os: fix PathError.Op for dirFS.Open

[gostls13.git] / src / 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.

// Package os provides a platform-independent interface to operating system
// functionality. The design is Unix-like, although the error handling is
// Go-like; failing calls return values of type error rather than error numbers.
// Often, more information is available within the error. For example,
// if a call that takes a file name fails, such as Open or Stat, the error
// will include the failing file name when printed and will be of type
// *PathError, which may be unpacked for more information.
//
// The os interface is intended to be uniform across all operating systems.
// Features not generally available appear in the system-specific package syscall.
//
// Here is a simple example, opening a file and reading some of it.
//
//      file, err := os.Open("file.go") // For read access.
//      if err != nil {
//              log.Fatal(err)
//      }
//
// If the open fails, the error string will be self-explanatory, like
//
//      open file.go: no such file or directory
//
// The file's data can then be read into a slice of bytes. Read and
// Write take their byte counts from the length of the argument slice.
//
//      data := make([]byte, 100)
//      count, err := file.Read(data)
//      if err != nil {
//              log.Fatal(err)
//      }
//      fmt.Printf("read %d bytes: %q\n", count, data[:count])
//
// Note: The maximum number of concurrent operations on a File may be limited by
// the OS or the system. The number should be high, but exceeding it may degrade
// performance or cause other issues.
package os

import (
        "errors"
        "internal/poll"
        "internal/safefilepath"
        "internal/testlog"
        "io"
        "io/fs"
        "runtime"
        "syscall"
        "time"
        "unsafe"
)

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

// Stdin, Stdout, and Stderr are open Files pointing to the standard input,
// standard output, and standard error file descriptors.
//
// Note that the Go runtime writes to standard error for panics and crashes;
// closing Stderr may cause those messages to go elsewhere, perhaps
// to a file opened later.
var (
        Stdin  = NewFile(uintptr(syscall.Stdin), "/dev/stdin")
        Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout")
        Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr")
)

// Flags to OpenFile wrapping those of the underlying system. Not all
// flags may be implemented on a given system.
const (
        // Exactly one of O_RDONLY, O_WRONLY, or O_RDWR must be specified.
        O_RDONLY int = syscall.O_RDONLY // open the file read-only.
        O_WRONLY int = syscall.O_WRONLY // open the file write-only.
        O_RDWR   int = syscall.O_RDWR   // open the file read-write.
        // The remaining values may be or'ed in to control behavior.
        O_APPEND int = syscall.O_APPEND // append data to the file when writing.
        O_CREATE int = syscall.O_CREAT  // create a new file if none exists.
        O_EXCL   int = syscall.O_EXCL   // used with O_CREATE, file must not exist.
        O_SYNC   int = syscall.O_SYNC   // open for synchronous I/O.
        O_TRUNC  int = syscall.O_TRUNC  // truncate regular writable file when opened.
)

// Seek whence values.
//
// Deprecated: Use io.SeekStart, io.SeekCurrent, and io.SeekEnd.
const (
        SEEK_SET int = 0 // seek relative to the origin of the file
        SEEK_CUR int = 1 // seek relative to the current offset
        SEEK_END int = 2 // seek relative to the end
)

// 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
        Err error
}

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

func (e *LinkError) Unwrap() error {
        return e.Err
}

// Read reads up to len(b) bytes from the File and stores them in b.
// It returns the number of bytes read and any error encountered.
// At end of file, Read returns 0, io.EOF.
func (f *File) Read(b []byte) (n int, err error) {
        if err := f.checkValid("read"); err != nil {
                return 0, err
        }
        n, e := f.read(b)
        return n, f.wrapErr("read", e)
}

// 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.
// ReadAt always returns a non-nil error when n < len(b).
// At end of file, that error is io.EOF.
func (f *File) ReadAt(b []byte, off int64) (n int, err error) {
        if err := f.checkValid("read"); err != nil {
                return 0, err
        }

        if off < 0 {
                return 0, &PathError{Op: "readat", Path: f.name, Err: errors.New("negative offset")}
        }

        for len(b) > 0 {
                m, e := f.pread(b, off)
                if e != nil {
                        err = f.wrapErr("read", e)
                        break
                }
                n += m
                b = b[m:]
                off += int64(m)
        }
        return
}

// ReadFrom implements io.ReaderFrom.
func (f *File) ReadFrom(r io.Reader) (n int64, err error) {
        if err := f.checkValid("write"); err != nil {
                return 0, err
        }
        n, handled, e := f.readFrom(r)
        if !handled {
                return genericReadFrom(f, r) // without wrapping
        }
        return n, f.wrapErr("write", e)
}

func genericReadFrom(f *File, r io.Reader) (int64, error) {
        return io.Copy(fileWithoutReadFrom{f}, r)
}

// fileWithoutReadFrom implements all the methods of *File other
// than ReadFrom. This is used to permit ReadFrom to call io.Copy
// without leading to a recursive call to ReadFrom.
type fileWithoutReadFrom struct {
        *File
}

// This ReadFrom method hides the *File ReadFrom method.
func (fileWithoutReadFrom) ReadFrom(fileWithoutReadFrom) {
        panic("unreachable")
}

// Write writes len(b) bytes from b 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 (f *File) Write(b []byte) (n int, err error) {
        if err := f.checkValid("write"); err != nil {
                return 0, err
        }
        n, e := f.write(b)
        if n < 0 {
                n = 0
        }
        if n != len(b) {
                err = io.ErrShortWrite
        }

        epipecheck(f, e)

        if e != nil {
                err = f.wrapErr("write", e)
        }

        return n, err
}

var errWriteAtInAppendMode = errors.New("os: invalid use of WriteAt on file opened with O_APPEND")

// 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).
//
// If file was opened with the O_APPEND flag, WriteAt returns an error.
func (f *File) WriteAt(b []byte, off int64) (n int, err error) {
        if err := f.checkValid("write"); err != nil {
                return 0, err
        }
        if f.appendMode {
                return 0, errWriteAtInAppendMode
        }

        if off < 0 {
                return 0, &PathError{Op: "writeat", Path: f.name, Err: errors.New("negative offset")}
        }

        for len(b) > 0 {
                m, e := f.pwrite(b, off)
                if e != nil {
                        err = f.wrapErr("write", 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.
// The behavior of Seek on a file opened with O_APPEND is not specified.
func (f *File) Seek(offset int64, whence int) (ret int64, err error) {
        if err := f.checkValid("seek"); err != nil {
                return 0, err
        }
        r, e := f.seek(offset, whence)
        if e == nil && f.dirinfo != nil && r != 0 {
                e = syscall.EISDIR
        }
        if e != nil {
                return 0, f.wrapErr("seek", e)
        }
        return r, nil
}

// WriteString is like Write, but writes the contents of string s rather than
// a slice of bytes.
func (f *File) WriteString(s string) (n int, err error) {
        b := unsafe.Slice(unsafe.StringData(s), len(s))
        return f.Write(b)
}

// Mkdir creates a new directory with the specified name and permission
// bits (before umask).
// If there is an error, it will be of type *PathError.
func Mkdir(name string, perm FileMode) error {
        longName := fixLongPath(name)
        e := ignoringEINTR(func() error {
                return syscall.Mkdir(longName, syscallMode(perm))
        })

        if e != nil {
                return &PathError{Op: "mkdir", Path: name, Err: e}
        }

        // mkdir(2) itself won't handle the sticky bit on *BSD and Solaris
        if !supportsCreateWithStickyBit && perm&ModeSticky != 0 {
                e = setStickyBit(name)

                if e != nil {
                        Remove(name)
                        return e
                }
        }

        return nil
}

// setStickyBit adds ModeSticky to the permission bits of path, non atomic.
func setStickyBit(name string) error {
        fi, err := Stat(name)
        if err != nil {
                return err
        }
        return Chmod(name, fi.Mode()|ModeSticky)
}

// Chdir changes the current working directory to the named directory.
// If there is an error, it will be of type *PathError.
func Chdir(dir string) error {
        if e := syscall.Chdir(dir); e != nil {
                testlog.Open(dir) // observe likely non-existent directory
                return &PathError{Op: "chdir", Path: dir, Err: e}
        }
        if log := testlog.Logger(); log != nil {
                wd, err := Getwd()
                if err == nil {
                        log.Chdir(wd)
                }
        }
        return nil
}

// Open opens the named file for reading. If successful, methods on
// the returned file can be used for reading; the associated file
// descriptor has mode O_RDONLY.
// If there is an error, it will be of type *PathError.
func Open(name string) (*File, error) {
        return OpenFile(name, O_RDONLY, 0)
}

// Create creates or truncates the named file. If the file already exists,
// it is truncated. If the file does not exist, it is created with mode 0666
// (before umask). If successful, methods on the returned File can
// be used for I/O; the associated file descriptor has mode O_RDWR.
// If there is an error, it will be of type *PathError.
func Create(name string) (*File, error) {
        return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666)
}

// 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.). If the file does not exist, and the O_CREATE flag
// is passed, it is created with mode perm (before umask). If successful,
// methods on the returned File can be used for I/O.
// If there is an error, it will be of type *PathError.
func OpenFile(name string, flag int, perm FileMode) (*File, error) {
        testlog.Open(name)
        f, err := openFileNolog(name, flag, perm)
        if err != nil {
                return nil, err
        }
        f.appendMode = flag&O_APPEND != 0

        return f, nil
}

// lstat is overridden in tests.
var lstat = Lstat

// Rename renames (moves) oldpath to newpath.
// If newpath already exists and is not a directory, Rename replaces it.
// OS-specific restrictions may apply when oldpath and newpath are in different directories.
// Even within the same directory, on non-Unix platforms Rename is not an atomic operation.
// If there is an error, it will be of type *LinkError.
func Rename(oldpath, newpath string) error {
        return rename(oldpath, newpath)
}

// Many functions in package syscall return a count of -1 instead of 0.
// Using fixCount(call()) instead of call() corrects the count.
func fixCount(n int, err error) (int, error) {
        if n < 0 {
                n = 0
        }
        return n, err
}

// checkWrapErr is the test hook to enable checking unexpected wrapped errors of poll.ErrFileClosing.
// It is set to true in the export_test.go for tests (including fuzz tests).
var checkWrapErr = false

// wrapErr wraps an error that occurred during an operation on an open file.
// It passes io.EOF through unchanged, otherwise converts
// poll.ErrFileClosing to ErrClosed and wraps the error in a PathError.
func (f *File) wrapErr(op string, err error) error {
        if err == nil || err == io.EOF {
                return err
        }
        if err == poll.ErrFileClosing {
                err = ErrClosed
        } else if checkWrapErr && errors.Is(err, poll.ErrFileClosing) {
                panic("unexpected error wrapping poll.ErrFileClosing: " + err.Error())
        }
        return &PathError{Op: op, Path: f.name, Err: err}
}

// TempDir returns the default directory to use for temporary files.
//
// On Unix systems, it returns $TMPDIR if non-empty, else /tmp.
// On Windows, it uses GetTempPath, returning the first non-empty
// value from %TMP%, %TEMP%, %USERPROFILE%, or the Windows directory.
// On Plan 9, it returns /tmp.
//
// The directory is neither guaranteed to exist nor have accessible
// permissions.
func TempDir() string {
        return tempDir()
}

// UserCacheDir returns the default root directory to use for user-specific
// cached data. Users should create their own application-specific subdirectory
// within this one and use that.
//
// On Unix systems, it returns $XDG_CACHE_HOME as specified by
// https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if
// non-empty, else $HOME/.cache.
// On Darwin, it returns $HOME/Library/Caches.
// On Windows, it returns %LocalAppData%.
// On Plan 9, it returns $home/lib/cache.
//
// If the location cannot be determined (for example, $HOME is not defined),
// then it will return an error.
func UserCacheDir() (string, error) {
        var dir string

        switch runtime.GOOS {
        case "windows":
                dir = Getenv("LocalAppData")
                if dir == "" {
                        return "", errors.New("%LocalAppData% is not defined")
                }

        case "darwin", "ios":
                dir = Getenv("HOME")
                if dir == "" {
                        return "", errors.New("$HOME is not defined")
                }
                dir += "/Library/Caches"

        case "plan9":
                dir = Getenv("home")
                if dir == "" {
                        return "", errors.New("$home is not defined")
                }
                dir += "/lib/cache"

        default: // Unix
                dir = Getenv("XDG_CACHE_HOME")
                if dir == "" {
                        dir = Getenv("HOME")
                        if dir == "" {
                                return "", errors.New("neither $XDG_CACHE_HOME nor $HOME are defined")
                        }
                        dir += "/.cache"
                }
        }

        return dir, nil
}

// UserConfigDir returns the default root directory to use for user-specific
// configuration data. Users should create their own application-specific
// subdirectory within this one and use that.
//
// On Unix systems, it returns $XDG_CONFIG_HOME as specified by
// https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html if
// non-empty, else $HOME/.config.
// On Darwin, it returns $HOME/Library/Application Support.
// On Windows, it returns %AppData%.
// On Plan 9, it returns $home/lib.
//
// If the location cannot be determined (for example, $HOME is not defined),
// then it will return an error.
func UserConfigDir() (string, error) {
        var dir string

        switch runtime.GOOS {
        case "windows":
                dir = Getenv("AppData")
                if dir == "" {
                        return "", errors.New("%AppData% is not defined")
                }

        case "darwin", "ios":
                dir = Getenv("HOME")
                if dir == "" {
                        return "", errors.New("$HOME is not defined")
                }
                dir += "/Library/Application Support"

        case "plan9":
                dir = Getenv("home")
                if dir == "" {
                        return "", errors.New("$home is not defined")
                }
                dir += "/lib"

        default: // Unix
                dir = Getenv("XDG_CONFIG_HOME")
                if dir == "" {
                        dir = Getenv("HOME")
                        if dir == "" {
                                return "", errors.New("neither $XDG_CONFIG_HOME nor $HOME are defined")
                        }
                        dir += "/.config"
                }
        }

        return dir, nil
}

// UserHomeDir returns the current user's home directory.
//
// On Unix, including macOS, it returns the $HOME environment variable.
// On Windows, it returns %USERPROFILE%.
// On Plan 9, it returns the $home environment variable.
//
// If the expected variable is not set in the environment, UserHomeDir
// returns either a platform-specific default value or a non-nil error.
func UserHomeDir() (string, error) {
        env, enverr := "HOME", "$HOME"
        switch runtime.GOOS {
        case "windows":
                env, enverr = "USERPROFILE", "%userprofile%"
        case "plan9":
                env, enverr = "home", "$home"
        }
        if v := Getenv(env); v != "" {
                return v, nil
        }
        // On some geese the home directory is not always defined.
        switch runtime.GOOS {
        case "android":
                return "/sdcard", nil
        case "ios":
                return "/", nil
        }
        return "", errors.New(enverr + " is not defined")
}

// 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.
// If there is an error, it will be of type *PathError.
//
// A different subset of the mode bits are used, depending on the
// operating system.
//
// On Unix, the mode's permission bits, ModeSetuid, ModeSetgid, and
// ModeSticky are used.
//
// On Windows, only the 0200 bit (owner writable) of mode is used; it
// controls whether the file's read-only attribute is set or cleared.
// The other bits are currently unused. For compatibility with Go 1.12
// and earlier, use a non-zero mode. Use mode 0400 for a read-only
// file and 0600 for a readable+writable file.
//
// On Plan 9, the mode's permission bits, ModeAppend, ModeExclusive,
// and ModeTemporary are used.
func Chmod(name string, mode FileMode) error { return chmod(name, mode) }

// Chmod changes the mode of the file to mode.
// If there is an error, it will be of type *PathError.
func (f *File) Chmod(mode FileMode) error { return f.chmod(mode) }

// SetDeadline sets the read and write deadlines for a File.
// It is equivalent to calling both SetReadDeadline and SetWriteDeadline.
//
// Only some kinds of files support setting a deadline. Calls to SetDeadline
// for files that do not support deadlines will return ErrNoDeadline.
// On most systems ordinary files do not support deadlines, but pipes do.
//
// A deadline is an absolute time after which I/O operations fail with an
// error instead of blocking. The deadline applies to all future and pending
// I/O, not just the immediately following call to Read or Write.
// After a deadline has been exceeded, the connection can be refreshed
// by setting a deadline in the future.
//
// If the deadline is exceeded a call to Read or Write or to other I/O
// methods will return an error that wraps ErrDeadlineExceeded.
// This can be tested using errors.Is(err, os.ErrDeadlineExceeded).
// That error implements the Timeout method, and calling the Timeout
// method will return true, but there are other possible errors for which
// the Timeout will return true even if the deadline has not been exceeded.
//
// An idle timeout can be implemented by repeatedly extending
// the deadline after successful Read or Write calls.
//
// A zero value for t means I/O operations will not time out.
func (f *File) SetDeadline(t time.Time) error {
        return f.setDeadline(t)
}

// SetReadDeadline sets the deadline for future Read calls and any
// currently-blocked Read call.
// A zero value for t means Read will not time out.
// Not all files support setting deadlines; see SetDeadline.
func (f *File) SetReadDeadline(t time.Time) error {
        return f.setReadDeadline(t)
}

// SetWriteDeadline sets the deadline for any future Write calls and any
// currently-blocked Write call.
// Even if Write times out, it may return n > 0, indicating that
// some of the data was successfully written.
// A zero value for t means Write will not time out.
// Not all files support setting deadlines; see SetDeadline.
func (f *File) SetWriteDeadline(t time.Time) error {
        return f.setWriteDeadline(t)
}

// SyscallConn returns a raw file.
// This implements the syscall.Conn interface.
func (f *File) SyscallConn() (syscall.RawConn, error) {
        if err := f.checkValid("SyscallConn"); err != nil {
                return nil, err
        }
        return newRawConn(f)
}

// DirFS returns a file system (an fs.FS) for the tree of files rooted at the directory dir.
//
// Note that DirFS("/prefix") only guarantees that the Open calls it makes to the
// operating system will begin with "/prefix": DirFS("/prefix").Open("file") is the
// same as os.Open("/prefix/file"). So if /prefix/file is a symbolic link pointing outside
// the /prefix tree, then using DirFS does not stop the access any more than using
// os.Open does. Additionally, the root of the fs.FS returned for a relative path,
// DirFS("prefix"), will be affected by later calls to Chdir. DirFS is therefore not
// a general substitute for a chroot-style security mechanism when the directory tree
// contains arbitrary content.
//
// The directory dir must not be "".
//
// The result implements [io/fs.StatFS], [io/fs.ReadFileFS] and
// [io/fs.ReadDirFS].
func DirFS(dir string) fs.FS {
        return dirFS(dir)
}

type dirFS string

func (dir dirFS) Open(name string) (fs.File, error) {
        fullname, err := dir.join(name)
        if err != nil {
                return nil, &PathError{Op: "open", Path: name, Err: err}
        }
        f, err := Open(fullname)
        if err != nil {
                // DirFS takes a string appropriate for GOOS,
                // while the name argument here is always slash separated.
                // dir.join will have mixed the two; undo that for
                // error reporting.
                err.(*PathError).Path = name
                return nil, err
        }
        return f, nil
}

// The ReadFile method calls the [ReadFile] function for the file
// with the given name in the directory. The function provides
// robust handling for small files and special file systems.
// Through this method, dirFS implements [io/fs.ReadFileFS].
func (dir dirFS) ReadFile(name string) ([]byte, error) {
        fullname, err := dir.join(name)
        if err != nil {
                return nil, &PathError{Op: "readfile", Path: name, Err: err}
        }
        return ReadFile(fullname)
}

// ReadDir reads the named directory, returning all its directory entries sorted
// by filename. Through this method, dirFS implements [io/fs.ReadDirFS].
func (dir dirFS) ReadDir(name string) ([]DirEntry, error) {
        fullname, err := dir.join(name)
        if err != nil {
                return nil, &PathError{Op: "readdir", Path: name, Err: err}
        }
        return ReadDir(fullname)
}

func (dir dirFS) Stat(name string) (fs.FileInfo, error) {
        fullname, err := dir.join(name)
        if err != nil {
                return nil, &PathError{Op: "stat", Path: name, Err: err}
        }
        f, err := Stat(fullname)
        if err != nil {
                // See comment in dirFS.Open.
                err.(*PathError).Path = name
                return nil, err
        }
        return f, nil
}

// join returns the path for name in dir.
func (dir dirFS) join(name string) (string, error) {
        if dir == "" {
                return "", errors.New("os: DirFS with empty root")
        }
        if !fs.ValidPath(name) {
                return "", ErrInvalid
        }
        name, err := safefilepath.FromFS(name)
        if err != nil {
                return "", ErrInvalid
        }
        if IsPathSeparator(dir[len(dir)-1]) {
                return string(dir) + name, nil
        }
        return string(dir) + string(PathSeparator) + name, nil
}

// ReadFile reads the named file and returns the contents.
// A successful call returns err == nil, not err == EOF.
// Because ReadFile reads the whole file, it does not treat an EOF from Read
// as an error to be reported.
func ReadFile(name string) ([]byte, error) {
        f, err := Open(name)
        if err != nil {
                return nil, err
        }
        defer f.Close()

        var size int
        if info, err := f.Stat(); err == nil {
                size64 := info.Size()
                if int64(int(size64)) == size64 {
                        size = int(size64)
                }
        }
        size++ // one byte for final read at EOF

        // If a file claims a small size, read at least 512 bytes.
        // In particular, files in Linux's /proc claim size 0 but
        // then do not work right if read in small pieces,
        // so an initial read of 1 byte would not work correctly.
        if size < 512 {
                size = 512
        }

        data := make([]byte, 0, size)
        for {
                n, err := f.Read(data[len(data):cap(data)])
                data = data[:len(data)+n]
                if err != nil {
                        if err == io.EOF {
                                err = nil
                        }
                        return data, err
                }

                if len(data) >= cap(data) {
                        d := append(data[:cap(data)], 0)
                        data = d[:len(data)]
                }
        }
}

// WriteFile writes data to the named file, creating it if necessary.
// If the file does not exist, WriteFile creates it with permissions perm (before umask);
// otherwise WriteFile truncates it before writing, without changing permissions.
// Since WriteFile requires multiple system calls to complete, a failure mid-operation
// can leave the file in a partially written state.
func WriteFile(name string, data []byte, perm FileMode) error {
        f, err := OpenFile(name, O_WRONLY|O_CREATE|O_TRUNC, perm)
        if err != nil {
                return err
        }
        _, err = f.Write(data)
        if err1 := f.Close(); err1 != nil && err == nil {
                err = err1
        }
        return err
}