, support for sendmmsg is not available
			// an error of type os.SyscallError will be returned
			if operr, ok := err.(*net.OpError); ok {
				if se, ok := operr.Err.(*os.SyscallError); ok {
					if se.Syscall == "recvmmsg" {
						l.defaultMonitor()
						return
					}
				}
			}
			l.notifyReadError(errors.WithStack(err))
			return
		}
	}
}