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    // Copyright 2009 The Go Authors. All rights reserved.
    // Use of this source code is governed by a BSD-style
    // license that can be found in the LICENSE file.
    
    
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    // The os package provides a platform-independent interface to operating
    // system functionality.  The design is Unix-like.
    
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    package os
    
    
    import (
    	"os";
    	"syscall";
    )
    
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    // Auxiliary information if the File describes a directory
    
    type dirInfo struct {
    
    	buf	[]byte;	// buffer for directory I/O
    	nbuf	int64;	// length of buf; return value from Getdirentries
    	bufp	int64;	// location of next record in buf.
    }
    
    
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    // File represents an open file descriptor.
    type File struct {
    
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    	fd int64;
    	name	string;
    
    	dirinfo	*dirInfo;	// nil unless directory being read
    
    	nepipe	int;	// number of consecutive EPIPE in Write
    
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    // Fd returns the integer Unix file descriptor referencing the open file.
    
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    func (file *File) Fd() int64 {
    	return file.fd
    
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    }
    
    
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    // Name returns the name of the file as presented to Open.
    
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    func (file *File) Name() string {
    	return file.name
    
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    }
    
    
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    // NewFile returns a new File with the given file descriptor and name.
    func NewFile(file int64, name string) *File {
    	if file < 0 {
    
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    		return nil
    	}
    
    	return &File{file, name, nil, 0}
    
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    // Stdin, Stdout, and Stderr are open Files pointing to the standard input,
    
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    // standard output, and standard error file descriptors.
    
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    var (
    
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    	Stdin  = NewFile(0, "/dev/stdin");
    	Stdout = NewFile(1, "/dev/stdout");
    	Stderr = NewFile(2, "/dev/stderr");
    
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    // Flags to Open wrapping those of the underlying system. Not all flags
    // may be implemented on a given system.
    
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    const (
    
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    	O_RDONLY = syscall.O_RDONLY;	// open the file read-only.
    	O_WRONLY = syscall.O_WRONLY;	// open the file write-only.
    	O_RDWR = syscall.O_RDWR;	// open the file read-write.
    	O_APPEND = syscall.O_APPEND;	// open the file append-only.
    	O_ASYNC = syscall.O_ASYNC;	// generate a signal when I/O is available.
    	O_CREAT = syscall.O_CREAT;	// create a new file if none exists.
    	O_NOCTTY = syscall.O_NOCTTY;	// do not make file the controlling tty.
    	O_NONBLOCK = syscall.O_NONBLOCK;	// open in non-blocking mode.
    	O_NDELAY = O_NONBLOCK;		// synonym for O_NONBLOCK
    	O_SYNC = syscall.O_SYNC;	// open for synchronous I/O.
    	O_TRUNC = syscall.O_TRUNC;	// if possible, truncate file when opened.
    
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    // Open opens the named file with specified flag (O_RDONLY etc.) and perm, (0666 etc.)
    
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    // 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 Open(name string, flag int, perm int) (file *File, err Error) {
    
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    	r, e := syscall.Open(name, int64(flag | syscall.O_CLOEXEC), int64(perm));
    
    	if e != 0 {
    		return nil, ErrnoToError(e);
    	}
    
    	// There's a race here with fork/exec, which we are
    	// content to live with.  See ../syscall/exec.go
    	if syscall.O_CLOEXEC == 0 {	// O_CLOEXEC not supported
    		syscall.CloseOnExec(r);
    	}
    
    
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    	return NewFile(r, name), ErrnoToError(e)
    
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    // Close closes the File, rendering it unusable for I/O.
    
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    // It returns an Error, if any.
    
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    	if file == nil {
    
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    		return EINVAL
    	}
    
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    	r, e := syscall.Close(file.fd);
    	file.fd = -1;  // so it can't be closed again
    
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    	return ErrnoToError(e)
    }
    
    
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    // Read reads up to len(b) bytes from the File.
    
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    // It returns the number of bytes read and an Error, if any.
    // EOF is signaled by a zero count with a nil Error.
    // TODO(r): Add Pread, Pwrite (maybe ReadAt, WriteAt).
    
    func (file *File) Read(b []byte) (ret int, err Error) {
    
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    	if file == nil {
    
    	var r, e int64;
    	if len(b) > 0 {  // because we access b[0]
    
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    		r, e = syscall.Read(file.fd, &b[0], int64(len(b)));
    
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    	return int(r), ErrnoToError(e)
    
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    // Write writes len(b) bytes to the File.
    
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    // It returns the number of bytes written and an Error, if any.
    // If the byte count differs from len(b), it usually implies an error occurred.
    
    func (file *File) Write(b []byte) (ret int, err Error) {
    
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    	if file == nil {
    
    	var r, e int64;
    	if len(b) > 0 {  // because we access b[0]
    
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    		r, e = syscall.Write(file.fd, &b[0], int64(len(b)));
    
    	if e == syscall.EPIPE {
    		file.nepipe++;
    		if file.nepipe >= 10 {
    
    			os.Exit(syscall.EPIPE);
    
    		}
    	} else {
    		file.nepipe = 0;
    	}
    
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    	return int(r), ErrnoToError(e)
    
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    // Seek sets the offset for the next Read or Write on file to offset, interpreted
    
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    // 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 (file *File) Seek(offset int64, whence int) (ret int64, err Error) {
    
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    	r, e := syscall.Seek(file.fd, offset, int64(whence));
    
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    	if file.dirinfo != nil && r != 0 {
    
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    // WriteString is like Write, but writes the contents of string s rather than
    // an array of bytes.
    
    func (file *File) WriteString(s string) (ret int, err Error) {
    
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    	if file == nil {
    
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    	r, e := syscall.Write(file.fd, syscall.StringBytePtr(s), int64(len(s)));
    
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    	return int(r), ErrnoToError(e)
    
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    // Pipe returns a connected pair of Files; reads from r return bytes written to w.
    // It returns the files and an Error, if any.
    
    	var p [2]int64;
    
    
    	// See ../syscall/exec.go for description of lock.
    	syscall.ForkLock.RLock();
    
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    	ret, e := syscall.Pipe(&p);
    
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    	if e != 0 {
    
    		syscall.ForkLock.RUnlock();
    
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    		return nil, nil, ErrnoToError(e)
    	}
    
    	syscall.CloseOnExec(p[0]);
    	syscall.CloseOnExec(p[1]);
    	syscall.ForkLock.RUnlock();
    
    
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    	return NewFile(p[0], "|0"), NewFile(p[1], "|1"), nil
    
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    }
    
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    // Mkdir creates a new directory with the specified name and permission bits.
    // It returns an error, if any.
    
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    	r, e := syscall.Mkdir(name, int64(perm));
    
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    	return ErrnoToError(e)
    }
    
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    // Stat returns a Dir structure describing the named file and an error, if any.
    // If name names a valid symbolic link, the returned Dir describes
    // the file pointed at by the link and has dir.FollowedSymlink set to true.
    // If name names an invalid symbolic link, the returned Dir describes
    // the link itself and has dir.FollowedSymlink set to false.
    
    	var lstat, stat syscall.Stat_t;
    	r, e := syscall.Lstat(name, &lstat);
    
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    	if e != 0 {
    
    		return nil, ErrnoToError(e);
    
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    	}
    
    	statp := &lstat;
    	if lstat.Mode & syscall.S_IFMT == syscall.S_IFLNK {
    		r, e := syscall.Stat(name, &stat);
    		if e == 0 {
    			statp = &stat;
    		}
    	}
    	return dirFromStat(name, new(Dir), &lstat, statp), nil
    
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    }
    
    
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    // Stat returns the Dir structure describing file.
    
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    // It returns the Dir and an error, if any.
    
    func (file *File) Stat() (dir *Dir, err Error) {
    
    	var stat syscall.Stat_t;
    	r, e := syscall.Fstat(file.fd, &stat);
    
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    	if e != 0 {
    		return nil, ErrnoToError(e)
    	}
    
    	return dirFromStat(file.name, new(Dir), &stat, &stat), nil
    
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    }
    
    
    // Lstat returns the Dir structure describing the named file and an error, if any.
    // If the file is a symbolic link, the returned Dir describes the
    // symbolic link.  Lstat makes no attempt to follow the link.
    
    func Lstat(name string) (dir *Dir, err Error) {
    
    	var stat syscall.Stat_t;
    	r, e := syscall.Lstat(name, &stat);
    
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    	if e != 0 {
    		return nil, ErrnoToError(e)
    	}
    
    	return dirFromStat(name, new(Dir), &stat, &stat), nil
    
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    }
    
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    // Readdirnames has a non-portable implemenation so its code is separated into an
    // operating-system-dependent file.
    
    func readdirnames(file *File, count int) (names []string, err Error)
    
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    // Readdirnames reads the contents of the directory associated with file and
    
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    // returns an array of up to count names, in directory order.  Subsequent
    
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    // calls on the same file will yield further names.
    
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    // A negative count means to read until EOF.
    
    // Readdirnames returns the array and an Error, if any.
    
    func (file *File) Readdirnames(count int) (names []string, err Error) {
    
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    	return readdirnames(file, count);
    }
    
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    // Readdir reads the contents of the directory associated with file and
    
    // returns an array of up to count Dir structures, as would be returned
    // by Stat, in directory order.  Subsequent calls on the same file will yield further Dirs.
    
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    // A negative count means to read until EOF.
    
    // Readdir returns the array and an Error, if any.
    
    func (file *File) Readdir(count int) (dirs []Dir, err Error) {
    
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    	dirname := file.name;
    
    	if dirname == "" {
    		dirname = ".";
    	}
    	dirname += "/";
    
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    	names, err1 := file.Readdirnames(count);
    
    	if err1 != nil {
    		return nil, err1
    	}
    	dirs = make([]Dir, len(names));
    	for i, filename := range names {
    		dirp, err := Stat(dirname + filename);
    		if dirp ==  nil || err != nil {
    			dirs[i].Name = filename	// rest is already zeroed out
    		} else {
    			dirs[i] = *dirp
    		}
    	}
    	return
    }
    
    
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    // Chdir changes the current working directory to the named directory.
    
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    	r, e := syscall.Chdir(dir);
    	return ErrnoToError(e);
    }
    
    
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    // Chdir changes the current working directory to the file,
    // which must be a directory.
    func (f *File) Chdir() Error {
    	r, e := syscall.Fchdir(f.fd);
    	return ErrnoToError(e);
    }
    
    
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    // Remove removes the named file or directory.
    
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    	// System call interface forces us to know
    	// whether name is a file or directory.
    	// Try both: it is cheaper on average than
    	// doing a Stat plus the right one.
    	r, e := syscall.Unlink(name);
    	if e == 0 {
    		return nil;
    	}
    	r1, e1 := syscall.Rmdir(name);
    	if e1 == 0 {
    		return nil;
    	}
    
    	// Both failed: figure out which error to return.
    	// OS X and Linux differ on whether unlink(dir)
    	// returns EISDIR, so can't use that.  However,
    	// both agree that rmdir(file) returns ENOTDIR,
    	// so we can use that to decide which error is real.
    
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    	// Rmdir might also return ENOTDIR if given a bad
    
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    	// file path, like /etc/passwd/foo, but in that case,
    	// both errors will be ENOTDIR, so it's okay to
    	// use the error from unlink.
    	if e1 != syscall.ENOTDIR {
    		e = e1;
    	}
    
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    	return ErrnoToError(e);
    
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    }
    
    
    // Link creates a hard link.
    
    func Link(oldname, newname string) Error {
    	r, e := syscall.Link(oldname, newname);
    
    	return ErrnoToError(e);
    }
    
    // Symlink creates a symbolic link.
    
    func Symlink(oldname, newname string) Error {
    	r, e := syscall.Symlink(oldname, newname);
    
    	return ErrnoToError(e);
    }
    
    // Readlink reads the contents of a symbolic link: the destination of
    // the link.  It returns the contents and an Error, if any.
    
    func Readlink(name string) (string, Error) {
    
    	for len := int64(128); ; len *= 2 {
    		b := make([]byte, len);
    
    		r, e := syscall.Readlink(name, &b[0], len);
    
    		if r == -1 {
    			return "", ErrnoToError(e);
    		} else if r < len {
    			return string(b[0:r]), nil;
    		}
    	}
    	// Silence 6g.
    	return "", nil;
    }
    
    
    // Chmod changes the mode of the named file to mode.
    // If the file is a symbolic link, it changes the uid and gid of the link's target.
    func Chmod(name string, mode int) Error {
    	r, e := syscall.Chmod(name, int64(mode));
    	return ErrnoToError(e);
    }
    
    // Chmod changes the mode of the file to mode.
    func (f *File) Chmod(mode int) Error {
    	r, e := syscall.Fchmod(f.fd, int64(mode));
    	return ErrnoToError(e);
    }
    
    // Chown changes the numeric uid and gid of the named file.
    // If the file is a symbolic link, it changes the uid and gid of the link's target.
    func Chown(name string, uid, gid int) Error {
    	r, e := syscall.Chown(name, int64(uid), int64(gid));
    	return ErrnoToError(e);
    }
    
    // Lchown changes the numeric uid and gid of the named file.
    // If the file is a symbolic link, it changes the uid and gid of the link itself.
    func Lchown(name string, uid, gid int) Error {
    	r, e := syscall.Lchown(name, int64(uid), int64(gid));
    	return ErrnoToError(e);
    }
    
    // Chown changes the numeric uid and gid of the named file.
    func (f *File) Chown(uid, gid int) Error {
    	r, e := syscall.Fchown(f.fd, int64(uid), int64(gid));
    	return ErrnoToError(e);
    }
    
    // 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 {
    	r, e := syscall.Truncate(name, size);
    	return ErrnoToError(e);
    }
    
    // Truncate changes the size of the file.
    // It does not change the I/O offset.
    func (f *File) Truncate(size int64) Error {
    	r, e := syscall.Ftruncate(f.fd, size);
    	return ErrnoToError(e);
    }