Source file src/pkg/os/file.go

// 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.

// The os package provides a platform-independent interface to operating
// system functionality.  The design is Unix-like.
package os

import (
    "runtime"
    "syscall"
)

// File represents an open file descriptor.
type File struct {
    fd      int
    name    string
    dirinfo *dirInfo // nil unless directory being read
    nepipe  int      // number of consecutive EPIPE in Write
}

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

// Name returns the name of the file as presented to Open.
func (file *File) Name() string { return file.name }

// 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{fd, name, nil, 0}
    runtime.SetFinalizer(f, (*File).Close)
    return f
}

// Stdin, Stdout, and Stderr are open Files pointing to the standard input,
// standard output, and standard error file descriptors.
var (
    Stdin  = NewFile(syscall.Stdin, "/dev/stdin")
    Stdout = NewFile(syscall.Stdout, "/dev/stdout")
    Stderr = NewFile(syscall.Stderr, "/dev/stderr")
)

// Flags to Open wrapping those of the underlying system. Not all flags
// may be implemented on a given system.
const (
    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_EXCL     = syscall.O_EXCL     // used with O_CREAT, file must not exist
    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.
    O_CREATE   = O_CREAT            // create a new file if none exists.
)

type eofError int

func (eofError) String() string { return "EOF" }

// EOF is the Error returned by Read when no more input is available.
// Functions should return EOF only to signal a graceful end of input.
// If the EOF occurs unexpectedly in a structured data stream,
// the appropriate error is either io.ErrUnexpectedEOF or some other error
// giving more detail.
var EOF Error = eofError(0)

// Read reads up to len(b) bytes from the File.
// It returns the number of bytes read and an Error, if any.
// EOF is signaled by a zero count with err set to EOF.
func (file *File) Read(b []byte) (n int, err Error) {
    if file == nil {
        return 0, EINVAL
    }
    n, e := syscall.Read(file.fd, b)
    if n < 0 {
        n = 0
    }
    if n == 0 && e == 0 {
        return 0, EOF
    }
    if e != 0 {
        err = &PathError{"read", file.name, Errno(e)}
    }
    return n, err
}

// ReadAt 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 EOF.
// ReadAt always returns a non-nil Error when n != len(b).
func (file *File) ReadAt(b []byte, off int64) (n int, err Error) {
    if file == nil {
        return 0, EINVAL
    }
    for len(b) > 0 {
        m, e := syscall.Pread(file.fd, b, off)
        if m == 0 && e == 0 {
            return n, EOF
        }
        if e != 0 {
            err = &PathError{"read", file.name, Errno(e)}
            break
        }
        n += m
        b = b[m:]
        off += int64(m)
    }
    return
}

// Write writes len(b) bytes to the File.
// It returns the number of bytes written and an Error, if any.
// Write returns a non-nil Error when n != len(b).
func (file *File) Write(b []byte) (n int, err Error) {
    if file == nil {
        return 0, EINVAL
    }
    n, e := syscall.Write(file.fd, b)
    if n < 0 {
        n = 0
    }
    if e == syscall.EPIPE {
        file.nepipe++
        if file.nepipe >= 10 {
            Exit(syscall.EPIPE)
        }
    } else {
        file.nepipe = 0
    }
    if e != 0 {
        err = &PathError{"write", file.name, Errno(e)}
    }
    return n, err
}

// WriteAt writes len(b) bytes to the File starting at byte offset off.
// It returns the number of bytes written and an Error, if any.
// WriteAt returns a non-nil Error when n != len(b).
func (file *File) WriteAt(b []byte, off int64) (n int, err Error) {
    if file == nil {
        return 0, EINVAL
    }
    for len(b) > 0 {
        m, e := syscall.Pwrite(file.fd, b, off)
        if e != 0 {
            err = &PathError{"write", file.name, Errno(e)}
            break
        }
        n += m
        b = b[m:]
        off += int64(m)
    }
    return
}

// 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 (file *File) Seek(offset int64, whence int) (ret int64, err Error) {
    r, e := syscall.Seek(file.fd, offset, whence)
    if e == 0 && file.dirinfo != nil && r != 0 {
        e = syscall.EISDIR
    }
    if e != 0 {
        return 0, &PathError{"seek", file.name, Errno(e)}
    }
    return r, nil
}

// 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) {
    if file == nil {
        return 0, EINVAL
    }
    b := syscall.StringByteSlice(s)
    b = b[0 : len(b)-1]
    return file.Write(b)
}

// Pipe returns a connected pair of Files; reads from r return bytes written to w.
// It returns the files and an Error, if any.
func Pipe() (r *File, w *File, err Error) {
    var p [2]int

    // See ../syscall/exec.go for description of lock.
    syscall.ForkLock.RLock()
    e := syscall.Pipe(p[0:])
    if e != 0 {
        syscall.ForkLock.RUnlock()
        return nil, nil, NewSyscallError("pipe", e)
    }
    syscall.CloseOnExec(p[0])
    syscall.CloseOnExec(p[1])
    syscall.ForkLock.RUnlock()

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

// Mkdir creates a new directory with the specified name and permission bits.
// It returns an error, if any.
func Mkdir(name string, perm int) Error {
    e := syscall.Mkdir(name, perm)
    if e != 0 {
        return &PathError{"mkdir", name, Errno(e)}
    }
    return nil
}

// Stat returns a FileInfo structure describing the named file and an error, if any.
// If name names a valid symbolic link, the returned FileInfo describes
// the file pointed at by the link and has fi.FollowedSymlink set to true.
// If name names an invalid symbolic link, the returned FileInfo describes
// the link itself and has fi.FollowedSymlink set to false.
func Stat(name string) (fi *FileInfo, err Error) {
    var lstat, stat syscall.Stat_t
    e := syscall.Lstat(name, &lstat)
    if e != 0 {
        return nil, &PathError{"stat", name, Errno(e)}
    }
    statp := &lstat
    if lstat.Mode&syscall.S_IFMT == syscall.S_IFLNK {
        e := syscall.Stat(name, &stat)
        if e == 0 {
            statp = &stat
        }
    }
    return fileInfoFromStat(name, new(FileInfo), &lstat, statp), nil
}

// Lstat returns the FileInfo structure describing the named file and an
// error, if any.  If the file is a symbolic link, the returned FileInfo
// describes the symbolic link.  Lstat makes no attempt to follow the link.
func Lstat(name string) (fi *FileInfo, err Error) {
    var stat syscall.Stat_t
    e := syscall.Lstat(name, &stat)
    if e != 0 {
        return nil, &PathError{"lstat", name, Errno(e)}
    }
    return fileInfoFromStat(name, new(FileInfo), &stat, &stat), nil
}

// Chdir changes the current working directory to the named directory.
func Chdir(dir string) Error {
    if e := syscall.Chdir(dir); e != 0 {
        return &PathError{"chdir", dir, Errno(e)}
    }
    return nil
}

// Chdir changes the current working directory to the file,
// which must be a directory.
func (f *File) Chdir() Error {
    if e := syscall.Fchdir(f.fd); e != 0 {
        return &PathError{"chdir", f.name, Errno(e)}
    }
    return nil
}

// Remove removes the named file or directory.
func Remove(name string) Error {
    // 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.
    e := syscall.Unlink(name)
    if e == 0 {
        return nil
    }
    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.
    // Rmdir might also return ENOTDIR if given a bad
    // 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.
    // For windows syscall.ENOTDIR is set
    // to syscall.ERROR_DIRECTORY, hopefully it should
    // do the trick.
    if e1 != syscall.ENOTDIR {
        e = e1
    }
    return &PathError{"remove", name, Errno(e)}
}

// LinkError records an error during a link or symlink or rename
// system call and the paths that caused it.
type LinkError struct {
    Op    string
    Old   string
    New   string
    Error Error
}

func (e *LinkError) String() string {
    return e.Op + " " + e.Old + " " + e.New + ": " + e.Error.String()
}

// Link creates a hard link.
func Link(oldname, newname string) Error {
    e := syscall.Link(oldname, newname)
    if e != 0 {
        return &LinkError{"link", oldname, newname, Errno(e)}
    }
    return nil
}

// Symlink creates a symbolic link.
func Symlink(oldname, newname string) Error {
    e := syscall.Symlink(oldname, newname)
    if e != 0 {
        return &LinkError{"symlink", oldname, newname, Errno(e)}
    }
    return nil
}

// 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 := 128; ; len *= 2 {
        b := make([]byte, len)
        n, e := syscall.Readlink(name, b)
        if e != 0 {
            return "", &PathError{"readlink", name, Errno(e)}
        }
        if n < len {
            return string(b[0:n]), nil
        }
    }
    // Silence 6g.
    return "", nil
}

// Rename renames a file.
func Rename(oldname, newname string) Error {
    e := syscall.Rename(oldname, newname)
    if e != 0 {
        return &LinkError{"rename", oldname, newname, Errno(e)}
    }
    return nil
}

// Chmod changes the mode of the named file to mode.
// If the file is a symbolic link, it changes the mode of the link's target.
func Chmod(name string, mode int) Error {
    if e := syscall.Chmod(name, mode); e != 0 {
        return &PathError{"chmod", name, Errno(e)}
    }
    return nil
}

// Chmod changes the mode of the file to mode.
func (f *File) Chmod(mode int) Error {
    if e := syscall.Fchmod(f.fd, mode); e != 0 {
        return &PathError{"chmod", f.name, Errno(e)}
    }
    return nil
}

// 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 {
    if e := syscall.Chown(name, uid, gid); e != 0 {
        return &PathError{"chown", name, Errno(e)}
    }
    return nil
}

// 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 {
    if e := syscall.Lchown(name, uid, gid); e != 0 {
        return &PathError{"lchown", name, Errno(e)}
    }
    return nil
}

// Chown changes the numeric uid and gid of the named file.
func (f *File) Chown(uid, gid int) Error {
    if e := syscall.Fchown(f.fd, uid, gid); e != 0 {
        return &PathError{"chown", f.name, Errno(e)}
    }
    return nil
}

// Truncate changes the size of the file.
// It does not change the I/O offset.
func (f *File) Truncate(size int64) Error {
    if e := syscall.Ftruncate(f.fd, size); e != 0 {
        return &PathError{"truncate", f.name, Errno(e)}
    }
    return nil
}

// Chtimes changes the access and modification times of the named
// file, similar to the Unix utime() or utimes() functions.
//
// The argument times are in nanoseconds, although the underlying
// filesystem may truncate or round the values to a more
// coarse time unit.
func Chtimes(name string, atime_ns int64, mtime_ns int64) Error {
    var utimes [2]syscall.Timeval
    utimes[0] = syscall.NsecToTimeval(atime_ns)
    utimes[1] = syscall.NsecToTimeval(mtime_ns)
    if e := syscall.Utimes(name, utimes[0:]); e != 0 {
        return &PathError{"chtimes", name, Errno(e)}
    }
    return nil
}