Initial QSfera import

Server/vendor/github.com/pkg/xattr/xattr.go

@@ -0,0 +1,258 @@
+/*
+Package xattr provides support for extended attributes on linux, darwin and freebsd.
+Extended attributes are name:value pairs associated permanently with files and directories,
+similar to the environment strings associated with a process.
+An attribute may be defined or undefined. If it is defined, its value may be empty or non-empty.
+More details you can find here: https://en.wikipedia.org/wiki/Extended_file_attributes .
+
+All functions are provided in triples: Get/LGet/FGet, Set/LSet/FSet etc. The "L"
+variant will not follow a symlink at the end of the path, and "F" variant accepts
+a file descriptor instead of a path.
+
+Example for "L" variant, assuming path is "/symlink1/symlink2", where both components are
+symlinks:
+Get will follow "symlink1" and "symlink2" and operate on the target of
+"symlink2". LGet will follow "symlink1" but operate directly on "symlink2".
+*/
+package xattr
+
+import (
+	"os"
+	"syscall"
+)
+
+// Error records an error and the operation, file path and attribute that caused it.
+type Error struct {
+	Op   string
+	Path string
+	Name string
+	Err  error
+}
+
+func (e *Error) Unwrap() error { return e.Err }
+
+func (e *Error) Error() (errstr string) {
+	if e.Op != "" {
+		errstr += e.Op
+	}
+	if e.Path != "" {
+		if errstr != "" {
+			errstr += " "
+		}
+		errstr += e.Path
+	}
+	if e.Name != "" {
+		if errstr != "" {
+			errstr += " "
+		}
+		errstr += e.Name
+	}
+	if e.Err != nil {
+		if errstr != "" {
+			errstr += ": "
+		}
+		errstr += e.Err.Error()
+	}
+	return
+}
+
+// Get retrieves extended attribute data associated with path. It will follow
+// all symlinks along the path.
+func Get(path, name string) ([]byte, error) {
+	return get(path, name, func(name string, data []byte) (int, error) {
+		return getxattr(path, name, data)
+	})
+}
+
+// LGet is like Get but does not follow a symlink at the end of the path.
+func LGet(path, name string) ([]byte, error) {
+	return get(path, name, func(name string, data []byte) (int, error) {
+		return lgetxattr(path, name, data)
+	})
+}
+
+// FGet is like Get but accepts a os.File instead of a file path.
+func FGet(f *os.File, name string) ([]byte, error) {
+	return get(f.Name(), name, func(name string, data []byte) (int, error) {
+		return fgetxattr(f, name, data)
+	})
+}
+
+type getxattrFunc func(name string, data []byte) (int, error)
+
+// get contains the buffer allocation logic used by both Get and LGet.
+func get(path string, name string, getxattrFunc getxattrFunc) ([]byte, error) {
+	const (
+		// Start with a 1 KB buffer for the xattr value
+		initialBufSize = 1024
+
+		// The theoretical maximum xattr value size on MacOS is 64 MB. On Linux it's
+		// much smaller: documented at 64 KB. However, at least on TrueNAS SCALE, a
+		// Debian-based Linux distro, it can be larger.
+		maxBufSize = 64 * 1024 * 1024
+
+		// Function name as reported in error messages
+		myname = "xattr.get"
+	)
+
+	size := initialBufSize
+	for {
+		data := make([]byte, size)
+		read, err := getxattrFunc(name, data)
+
+		// If the buffer was too small to fit the value, Linux and MacOS react
+		// differently:
+		// Linux: returns an ERANGE error and "-1" bytes. However, the TrueNAS
+		//   SCALE distro sometimes returns E2BIG.
+		// MacOS: truncates the value and returns "size" bytes. If the value
+		//   happens to be exactly as big as the buffer, we cannot know if it was
+		//   truncated, and we retry with a bigger buffer. Contrary to documentation,
+		//   MacOS never seems to return ERANGE!
+		// To keep the code simple, we always check both conditions, and sometimes
+		// double the buffer size without it being strictly necessary.
+		if err == syscall.ERANGE || err == syscall.E2BIG || read == size {
+			// The buffer was too small. Try again.
+			size <<= 1
+			if size >= maxBufSize {
+				return nil, &Error{myname, path, name, syscall.EOVERFLOW}
+			}
+			continue
+		}
+		if err != nil {
+			return nil, &Error{myname, path, name, err}
+		}
+		return data[:read], nil
+	}
+}
+
+// Set associates name and data together as an attribute of path.
+func Set(path, name string, data []byte) error {
+	if err := setxattr(path, name, data, 0); err != nil {
+		return &Error{"xattr.Set", path, name, err}
+	}
+	return nil
+}
+
+// LSet is like Set but does not follow a symlink at
+// the end of the path.
+func LSet(path, name string, data []byte) error {
+	if err := lsetxattr(path, name, data, 0); err != nil {
+		return &Error{"xattr.LSet", path, name, err}
+	}
+	return nil
+}
+
+// FSet is like Set but accepts a os.File instead of a file path.
+func FSet(f *os.File, name string, data []byte) error {
+	if err := fsetxattr(f, name, data, 0); err != nil {
+		return &Error{"xattr.FSet", f.Name(), name, err}
+	}
+	return nil
+}
+
+// SetWithFlags associates name and data together as an attribute of path.
+// Forwards the flags parameter to the syscall layer.
+func SetWithFlags(path, name string, data []byte, flags int) error {
+	if err := setxattr(path, name, data, flags); err != nil {
+		return &Error{"xattr.SetWithFlags", path, name, err}
+	}
+	return nil
+}
+
+// LSetWithFlags is like SetWithFlags but does not follow a symlink at
+// the end of the path.
+func LSetWithFlags(path, name string, data []byte, flags int) error {
+	if err := lsetxattr(path, name, data, flags); err != nil {
+		return &Error{"xattr.LSetWithFlags", path, name, err}
+	}
+	return nil
+}
+
+// FSetWithFlags is like SetWithFlags but accepts a os.File instead of a file path.
+func FSetWithFlags(f *os.File, name string, data []byte, flags int) error {
+	if err := fsetxattr(f, name, data, flags); err != nil {
+		return &Error{"xattr.FSetWithFlags", f.Name(), name, err}
+	}
+	return nil
+}
+
+// Remove removes the attribute associated with the given path.
+func Remove(path, name string) error {
+	if err := removexattr(path, name); err != nil {
+		return &Error{"xattr.Remove", path, name, err}
+	}
+	return nil
+}
+
+// LRemove is like Remove but does not follow a symlink at the end of the
+// path.
+func LRemove(path, name string) error {
+	if err := lremovexattr(path, name); err != nil {
+		return &Error{"xattr.LRemove", path, name, err}
+	}
+	return nil
+}
+
+// FRemove is like Remove but accepts a os.File instead of a file path.
+func FRemove(f *os.File, name string) error {
+	if err := fremovexattr(f, name); err != nil {
+		return &Error{"xattr.FRemove", f.Name(), name, err}
+	}
+	return nil
+}
+
+// List retrieves a list of names of extended attributes associated
+// with the given path in the file system.
+func List(path string) ([]string, error) {
+	return list(path, func(data []byte) (int, error) {
+		return listxattr(path, data)
+	})
+}
+
+// LList is like List but does not follow a symlink at the end of the
+// path.
+func LList(path string) ([]string, error) {
+	return list(path, func(data []byte) (int, error) {
+		return llistxattr(path, data)
+	})
+}
+
+// FList is like List but accepts a os.File instead of a file path.
+func FList(f *os.File) ([]string, error) {
+	return list(f.Name(), func(data []byte) (int, error) {
+		return flistxattr(f, data)
+	})
+}
+
+type listxattrFunc func(data []byte) (int, error)
+
+// list contains the buffer allocation logic used by both List and LList.
+func list(path string, listxattrFunc listxattrFunc) ([]string, error) {
+	myname := "xattr.list"
+	// find size.
+	size, err := listxattrFunc(nil)
+	if err != nil {
+		return nil, &Error{myname, path, "", err}
+	}
+	if size > 0 {
+		// `size + 1` because of ERANGE error when reading
+		// from a SMB1 mount point (https://github.com/pkg/xattr/issues/16).
+		buf := make([]byte, size+1)
+		// Read into buffer of that size.
+		read, err := listxattrFunc(buf)
+		if err != nil {
+			return nil, &Error{myname, path, "", err}
+		}
+		return stringsFromByteSlice(buf[:read]), nil
+	}
+	return []string{}, nil
+}
+
+// bytePtrFromSlice returns a pointer to array of bytes and a size.
+func bytePtrFromSlice(data []byte) (ptr *byte, size int) {
+	size = len(data)
+	if size > 0 {
+		ptr = &data[0]
+	}
+	return
+}