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// Copyright 2011 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 os

import (
        "runtime"
        "syscall"
        "time"
)

// File represents an open file descriptor.
type File struct {
        *file
}

// file is the real representation of *File.
// The extra level of indirection ensures that no clients of os
// can overwrite this data, which could cause the finalizer
// to close the wrong file descriptor.
type file struct {
        fd      int
        name    string
        dirinfo *dirInfo // nil unless directory being read
}

// Fd returns the integer Unix file descriptor referencing the open file.
func (file *File) Fd() int {
        if file == nil {
                return -1
        }
        return file.fd
}

// NewFile returns a new File with the given file descriptor and name.
func NewFile(fd int, name string) *File {
        if fd < 0 {
                return nil
        }
        f := &File{&file{fd: fd, name: name}}
        runtime.SetFinalizer(f.file, (*file).close)
        return f
}

// Auxiliary information if the File describes a directory
type dirInfo struct {
        buf  [syscall.STATMAX]byte // buffer for directory I/O
        nbuf int                   // length of buf; return value from Read
        bufp int                   // location of next record in buf.
}

func epipecheck(file *File, e error) {
}

// DevNull is the name of the operating system's ``null device.''
// On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
const DevNull = "/dev/null"

// syscallMode returns the syscall-specific mode bits from Go's portable mode bits.
func syscallMode(i FileMode) (o uint32) {
        o |= uint32(i.Perm())
        if i&ModeAppend != 0 {
                o |= syscall.DMAPPEND
        }
        if i&ModeExclusive != 0 {
                o |= syscall.DMEXCL
        }
        if i&ModeTemporary != 0 {
                o |= syscall.DMTMP
        }
        return
}

// OpenFile is the generalized open call; most users will use Open
// or Create instead.  It opens the named file with specified flag
// (O_RDONLY etc.) and perm, (0666 etc.) if applicable.  If successful,
// methods on the returned File can be used for I/O.
// It returns the File and an error, if any.
func OpenFile(name string, flag int, perm FileMode) (file *File, err error) {
        var (
                fd     int
                e      error
                create bool
                excl   bool
                trunc  bool
                append bool
        )

        if flag&O_CREATE == O_CREATE {
                flag = flag & ^O_CREATE
                create = true
        }
        if flag&O_EXCL == O_EXCL {
                excl = true
        }
        if flag&O_TRUNC == O_TRUNC {
                trunc = true
        }
        // O_APPEND is emulated on Plan 9
        if flag&O_APPEND == O_APPEND {
                flag = flag &^ O_APPEND
                append = true
        }

        syscall.ForkLock.RLock()
        if (create && trunc) || excl {
                fd, e = syscall.Create(name, flag, syscallMode(perm))
        } else {
                fd, e = syscall.Open(name, flag)
                if e != nil && create {
                        var e1 error
                        fd, e1 = syscall.Create(name, flag, syscallMode(perm))
                        if e1 == nil {
                                e = nil
                        }
                }
        }
        syscall.ForkLock.RUnlock()

        if e != nil {
                return nil, &PathError{"open", name, e}
        }

        if append {
                if _, e = syscall.Seek(fd, 0, SEEK_END); e != nil {
                        return nil, &PathError{"seek", name, e}
                }
        }

        return NewFile(fd, name), nil
}

// Close closes the File, rendering it unusable for I/O.
// It returns an error, if any.
func (file *File) Close() error {
        return file.file.close()
}

func (file *file) close() error {
        if file == nil || file.fd < 0 {
                return Ebadfd
        }
        var err error
        syscall.ForkLock.RLock()
        if e := syscall.Close(file.fd); e != nil {
                err = &PathError{"close", file.name, e}
        }
        syscall.ForkLock.RUnlock()
        file.fd = -1 // so it can't be closed again

        // no need for a finalizer anymore
        runtime.SetFinalizer(file, nil)
        return err
}

// Stat returns the FileInfo structure describing file.
// It returns the FileInfo and an error, if any.
func (f *File) Stat() (FileInfo, error) {
        d, err := dirstat(f)
        if err != nil {
                return nil, err
        }
        return fileInfoFromStat(d), nil
}

// Truncate changes the size of the file.
// It does not change the I/O offset.
func (f *File) Truncate(size int64) error {
        var d Dir
        d.Null()

        d.Length = uint64(size)

        if e := syscall.Fwstat(f.fd, pdir(nil, &d)); e != nil {
                return &PathError{"truncate", f.name, e}
        }
        return nil
}

const chmodMask = uint32(syscall.DMAPPEND | syscall.DMEXCL | syscall.DMTMP | ModePerm)

// Chmod changes the mode of the file to mode.
func (f *File) Chmod(mode FileMode) error {
        var d Dir

        odir, e := dirstat(f)
        if e != nil {
                return &PathError{"chmod", f.name, e}
        }
        d.Null()
        d.Mode = odir.Mode&^chmodMask | syscallMode(mode)&chmodMask
        if e := syscall.Fwstat(f.fd, pdir(nil, &d)); e != nil {
                return &PathError{"chmod", f.name, e}
        }
        return nil
}

// Sync commits the current contents of the file to stable storage.
// Typically, this means flushing the file system's in-memory copy
// of recently written data to disk.
func (f *File) Sync() (err error) {
        if f == nil {
                return EINVAL
        }

        var d Dir
        d.Null()

        if e := syscall.Fwstat(f.fd, pdir(nil, &d)); e != nil {
                return NewSyscallError("fsync", e)
        }
        return nil
}

// read reads up to len(b) bytes from the File.
// It returns the number of bytes read and an error, if any.
func (f *File) read(b []byte) (n int, err error) {
        return syscall.Read(f.fd, b)
}

// pread reads len(b) bytes from the File starting at byte offset off.
// It returns the number of bytes read and the error, if any.
// EOF is signaled by a zero count with err set to nil.
func (f *File) pread(b []byte, off int64) (n int, err error) {
        return syscall.Pread(f.fd, b, off)
}

// write writes len(b) bytes to the File.
// It returns the number of bytes written and an error, if any.
func (f *File) write(b []byte) (n int, err error) {
        return syscall.Write(f.fd, b)
}

// pwrite writes len(b) bytes to the File starting at byte offset off.
// It returns the number of bytes written and an error, if any.
func (f *File) pwrite(b []byte, off int64) (n int, err error) {
        return syscall.Pwrite(f.fd, b, off)
}

// seek sets the offset for the next Read or Write on file to offset, interpreted
// according to whence: 0 means relative to the origin of the file, 1 means
// relative to the current offset, and 2 means relative to the end.
// It returns the new offset and an error, if any.
func (f *File) seek(offset int64, whence int) (ret int64, err error) {
        return syscall.Seek(f.fd, offset, whence)
}

// Truncate changes the size of the named file.
// If the file is a symbolic link, it changes the size of the link's target.
func Truncate(name string, size int64) error {
        var d Dir
        d.Null()

        d.Length = uint64(size)

        if e := syscall.Wstat(name, pdir(nil, &d)); e != nil {
                return &PathError{"truncate", name, e}
        }
        return nil
}

// Remove removes the named file or directory.
func Remove(name string) error {
        if e := syscall.Remove(name); e != nil {
                return &PathError{"remove", name, e}
        }
        return nil
}

// Rename renames a file.
func Rename(oldname, newname string) error {
        var d Dir
        d.Null()

        d.Name = newname

        if e := syscall.Wstat(oldname, pdir(nil, &d)); e != nil {
                return &PathError{"rename", oldname, e}
        }
        return nil
}

// Chmod changes the mode of the named file to mode.
func Chmod(name string, mode FileMode) error {
        var d Dir

        odir, e := dirstat(name)
        if e != nil {
                return &PathError{"chmod", name, e}
        }
        d.Null()
        d.Mode = odir.Mode&^chmodMask | syscallMode(mode)&chmodMask
        if e := syscall.Wstat(name, pdir(nil, &d)); e != nil {
                return &PathError{"chmod", name, e}
        }
        return nil
}

// Chtimes changes the access and modification times of the named
// file, similar to the Unix utime() or utimes() functions.
//
// The underlying filesystem may truncate or round the values to a
// less precise time unit.
func Chtimes(name string, atime time.Time, mtime time.Time) error {
        var d Dir
        d.Null()

        d.Atime = uint32(atime.Unix())
        d.Mtime = uint32(mtime.Unix())

        if e := syscall.Wstat(name, pdir(nil, &d)); e != nil {
                return &PathError{"chtimes", name, e}
        }
        return nil
}

func Pipe() (r *File, w *File, err error) {
        var p [2]int

        syscall.ForkLock.RLock()
        if e := syscall.Pipe(p[0:]); e != nil {
                syscall.ForkLock.RUnlock()
                return nil, nil, NewSyscallError("pipe", e)
        }
        syscall.ForkLock.RUnlock()

        return NewFile(p[0], "|0"), NewFile(p[1], "|1"), nil
}

// not supported on Plan 9

// Link creates a hard link.
func Link(oldname, newname string) error {
        return EPLAN9
}

func Symlink(oldname, newname string) error {
        return EPLAN9
}

func Readlink(name string) (string, error) {
        return "", EPLAN9
}

func Chown(name string, uid, gid int) error {
        return EPLAN9
}

func Lchown(name string, uid, gid int) error {
        return EPLAN9
}

func (f *File) Chown(uid, gid int) error {
        return EPLAN9
}

// TempDir returns the default directory to use for temporary files.
func TempDir() string {
        return "/tmp"
}