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// Copyright 2010 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 net

import (
        "io"
        "os"
        "runtime"
        "sync"
        "syscall"
        "time"
        "unsafe"
)

var initErr error

func init() {
        var d syscall.WSAData
        e := syscall.WSAStartup(uint32(0x202), &d)
        if e != nil {
                initErr = os.NewSyscallError("WSAStartup", e)
        }
}

func closesocket(s syscall.Handle) error {
        return syscall.Closesocket(s)
}

// Interface for all io operations.
type anOpIface interface {
        Op() *anOp
        Name() string
        Submit() error
}

// IO completion result parameters.
type ioResult struct {
        qty uint32
        err error
}

// anOp implements functionality common to all io operations.
type anOp struct {
        // Used by IOCP interface, it must be first field
        // of the struct, as our code rely on it.
        o syscall.Overlapped

        resultc chan ioResult
        errnoc  chan error
        fd      *netFD
}

func (o *anOp) Init(fd *netFD, mode int) {
        o.fd = fd
        var i int
        if mode == 'r' {
                i = 0
        } else {
                i = 1
        }
        if fd.resultc[i] == nil {
                fd.resultc[i] = make(chan ioResult, 1)
        }
        o.resultc = fd.resultc[i]
        if fd.errnoc[i] == nil {
                fd.errnoc[i] = make(chan error)
        }
        o.errnoc = fd.errnoc[i]
}

func (o *anOp) Op() *anOp {
        return o
}

// bufOp is used by io operations that read / write
// data from / to client buffer.
type bufOp struct {
        anOp
        buf syscall.WSABuf
}

func (o *bufOp) Init(fd *netFD, buf []byte, mode int) {
        o.anOp.Init(fd, mode)
        o.buf.Len = uint32(len(buf))
        if len(buf) == 0 {
                o.buf.Buf = nil
        } else {
                o.buf.Buf = (*byte)(unsafe.Pointer(&buf[0]))
        }
}

// resultSrv will retrieve all io completion results from
// iocp and send them to the correspondent waiting client
// goroutine via channel supplied in the request.
type resultSrv struct {
        iocp syscall.Handle
}

func (s *resultSrv) Run() {
        var o *syscall.Overlapped
        var key uint32
        var r ioResult
        for {
                r.err = syscall.GetQueuedCompletionStatus(s.iocp, &(r.qty), &key, &o, syscall.INFINITE)
                switch {
                case r.err == nil:
                        // Dequeued successfully completed io packet.
                case r.err == syscall.Errno(syscall.WAIT_TIMEOUT) && o == nil:
                        // Wait has timed out (should not happen now, but might be used in the future).
                        panic("GetQueuedCompletionStatus timed out")
                case o == nil:
                        // Failed to dequeue anything -> report the error.
                        panic("GetQueuedCompletionStatus failed " + r.err.Error())
                default:
                        // Dequeued failed io packet.
                }
                (*anOp)(unsafe.Pointer(o)).resultc <- r
        }
}

// ioSrv executes net io requests.
type ioSrv struct {
        submchan chan anOpIface // submit io requests
        canchan  chan anOpIface // cancel io requests
}

// ProcessRemoteIO will execute submit io requests on behalf
// of other goroutines, all on a single os thread, so it can
// cancel them later. Results of all operations will be sent
// back to their requesters via channel supplied in request.
func (s *ioSrv) ProcessRemoteIO() {
        runtime.LockOSThread()
        defer runtime.UnlockOSThread()
        for {
                select {
                case o := <-s.submchan:
                        o.Op().errnoc <- o.Submit()
                case o := <-s.canchan:
                        o.Op().errnoc <- syscall.CancelIo(syscall.Handle(o.Op().fd.sysfd))
                }
        }
}

// ExecIO executes a single io operation. It either executes it
// inline, or, if a deadline is employed, passes the request onto
// a special goroutine and waits for completion or cancels request.
// deadline is unix nanos.
func (s *ioSrv) ExecIO(oi anOpIface, deadline int64) (int, error) {
        var err error
        o := oi.Op()
        if deadline != 0 {
                // Send request to a special dedicated thread,
                // so it can stop the io with CancelIO later.
                s.submchan <- oi
                err = <-o.errnoc
        } else {
                err = oi.Submit()
        }
        switch err {
        case nil:
                // IO completed immediately, but we need to get our completion message anyway.
        case syscall.ERROR_IO_PENDING:
                // IO started, and we have to wait for its completion.
                err = nil
        default:
                return 0, &OpError{oi.Name(), o.fd.net, o.fd.laddr, err}
        }
        // Wait for our request to complete.
        var r ioResult
        if deadline != 0 {
                dt := deadline - time.Now().UnixNano()
                if dt < 1 {
                        dt = 1
                }
                timer := time.NewTimer(time.Duration(dt) * time.Nanosecond)
                defer timer.Stop()
                select {
                case r = <-o.resultc:
                case <-timer.C:
                        s.canchan <- oi
                        <-o.errnoc
                        r = <-o.resultc
                        if r.err == syscall.ERROR_OPERATION_ABORTED { // IO Canceled
                                r.err = syscall.EWOULDBLOCK
                        }
                }
        } else {
                r = <-o.resultc
        }
        if r.err != nil {
                err = &OpError{oi.Name(), o.fd.net, o.fd.laddr, r.err}
        }
        return int(r.qty), err
}

// Start helper goroutines.
var resultsrv *resultSrv
var iosrv *ioSrv
var onceStartServer sync.Once

func startServer() {
        resultsrv = new(resultSrv)
        var err error
        resultsrv.iocp, err = syscall.CreateIoCompletionPort(syscall.InvalidHandle, 0, 0, 1)
        if err != nil {
                panic("CreateIoCompletionPort: " + err.Error())
        }
        go resultsrv.Run()

        iosrv = new(ioSrv)
        iosrv.submchan = make(chan anOpIface)
        iosrv.canchan = make(chan anOpIface)
        go iosrv.ProcessRemoteIO()
}

// Network file descriptor.
type netFD struct {
        // locking/lifetime of sysfd
        sysmu   sync.Mutex
        sysref  int
        closing bool

        // immutable until Close
        sysfd       syscall.Handle
        family      int
        sotype      int
        isConnected bool
        net         string
        laddr       Addr
        raddr       Addr
        resultc     [2]chan ioResult // read/write completion results
        errnoc      [2]chan error    // read/write submit or cancel operation errors

        // owned by client
        rdeadline int64
        rio       sync.Mutex
        wdeadline int64
        wio       sync.Mutex
}

func allocFD(fd syscall.Handle, family, sotype int, net string) *netFD {
        netfd := &netFD{
                sysfd:  fd,
                family: family,
                sotype: sotype,
                net:    net,
        }
        runtime.SetFinalizer(netfd, (*netFD).Close)
        return netfd
}

func newFD(fd syscall.Handle, family, proto int, net string) (*netFD, error) {
        if initErr != nil {
                return nil, initErr
        }
        onceStartServer.Do(startServer)
        // Associate our socket with resultsrv.iocp.
        if _, err := syscall.CreateIoCompletionPort(syscall.Handle(fd), resultsrv.iocp, 0, 0); err != nil {
                return nil, err
        }
        return allocFD(fd, family, proto, net), nil
}

func (fd *netFD) setAddr(laddr, raddr Addr) {
        fd.laddr = laddr
        fd.raddr = raddr
}

func (fd *netFD) connect(ra syscall.Sockaddr) error {
        return syscall.Connect(fd.sysfd, ra)
}

// Add a reference to this fd.
func (fd *netFD) incref() {
        fd.sysmu.Lock()
        fd.sysref++
        fd.sysmu.Unlock()
}

// Remove a reference to this FD and close if we've been asked to do so (and
// there are no references left.
func (fd *netFD) decref() {
        fd.sysmu.Lock()
        fd.sysref--
        if fd.closing && fd.sysref == 0 && fd.sysfd != syscall.InvalidHandle {
                // In case the user has set linger, switch to blocking mode so
                // the close blocks.  As long as this doesn't happen often, we
                // can handle the extra OS processes.  Otherwise we'll need to
                // use the resultsrv for Close too.  Sigh.
                syscall.SetNonblock(fd.sysfd, false)
                closesocket(fd.sysfd)
                fd.sysfd = syscall.InvalidHandle
                // no need for a finalizer anymore
                runtime.SetFinalizer(fd, nil)
        }
        fd.sysmu.Unlock()
}

func (fd *netFD) Close() error {
        if fd == nil || fd.sysfd == syscall.InvalidHandle {
                return os.EINVAL
        }

        fd.incref()
        syscall.Shutdown(fd.sysfd, syscall.SHUT_RDWR)
        fd.closing = true
        fd.decref()
        return nil
}

func (fd *netFD) shutdown(how int) error {
        if fd == nil || fd.sysfd == syscall.InvalidHandle {
                return os.EINVAL
        }
        err := syscall.Shutdown(fd.sysfd, how)
        if err != nil {
                return &OpError{"shutdown", fd.net, fd.laddr, err}
        }
        return nil
}

func (fd *netFD) CloseRead() error {
        return fd.shutdown(syscall.SHUT_RD)
}

func (fd *netFD) CloseWrite() error {
        return fd.shutdown(syscall.SHUT_WR)
}

// Read from network.

type readOp struct {
        bufOp
}

func (o *readOp) Submit() error {
        var d, f uint32
        return syscall.WSARecv(syscall.Handle(o.fd.sysfd), &o.buf, 1, &d, &f, &o.o, nil)
}

func (o *readOp) Name() string {
        return "WSARecv"
}

func (fd *netFD) Read(buf []byte) (int, error) {
        if fd == nil {
                return 0, os.EINVAL
        }
        fd.rio.Lock()
        defer fd.rio.Unlock()
        fd.incref()
        defer fd.decref()
        if fd.sysfd == syscall.InvalidHandle {
                return 0, os.EINVAL
        }
        var o readOp
        o.Init(fd, buf, 'r')
        n, err := iosrv.ExecIO(&o, fd.rdeadline)
        if err == nil && n == 0 {
                err = io.EOF
        }
        return n, err
}

// ReadFrom from network.

type readFromOp struct {
        bufOp
        rsa  syscall.RawSockaddrAny
        rsan int32
}

func (o *readFromOp) Submit() error {
        var d, f uint32
        return syscall.WSARecvFrom(o.fd.sysfd, &o.buf, 1, &d, &f, &o.rsa, &o.rsan, &o.o, nil)
}

func (o *readFromOp) Name() string {
        return "WSARecvFrom"
}

func (fd *netFD) ReadFrom(buf []byte) (n int, sa syscall.Sockaddr, err error) {
        if fd == nil {
                return 0, nil, os.EINVAL
        }
        if len(buf) == 0 {
                return 0, nil, nil
        }
        fd.rio.Lock()
        defer fd.rio.Unlock()
        fd.incref()
        defer fd.decref()
        if fd.sysfd == syscall.InvalidHandle {
                return 0, nil, os.EINVAL
        }
        var o readFromOp
        o.Init(fd, buf, 'r')
        o.rsan = int32(unsafe.Sizeof(o.rsa))
        n, err = iosrv.ExecIO(&o, fd.rdeadline)
        if err != nil {
                return 0, nil, err
        }
        sa, _ = o.rsa.Sockaddr()
        return
}

// Write to network.

type writeOp struct {
        bufOp
}

func (o *writeOp) Submit() error {
        var d uint32
        return syscall.WSASend(o.fd.sysfd, &o.buf, 1, &d, 0, &o.o, nil)
}

func (o *writeOp) Name() string {
        return "WSASend"
}

func (fd *netFD) Write(buf []byte) (int, error) {
        if fd == nil {
                return 0, os.EINVAL
        }
        fd.wio.Lock()
        defer fd.wio.Unlock()
        fd.incref()
        defer fd.decref()
        if fd.sysfd == syscall.InvalidHandle {
                return 0, os.EINVAL
        }
        var o writeOp
        o.Init(fd, buf, 'w')
        return iosrv.ExecIO(&o, fd.wdeadline)
}

// WriteTo to network.

type writeToOp struct {
        bufOp
        sa syscall.Sockaddr
}

func (o *writeToOp) Submit() error {
        var d uint32
        return syscall.WSASendto(o.fd.sysfd, &o.buf, 1, &d, 0, o.sa, &o.o, nil)
}

func (o *writeToOp) Name() string {
        return "WSASendto"
}

func (fd *netFD) WriteTo(buf []byte, sa syscall.Sockaddr) (int, error) {
        if fd == nil {
                return 0, os.EINVAL
        }
        if len(buf) == 0 {
                return 0, nil
        }
        fd.wio.Lock()
        defer fd.wio.Unlock()
        fd.incref()
        defer fd.decref()
        if fd.sysfd == syscall.InvalidHandle {
                return 0, os.EINVAL
        }
        var o writeToOp
        o.Init(fd, buf, 'w')
        o.sa = sa
        return iosrv.ExecIO(&o, fd.wdeadline)
}

// Accept new network connections.

type acceptOp struct {
        anOp
        newsock syscall.Handle
        attrs   [2]syscall.RawSockaddrAny // space for local and remote address only
}

func (o *acceptOp) Submit() error {
        var d uint32
        l := uint32(unsafe.Sizeof(o.attrs[0]))
        return syscall.AcceptEx(o.fd.sysfd, o.newsock,
                (*byte)(unsafe.Pointer(&o.attrs[0])), 0, l, l, &d, &o.o)
}

func (o *acceptOp) Name() string {
        return "AcceptEx"
}

func (fd *netFD) accept(toAddr func(syscall.Sockaddr) Addr) (*netFD, error) {
        if fd == nil || fd.sysfd == syscall.InvalidHandle {
                return nil, os.EINVAL
        }
        fd.incref()
        defer fd.decref()

        // Get new socket.
        // See ../syscall/exec.go for description of ForkLock.
        syscall.ForkLock.RLock()
        s, err := syscall.Socket(fd.family, fd.sotype, 0)
        if err != nil {
                syscall.ForkLock.RUnlock()
                return nil, err
        }
        syscall.CloseOnExec(s)
        syscall.ForkLock.RUnlock()

        // Associate our new socket with IOCP.
        onceStartServer.Do(startServer)
        if _, err := syscall.CreateIoCompletionPort(s, resultsrv.iocp, 0, 0); err != nil {
                return nil, &OpError{"CreateIoCompletionPort", fd.net, fd.laddr, err}
        }

        // Submit accept request.
        var o acceptOp
        o.Init(fd, 'r')
        o.newsock = s
        _, err = iosrv.ExecIO(&o, 0)
        if err != nil {
                closesocket(s)
                return nil, err
        }

        // Inherit properties of the listening socket.
        err = syscall.Setsockopt(s, syscall.SOL_SOCKET, syscall.SO_UPDATE_ACCEPT_CONTEXT, (*byte)(unsafe.Pointer(&fd.sysfd)), int32(unsafe.Sizeof(fd.sysfd)))
        if err != nil {
                closesocket(s)
                return nil, err
        }

        // Get local and peer addr out of AcceptEx buffer.
        var lrsa, rrsa *syscall.RawSockaddrAny
        var llen, rlen int32
        l := uint32(unsafe.Sizeof(*lrsa))
        syscall.GetAcceptExSockaddrs((*byte)(unsafe.Pointer(&o.attrs[0])),
                0, l, l, &lrsa, &llen, &rrsa, &rlen)
        lsa, _ := lrsa.Sockaddr()
        rsa, _ := rrsa.Sockaddr()

        netfd := allocFD(s, fd.family, fd.sotype, fd.net)
        netfd.setAddr(toAddr(lsa), toAddr(rsa))
        return netfd, nil
}

// Unimplemented functions.

func (fd *netFD) dup() (*os.File, error) {
        // TODO: Implement this
        return nil, os.NewSyscallError("dup", syscall.EWINDOWS)
}

func (fd *netFD) ReadMsg(p []byte, oob []byte) (n, oobn, flags int, sa syscall.Sockaddr, err error) {
        return 0, 0, 0, nil, os.EAFNOSUPPORT
}

func (fd *netFD) WriteMsg(p []byte, oob []byte, sa syscall.Sockaddr) (n int, oobn int, err error) {
        return 0, 0, os.EAFNOSUPPORT
}