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// See the file LICENSE for copyright and licensing information.

// Adapted from Plan 9 from User Space's src/cmd/9pfuse/fuse.c,
// which carries this notice:
//
// The files in this directory are subject to the following license.
//
// The author of this software is Russ Cox.
//
//         Copyright (c) 2006 Russ Cox
//
// Permission to use, copy, modify, and distribute this software for any
// purpose without fee is hereby granted, provided that this entire notice
// is included in all copies of any software which is or includes a copy
// or modification of this software and in all copies of the supporting
// documentation for such software.
//
// THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
// WARRANTY.  IN PARTICULAR, THE AUTHOR MAKES NO REPRESENTATION OR WARRANTY
// OF ANY KIND CONCERNING THE MERCHANTABILITY OF THIS SOFTWARE OR ITS
// FITNESS FOR ANY PARTICULAR PURPOSE.

// Package fuse enables writing FUSE file systems on Linux, OS X, and FreeBSD.
//
// On OS X, it requires OSXFUSE (http://osxfuse.github.com/).
//
// There are two approaches to writing a FUSE file system.  The first is to speak
// the low-level message protocol, reading from a Conn using ReadRequest and
// writing using the various Respond methods.  This approach is closest to
// the actual interaction with the kernel and can be the simplest one in contexts
// such as protocol translators.
//
// Servers of synthesized file systems tend to share common
// bookkeeping abstracted away by the second approach, which is to
// call fs.Serve to serve the FUSE protocol using an implementation of
// the service methods in the interfaces FS* (file system), Node* (file
// or directory), and Handle* (opened file or directory).
// There are a daunting number of such methods that can be written,
// but few are required.
// The specific methods are described in the documentation for those interfaces.
//
// The hellofs subdirectory contains a simple illustration of the fs.Serve approach.
//
// Service Methods
//
// The required and optional methods for the FS, Node, and Handle interfaces
// have the general form
//
//  Op(ctx context.Context, req *OpRequest, resp *OpResponse) error
//
// where Op is the name of a FUSE operation. Op reads request
// parameters from req and writes results to resp. An operation whose
// only result is the error result omits the resp parameter.
//
// Multiple goroutines may call service methods simultaneously; the
// methods being called are responsible for appropriate
// synchronization.
//
// The operation must not hold on to the request or response,
// including any []byte fields such as WriteRequest.Data or
// SetxattrRequest.Xattr.
//
// Errors
//
// Operations can return errors. The FUSE interface can only
// communicate POSIX errno error numbers to file system clients, the
// message is not visible to file system clients. The returned error
// can implement ErrorNumber to control the errno returned. Without
// ErrorNumber, a generic errno (EIO) is returned.
//
// Error messages will be visible in the debug log as part of the
// response.
//
// Interrupted Operations
//
// In some file systems, some operations
// may take an undetermined amount of time.  For example, a Read waiting for
// a network message or a matching Write might wait indefinitely.  If the request
// is cancelled and no longer needed, the context will be cancelled.
// Blocking operations should select on a receive from ctx.Done() and attempt to
// abort the operation early if the receive succeeds (meaning the channel is closed).
// To indicate that the operation failed because it was aborted, return fuse.EINTR.
//
// If an operation does not block for an indefinite amount of time, supporting
// cancellation is not necessary.
//
// Authentication
//
// All requests types embed a Header, meaning that the method can
// inspect req.Pid, req.Uid, and req.Gid as necessary to implement
// permission checking. The kernel FUSE layer normally prevents other
// users from accessing the FUSE file system (to change this, see
// AllowOther, AllowRoot), but does not enforce access modes (to
// change this, see DefaultPermissions).
//
// Mount Options
//
// Behavior and metadata of the mounted file system can be changed by
// passing MountOption values to Mount.
//
package fuse // import "bazil.org/fuse"

import (
    "bytes"
    "encoding/json"
    "errors"
    "fmt"
    "io"
    "os"
    "sync"
    "syscall"
    "time"
    "unsafe"
)

// A Conn represents a connection to a mounted FUSE file system.
type Conn struct {
    // Ready is closed when the mount is complete or has failed.
    Ready <-chan struct{}

    // MountError stores any error from the mount process. Only valid
    // after Ready is closed.
    MountError error

    // File handle for kernel communication. Only safe to access if
    // rio or wio is held.
    dev *os.File
    wio sync.RWMutex
    rio sync.RWMutex

    // Protocol version negotiated with InitRequest/InitResponse.
    proto Protocol
}

// MountpointDoesNotExistError is an error returned when the
// mountpoint does not exist.
type MountpointDoesNotExistError struct {
    Path string
}

var _ error = (*MountpointDoesNotExistError)(nil)

func (e *MountpointDoesNotExistError) Error() string {
    return fmt.Sprintf("mountpoint does not exist: %v", e.Path)
}

// Mount mounts a new FUSE connection on the named directory
// and returns a connection for reading and writing FUSE messages.
//
// After a successful return, caller must call Close to free
// resources.
//
// Even on successful return, the new mount is not guaranteed to be
// visible until after Conn.Ready is closed. See Conn.MountError for
// possible errors. Incoming requests on Conn must be served to make
// progress.
func Mount(dir string, options ...MountOption) (*Conn, error) {
    conf := mountConfig{
        options: make(map[string]string),
    }
    for _, option := range options {
        if err := option(&conf); err != nil {
            return nil, err
        }
    }

    ready := make(chan struct{}, 1)
    c := &Conn{
        Ready: ready,
    }
    f, err := mount(dir, &conf, ready, &c.MountError)
    if err != nil {
        return nil, err
    }
    c.dev = f

    if err := initMount(c, &conf); err != nil {
        c.Close()
        if err == ErrClosedWithoutInit {
            // see if we can provide a better error
            <-c.Ready
            if err := c.MountError; err != nil {
                return nil, err
            }
        }
        return nil, err
    }

    return c, nil
}

type OldVersionError struct {
    Kernel     Protocol
    LibraryMin Protocol
}

func (e *OldVersionError) Error() string {
    return fmt.Sprintf("kernel FUSE version is too old: %v < %v", e.Kernel, e.LibraryMin)
}

var (
    ErrClosedWithoutInit = errors.New("fuse connection closed without init")
)

func initMount(c *Conn, conf *mountConfig) error {
    req, err := c.ReadRequest()
    if err != nil {
        if err == io.EOF {
            return ErrClosedWithoutInit
        }
        return err
    }
    r, ok := req.(*InitRequest)
    if !ok {
        return fmt.Errorf("missing init, got: %T", req)
    }

    min := Protocol{protoVersionMinMajor, protoVersionMinMinor}
    if r.Kernel.LT(min) {
        req.RespondError(Errno(syscall.EPROTO))
        c.Close()
        return &OldVersionError{
            Kernel:     r.Kernel,
            LibraryMin: min,
        }
    }

    proto := Protocol{protoVersionMaxMajor, protoVersionMaxMinor}
    if r.Kernel.LT(proto) {
        // Kernel doesn't support the latest version we have.
        proto = r.Kernel
    }
    c.proto = proto

    s := &InitResponse{
        Library:      proto,
        MaxReadahead: conf.maxReadahead,
        MaxWrite:     maxWrite,
        Flags:        InitBigWrites | conf.initFlags,
    }
    r.Respond(s)
    return nil
}

// A Request represents a single FUSE request received from the kernel.
// Use a type switch to determine the specific kind.
// A request of unrecognized type will have concrete type *Header.
type Request interface {
    // Hdr returns the Header associated with this request.
    Hdr() *Header

    // RespondError responds to the request with the given error.
    RespondError(error)

    String() string
}

// A RequestID identifies an active FUSE request.
type RequestID uint64

func (r RequestID) String() string {
    return fmt.Sprintf("%#x", uint64(r))
}

// A NodeID is a number identifying a directory or file.
// It must be unique among IDs returned in LookupResponses
// that have not yet been forgotten by ForgetRequests.
type NodeID uint64

func (n NodeID) String() string {
    return fmt.Sprintf("%#x", uint64(n))
}

// A HandleID is a number identifying an open directory or file.
// It only needs to be unique while the directory or file is open.
type HandleID uint64

func (h HandleID) String() string {
    return fmt.Sprintf("%#x", uint64(h))
}

// The RootID identifies the root directory of a FUSE file system.
const RootID NodeID = rootID

// A Header describes the basic information sent in every request.
type Header struct {
    Conn *Conn     `json:"-"` // connection this request was received on
    ID   RequestID // unique ID for request
    Node NodeID    // file or directory the request is about
    Uid  uint32    // user ID of process making request
    Gid  uint32    // group ID of process making request
    Pid  uint32    // process ID of process making request

    // for returning to reqPool
    msg *message
}

func (h *Header) String() string {
    return fmt.Sprintf("ID=%v Node=%v Uid=%d Gid=%d Pid=%d", h.ID, h.Node, h.Uid, h.Gid, h.Pid)
}

func (h *Header) Hdr() *Header {
    return h
}

func (h *Header) noResponse() {
    putMessage(h.msg)
}

func (h *Header) respond(msg []byte) {
    out := (*outHeader)(unsafe.Pointer(&msg[0]))
    out.Unique = uint64(h.ID)
    h.Conn.respond(msg)
    putMessage(h.msg)
}

// An ErrorNumber is an error with a specific error number.
//
// Operations may return an error value that implements ErrorNumber to
// control what specific error number (errno) to return.
type ErrorNumber interface {
    // Errno returns the the error number (errno) for this error.
    Errno() Errno
}

const (
    // ENOSYS indicates that the call is not supported.
    ENOSYS = Errno(syscall.ENOSYS)

    // ESTALE is used by Serve to respond to violations of the FUSE protocol.
    ESTALE = Errno(syscall.ESTALE)

    ENOENT = Errno(syscall.ENOENT)
    EIO    = Errno(syscall.EIO)
    EPERM  = Errno(syscall.EPERM)

    // EINTR indicates request was interrupted by an InterruptRequest.
    // See also fs.Intr.
    EINTR = Errno(syscall.EINTR)

    ERANGE  = Errno(syscall.ERANGE)
    ENOTSUP = Errno(syscall.ENOTSUP)
    EEXIST  = Errno(syscall.EEXIST)
)

// DefaultErrno is the errno used when error returned does not
// implement ErrorNumber.
const DefaultErrno = EIO

var errnoNames = map[Errno]string{
    ENOSYS: "ENOSYS",
    ESTALE: "ESTALE",
    ENOENT: "ENOENT",
    EIO:    "EIO",
    EPERM:  "EPERM",
    EINTR:  "EINTR",
    EEXIST: "EEXIST",
}

// Errno implements Error and ErrorNumber using a syscall.Errno.
type Errno syscall.Errno

var _ = ErrorNumber(Errno(0))
var _ = error(Errno(0))

func (e Errno) Errno() Errno {
    return e
}

func (e Errno) String() string {
    return syscall.Errno(e).Error()
}

func (e Errno) Error() string {
    return syscall.Errno(e).Error()
}

// ErrnoName returns the short non-numeric identifier for this errno.
// For example, "EIO".
func (e Errno) ErrnoName() string {
    s := errnoNames[e]
    if s == "" {
        s = fmt.Sprint(e.Errno())
    }
    return s
}

func (e Errno) MarshalText() ([]byte, error) {
    s := e.ErrnoName()
    return []byte(s), nil
}

func (h *Header) RespondError(err error) {
    errno := DefaultErrno
    if ferr, ok := err.(ErrorNumber); ok {
        errno = ferr.Errno()
    }
    // FUSE uses negative errors!
    // TODO: File bug report against OSXFUSE: positive error causes kernel panic.
    buf := newBuffer(0)
    hOut := (*outHeader)(unsafe.Pointer(&buf[0]))
    hOut.Error = -int32(errno)
    h.respond(buf)
}

// All requests read from the kernel, without data, are shorter than
// this.
var maxRequestSize = syscall.Getpagesize()
var bufSize = maxRequestSize + maxWrite

// reqPool is a pool of messages.
//
// Lifetime of a logical message is from getMessage to putMessage.
// getMessage is called by ReadRequest. putMessage is called by
// Conn.ReadRequest, Request.Respond, or Request.RespondError.
//
// Messages in the pool are guaranteed to have conn and off zeroed,
// buf allocated and len==bufSize, and hdr set.
var reqPool = sync.Pool{
    New: allocMessage,
}

func allocMessage() interface{} {
    m := &message{buf: make([]byte, bufSize)}
    m.hdr = (*inHeader)(unsafe.Pointer(&m.buf[0]))
    return m
}

func getMessage(c *Conn) *message {
    m := reqPool.Get().(*message)
    m.conn = c
    return m
}

func putMessage(m *message) {
    m.buf = m.buf[:bufSize]
    m.conn = nil
    m.off = 0
    reqPool.Put(m)
}

// a message represents the bytes of a single FUSE message
type message struct {
    conn *Conn
    buf  []byte    // all bytes
    hdr  *inHeader // header
    off  int       // offset for reading additional fields
}

func (m *message) len() uintptr {
    return uintptr(len(m.buf) - m.off)
}

func (m *message) data() unsafe.Pointer {
    var p unsafe.Pointer
    if m.off < len(m.buf) {
        p = unsafe.Pointer(&m.buf[m.off])
    }
    return p
}

func (m *message) bytes() []byte {
    return m.buf[m.off:]
}

func (m *message) Header() Header {
    h := m.hdr
    return Header{
        Conn: m.conn,
        ID:   RequestID(h.Unique),
        Node: NodeID(h.Nodeid),
        Uid:  h.Uid,
        Gid:  h.Gid,
        Pid:  h.Pid,

        msg: m,
    }
}

// fileMode returns a Go os.FileMode from a Unix mode.
func fileMode(unixMode uint32) os.FileMode {
    mode := os.FileMode(unixMode & 0777)
    switch unixMode & syscall.S_IFMT {
    case syscall.S_IFREG:
        // nothing
    case syscall.S_IFDIR:
        mode |= os.ModeDir
    case syscall.S_IFCHR:
        mode |= os.ModeCharDevice | os.ModeDevice
    case syscall.S_IFBLK:
        mode |= os.ModeDevice
    case syscall.S_IFIFO:
        mode |= os.ModeNamedPipe
    case syscall.S_IFLNK:
        mode |= os.ModeSymlink
    case syscall.S_IFSOCK:
        mode |= os.ModeSocket
    default:
        // no idea
        mode |= os.ModeDevice
    }
    if unixMode&syscall.S_ISUID != 0 {
        mode |= os.ModeSetuid
    }
    if unixMode&syscall.S_ISGID != 0 {
        mode |= os.ModeSetgid
    }
    return mode
}

type noOpcode struct {
    Opcode uint32
}

func (m noOpcode) String() string {
    return fmt.Sprintf("No opcode %v", m.Opcode)
}

type malformedMessage struct {
}

func (malformedMessage) String() string {
    return "malformed message"
}

// Close closes the FUSE connection.
func (c *Conn) Close() error {
    c.wio.Lock()
    defer c.wio.Unlock()
    c.rio.Lock()
    defer c.rio.Unlock()
    return c.dev.Close()
}

// caller must hold wio or rio
func (c *Conn) fd() int {
    return int(c.dev.Fd())
}

func (c *Conn) Protocol() Protocol {
    return c.proto
}

// ReadRequest returns the next FUSE request from the kernel.
//
// Caller must call either Request.Respond or Request.RespondError in
// a reasonable time. Caller must not retain Request after that call.
func (c *Conn) ReadRequest() (Request, error) {
    m := getMessage(c)
loop:
    c.rio.RLock()
    n, err := syscall.Read(c.fd(), m.buf)
    c.rio.RUnlock()
    if err == syscall.EINTR {
        // OSXFUSE sends EINTR to userspace when a request interrupt
        // completed before it got sent to userspace?
        goto loop
    }
    if err != nil && err != syscall.ENODEV {
        putMessage(m)
        return nil, err
    }
    if n <= 0 {
        putMessage(m)
        return nil, io.EOF
    }
    m.buf = m.buf[:n]

    if n < inHeaderSize {
        putMessage(m)
        return nil, errors.New("fuse: message too short")
    }

    // FreeBSD FUSE sends a short length in the header
    // for FUSE_INIT even though the actual read length is correct.
    if n == inHeaderSize+initInSize && m.hdr.Opcode == opInit && m.hdr.Len < uint32(n) {
        m.hdr.Len = uint32(n)
    }

    // OSXFUSE sometimes sends the wrong m.hdr.Len in a FUSE_WRITE message.
    if m.hdr.Len < uint32(n) && m.hdr.Len >= uint32(unsafe.Sizeof(writeIn{})) && m.hdr.Opcode == opWrite {
        m.hdr.Len = uint32(n)
    }

    if m.hdr.Len != uint32(n) {
        // prepare error message before returning m to pool
        err := fmt.Errorf("fuse: read %d opcode %d but expected %d", n, m.hdr.Opcode, m.hdr.Len)
        putMessage(m)
        return nil, err
    }

    m.off = inHeaderSize

    // Convert to data structures.
    // Do not trust kernel to hand us well-formed data.
    var req Request
    switch m.hdr.Opcode {
    default:
        Debug(noOpcode{Opcode: m.hdr.Opcode})
        goto unrecognized

    case opLookup:
        buf := m.bytes()
        n := len(buf)
        if n == 0 || buf[n-1] != '\x00' {
            goto corrupt
        }
        req = &LookupRequest{
            Header: m.Header(),
            Name:   string(buf[:n-1]),
        }

    case opForget:
        in := (*forgetIn)(m.data())
        if m.len() < unsafe.Sizeof(*in) {
            goto corrupt
        }
        req = &ForgetRequest{
            Header: m.Header(),
            N:      in.Nlookup,
        }

    case opGetattr:
        switch {
        case c.proto.LT(Protocol{7, 9}):
            req = &GetattrRequest{
                Header: m.Header(),
            }

        default:
            in := (*getattrIn)(m.data())
            if m.len() < unsafe.Sizeof(*in) {
                goto corrupt
            }
            req = &GetattrRequest{
                Header: m.Header(),
                Flags:  GetattrFlags(in.GetattrFlags),
                Handle: HandleID(in.Fh),
            }
        }

    case opSetattr:
        in := (*setattrIn)(m.data())
        if m.len() < unsafe.Sizeof(*in) {
            goto corrupt
        }
        req = &SetattrRequest{
            Header:   m.Header(),
            Valid:    SetattrValid(in.Valid),
            Handle:   HandleID(in.Fh),
            Size:     in.Size,
            Atime:    time.Unix(int64(in.Atime), int64(in.AtimeNsec)),
            Mtime:    time.Unix(int64(in.Mtime), int64(in.MtimeNsec)),
            Mode:     fileMode(in.Mode),
            Uid:      in.Uid,
            Gid:      in.Gid,
            Bkuptime: in.BkupTime(),
            Chgtime:  in.Chgtime(),
            Flags:    in.Flags(),
        }

    case opReadlink:
        if len(m.bytes()) > 0 {
            goto corrupt
        }
        req = &ReadlinkRequest{
            Header: m.Header(),
        }

    case opSymlink:
        // m.bytes() is "newName\0target\0"
        names := m.bytes()
        if len(names) == 0 || names[len(names)-1] != 0 {
            goto corrupt
        }
        i := bytes.IndexByte(names, '\x00')
        if i < 0 {
            goto corrupt
        }
        newName, target := names[0:i], names[i+1:len(names)-1]
        req = &SymlinkRequest{
            Header:  m.Header(),
            NewName: string(newName),
            Target:  string(target),
        }

    case opLink:
        in := (*linkIn)(m.data())
        if m.len() < unsafe.Sizeof(*in) {
            goto corrupt
        }
        newName := m.bytes()[unsafe.Sizeof(*in):]
        if len(newName) < 2 || newName[len(newName)-1] != 0 {
            goto corrupt
        }
        newName = newName[:len(newName)-1]
        req = &LinkRequest{
            Header:  m.Header(),
            OldNode: NodeID(in.Oldnodeid),
            NewName: string(newName),
        }

    case opMknod:
        size := mknodInSize(c.proto)
        if m.len() < size {
            goto corrupt
        }
        in := (*mknodIn)(m.data())
        name := m.bytes()[size:]
        if len(name) < 2 || name[len(name)-1] != '\x00' {
            goto corrupt
        }
        name = name[:len(name)-1]
        r := &MknodRequest{
            Header: m.Header(),
            Mode:   fileMode(in.Mode),
            Rdev:   in.Rdev,
            Name:   string(name),
        }
        if c.proto.GE(Protocol{7, 12}) {
            r.Umask = fileMode(in.Umask) & os.ModePerm
        }
        req = r

    case opMkdir:
        size := mkdirInSize(c.proto)
        if m.len() < size {
            goto corrupt
        }
        in := (*mkdirIn)(m.data())
        name := m.bytes()[size:]
        i := bytes.IndexByte(name, '\x00')
        if i < 0 {
            goto corrupt
        }
        r := &MkdirRequest{
            Header: m.Header(),
            Name:   string(name[:i]),
            // observed on Linux: mkdirIn.Mode & syscall.S_IFMT == 0,
            // and this causes fileMode to go into it's "no idea"
            // code branch; enforce type to directory
            Mode: fileMode((in.Mode &^ syscall.S_IFMT) | syscall.S_IFDIR),
        }
        if c.proto.GE(Protocol{7, 12}) {
            r.Umask = fileMode(in.Umask) & os.ModePerm
        }
        req = r

    case opUnlink, opRmdir:
        buf := m.bytes()
        n := len(buf)
        if n == 0 || buf[n-1] != '\x00' {
            goto corrupt
        }
        req = &RemoveRequest{
            Header: m.Header(),
            Name:   string(buf[:n-1]),
            Dir:    m.hdr.Opcode == opRmdir,
        }

    case opRename:
        in := (*renameIn)(m.data())
        if m.len() < unsafe.Sizeof(*in) {
            goto corrupt
        }
        newDirNodeID := NodeID(in.Newdir)
        oldNew := m.bytes()[unsafe.Sizeof(*in):]
        // oldNew should be "old\x00new\x00"
        if len(oldNew) < 4 {
            goto corrupt
        }
        if oldNew[len(oldNew)-1] != '\x00' {
            goto corrupt
        }
        i := bytes.IndexByte(oldNew, '\x00')
        if i < 0 {
            goto corrupt
        }
        oldName, newName := string(oldNew[:i]), string(oldNew[i+1:len(oldNew)-1])
        req = &RenameRequest{
            Header:  m.Header(),
            NewDir:  newDirNodeID,
            OldName: oldName,
            NewName: newName,
        }

    case opOpendir, opOpen:
        in := (*openIn)(m.data())
        if m.len() < unsafe.Sizeof(*in) {
            goto corrupt
        }
        req = &OpenRequest{
            Header: m.Header(),
            Dir:    m.hdr.Opcode == opOpendir,
            Flags:  openFlags(in.Flags),
        }

    case opRead, opReaddir:
        in := (*readIn)(m.data())
        if m.len() < readInSize(c.proto) {
            goto corrupt
        }
        r := &ReadRequest{
            Header: m.Header(),
            Dir:    m.hdr.Opcode == opReaddir,
            Handle: HandleID(in.Fh),
            Offset: int64(in.Offset),
            Size:   int(in.Size),
        }
        if c.proto.GE(Protocol{7, 9}) {
            r.Flags = ReadFlags(in.ReadFlags)
            r.LockOwner = in.LockOwner
            r.FileFlags = openFlags(in.Flags)
        }
        req = r

    case opWrite:
        in := (*writeIn)(m.data())
        if m.len() < writeInSize(c.proto) {
            goto corrupt
        }
        r := &WriteRequest{
            Header: m.Header(),
            Handle: HandleID(in.Fh),
            Offset: int64(in.Offset),
            Flags:  WriteFlags(in.WriteFlags),
        }
        if c.proto.GE(Protocol{7, 9}) {
            r.LockOwner = in.LockOwner
            r.FileFlags = openFlags(in.Flags)
        }
        buf := m.bytes()[writeInSize(c.proto):]
        if uint32(len(buf)) < in.Size {
            goto corrupt
        }
        r.Data = buf
        req = r

    case opStatfs:
        req = &StatfsRequest{
            Header: m.Header(),
        }

    case opRelease, opReleasedir:
        in := (*releaseIn)(m.data())
        if m.len() < unsafe.Sizeof(*in) {
            goto corrupt
        }
        req = &ReleaseRequest{
            Header:       m.Header(),
            Dir:          m.hdr.Opcode == opReleasedir,
            Handle:       HandleID(in.Fh),
            Flags:        openFlags(in.Flags),
            ReleaseFlags: ReleaseFlags(in.ReleaseFlags),
            LockOwner:    in.LockOwner,
        }

    case opFsync, opFsyncdir:
        in := (*fsyncIn)(m.data())
        if m.len() < unsafe.Sizeof(*in) {
            goto corrupt
        }
        req = &FsyncRequest{
            Dir:    m.hdr.Opcode == opFsyncdir,
            Header: m.Header(),
            Handle: HandleID(in.Fh),
            Flags:  in.FsyncFlags,
        }

    case opSetxattr:
        in := (*setxattrIn)(m.data())
        if m.len() < unsafe.Sizeof(*in) {
            goto corrupt
        }
        m.off += int(unsafe.Sizeof(*in))
        name := m.bytes()
        i := bytes.IndexByte(name, '\x00')
        if i < 0 {
            goto corrupt
        }
        xattr := name[i+1:]
        if uint32(len(xattr)) < in.Size {
            goto corrupt
        }
        xattr = xattr[:in.Size]
        req = &SetxattrRequest{
            Header:   m.Header(),
            Flags:    in.Flags,
            Position: in.position(),
            Name:     string(name[:i]),
            Xattr:    xattr,
        }

    case opGetxattr:
        in := (*getxattrIn)(m.data())
        if m.len() < unsafe.Sizeof(*in) {
            goto corrupt
        }
        name := m.bytes()[unsafe.Sizeof(*in):]
        i := bytes.IndexByte(name, '\x00')
        if i < 0 {
            goto corrupt
        }
        req = &GetxattrRequest{
            Header:   m.Header(),
            Name:     string(name[:i]),
            Size:     in.Size,
            Position: in.position(),
        }

    case opListxattr:
        in := (*getxattrIn)(m.data())
        if m.len() < unsafe.Sizeof(*in) {
            goto corrupt
        }
        req = &ListxattrRequest{
            Header:   m.Header(),
            Size:     in.Size,
            Position: in.position(),
        }

    case opRemovexattr:
        buf := m.bytes()
        n := len(buf)
        if n == 0 || buf[n-1] != '\x00' {
            goto corrupt
        }
        req = &RemovexattrRequest{
            Header: m.Header(),
            Name:   string(buf[:n-1]),
        }

    case opFlush:
        in := (*flushIn)(m.data())
        if m.len() < unsafe.Sizeof(*in) {
            goto corrupt
        }
        req = &FlushRequest{
            Header:    m.Header(),
            Handle:    HandleID(in.Fh),
            Flags:     in.FlushFlags,
            LockOwner: in.LockOwner,
        }

    case opInit:
        in := (*initIn)(m.data())
        if m.len() < unsafe.Sizeof(*in) {
            goto corrupt
        }
        req = &InitRequest{
            Header:       m.Header(),
            Kernel:       Protocol{in.Major, in.Minor},
            MaxReadahead: in.MaxReadahead,
            Flags:        InitFlags(in.Flags),
        }

    case opGetlk:
        panic("opGetlk")
    case opSetlk:
        panic("opSetlk")
    case opSetlkw:
        panic("opSetlkw")

    case opAccess:
        in := (*accessIn)(m.data())
        if m.len() < unsafe.Sizeof(*in) {
            goto corrupt
        }
        req = &AccessRequest{
            Header: m.Header(),
            Mask:   in.Mask,
        }

    case opCreate:
        size := createInSize(c.proto)
        if m.len() < size {
            goto corrupt
        }
        in := (*createIn)(m.data())
        name := m.bytes()[size:]
        i := bytes.IndexByte(name, '\x00')
        if i < 0 {
            goto corrupt
        }
        r := &CreateRequest{
            Header: m.Header(),
            Flags:  openFlags(in.Flags),
            Mode:   fileMode(in.Mode),
            Name:   string(name[:i]),
        }
        if c.proto.GE(Protocol{7, 12}) {
            r.Umask = fileMode(in.Umask) & os.ModePerm
        }
        req = r

    case opInterrupt:
        in := (*interruptIn)(m.data())
        if m.len() < unsafe.Sizeof(*in) {
            goto corrupt
        }
        req = &InterruptRequest{
            Header: m.Header(),
            IntrID: RequestID(in.Unique),
        }

    case opBmap:
        panic("opBmap")

    case opDestroy:
        req = &DestroyRequest{
            Header: m.Header(),
        }

    // OS X
    case opSetvolname:
        panic("opSetvolname")
    case opGetxtimes:
        panic("opGetxtimes")
    case opExchange:
        in := (*exchangeIn)(m.data())
        if m.len() < unsafe.Sizeof(*in) {
            goto corrupt
        }
        oldDirNodeID := NodeID(in.Olddir)
        newDirNodeID := NodeID(in.Newdir)
        oldNew := m.bytes()[unsafe.Sizeof(*in):]
        // oldNew should be "oldname\x00newname\x00"
        if len(oldNew) < 4 {
            goto corrupt
        }
        if oldNew[len(oldNew)-1] != '\x00' {
            goto corrupt
        }
        i := bytes.IndexByte(oldNew, '\x00')
        if i < 0 {
            goto corrupt
        }
        oldName, newName := string(oldNew[:i]), string(oldNew[i+1:len(oldNew)-1])
        req = &ExchangeDataRequest{
            Header:  m.Header(),
            OldDir:  oldDirNodeID,
            NewDir:  newDirNodeID,
            OldName: oldName,
            NewName: newName,
            // TODO options
        }
    }

    return req, nil

corrupt:
    Debug(malformedMessage{})
    putMessage(m)
    return nil, fmt.Errorf("fuse: malformed message")

unrecognized:
    // Unrecognized message.
    // Assume higher-level code will send a "no idea what you mean" error.
    h := m.Header()
    return &h, nil
}

type bugShortKernelWrite struct {
    Written int64
    Length  int64
    Error   string
    Stack   string
}

func (b bugShortKernelWrite) String() string {
    return fmt.Sprintf("short kernel write: written=%d/%d error=%q stack=\n%s", b.Written, b.Length, b.Error, b.Stack)
}

type bugKernelWriteError struct {
    Error string
    Stack string
}

func (b bugKernelWriteError) String() string {
    return fmt.Sprintf("kernel write error: error=%q stack=\n%s", b.Error, b.Stack)
}

// safe to call even with nil error
func errorString(err error) string {
    if err == nil {
        return ""
    }
    return err.Error()
}

func (c *Conn) writeToKernel(msg []byte) error {
    out := (*outHeader)(unsafe.Pointer(&msg[0]))
    out.Len = uint32(len(msg))

    c.wio.RLock()
    defer c.wio.RUnlock()
    nn, err := syscall.Write(c.fd(), msg)
    if err == nil && nn != len(msg) {
        Debug(bugShortKernelWrite{
            Written: int64(nn),
            Length:  int64(len(msg)),
            Error:   errorString(err),
            Stack:   stack(),
        })
    }
    return err
}

func (c *Conn) respond(msg []byte) {
    if err := c.writeToKernel(msg); err != nil {
        Debug(bugKernelWriteError{
            Error: errorString(err),
            Stack: stack(),
        })
    }
}

type notCachedError struct{}

func (notCachedError) Error() string {
    return "node not cached"
}

var _ ErrorNumber = notCachedError{}

func (notCachedError) Errno() Errno {
    // Behave just like if the original syscall.ENOENT had been passed
    // straight through.
    return ENOENT
}

var (
    ErrNotCached = notCachedError{}
)

// sendInvalidate sends an invalidate notification to kernel.
//
// A returned ENOENT is translated to a friendlier error.
func (c *Conn) sendInvalidate(msg []byte) error {
    switch err := c.writeToKernel(msg); err {
    case syscall.ENOENT:
        return ErrNotCached
    default:
        return err
    }
}

// InvalidateNode invalidates the kernel cache of the attributes and a
// range of the data of a node.
//
// Giving offset 0 and size -1 means all data. To invalidate just the
// attributes, give offset 0 and size 0.
//
// Returns ErrNotCached if the kernel is not currently caching the
// node.
func (c *Conn) InvalidateNode(nodeID NodeID, off int64, size int64) error {
    buf := newBuffer(unsafe.Sizeof(notifyInvalInodeOut{}))
    h := (*outHeader)(unsafe.Pointer(&buf[0]))
    // h.Unique is 0
    h.Error = notifyCodeInvalInode
    out := (*notifyInvalInodeOut)(buf.alloc(unsafe.Sizeof(notifyInvalInodeOut{})))
    out.Ino = uint64(nodeID)
    out.Off = off
    out.Len = size
    return c.sendInvalidate(buf)
}

// InvalidateEntry invalidates the kernel cache of the directory entry
// identified by parent directory node ID and entry basename.
//
// Kernel may or may not cache directory listings. To invalidate
// those, use InvalidateNode to invalidate all of the data for a
// directory. (As of 2015-06, Linux FUSE does not cache directory
// listings.)
//
// Returns ErrNotCached if the kernel is not currently caching the
// node.
func (c *Conn) InvalidateEntry(parent NodeID, name string) error {
    const maxUint32 = ^uint32(0)
    if uint64(len(name)) > uint64(maxUint32) {
        // very unlikely, but we don't want to silently truncate
        return syscall.ENAMETOOLONG
    }
    buf := newBuffer(unsafe.Sizeof(notifyInvalEntryOut{}) + uintptr(len(name)) + 1)
    h := (*outHeader)(unsafe.Pointer(&buf[0]))
    // h.Unique is 0
    h.Error = notifyCodeInvalEntry
    out := (*notifyInvalEntryOut)(buf.alloc(unsafe.Sizeof(notifyInvalEntryOut{})))
    out.Parent = uint64(parent)
    out.Namelen = uint32(len(name))
    buf = append(buf, name...)
    buf = append(buf, '\x00')
    return c.sendInvalidate(buf)
}

// An InitRequest is the first request sent on a FUSE file system.
type InitRequest struct {
    Header `json:"-"`
    Kernel Protocol
    // Maximum readahead in bytes that the kernel plans to use.
    MaxReadahead uint32
    Flags        InitFlags
}

var _ = Request(&InitRequest{})

func (r *InitRequest) String() string {
    return fmt.Sprintf("Init [%v] %v ra=%d fl=%v", &r.Header, r.Kernel, r.MaxReadahead, r.Flags)
}

// An InitResponse is the response to an InitRequest.
type InitResponse struct {
    Library Protocol
    // Maximum readahead in bytes that the kernel can use. Ignored if
    // greater than InitRequest.MaxReadahead.
    MaxReadahead uint32
    Flags        InitFlags
    // Maximum size of a single write operation.
    // Linux enforces a minimum of 4 KiB.
    MaxWrite uint32
}

func (r *InitResponse) String() string {
    return fmt.Sprintf("Init %v ra=%d fl=%v w=%d", r.Library, r.MaxReadahead, r.Flags, r.MaxWrite)
}

// Respond replies to the request with the given response.
func (r *InitRequest) Respond(resp *InitResponse) {
    buf := newBuffer(unsafe.Sizeof(initOut{}))
    out := (*initOut)(buf.alloc(unsafe.Sizeof(initOut{})))
    out.Major = resp.Library.Major
    out.Minor = resp.Library.Minor
    out.MaxReadahead = resp.MaxReadahead
    out.Flags = uint32(resp.Flags)
    out.MaxWrite = resp.MaxWrite

    // MaxWrite larger than our receive buffer would just lead to
    // errors on large writes.
    if out.MaxWrite > maxWrite {
        out.MaxWrite = maxWrite
    }
    r.respond(buf)
}

// A StatfsRequest requests information about the mounted file system.
type StatfsRequest struct {
    Header `json:"-"`
}

var _ = Request(&StatfsRequest{})

func (r *StatfsRequest) String() string {
    return fmt.Sprintf("Statfs [%s]", &r.Header)
}

// Respond replies to the request with the given response.
func (r *StatfsRequest) Respond(resp *StatfsResponse) {
    buf := newBuffer(unsafe.Sizeof(statfsOut{}))
    out := (*statfsOut)(buf.alloc(unsafe.Sizeof(statfsOut{})))
    out.St = kstatfs{
        Blocks:  resp.Blocks,
        Bfree:   resp.Bfree,
        Bavail:  resp.Bavail,
        Files:   resp.Files,
        Bsize:   resp.Bsize,
        Namelen: resp.Namelen,
        Frsize:  resp.Frsize,
    }
    r.respond(buf)
}

// A StatfsResponse is the response to a StatfsRequest.
type StatfsResponse struct {
    Blocks  uint64 // Total data blocks in file system.
    Bfree   uint64 // Free blocks in file system.
    Bavail  uint64 // Free blocks in file system if you're not root.
    Files   uint64 // Total files in file system.
    Ffree   uint64 // Free files in file system.
    Bsize   uint32 // Block size
    Namelen uint32 // Maximum file name length?
    Frsize  uint32 // Fragment size, smallest addressable data size in the file system.
}

func (r *StatfsResponse) String() string {
    return fmt.Sprintf("Statfs blocks=%d/%d/%d files=%d/%d bsize=%d frsize=%d namelen=%d",
        r.Bavail, r.Bfree, r.Blocks,
        r.Ffree, r.Files,
        r.Bsize,
        r.Frsize,
        r.Namelen,
    )
}

// An AccessRequest asks whether the file can be accessed
// for the purpose specified by the mask.
type AccessRequest struct {
    Header `json:"-"`
    Mask   uint32
}

var _ = Request(&AccessRequest{})

func (r *AccessRequest) String() string {
    return fmt.Sprintf("Access [%s] mask=%#x", &r.Header, r.Mask)
}

// Respond replies to the request indicating that access is allowed.
// To deny access, use RespondError.
func (r *AccessRequest) Respond() {
    buf := newBuffer(0)
    r.respond(buf)
}

// An Attr is the metadata for a single file or directory.
type Attr struct {
    Valid time.Duration // how long Attr can be cached

    Inode     uint64      // inode number
    Size      uint64      // size in bytes
    Blocks    uint64      // size in 512-byte units
    Atime     time.Time   // time of last access
    Mtime     time.Time   // time of last modification
    Ctime     time.Time   // time of last inode change
    Crtime    time.Time   // time of creation (OS X only)
    Mode      os.FileMode // file mode
    Nlink     uint32      // number of links (usually 1)
    Uid       uint32      // owner uid
    Gid       uint32      // group gid
    Rdev      uint32      // device numbers
    Flags     uint32      // chflags(2) flags (OS X only)
    BlockSize uint32      // preferred blocksize for filesystem I/O
}

func (a Attr) String() string {
    return fmt.Sprintf("valid=%v ino=%v size=%d mode=%v", a.Valid, a.Inode, a.Size, a.Mode)
}

func unix(t time.Time) (sec uint64, nsec uint32) {
    nano := t.UnixNano()
    sec = uint64(nano / 1e9)
    nsec = uint32(nano % 1e9)
    return
}

func (a *Attr) attr(out *attr, proto Protocol) {
    out.Ino = a.Inode
    out.Size = a.Size
    out.Blocks = a.Blocks
    out.Atime, out.AtimeNsec = unix(a.Atime)
    out.Mtime, out.MtimeNsec = unix(a.Mtime)
    out.Ctime, out.CtimeNsec = unix(a.Ctime)
    out.SetCrtime(unix(a.Crtime))
    out.Mode = uint32(a.Mode) & 0777
    switch {
    default:
        out.Mode |= syscall.S_IFREG
    case a.Mode&os.ModeDir != 0:
        out.Mode |= syscall.S_IFDIR
    case a.Mode&os.ModeDevice != 0:
        if a.Mode&os.ModeCharDevice != 0 {
            out.Mode |= syscall.S_IFCHR
        } else {
            out.Mode |= syscall.S_IFBLK
        }
    case a.Mode&os.ModeNamedPipe != 0:
        out.Mode |= syscall.S_IFIFO
    case a.Mode&os.ModeSymlink != 0:
        out.Mode |= syscall.S_IFLNK
    case a.Mode&os.ModeSocket != 0:
        out.Mode |= syscall.S_IFSOCK
    }
    if a.Mode&os.ModeSetuid != 0 {
        out.Mode |= syscall.S_ISUID
    }
    if a.Mode&os.ModeSetgid != 0 {
        out.Mode |= syscall.S_ISGID
    }
    out.Nlink = a.Nlink
    out.Uid = a.Uid
    out.Gid = a.Gid
    out.Rdev = a.Rdev
    out.SetFlags(a.Flags)
    if proto.GE(Protocol{7, 9}) {
        out.Blksize = a.BlockSize
    }

    return
}

// A GetattrRequest asks for the metadata for the file denoted by r.Node.
type GetattrRequest struct {
    Header `json:"-"`
    Flags  GetattrFlags
    Handle HandleID
}

var _ = Request(&GetattrRequest{})

func (r *GetattrRequest) String() string {
    return fmt.Sprintf("Getattr [%s] %v fl=%v", &r.Header, r.Handle, r.Flags)
}

// Respond replies to the request with the given response.
func (r *GetattrRequest) Respond(resp *GetattrResponse) {
    size := attrOutSize(r.Header.Conn.proto)
    buf := newBuffer(size)
    out := (*attrOut)(buf.alloc(size))
    out.AttrValid = uint64(resp.Attr.Valid / time.Second)
    out.AttrValidNsec = uint32(resp.Attr.Valid % time.Second / time.Nanosecond)
    resp.Attr.attr(&out.Attr, r.Header.Conn.proto)
    r.respond(buf)
}

// A GetattrResponse is the response to a GetattrRequest.
type GetattrResponse struct {
    Attr Attr // file attributes
}

func (r *GetattrResponse) String() string {
    return fmt.Sprintf("Getattr %v", r.Attr)
}

// A GetxattrRequest asks for the extended attributes associated with r.Node.
type GetxattrRequest struct {
    Header `json:"-"`

    // Maximum size to return.
    Size uint32

    // Name of the attribute requested.
    Name string

    // Offset within extended attributes.
    //
    // Only valid for OS X, and then only with the resource fork
    // attribute.
    Position uint32
}

var _ = Request(&GetxattrRequest{})

func (r *GetxattrRequest) String() string {
    return fmt.Sprintf("Getxattr [%s] %q %d @%d", &r.Header, r.Name, r.Size, r.Position)
}

// Respond replies to the request with the given response.
func (r *GetxattrRequest) Respond(resp *GetxattrResponse) {
    if r.Size == 0 {
        buf := newBuffer(unsafe.Sizeof(getxattrOut{}))
        out := (*getxattrOut)(buf.alloc(unsafe.Sizeof(getxattrOut{})))
        out.Size = uint32(len(resp.Xattr))
        r.respond(buf)
    } else {
        buf := newBuffer(uintptr(len(resp.Xattr)))
        buf = append(buf, resp.Xattr...)
        r.respond(buf)
    }
}

// A GetxattrResponse is the response to a GetxattrRequest.
type GetxattrResponse struct {
    Xattr []byte
}

func (r *GetxattrResponse) String() string {
    return fmt.Sprintf("Getxattr %x", r.Xattr)
}

// A ListxattrRequest asks to list the extended attributes associated with r.Node.
type ListxattrRequest struct {
    Header   `json:"-"`
    Size     uint32 // maximum size to return
    Position uint32 // offset within attribute list
}

var _ = Request(&ListxattrRequest{})

func (r *ListxattrRequest) String() string {
    return fmt.Sprintf("Listxattr [%s] %d @%d", &r.Header, r.Size, r.Position)
}

// Respond replies to the request with the given response.
func (r *ListxattrRequest) Respond(resp *ListxattrResponse) {
    if r.Size == 0 {
        buf := newBuffer(unsafe.Sizeof(getxattrOut{}))
        out := (*getxattrOut)(buf.alloc(unsafe.Sizeof(getxattrOut{})))
        out.Size = uint32(len(resp.Xattr))
        r.respond(buf)
    } else {
        buf := newBuffer(uintptr(len(resp.Xattr)))
        buf = append(buf, resp.Xattr...)
        r.respond(buf)
    }
}

// A ListxattrResponse is the response to a ListxattrRequest.
type ListxattrResponse struct {
    Xattr []byte
}

func (r *ListxattrResponse) String() string {
    return fmt.Sprintf("Listxattr %x", r.Xattr)
}

// Append adds an extended attribute name to the response.
func (r *ListxattrResponse) Append(names ...string) {
    for _, name := range names {
        r.Xattr = append(r.Xattr, name...)
        r.Xattr = append(r.Xattr, '\x00')
    }
}

// A RemovexattrRequest asks to remove an extended attribute associated with r.Node.
type RemovexattrRequest struct {
    Header `json:"-"`
    Name   string // name of extended attribute
}

var _ = Request(&RemovexattrRequest{})

func (r *RemovexattrRequest) String() string {
    return fmt.Sprintf("Removexattr [%s] %q", &r.Header, r.Name)
}

// Respond replies to the request, indicating that the attribute was removed.
func (r *RemovexattrRequest) Respond() {
    buf := newBuffer(0)
    r.respond(buf)
}

// A SetxattrRequest asks to set an extended attribute associated with a file.
type SetxattrRequest struct {
    Header `json:"-"`

    // Flags can make the request fail if attribute does/not already
    // exist. Unfortunately, the constants are platform-specific and
    // not exposed by Go1.2. Look for XATTR_CREATE, XATTR_REPLACE.
    //
    // TODO improve this later
    //
    // TODO XATTR_CREATE and exist -> EEXIST
    //
    // TODO XATTR_REPLACE and not exist -> ENODATA
    Flags uint32

    // Offset within extended attributes.
    //
    // Only valid for OS X, and then only with the resource fork
    // attribute.
    Position uint32

    Name  string
    Xattr []byte
}

var _ = Request(&SetxattrRequest{})

func trunc(b []byte, max int) ([]byte, string) {
    if len(b) > max {
        return b[:max], "..."
    }
    return b, ""
}

func (r *SetxattrRequest) String() string {
    xattr, tail := trunc(r.Xattr, 16)
    return fmt.Sprintf("Setxattr [%s] %q %x%s fl=%v @%#x", &r.Header, r.Name, xattr, tail, r.Flags, r.Position)
}

// Respond replies to the request, indicating that the extended attribute was set.
func (r *SetxattrRequest) Respond() {
    buf := newBuffer(0)
    r.respond(buf)
}

// A LookupRequest asks to look up the given name in the directory named by r.Node.
type LookupRequest struct {
    Header `json:"-"`
    Name   string
}

var _ = Request(&LookupRequest{})

func (r *LookupRequest) String() string {
    return fmt.Sprintf("Lookup [%s] %q", &r.Header, r.Name)
}

// Respond replies to the request with the given response.
func (r *LookupRequest) Respond(resp *LookupResponse) {
    size := entryOutSize(r.Header.Conn.proto)
    buf := newBuffer(size)
    out := (*entryOut)(buf.alloc(size))
    out.Nodeid = uint64(resp.Node)
    out.Generation = resp.Generation
    out.EntryValid = uint64(resp.EntryValid / time.Second)
    out.EntryValidNsec = uint32(resp.EntryValid % time.Second / time.Nanosecond)
    out.AttrValid = uint64(resp.Attr.Valid / time.Second)
    out.AttrValidNsec = uint32(resp.Attr.Valid % time.Second / time.Nanosecond)
    resp.Attr.attr(&out.Attr, r.Header.Conn.proto)
    r.respond(buf)
}

// A LookupResponse is the response to a LookupRequest.
type LookupResponse struct {
    Node       NodeID
    Generation uint64
    EntryValid time.Duration
    Attr       Attr
}

func (r *LookupResponse) string() string {
    return fmt.Sprintf("%v gen=%d valid=%v attr={%v}", r.Node, r.Generation, r.EntryValid, r.Attr)
}

func (r *LookupResponse) String() string {
    return fmt.Sprintf("Lookup %s", r.string())
}

// An OpenRequest asks to open a file or directory
type OpenRequest struct {
    Header `json:"-"`
    Dir    bool // is this Opendir?
    Flags  OpenFlags
}

var _ = Request(&OpenRequest{})

func (r *OpenRequest) String() string {
    return fmt.Sprintf("Open [%s] dir=%v fl=%v", &r.Header, r.Dir, r.Flags)
}

// Respond replies to the request with the given response.
func (r *OpenRequest) Respond(resp *OpenResponse) {
    buf := newBuffer(unsafe.Sizeof(openOut{}))
    out := (*openOut)(buf.alloc(unsafe.Sizeof(openOut{})))
    out.Fh = uint64(resp.Handle)
    out.OpenFlags = uint32(resp.Flags)
    r.respond(buf)
}

// A OpenResponse is the response to a OpenRequest.
type OpenResponse struct {
    Handle HandleID
    Flags  OpenResponseFlags
}

func (r *OpenResponse) string() string {
    return fmt.Sprintf("%v fl=%v", r.Handle, r.Flags)
}

func (r *OpenResponse) String() string {
    return fmt.Sprintf("Open %s", r.string())
}

// A CreateRequest asks to create and open a file (not a directory).
type CreateRequest struct {
    Header `json:"-"`
    Name   string
    Flags  OpenFlags
    Mode   os.FileMode
    // Umask of the request. Not supported on OS X.
    Umask os.FileMode
}

var _ = Request(&CreateRequest{})

func (r *CreateRequest) String() string {
    return fmt.Sprintf("Create [%s] %q fl=%v mode=%v umask=%v", &r.Header, r.Name, r.Flags, r.Mode, r.Umask)
}

// Respond replies to the request with the given response.
func (r *CreateRequest) Respond(resp *CreateResponse) {
    eSize := entryOutSize(r.Header.Conn.proto)
    buf := newBuffer(eSize + unsafe.Sizeof(openOut{}))

    e := (*entryOut)(buf.alloc(eSize))
    e.Nodeid = uint64(resp.Node)
    e.Generation = resp.Generation
    e.EntryValid = uint64(resp.EntryValid / time.Second)
    e.EntryValidNsec = uint32(resp.EntryValid % time.Second / time.Nanosecond)
    e.AttrValid = uint64(resp.Attr.Valid / time.Second)
    e.AttrValidNsec = uint32(resp.Attr.Valid % time.Second / time.Nanosecond)
    resp.Attr.attr(&e.Attr, r.Header.Conn.proto)

    o := (*openOut)(buf.alloc(unsafe.Sizeof(openOut{})))
    o.Fh = uint64(resp.Handle)
    o.OpenFlags = uint32(resp.Flags)

    r.respond(buf)
}

// A CreateResponse is the response to a CreateRequest.
// It describes the created node and opened handle.
type CreateResponse struct {
    LookupResponse
    OpenResponse
}

func (r *CreateResponse) String() string {
    return fmt.Sprintf("Create {%s} {%s}", r.LookupResponse.string(), r.OpenResponse.string())
}

// A MkdirRequest asks to create (but not open) a directory.
type MkdirRequest struct {
    Header `json:"-"`
    Name   string
    Mode   os.FileMode
    // Umask of the request. Not supported on OS X.
    Umask os.FileMode
}

var _ = Request(&MkdirRequest{})

func (r *MkdirRequest) String() string {
    return fmt.Sprintf("Mkdir [%s] %q mode=%v umask=%v", &r.Header, r.Name, r.Mode, r.Umask)
}

// Respond replies to the request with the given response.
func (r *MkdirRequest) Respond(resp *MkdirResponse) {
    size := entryOutSize(r.Header.Conn.proto)
    buf := newBuffer(size)
    out := (*entryOut)(buf.alloc(size))
    out.Nodeid = uint64(resp.Node)
    out.Generation = resp.Generation
    out.EntryValid = uint64(resp.EntryValid / time.Second)
    out.EntryValidNsec = uint32(resp.EntryValid % time.Second / time.Nanosecond)
    out.AttrValid = uint64(resp.Attr.Valid / time.Second)
    out.AttrValidNsec = uint32(resp.Attr.Valid % time.Second / time.Nanosecond)
    resp.Attr.attr(&out.Attr, r.Header.Conn.proto)
    r.respond(buf)
}

// A MkdirResponse is the response to a MkdirRequest.
type MkdirResponse struct {
    LookupResponse
}

func (r *MkdirResponse) String() string {
    return fmt.Sprintf("Mkdir %v", r.LookupResponse.string())
}

// A ReadRequest asks to read from an open file.
type ReadRequest struct {
    Header    `json:"-"`
    Dir       bool // is this Readdir?
    Handle    HandleID
    Offset    int64
    Size      int
    Flags     ReadFlags
    LockOwner uint64
    FileFlags OpenFlags
}

var _ = Request(&ReadRequest{})

func (r *ReadRequest) String() string {
    return fmt.Sprintf("Read [%s] %v %d @%#x dir=%v fl=%v lock=%d ffl=%v", &r.Header, r.Handle, r.Size, r.Offset, r.Dir, r.Flags, r.LockOwner, r.FileFlags)
}

// Respond replies to the request with the given response.
func (r *ReadRequest) Respond(resp *ReadResponse) {
    buf := newBuffer(uintptr(len(resp.Data)))
    buf = append(buf, resp.Data...)
    r.respond(buf)
}

// A ReadResponse is the response to a ReadRequest.
type ReadResponse struct {
    Data []byte
}

func (r *ReadResponse) String() string {
    return fmt.Sprintf("Read %d", len(r.Data))
}

type jsonReadResponse struct {
    Len uint64
}

func (r *ReadResponse) MarshalJSON() ([]byte, error) {
    j := jsonReadResponse{
        Len: uint64(len(r.Data)),
    }
    return json.Marshal(j)
}

// A ReleaseRequest asks to release (close) an open file handle.
type ReleaseRequest struct {
    Header       `json:"-"`
    Dir          bool // is this Releasedir?
    Handle       HandleID
    Flags        OpenFlags // flags from OpenRequest
    ReleaseFlags ReleaseFlags
    LockOwner    uint32
}

var _ = Request(&ReleaseRequest{})

func (r *ReleaseRequest) String() string {
    return fmt.Sprintf("Release [%s] %v fl=%v rfl=%v owner=%#x", &r.Header, r.Handle, r.Flags, r.ReleaseFlags, r.LockOwner)
}

// Respond replies to the request, indicating that the handle has been released.
func (r *ReleaseRequest) Respond() {
    buf := newBuffer(0)
    r.respond(buf)
}

// A DestroyRequest is sent by the kernel when unmounting the file system.
// No more requests will be received after this one, but it should still be
// responded to.
type DestroyRequest struct {
    Header `json:"-"`
}

var _ = Request(&DestroyRequest{})

func (r *DestroyRequest) String() string {
    return fmt.Sprintf("Destroy [%s]", &r.Header)
}

// Respond replies to the request.
func (r *DestroyRequest) Respond() {
    buf := newBuffer(0)
    r.respond(buf)
}

// A ForgetRequest is sent by the kernel when forgetting about r.Node
// as returned by r.N lookup requests.
type ForgetRequest struct {
    Header `json:"-"`
    N      uint64
}

var _ = Request(&ForgetRequest{})

func (r *ForgetRequest) String() string {
    return fmt.Sprintf("Forget [%s] %d", &r.Header, r.N)
}

// Respond replies to the request, indicating that the forgetfulness has been recorded.
func (r *ForgetRequest) Respond() {
    // Don't reply to forget messages.
    r.noResponse()
}

// A Dirent represents a single directory entry.
type Dirent struct {
    // Inode this entry names.
    Inode uint64

    // Type of the entry, for example DT_File.
    //
    // Setting this is optional. The zero value (DT_Unknown) means
    // callers will just need to do a Getattr when the type is
    // needed. Providing a type can speed up operations
    // significantly.
    Type DirentType

    // Name of the entry
    Name string
}

// Type of an entry in a directory listing.
type DirentType uint32

const (
    // These don't quite match os.FileMode; especially there's an
    // explicit unknown, instead of zero value meaning file. They
    // are also not quite syscall.DT_*; nothing says the FUSE
    // protocol follows those, and even if they were, we don't
    // want each fs to fiddle with syscall.

    // The shift by 12 is hardcoded in the FUSE userspace
    // low-level C library, so it's safe here.

    DT_Unknown DirentType = 0
    DT_Socket  DirentType = syscall.S_IFSOCK >> 12
    DT_Link    DirentType = syscall.S_IFLNK >> 12
    DT_File    DirentType = syscall.S_IFREG >> 12
    DT_Block   DirentType = syscall.S_IFBLK >> 12
    DT_Dir     DirentType = syscall.S_IFDIR >> 12
    DT_Char    DirentType = syscall.S_IFCHR >> 12
    DT_FIFO    DirentType = syscall.S_IFIFO >> 12
)

func (t DirentType) String() string {
    switch t {
    case DT_Unknown:
        return "unknown"
    case DT_Socket:
        return "socket"
    case DT_Link:
        return "link"
    case DT_File:
        return "file"
    case DT_Block:
        return "block"
    case DT_Dir:
        return "dir"
    case DT_Char:
        return "char"
    case DT_FIFO:
        return "fifo"
    }
    return "invalid"
}

// AppendDirent appends the encoded form of a directory entry to data
// and returns the resulting slice.
func AppendDirent(data []byte, dir Dirent) []byte {
    de := dirent{
        Ino:     dir.Inode,
        Namelen: uint32(len(dir.Name)),
        Type:    uint32(dir.Type),
    }
    de.Off = uint64(len(data) + direntSize + (len(dir.Name)+7)&^7)
    data = append(data, (*[direntSize]byte)(unsafe.Pointer(&de))[:]...)
    data = append(data, dir.Name...)
    n := direntSize + uintptr(len(dir.Name))
    if n%8 != 0 {
        var pad [8]byte
        data = append(data, pad[:8-n%8]...)
    }
    return data
}

// A WriteRequest asks to write to an open file.
type WriteRequest struct {
    Header
    Handle    HandleID
    Offset    int64
    Data      []byte
    Flags     WriteFlags
    LockOwner uint64
    FileFlags OpenFlags
}

var _ = Request(&WriteRequest{})

func (r *WriteRequest) String() string {
    return fmt.Sprintf("Write [%s] %v %d @%d fl=%v lock=%d ffl=%v", &r.Header, r.Handle, len(r.Data), r.Offset, r.Flags, r.LockOwner, r.FileFlags)
}

type jsonWriteRequest struct {
    Handle HandleID
    Offset int64
    Len    uint64
    Flags  WriteFlags
}

func (r *WriteRequest) MarshalJSON() ([]byte, error) {
    j := jsonWriteRequest{
        Handle: r.Handle,
        Offset: r.Offset,
        Len:    uint64(len(r.Data)),
        Flags:  r.Flags,
    }
    return json.Marshal(j)
}

// Respond replies to the request with the given response.
func (r *WriteRequest) Respond(resp *WriteResponse) {
    buf := newBuffer(unsafe.Sizeof(writeOut{}))
    out := (*writeOut)(buf.alloc(unsafe.Sizeof(writeOut{})))
    out.Size = uint32(resp.Size)
    r.respond(buf)
}

// A WriteResponse replies to a write indicating how many bytes were written.
type WriteResponse struct {
    Size int
}

func (r *WriteResponse) String() string {
    return fmt.Sprintf("Write %d", r.Size)
}

// A SetattrRequest asks to change one or more attributes associated with a file,
// as indicated by Valid.
type SetattrRequest struct {
    Header `json:"-"`
    Valid  SetattrValid
    Handle HandleID
    Size   uint64
    Atime  time.Time
    Mtime  time.Time
    Mode   os.FileMode
    Uid    uint32
    Gid    uint32

    // OS X only
    Bkuptime time.Time
    Chgtime  time.Time
    Crtime   time.Time
    Flags    uint32 // see chflags(2)
}

var _ = Request(&SetattrRequest{})

func (r *SetattrRequest) String() string {
    var buf bytes.Buffer
    fmt.Fprintf(&buf, "Setattr [%s]", &r.Header)
    if r.Valid.Mode() {
        fmt.Fprintf(&buf, " mode=%v", r.Mode)
    }
    if r.Valid.Uid() {
        fmt.Fprintf(&buf, " uid=%d", r.Uid)
    }
    if r.Valid.Gid() {
        fmt.Fprintf(&buf, " gid=%d", r.Gid)
    }
    if r.Valid.Size() {
        fmt.Fprintf(&buf, " size=%d", r.Size)
    }
    if r.Valid.Atime() {
        fmt.Fprintf(&buf, " atime=%v", r.Atime)
    }
    if r.Valid.AtimeNow() {
        fmt.Fprintf(&buf, " atime=now")
    }
    if r.Valid.Mtime() {
        fmt.Fprintf(&buf, " mtime=%v", r.Mtime)
    }
    if r.Valid.MtimeNow() {
        fmt.Fprintf(&buf, " mtime=now")
    }
    if r.Valid.Handle() {
        fmt.Fprintf(&buf, " handle=%v", r.Handle)
    } else {
        fmt.Fprintf(&buf, " handle=INVALID-%v", r.Handle)
    }
    if r.Valid.LockOwner() {
        fmt.Fprintf(&buf, " lockowner")
    }
    if r.Valid.Crtime() {
        fmt.Fprintf(&buf, " crtime=%v", r.Crtime)
    }
    if r.Valid.Chgtime() {
        fmt.Fprintf(&buf, " chgtime=%v", r.Chgtime)
    }
    if r.Valid.Bkuptime() {
        fmt.Fprintf(&buf, " bkuptime=%v", r.Bkuptime)
    }
    if r.Valid.Flags() {
        fmt.Fprintf(&buf, " flags=%v", r.Flags)
    }
    return buf.String()
}

// Respond replies to the request with the given response,
// giving the updated attributes.
func (r *SetattrRequest) Respond(resp *SetattrResponse) {
    size := attrOutSize(r.Header.Conn.proto)
    buf := newBuffer(size)
    out := (*attrOut)(buf.alloc(size))
    out.AttrValid = uint64(resp.Attr.Valid / time.Second)
    out.AttrValidNsec = uint32(resp.Attr.Valid % time.Second / time.Nanosecond)
    resp.Attr.attr(&out.Attr, r.Header.Conn.proto)
    r.respond(buf)
}

// A SetattrResponse is the response to a SetattrRequest.
type SetattrResponse struct {
    Attr Attr // file attributes
}

func (r *SetattrResponse) String() string {
    return fmt.Sprintf("Setattr %v", r.Attr)
}

// A FlushRequest asks for the current state of an open file to be flushed
// to storage, as when a file descriptor is being closed.  A single opened Handle
// may receive multiple FlushRequests over its lifetime.
type FlushRequest struct {
    Header    `json:"-"`
    Handle    HandleID
    Flags     uint32
    LockOwner uint64
}

var _ = Request(&FlushRequest{})

func (r *FlushRequest) String() string {
    return fmt.Sprintf("Flush [%s] %v fl=%#x lk=%#x", &r.Header, r.Handle, r.Flags, r.LockOwner)
}

// Respond replies to the request, indicating that the flush succeeded.
func (r *FlushRequest) Respond() {
    buf := newBuffer(0)
    r.respond(buf)
}

// A RemoveRequest asks to remove a file or directory from the
// directory r.Node.
type RemoveRequest struct {
    Header `json:"-"`
    Name   string // name of the entry to remove
    Dir    bool   // is this rmdir?
}

var _ = Request(&RemoveRequest{})

func (r *RemoveRequest) String() string {
    return fmt.Sprintf("Remove [%s] %q dir=%v", &r.Header, r.Name, r.Dir)
}

// Respond replies to the request, indicating that the file was removed.
func (r *RemoveRequest) Respond() {
    buf := newBuffer(0)
    r.respond(buf)
}

// A SymlinkRequest is a request to create a symlink making NewName point to Target.
type SymlinkRequest struct {
    Header          `json:"-"`
    NewName, Target string
}

var _ = Request(&SymlinkRequest{})

func (r *SymlinkRequest) String() string {
    return fmt.Sprintf("Symlink [%s] from %q to target %q", &r.Header, r.NewName, r.Target)
}

// Respond replies to the request, indicating that the symlink was created.
func (r *SymlinkRequest) Respond(resp *SymlinkResponse) {
    size := entryOutSize(r.Header.Conn.proto)
    buf := newBuffer(size)
    out := (*entryOut)(buf.alloc(size))
    out.Nodeid = uint64(resp.Node)
    out.Generation = resp.Generation
    out.EntryValid = uint64(resp.EntryValid / time.Second)
    out.EntryValidNsec = uint32(resp.EntryValid % time.Second / time.Nanosecond)
    out.AttrValid = uint64(resp.Attr.Valid / time.Second)
    out.AttrValidNsec = uint32(resp.Attr.Valid % time.Second / time.Nanosecond)
    resp.Attr.attr(&out.Attr, r.Header.Conn.proto)
    r.respond(buf)
}

// A SymlinkResponse is the response to a SymlinkRequest.
type SymlinkResponse struct {
    LookupResponse
}

func (r *SymlinkResponse) String() string {
    return fmt.Sprintf("Symlink %v", r.LookupResponse.string())
}

// A ReadlinkRequest is a request to read a symlink's target.
type ReadlinkRequest struct {
    Header `json:"-"`
}

var _ = Request(&ReadlinkRequest{})

func (r *ReadlinkRequest) String() string {
    return fmt.Sprintf("Readlink [%s]", &r.Header)
}

func (r *ReadlinkRequest) Respond(target string) {
    buf := newBuffer(uintptr(len(target)))
    buf = append(buf, target...)
    r.respond(buf)
}

// A LinkRequest is a request to create a hard link.
type LinkRequest struct {
    Header  `json:"-"`
    OldNode NodeID
    NewName string
}

var _ = Request(&LinkRequest{})

func (r *LinkRequest) String() string {
    return fmt.Sprintf("Link [%s] node %d to %q", &r.Header, r.OldNode, r.NewName)
}

func (r *LinkRequest) Respond(resp *LookupResponse) {
    size := entryOutSize(r.Header.Conn.proto)
    buf := newBuffer(size)
    out := (*entryOut)(buf.alloc(size))
    out.Nodeid = uint64(resp.Node)
    out.Generation = resp.Generation
    out.EntryValid = uint64(resp.EntryValid / time.Second)
    out.EntryValidNsec = uint32(resp.EntryValid % time.Second / time.Nanosecond)
    out.AttrValid = uint64(resp.Attr.Valid / time.Second)
    out.AttrValidNsec = uint32(resp.Attr.Valid % time.Second / time.Nanosecond)
    resp.Attr.attr(&out.Attr, r.Header.Conn.proto)
    r.respond(buf)
}

// A RenameRequest is a request to rename a file.
type RenameRequest struct {
    Header           `json:"-"`
    NewDir           NodeID
    OldName, NewName string
}

var _ = Request(&RenameRequest{})

func (r *RenameRequest) String() string {
    return fmt.Sprintf("Rename [%s] from %q to dirnode %v %q", &r.Header, r.OldName, r.NewDir, r.NewName)
}

func (r *RenameRequest) Respond() {
    buf := newBuffer(0)
    r.respond(buf)
}

type MknodRequest struct {
    Header `json:"-"`
    Name   string
    Mode   os.FileMode
    Rdev   uint32
    // Umask of the request. Not supported on OS X.
    Umask os.FileMode
}

var _ = Request(&MknodRequest{})

func (r *MknodRequest) String() string {
    return fmt.Sprintf("Mknod [%s] Name %q mode=%v umask=%v rdev=%d", &r.Header, r.Name, r.Mode, r.Umask, r.Rdev)
}

func (r *MknodRequest) Respond(resp *LookupResponse) {
    size := entryOutSize(r.Header.Conn.proto)
    buf := newBuffer(size)
    out := (*entryOut)(buf.alloc(size))
    out.Nodeid = uint64(resp.Node)
    out.Generation = resp.Generation
    out.EntryValid = uint64(resp.EntryValid / time.Second)
    out.EntryValidNsec = uint32(resp.EntryValid % time.Second / time.Nanosecond)
    out.AttrValid = uint64(resp.Attr.Valid / time.Second)
    out.AttrValidNsec = uint32(resp.Attr.Valid % time.Second / time.Nanosecond)
    resp.Attr.attr(&out.Attr, r.Header.Conn.proto)
    r.respond(buf)
}

type FsyncRequest struct {
    Header `json:"-"`
    Handle HandleID
    // TODO bit 1 is datasync, not well documented upstream
    Flags uint32
    Dir   bool
}

var _ = Request(&FsyncRequest{})

func (r *FsyncRequest) String() string {
    return fmt.Sprintf("Fsync [%s] Handle %v Flags %v", &r.Header, r.Handle, r.Flags)
}

func (r *FsyncRequest) Respond() {
    buf := newBuffer(0)
    r.respond(buf)
}

// An InterruptRequest is a request to interrupt another pending request. The
// response to that request should return an error status of EINTR.
type InterruptRequest struct {
    Header `json:"-"`
    IntrID RequestID // ID of the request to be interrupt.
}

var _ = Request(&InterruptRequest{})

func (r *InterruptRequest) Respond() {
    // nothing to do here
    r.noResponse()
}

func (r *InterruptRequest) String() string {
    return fmt.Sprintf("Interrupt [%s] ID %v", &r.Header, r.IntrID)
}

// An ExchangeDataRequest is a request to exchange the contents of two
// files, while leaving most metadata untouched.
//
// This request comes from OS X exchangedata(2) and represents its
// specific semantics. Crucially, it is very different from Linux
// renameat(2) RENAME_EXCHANGE.
//
// https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man2/exchangedata.2.html
type ExchangeDataRequest struct {
    Header           `json:"-"`
    OldDir, NewDir   NodeID
    OldName, NewName string
    // TODO options
}

var _ = Request(&ExchangeDataRequest{})

func (r *ExchangeDataRequest) String() string {
    // TODO options
    return fmt.Sprintf("ExchangeData [%s] %v %q and %v %q", &r.Header, r.OldDir, r.OldName, r.NewDir, r.NewName)
}

func (r *ExchangeDataRequest) Respond() {
    buf := newBuffer(0)
    r.respond(buf)
}