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Diffstat (limited to 'src/os/file.go')
| -rw-r--r-- | src/os/file.go | 705 |
1 files changed, 705 insertions, 0 deletions
diff --git a/src/os/file.go b/src/os/file.go new file mode 100644 index 0000000..52dd943 --- /dev/null +++ b/src/os/file.go @@ -0,0 +1,705 @@ +// 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/testlog" + "io" + "io/fs" + "runtime" + "syscall" + "time" +) + +// 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. +// 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(onlyWriter{f}, r) +} + +type onlyWriter struct { + io.Writer +} + +// 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 (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. +// +// If f is a directory, the behavior of Seek varies by operating +// system; you can seek to the beginning of the directory on Unix-like +// operating systems, but not on Windows. +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) { + return f.Write([]byte(s)) +} + +// 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 { + if runtime.GOOS == "windows" && isWindowsNulName(name) { + return &PathError{Op: "mkdir", Path: name, Err: syscall.ENOTDIR} + } + 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. +// 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 +} + +// 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 + } + 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 $home environment variable. +func UserHomeDir() (string, error) { + env, enverr := "HOME", "$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) +} + +// isWindowsNulName reports whether name is os.DevNull ('NUL') on Windows. +// True is returned if name is 'NUL' whatever the case. +func isWindowsNulName(name string) bool { + if len(name) != 3 { + return false + } + if name[0] != 'n' && name[0] != 'N' { + return false + } + if name[1] != 'u' && name[1] != 'U' { + return false + } + if name[2] != 'l' && name[2] != 'L' { + return false + } + return true +} + +// 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. DirFS is therefore not a general substitute for a chroot-style security +// mechanism when the directory tree contains arbitrary content. +func DirFS(dir string) fs.FS { + return dirFS(dir) +} + +func containsAny(s, chars string) bool { + for i := 0; i < len(s); i++ { + for j := 0; j < len(chars); j++ { + if s[i] == chars[j] { + return true + } + } + } + return false +} + +type dirFS string + +func (dir dirFS) Open(name string) (fs.File, error) { + if !fs.ValidPath(name) || runtime.GOOS == "windows" && containsAny(name, `\:`) { + return nil, &PathError{Op: "open", Path: name, Err: ErrInvalid} + } + f, err := Open(string(dir) + "/" + name) + if err != nil { + return nil, err // nil fs.File + } + return f, 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 { + if len(data) >= cap(data) { + d := append(data[:cap(data)], 0) + data = d[:len(data)] + } + 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 + } + } +} + +// 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. +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 +} |