file-mode 0.1.2

/*!
Decode Unix file mode bits, change them and apply them to files.

All file type, special and protection bits described in `sys/stat.h` are represented.

The [Mode] can represent a file mode partially by the use of a bitmask. Only modified bits will be changed in the target file.
Modifications specific only to directories (search) are handled correctly.

# Usage examples

## Decoding mode bits

```
use std::path::Path;
use file_mode::{ModePath, User};

let mode = Path::new("LICENSE").mode().unwrap();

assert!(mode.file_type().unwrap().is_regular_file());
assert!(mode.user_protection(User::Owner).is_read_set());
assert!(mode.user_protection(User::Group).is_write_set());
assert!(!mode.user_protection(User::Other).is_execute_set());
```

## Applying chmod strings

```
use std::path::Path;
use file_mode::ModePath;

Path::new("LICENSE").set_mode("u+r,g+u").unwrap();
```

## Applying octal modes

```
use std::path::Path;
use file_mode::ModePath;

Path::new("LICENSE").set_mode(0o664).unwrap();
```

## Printing standard mode strings

```
use std::path::Path;
use file_mode::ModePath;

let mode = Path::new("LICENSE").mode().unwrap();

println!("{}", mode); // -rw-rw-r--
assert_eq!(&mode.to_string(), "-rw-rw-r--");
```

## Constructing Mode programmatically

```
use file_mode::{Mode, Protection, ProtectionBit, User};

let mut mode = Mode::empty();
let mut rw = Protection::empty();

rw.set(ProtectionBit::Read);
rw.set(ProtectionBit::Write);

mode.set_protection(User::Owner, &rw);
mode.set_protection(User::Group, &rw);
mode.set_protection(User::Other, &ProtectionBit::Read.into());

assert_eq!(mode.mode(), 0o664);

mode.set_mode_path("LICENSE").unwrap();
```

## For non-Unix systems mode can still be used but not set to files

```rust
use file_mode::{Mode, Protection, ProtectionBit, User};

let mut mode = Mode::empty();
let mut rw = Protection::empty();

rw.set(ProtectionBit::Read);
rw.set(ProtectionBit::Write);

mode.set_protection(User::Owner, &rw);
mode.set_protection(User::Group, &rw);
mode.set_protection(User::Other, &ProtectionBit::Read.into());

assert_eq!(mode.apply_to(0o600), 0o664);
```

Use `Mode::from` to construct mode as if it was read from a file:

```rust
use file_mode::Mode;

let mut mode = Mode::from(0o600);

mode.set_str("g+rw,o+r").unwrap();

assert_eq!(mode.mode(), 0o664);
```

# Features and platform support

This carte should compile on all platforms.
On non-Unix (not `target_family = "unix"`) systems, functions related to setting mode to files will not be available.

## The calling process's umask

On non-Unix systems, the calling process's umask is emulated via global variable and defaults to `0o002`.

## Serde

Implementations of `Serialize` and `Deserialize` for [Mode] can be enabled with `serde` feature flag.

*/

#[cfg(target_family = "unix")]
use std::io;
use std::fmt::{self, Debug, Display};
#[cfg(target_family = "unix")]
use std::path::Path;
#[cfg(target_family = "unix")]
use std::fs::{metadata, symlink_metadata, set_permissions, File};
use std::iter::FromIterator;

#[cfg(target_family = "unix")]
use std::os::unix::fs::PermissionsExt;

#[cfg(feature = "serde")]
use serde::{Serialize, Deserialize};

mod parser;
pub use parser::ModeParseError;

/* Encoding of the file mode.  */
const S_IFMT: u32 =		0o170000;	/* These bits determine file type.  */

/* File types.  */
const S_IFDIR: u32 =	0o040000;	/* Directory.  */
const S_IFCHR: u32 =	0o020000;	/* Character device.  */
const S_IFBLK: u32 =	0o060000;	/* Block device.  */
const S_IFREG: u32 =	0o100000;	/* Regular file.  */
const S_IFIFO: u32 =	0o010000;	/* FIFO.  */
const S_IFLNK: u32 =	0o120000;	/* Symbolic link.  */
const S_IFSOCK: u32 =	0o140000;	/* Socket.  */


/* Protection bits.  */
const S_ISUID: u32 =	0o4000;		/* Set user ID on execution.  */
const S_ISGID: u32 =	0o2000;		/* Set group ID on execution.  */
const S_ISVTX: u32 =	0o1000;		/* Save swapped text after use (sticky).  */
const S_IREAD: u32 =	0o400;		/* Read by owner.  */
const S_IWRITE: u32 =	0o200;		/* Write by owner.  */
const S_IEXEC: u32 =	0o100;		/* Execute by owner.  */

/// Represents which user's access to the file will be changed.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum User {
    /// Represents 'u' flag
    Owner,
    /// Represents 'g' flag
    Group,
    /// Represents 'o' flag
    Other,
}

/// Type of the file as encoded in the mode value.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum FileType {
    Directory,
    CharacterDevice,
    BlockDevice,
    RegularFile,
    FIFO,
    SymbolicLink,
    Socket,
}

impl FileType {
    /// Gets [FileType] from mode value.
    pub fn from_mode(mode: u32) -> Option<FileType> {
        use FileType::*;
        match mode & S_IFMT {
            S_IFDIR => Some(Directory),
            S_IFCHR => Some(CharacterDevice),
            S_IFBLK => Some(BlockDevice),
            S_IFREG => Some(RegularFile),
            S_IFIFO => Some(FIFO),
            S_IFLNK => Some(SymbolicLink),
            S_IFSOCK => Some(Socket),
            _ => None
        }
    }

    /// Returns [true] if file is a directory.
    pub fn is_directory(&self) -> bool {
        *self == FileType::Directory
    }

    /// Returns [true] if file is a character device.
    pub fn is_character_device(&self) -> bool {
        *self == FileType::CharacterDevice
    }

    /// Returns [true] if file is a block device.
    pub fn is_block_device(&self) -> bool {
        *self == FileType::BlockDevice
    }

    /// Returns [true] if file is a regular file.
    pub fn is_regular_file(&self) -> bool {
        *self == FileType::RegularFile
    }

    /// Returns [true] if file is a first-in first-out special file.
    pub fn is_fifo(&self) -> bool {
        *self == FileType::FIFO
    }

    /// Returns [true] if file is a symbolic link.
    pub fn is_symbolic_link(&self) -> bool {
        *self == FileType::SymbolicLink
    }

    /// Returns [true] if file is a socket endpoint.
    pub fn is_socket(&self) -> bool {
        *self == FileType::Socket
    }

    /// Gets [Mode] with corresponding file type bits set.
    pub fn mode(&self) -> Mode {
        use FileType::*;
        let mode = match self {
            Directory =>          S_IFDIR,
            CharacterDevice =>    S_IFCHR,
            BlockDevice =>        S_IFBLK,
            RegularFile =>        S_IFREG,
            FIFO =>               S_IFIFO,
            SymbolicLink =>       S_IFLNK,
            Socket =>             S_IFSOCK,
        };

        Mode::new(mode, S_IFMT)
    }
}

/// Protection bit that can be set for a [User].
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum ProtectionBit {
    /// Permission to read.
    Read,
    /// Permission to write.
    Write,
    /// Permission to execute.
    Execute,
    /// Permission to search a directory - like execute but only applies to directories.
    Search,
}

impl From<ProtectionBit> for Protection {
    fn from(bit: ProtectionBit) -> Protection {
        Protection::empty().with_set(bit)
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
enum ExecuteOrSearch {
    Execute(bool),
    Search(bool),
}

/// Protection bits for user's access to a file.
#[derive(Debug, Clone)]
pub struct Protection {
    read: Option<bool>,
    write: Option<bool>,
    execute: Option<ExecuteOrSearch>,
}

impl Protection {
    /// Constructs [Protection] with all bits forgotten.
    pub fn empty() -> Protection {
        Protection {
            read: None,
            write: None,
            execute: None,
        }
    }

    /// Constructs [Protection] with all bits set.
    pub fn all_set() -> Protection {
        Protection {
            read: Some(true),
            write: Some(true),
            execute: Some(ExecuteOrSearch::Execute(true)),
        }
    }

    /// Constructs [Protection] with all bits cleared.
    pub fn all_clear() -> Protection {
        Protection {
            read: Some(false),
            write: Some(false),
            execute: Some(ExecuteOrSearch::Execute(false)),
        }
    }

    /// Constructs [Protection] representing [User] access to the file described by [Mode].
    pub fn from_mode_user(mode: &Mode, user: User) -> Protection {
        let mut mask = mode.mask;
        let mut dir_mask = mode.dir_mask;
        let mut mode = mode.mode;

        let owner_mask = S_IREAD | S_IWRITE | S_IEXEC;

        let shift = Self::user_shift(user);
        mode <<= shift;
        mask <<= shift;
        dir_mask <<= shift;

        mode &= owner_mask;
        mask &= owner_mask;
        dir_mask &= owner_mask;

        let mut ret = Protection::empty();

        if mask & S_IREAD > 0 {
            ret.read = Some(mode & S_IREAD > 0);
        }

        if mask & S_IWRITE > 0 {
            ret.write = Some(mode & S_IWRITE > 0);
        }

        if mask & S_IEXEC > 0 {
            if dir_mask & S_IEXEC > 0 {
                ret.execute = Some(ExecuteOrSearch::Search(mode & S_IEXEC > 0));
            } else {
                ret.execute = Some(ExecuteOrSearch::Execute(mode & S_IEXEC > 0));
            }
        }

        ret
    }

    /// Returns [true] if read permission bit is set.
    pub fn is_read_set(&self) -> bool {
        self.read == Some(true)
    }

    /// Returns [true] if write permission bit is set.
    pub fn is_write_set(&self) -> bool {
        self.write == Some(true)
    }

    /// Returns [true] if execute permission bit is set.
    pub fn is_execute_set(&self) -> bool {
        self.execute == Some(ExecuteOrSearch::Execute(true))
    }

    /// Returns [true] if execute or search permission bits are set.
    pub fn is_search_set(&self) -> bool {
        self.execute == Some(ExecuteOrSearch::Execute(true)) ||
        self.execute == Some(ExecuteOrSearch::Search(true))
    }

    /// Returns self with given [ProtectionBit] set.
    pub fn with_set(mut self, bit: ProtectionBit) -> Protection {
        self.set(bit);
        self
    }

    /// Returns self with given [ProtectionBit] cleared.
    pub fn with_cleared(mut self, bit: ProtectionBit) -> Protection {
        self.clear(bit);
        self
    }

    /// Returns self with given [ProtectionBit] value forgotten.
    pub fn with_forgotten(mut self, bit: ProtectionBit) -> Protection {
        self.forget(bit);
        self
    }

    /// Sets given [ProtectionBit].
    pub fn set(&mut self, bit: ProtectionBit) {
        match bit {
            ProtectionBit::Read => self.read = Some(true),
            ProtectionBit::Write => self.write = Some(true),
            ProtectionBit::Execute => self.execute = Some(ExecuteOrSearch::Execute(true)),
            ProtectionBit::Search => self.execute = Some(ExecuteOrSearch::Search(true)),
        }
    }

    /// Clears given [ProtectionBit].
    pub fn clear(&mut self, bit: ProtectionBit) {
        match bit {
            ProtectionBit::Read => self.read = Some(false),
            ProtectionBit::Write => self.write = Some(false),
            ProtectionBit::Execute => self.execute = Some(ExecuteOrSearch::Execute(false)),
            ProtectionBit::Search => self.execute = Some(ExecuteOrSearch::Search(false)),
        }
    }

    /// Forgets the value of given [ProtectionBit].
    pub fn forget(&mut self, bit: ProtectionBit) {
        match bit {
            ProtectionBit::Read => self.read = None,
            ProtectionBit::Write => self.write = None,
            ProtectionBit::Execute | ProtectionBit::Search => self.execute = None,
        }
    }

    fn user_shift(user: User) -> u32 {
        match user {
                User::Owner => 0,
                User::Group => 3,
                User::Other => 6,
        }
    }

    /// Constructs [Mode] with protection bits set for [User].
    pub fn for_user(&self, user: User) -> Mode {
        let mut mode = Mode::empty();

        if let Some(read) = self.read {
            if read {
                mode.mode |= S_IREAD;
            } else {
                mode.mode &= !S_IREAD;
            }
            mode.mask |= S_IREAD;
        }

        if let Some(write) = self.write {
            if write {
                mode.mode |= S_IWRITE;
            } else {
                mode.mode &= !S_IWRITE;
            }
            mode.mask |= S_IWRITE;
        }

        if let Some(execute) = self.execute {
            match execute {
                ExecuteOrSearch::Execute(execute) | ExecuteOrSearch::Search(execute) => if execute {
                    mode.mode |= S_IEXEC;
                } else {
                    mode.mode &= !S_IEXEC;
                }
            }
            mode.mask |= S_IEXEC;

            if let ExecuteOrSearch::Search(_) = execute {
                mode.dir_mask |= S_IEXEC;
            }
        }

        let shift = Self::user_shift(user);
        mode.mode >>= shift;
        mode.mask >>= shift;
        mode.dir_mask >>= shift;

        mode
    }
}

/// Special bit that can be set for a [User].
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum SpecialBit {
    /// Sets the effective user ID of the calling process.
    SetId,
    /// Sticky Bit.
    Sticky,
}

impl From<SpecialBit> for Special {
    fn from(bit: SpecialBit) -> Special {
        Special::empty().with_set(bit)
    }
}

/// Special bits set on a file.
#[derive(Debug, Clone)]
pub struct Special {
    set_id: Option<bool>,
    sticky: Option<bool>,
}

impl Special {
    pub fn empty() -> Special {
        Special {
            set_id: None,
            sticky: None,
        }
    }

    /// Constructs [Special] representing [User]-specific special bits set on the file described by [Mode].
    ///
    /// * For [User::Owner] the [SpecialBit::SetId] bit will represent the `set-user-ID` mode bit.
    /// * For [User::Group] the [SpecialBit::SetId] bit will represent the `set-group-ID` mode bit.
    pub fn from_mode_user(mode: &Mode, user: User) -> Special {
        let mut ret = Special::empty();

        match user {
            User::Owner if mode.mask & S_ISUID > 0 => ret.set_id = Some(mode.mode & S_ISUID > 0),
            User::Group if mode.mask & S_ISGID > 0 => ret.set_id = Some(mode.mode & S_ISGID > 0),
            _ => (),
        }

        if mode.mask & S_ISVTX > 0 {
            ret.sticky = Some(mode.mode & S_ISVTX > 0);
        }

        ret
    }

    /// Returns [true] if set ID bit is set.
    ///
    /// * For [User::Owner] the bit will represent the `set-user-ID` mode bit.
    /// * For [User::Group] the bit will represent the `set-group-ID` mode bit.
    pub fn is_set_id_set(&self) -> bool {
        self.set_id == Some(true)
    }

    /// Returns [true] if sticky bit is set.
    pub fn is_sticky_set(&self) -> bool {
        self.sticky == Some(true)
    }

    /// Returns self with given [SpecialBit] set.
    pub fn with_set(mut self, bit: SpecialBit) -> Special {
        self.set(bit);
        self
    }

    /// Returns self with given [SpecialBit] cleared.
    pub fn with_cleared(mut self, bit: SpecialBit) -> Special {
        self.clear(bit);
        self
    }

    /// Returns self with given [SpecialBit] value forgotten.
    pub fn with_forgotten(mut self, bit: SpecialBit) -> Special {
        self.forget(bit);
        self
    }

    /// Sets given [SpecialBit].
    pub fn set(&mut self, bit: SpecialBit) {
        match bit {
            SpecialBit::SetId => self.set_id = Some(true),
            SpecialBit::Sticky => self.sticky = Some(true),
        }
    }

    /// Clears given [SpecialBit].
    pub fn clear(&mut self, bit: SpecialBit) {
        match bit {
            SpecialBit::SetId => self.set_id = Some(false),
            SpecialBit::Sticky => self.sticky = Some(false),
        }
    }

    /// Forgets the value of given [SpecialBit].
    pub fn forget(&mut self, bit: SpecialBit) {
        match bit {
            SpecialBit::SetId => self.set_id = None,
            SpecialBit::Sticky => self.sticky = None,
        }
    }

    /// Constructs [Mode] with special bits set according to [User].
    ///
    /// * For [User::Owner] the [SpecialBit::SetId] bit will represent the `set-user-ID` mode bit.
    /// * For [User::Group] the [SpecialBit::SetId] bit will represent the `set-group-ID` mode bit.
    pub fn for_user(&self, user: User) -> Mode {
        let mut mode = Mode::empty();

        if let Some(sticky) = self.sticky {
            if sticky {
                mode.mode |= S_ISVTX;
            } else {
                mode.mode &= !S_ISVTX;
            }
            mode.mask |= S_ISVTX;
        }

        if let Some(set_id) = self.set_id {
            match user {
                User::Owner => {
                    if set_id {
                        mode.mode |= S_ISUID;
                    } else {
                        mode.mode &= !S_ISUID;
                    }
                    mode.mask |= S_ISUID;
                }
                User::Group => {
                    if set_id {
                        mode.mode |= S_ISGID;
                    } else {
                        mode.mode &= !S_ISGID;
                    }
                    mode.mask |= S_ISGID;
                }
                _ => (), // don't set for other
            }
        }

        mode
    }
}

/// Unix file mode.
///
/// All file type, special and protection bits described in `sys/stat.h` are represented.
///
/// The `Mode` can represent a file mode partially by the use of a bitmask. Only modified bits will be changed in the target file.
/// Modifications specific only to directories (see [ProtectionBit::Search]) are handled correctly.
///
/// The `Mode` can be displayed as a string according to the POSIX standard for the `ls` command.
///
/// Mode bits can be set with `chmod` compatible string.
#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
#[derive(Clone, PartialEq, Eq, Hash)]
pub struct Mode {
    mode: u32,
    mask: u32,
    // bits set only apply to directories
    dir_mask: u32,
}

impl Debug for Mode {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Mode")
            .field("mode", &format_args!("{:06o}", self.mode))
            .field("mask", &format_args!("{:06o}", self.mask))
            .field("dirm", &format_args!("{:06o}", self.dir_mask))
            .finish()
    }
}

impl Display for Mode {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        use FileType::*;
        match self.file_type() {
            Some(Directory) =>          f.write_str("d")?,
            Some(CharacterDevice) =>    f.write_str("c")?,
            Some(BlockDevice) =>        f.write_str("b")?,
            Some(RegularFile) =>        f.write_str("-")?,
            Some(FIFO) =>               f.write_str("p")?,
            Some(SymbolicLink) =>       f.write_str("l")?,
            Some(Socket) =>             f.write_str("s")?,
            None =>                     f.write_str("?")?,
        }

        use User::*;
        for user in &[Owner, Group, Other] {
            let special = self.user_special(*user);
            let protection = self.user_protection(*user);

            if protection.is_read_set() {
                f.write_str("r")?;
            } else {
                f.write_str("-")?;
            }

            if protection.is_write_set() {
                f.write_str("w")?;
            } else {
                f.write_str("-")?;
            }

            match user {
                Owner | Group => match (special.is_set_id_set(), protection.is_execute_set(), protection.is_search_set()) {
                    (true, true, _) => f.write_str("s")?,
                    (true, false, _) => f.write_str("S")?,
                    (false, false, true) => f.write_str("X")?,
                    (false, true, _) => f.write_str("x")?,
                    (false, false, _) => f.write_str("-")?,
                }
                Other => match (special.is_sticky_set(), protection.is_execute_set(), protection.is_search_set()) {
                    (true, true, _) => f.write_str("t")?,
                    (true, false, _) => f.write_str("T")?,
                    (false, false, true) => f.write_str("X")?,
                    (false, true, _) => f.write_str("x")?,
                    (false, false, _) => f.write_str("-")?,
                }
            }
        }

        Ok(())
    }
}

impl Mode {
    /// Constructs [Mode] from mode value and mask representing which special and permissions bits
    /// will be applied to the target file mode.
    pub fn new(mode: u32, mask: u32) -> Mode {
        Mode {
            mode: mode & (mask | S_IFMT),
            mask,
            dir_mask: 0,
        }
    }

    /// Constructs [Mode] with no bits sets and empty mask.
    pub fn empty() -> Mode {
        Mode {
            mode: 0,
            mask: 0,
            dir_mask: 0,
        }
    }

    /// Constructs [Mode] from mode value of the file represented by the path.
    ///
    /// The mask will be set to `0o7777` meaning that all the special and permissions bits will be applied
    /// to the target file mode.
    #[cfg(target_family = "unix")]
    pub fn from_path(path: impl AsRef<Path>) -> Result<Mode, io::Error> {
        Ok(Mode::new(metadata(path.as_ref())?.permissions().mode(), 0o7777 | S_IFMT))
    }

    /// Like [Mode::from_path] but will not follow symbolic links.
    #[cfg(target_family = "unix")]
    pub fn from_path_nofollow(path: impl AsRef<Path>) -> Result<Mode, io::Error> {
        Ok(Mode::new(symlink_metadata(path.as_ref())?.permissions().mode(), 0o7777 | S_IFMT))
    }

    /// Constructs [Mode] from mode value of the file.
    ///
    /// The mask will be set to `0o7777` meaning that all the special and permissions bits will be applied
    /// to the target file mode.
    #[cfg(target_family = "unix")]
    pub fn from_file(file: &File) -> Result<Mode, io::Error> {
        Ok(Mode::new(file.metadata()?.permissions().mode(), 0o7777 | S_IFMT))
    }

    /// Gets mode value.
    pub fn mode(&self) -> u32 {
        self.mode_mask().0
    }

    /// Gets mode value and mask that represents bits of the mode that would be applied to the target
    /// file mode.
    ///
    /// If the mode represents a directory the search bit will be handled accordingly.
    pub fn mode_mask(&self) -> (u32, u32) {
        if let Some(true) = self.file_type().map(|m| m.is_directory()) {
            (self.mode, self.mask)
        } else {
            (self.mode & !self.dir_mask, self.mask & !self.dir_mask)
        }
    }

    /// Gets [FileType] if corresponding bit patterns are present and valid in the mode value.
    pub fn file_type(&self) -> Option<FileType> {
        FileType::from_mode(self.mode)
    }

    /// Gets [Protection] bits for [User].
    pub fn user_protection(&self, user: User) -> Protection {
        Protection::from_mode_user(self, user)
    }

    /// Gets [Special] bits for [User].
    ///
    /// * For [User::Owner] the [SpecialBit::SetId] bit will represent the `set-user-ID` mode bit.
    /// * For [User::Group] the [SpecialBit::SetId] bit will represent the `set-group-ID` mode bit.
    pub fn user_special(&self, user: User) -> Special {
        Special::from_mode_user(self, user)
    }

    /// Sets bits that are set in the given mode according to mask.
    pub fn add(&mut self, mode: &Mode) {
        self.mode |= mode.mode;
        self.mask |= mode.mask;
        self.dir_mask |= mode.dir_mask;
    }

    /// Clears bits that are set in the given mode according to mask.
    pub fn sub(&mut self, mode: &Mode) {
        self.mode &= !mode.mode;
        self.mask |= mode.mask;
        self.dir_mask |= mode.dir_mask;
    }

    /// Sets values of bits that are set or clear in the given mode according to mask.
    pub fn set(&mut self, mode: &Mode) {
        self.mode &= !mode.mask;
        self.mode |= mode.mode;
        self.mask |= mode.mask;
        self.dir_mask |= mode.dir_mask;
    }

    /// Forgets values of bits that are set or clear in the given mode by clearing bits in the mask.
    pub fn forget(&mut self, mode: &Mode) {
        self.mode &= !mode.mask;
        self.mask &= !mode.mask;
        self.dir_mask &= !mode.dir_mask;
    }

    /// Returns self with given bit pattern representing [FileType] set.
    pub fn with_file_type(mut self, file_type: FileType) -> Mode {
        self.set(&file_type.mode());
        self
    }

    /// Returns self with bit pattern and mask for [Protection] bits set for [User].
    pub fn with_protection(mut self, user: User, protection: &Protection) -> Mode {
        self.set(&protection.for_user(user));
        self
    }

    /// Returns self with bit pattern and mask for [Special] bits set for [User].
    ///
    /// * For [User::Owner] the [SpecialBit::SetId] bit will represent the `set-user-ID` mode bit.
    /// * For [User::Group] the [SpecialBit::SetId] bit will represent the `set-group-ID` mode bit.
    pub fn with_special(mut self, user: User, special: &Special) -> Mode {
        self.set(&special.for_user(user));
        self
    }

    /// Sets bit pattern representing given [FileType].
    pub fn set_file_type(&mut self, file_type: FileType) {
        self.set(&file_type.mode())
    }

    /// Sets bit pattern and mask for [Protection] bits for [User].
    pub fn set_protection(&mut self, user: User, protection: &Protection) {
        self.set(&protection.for_user(user))
    }

    /// Sets bit pattern and mask for [Special] bits for [User].
    ///
    /// * For [User::Owner] the [SpecialBit::SetId] bit will represent the `set-user-ID` mode bit.
    /// * For [User::Group] the [SpecialBit::SetId] bit will represent the `set-group-ID` mode bit.
    pub fn set_special(&mut self, user: User, special: &Special) {
        self.set(&special.for_user(user))
    }

    /// Sets bits according to the mode string (as described in Linux `chmod` manual).
    ///
    /// Only bits described by the string will be represented in the mask.
    ///
    /// Note: Current value of mode is used as a reference for operations that use the
    /// user as the source of bits (like `g+u`). Consider constructing [Mode]
    /// using [Mode::from_file] or [Mode::from_path] before using this method.
    pub fn set_str(&mut self, mode_str: &str) -> Result<(), ModeParseError> {
        self.set_str_umask(mode_str, umask())
    }

    /// Like [Mode::set_str] but allows to specify umask value to use instead of the calling process's umask.
    pub fn set_str_umask(&mut self, mode_str: &str, umask: u32) -> Result<(), ModeParseError> {
        parser::mode_set_from_str(self, mode_str, umask)
    }

    /// Clears protection bits set in the umask value if they were set.
    pub fn apply_umask(&mut self, mut umask: u32) {
        umask &= 0o777;
        self.mode &= !umask;
    }

    /// Applies mode changes to given mode value.
    ///
    /// Only bits set in the mask are modified.
    ///
    /// Returns the resulting mode value.
    ///
    /// If the mode value passed as an argument represents a directory the search bit will be handled
    /// accordingly.
    pub fn apply_to(&self, mut mode: u32) -> u32 {
        let (amode, amask) = if let Some(true) = FileType::from_mode(mode).map(|m| m.is_directory()) {
            (self.mode, self.mask)
        } else {
            (self.mode & !self.dir_mask, self.mask & !self.dir_mask)
        };

        mode &= !amask;
        mode | amode
    }

    /// Applies mode changes to the mode of a file represented by the path.
    ///
    /// Only bits set in the mask are modified.
    ///
    /// Returns the resulting mode value.
    ///
    /// If the mode value of the file passed as an argument represents a directory the search bit will be handled accordingly.
    ///
    /// The file's mode is not modified.
    #[cfg(target_family = "unix")]
    pub fn apply_to_path(&self, path: impl AsRef<Path>) -> Result<u32, io::Error> {
        let file_mode = metadata(path.as_ref())?.permissions().mode();
        Ok(self.apply_to(file_mode))
    }

    /// Like [Mode::apply_to_path] but does not follow symbolic links.
    #[cfg(target_family = "unix")]
    pub fn apply_to_path_nofollow(&self, path: impl AsRef<Path>) -> Result<u32, io::Error> {
        let file_mode = symlink_metadata(path.as_ref())?.permissions().mode();
        Ok(self.apply_to(file_mode))
    }

    /// Sets the mode of the file, represented by the path, by applying the mode changes to its
    /// current mode.
    ///
    /// Only bits set in the mask are modified.
    ///
    /// Returns the new file mode value.
    ///
    /// If the mode value of the file passed as an argument represents a directory the search bit will be handled accordingly.
    ///
    /// The file's mode **is** modified.
    #[cfg(target_family = "unix")]
    pub fn set_mode_path(&self, path: impl AsRef<Path>) -> Result<u32, io::Error> {
        let path = path.as_ref();
        let mut perms = metadata(path)?.permissions();
        let mode = self.apply_to(perms.mode());
        perms.set_mode(mode);
        set_permissions(path, perms)?;
        Ok(mode)
    }

    /// Like [Mode::set_mode_path] but does not follow symbolic links.
    #[cfg(target_family = "unix")]
    pub fn set_mode_path_nofollow(&self, path: impl AsRef<Path>) -> Result<u32, io::Error> {
        let path = path.as_ref();
        let mut perms = symlink_metadata(path)?.permissions();
        let mode = self.apply_to(perms.mode());
        perms.set_mode(mode);
        set_permissions(path, perms)?;
        Ok(mode)
    }

    /// Sets the mode of the file by applying the mode changes to its current mode.
    ///
    /// Only bits set in the mask are modified.
    ///
    /// Returns the new file mode value.
    ///
    /// If the mode value of the file passed as an argument represents a directory the search bit will be handled accordingly.
    ///
    /// The file's mode **is** modified.
    #[cfg(target_family = "unix")]
    pub fn set_mode_file(&self, file: &File) -> Result<u32, io::Error> {
        let mut perms = file.metadata()?.permissions();
        let mode = self.apply_to(perms.mode());
        perms.set_mode(mode);
        file.set_permissions(perms)?;
        Ok(mode)
    }
}

impl From<u32> for Mode {
    fn from(mode: u32) -> Mode {
        Mode::new(mode, 0o7777)
    }
}

impl FromIterator<Mode> for Mode {
    fn from_iter<I: IntoIterator<Item=Mode>>(iter: I) -> Self {
        let mut mode = Mode::empty();

        for m in iter {
            mode.set(&m);
        }

        mode
    }
}


#[cfg(target_family = "unix")]
mod unix {
    use super::*;
    use std::error::Error;
    use std::convert::Infallible;

    /// Error setting mode to a file.
    #[derive(Debug)]
    pub enum ModeError {
        ModeParseError(ModeParseError),
        IoError(io::Error),
    }

    impl Display for ModeError {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            use ModeError::*;
            match self {
                ModeParseError(_) => write!(f, "error parsing file mode string"),
                IoError(_) => write!(f, "I/O error setting file mode"),
            }
        }
    }

    impl Error for ModeError {
        fn source(&self) -> Option<&(dyn Error + 'static)> {
            use ModeError::*;
            match self {
                ModeParseError(err) => Some(err),
                IoError(err) => Some(err),
            }
        }
    }

    impl From<ModeParseError> for ModeError {
        fn from(err: ModeParseError) -> ModeError {
            ModeError::ModeParseError(err)
        }
    }

    impl From<io::Error> for ModeError {
        fn from(err: io::Error) -> ModeError {
            ModeError::IoError(err)
        }
    }

    impl From<Infallible> for ModeError {
        fn from(_err: Infallible) -> ModeError {
            unreachable!()
        }
    }

    /// Types that convert to this type can be used with `set_mode` methods.
    pub enum SetMode<'s> {
        Value(Mode),
        Str(&'s str),
    }

    impl<'s, M: Into<Mode>> From<M> for SetMode<'s> {
        fn from(val: M) -> SetMode<'s> {
            SetMode::Value(val.into())
        }
    }

    impl<'s> From<&'s str> for SetMode<'s> {
        fn from(val: &'s str) -> SetMode<'s> {
            SetMode::Str(val)
        }
    }

    /// Extension methods for objects that can reference as [Path](std::path::Path).
    pub trait ModePath {
        /// Constructs [Mode] from mode value of the file.
        ///
        /// See [Mode::from_path] for details.
        fn mode(&self) -> Result<Mode, io::Error>;

        /// Sets the mode of the file, represented by this path, by applying the mode changes to its
        /// current mode.
        ///
        /// See [Mode::set_mode_path] for details.
        fn set_mode<'s, M: Into<SetMode<'s>>>(&self, mode: M) -> Result<u32, ModeError>;
    }

    impl<T: AsRef<Path>> ModePath for T {
        fn mode(&self) -> Result<Mode, io::Error> {
            Mode::from_path(self.as_ref())
        }

        fn set_mode<'s, M: Into<SetMode<'s>>>(&self, mode: M) -> Result<u32, ModeError> {
            let mut m = Mode::from_path(self)?; // need file mode as reference
            match mode.into() {
                SetMode::Value(val) => m.set(&val),
                SetMode::Str(val) => m.set_str(val)?, // this will use file mode as reference
            }
            Ok(m.set_mode_path(self)?)
        }
    }

    /// Extension methods for [File](std::fs::File).
    pub trait ModeFile {
        /// Constructs [Mode] from mode value of the file.
        ///
        /// See [Mode::from_path] for details.
        fn mode(&self) -> Result<Mode, io::Error>;

        /// Sets the mode of this file by applying the mode changes to its current mode.
        ///
        /// See [Mode::set_mode_file].
        fn set_mode<'s, M: Into<SetMode<'s>>>(&self, mode: M) -> Result<u32, ModeError>;
    }

    impl ModeFile for File {
        fn mode(&self) -> Result<Mode, io::Error> {
            Mode::from_file(&self)
        }

        fn set_mode<'s, M: Into<SetMode<'s>>>(&self, mode: M) -> Result<u32, ModeError> {
            let mut m = Mode::from_file(self)?; // need file mode as reference
            match mode.into() {
                SetMode::Value(val) => m.set(&val),
                SetMode::Str(val) => m.set_str(val)?, // this will use file mode as reference
            }
            Ok(m.set_mode_file(self)?)
        }
    }

    /// Sets the calling process's umask.
    ///
    /// Note: On non-Unix systems this is emulated by global variable.
    pub fn set_umask(umask: u32) -> u32 {
        unsafe {
            libc::umask(umask as libc::mode_t) as u32
        }
    }

    /// Gets the calling process's umask.
    ///
    /// Note: On non-Unix systems this is emulated by global variable.
    pub fn umask() -> u32 {
        let m = set_umask(0);
        set_umask(m);
        m
    }
}

#[cfg(target_family = "unix")]
pub use unix::*;

#[cfg(not(target_family = "unix"))]
mod non_unix {
    use std::sync::atomic::{AtomicU32, Ordering};

    static UMASK: AtomicU32 = AtomicU32::new(0o002);

    /// Sets the calling process's umask.
    ///
    /// Note: On non-Unix systems this is emulated by global variable.
    pub fn set_umask(umask: u32) -> u32 {
        UMASK.swap(umask, Ordering::Release)
    }

    /// Gets the calling process's umask.
    ///
    /// Note: On non-Unix systems this is emulated by global variable.
    pub fn umask() -> u32 {
        UMASK.load(Ordering::Acquire)
    }
}

#[cfg(not(target_family = "unix"))]
pub use non_unix::*;

#[cfg(test)]
mod tests {
    use super::*;
    use parking_lot::Mutex;

    const UMASK_LOCK: Mutex<()> = parking_lot::const_mutex(());

    #[test]
    fn test_mode() {
        assert_eq!(Mode::new(0o700, 0o700).apply_to(0o412), 0o712);
        assert_eq!(Mode::new(0o700, 0o400).apply_to(0o412), 0o412);
        assert_eq!(Mode::new(0o000, 0o700).apply_to(0o412), 0o012);
        assert_eq!(Mode::new(0o000, 0o111).apply_to(0o412), 0o402);
        assert_eq!(Mode::new(0o111, 0o111).apply_to(0o412), 0o513);
        assert_eq!(Mode::new(0o777, 0o111).apply_to(0o412), 0o513);
    }

    #[test]
    fn test_protection() {
        use ProtectionBit::*;
        use User::*;

        let mut o_700 = Protection::empty();
        o_700.set(Read);
        assert!(o_700.is_read_set());
        assert!(!o_700.is_write_set());
        assert!(!o_700.is_execute_set());

        o_700.set(Write);
        assert!(o_700.is_read_set());
        assert!(o_700.is_write_set());
        assert!(!o_700.is_execute_set());

        o_700.set(Execute);
        assert!(o_700.is_read_set());
        assert!(o_700.is_write_set());
        assert!(o_700.is_execute_set());

        assert_eq!(o_700.for_user(Owner), Mode::new(0o700, 0o700));
        assert_eq!(o_700.for_user(Group), Mode::new(0o070, 0o070));
        assert_eq!(o_700.for_user(Other), Mode::new(0o007, 0o007));

        let mut o_100 = Protection::empty();
        o_100.set(Execute);

        assert_eq!(o_100.for_user(Owner), Mode::new(0o100, 0o100));
        assert_eq!(o_100.for_user(Group), Mode::new(0o010, 0o010));
        assert_eq!(o_100.for_user(Other), Mode::new(0o001, 0o001));

        let mut o_200 = Protection::empty();
        o_200.set(Write);

        assert_eq!(o_200.for_user(Owner), Mode::new(0o200, 0o200));
        assert_eq!(o_200.for_user(Group), Mode::new(0o020, 0o020));
        assert_eq!(o_200.for_user(Other), Mode::new(0o002, 0o002));

        let mut o_600 = o_700.clone();
        o_600.clear(Execute);
        assert_eq!(o_600.for_user(Owner), Mode::new(0o600, 0o700));

        let mut o_777 = o_700.for_user(Owner);
        o_777.set(&o_700.for_user(Group));
        o_777.set(&o_700.for_user(Other));

        assert_eq!(o_777, Mode::new(0o777, 0o777));

        let mut o_123 = Mode::empty();
        o_123.set_protection(Owner, &Protection::empty().with_set(Execute));
        o_123.set_protection(Group, &Protection::empty().with_set(Write));
        o_123.set_protection(Other, &Protection::empty().with_set(Execute).with_set(Write));

        assert_eq!(o_123, Mode::new(0o123, 0o123));

        let mut o_102 = o_123;
        o_102.set_protection(Group, &Protection::empty().with_cleared(Write));
        o_102.set_protection(Other, &Protection::empty().with_cleared(Execute));

        assert_eq!(o_102, Mode::new(0o102, 0o123));
    }

    #[test]
    fn test_special() {
        use SpecialBit::*;

        let mut mode = Mode::empty();
        mode.set_special(User::Owner, &SetId.into());
        assert_eq!(mode, Mode::new(0o4000, 0o4000));
        mode.set_special(User::Group, &SetId.into());
        assert_eq!(mode, Mode::new(0o6000, 0o6000));

        let mut mode = Mode::empty();
        mode.set_special(User::Other, &SetId.into());
        assert_eq!(mode, Mode::new(0o0000, 0o0000)); // according to chmod behaviour

        let mut mode = Mode::empty();
        mode.set_special(User::Owner, &Sticky.into());
        assert_eq!(mode, Mode::new(0o1000, 0o1000));
        mode.set_special(User::Group, &Sticky.into());
        assert_eq!(mode, Mode::new(0o1000, 0o1000));
        mode.set_special(User::Other, &Sticky.into());
        assert_eq!(mode, Mode::new(0o1000, 0o1000));

        mode.set_special(User::Group, &SetId.into());
        assert_eq!(mode, Mode::new(0o3000, 0o3000));

        mode.set_special(User::Owner, &SetId.into());
        assert_eq!(mode, Mode::new(0o7000, 0o7000));

        let mut mode = Mode::empty();
        let special = Special::empty();
        mode.set_special(User::Owner, &special);
        assert_eq!(mode, Mode::new(0o0000, 0o0000));

        let special = mode.user_special(User::Owner);
        assert!(!special.is_set_id_set());
        assert!(!special.is_sticky_set());

        mode.set_special(User::Group, &special);
        assert_eq!(mode, Mode::new(0o0000, 0o0000));

        let special = mode.user_special(User::Owner);
        assert!(!special.is_set_id_set());
        assert!(!special.is_sticky_set());

        let mut mode = Mode::empty();
        let mut special = Special::empty();

        special.set(SetId);
        special.set(Sticky);

        mode.set_special(User::Owner, &special);
        assert_eq!(mode, Mode::new(0o5000, 0o5000));

        let special = mode.user_special(User::Owner);
        assert!(special.is_set_id_set());
        assert!(special.is_sticky_set());

        mode.set_special(User::Group, &special);
        assert_eq!(mode, Mode::new(0o7000, 0o7000));

        let special = mode.user_special(User::Owner);
        assert!(special.is_set_id_set());
        assert!(special.is_sticky_set());
    }

    #[test]
    fn test_set_str_umask_symbolic() {
        let mut mode = Mode::empty();
        mode.set_str("u=rwx,g=rw,o+x").unwrap();
        assert_eq!(mode, Mode::new(0o761, 0o771));

        let mut mode = Mode::new(0o2777, 0o2777);
        mode.set_str_umask("o=t", 0o002).unwrap();
        assert_eq!(mode, Mode::new(0o3770, 0o3777)); // according to chmod behaviour

        let mut mode = Mode::new(0o1770, 0o1770);
        mode.set_str_umask("g+s", 0o002).unwrap();
        assert_eq!(mode, Mode::new(0o3770, 0o3770)); // according to chmod behaviour

        let mut mode = Mode::new(0o0, 0o0);
        mode.set_str_umask("=rwx", 0o002).unwrap();
        assert_eq!(mode, Mode::new(0o0775, 0o0777)); // according to chmod behaviour; with umask 0o002

        let mut mode = Mode::new(0o0, 0o0);
        mode.set_str_umask("=s", 0o002).unwrap();
        assert_eq!(mode, Mode::new(0o6000, 0o6777)); // according to chmod behaviour; with umask 0o002

        let mut mode = Mode::new(0o0, 0o0);
        mode.set_str_umask("=", 0o002).unwrap();
        assert_eq!(mode, Mode::new(0o0000, 0o0777)); // according to chmod behaviour; with umask 0o002

        let mut mode = Mode::new(0o777, 0o7777);
        mode.set_str_umask("+w", 0o002).unwrap();
        assert_eq!(mode, Mode::new(0o777, 0o7777));

        let mut mode = Mode::new(0o000, 0o7777);
        mode.set_str_umask("+w", 0o002).unwrap();
        assert_eq!(mode, Mode::new(0o220, 0o7777));

        let mut mode = Mode::new(0o700, 0o700);
        mode.set_str_umask("o=u", 0o002).unwrap();
        assert_eq!(mode, Mode::new(0o707, 0o707)); // according to chmod behaviour

        let mut mode = Mode::new(0o100, 0o100);
        mode.set_str_umask("o=u", 0o002).unwrap();
        assert_eq!(mode, Mode::new(0o101, 0o107)); // according to chmod behaviour

        let mut mode = Mode::new(0o000, 0o000);
        mode.set_str_umask("u=rw,og=u", 0o002).unwrap();
        assert_eq!(mode, Mode::new(0o666, 0o777)); // according to chmod behaviour

        let mut mode = Mode::new(0o700, 0o700);
        mode.set_str_umask("o=u,g=o", 0o002).unwrap();
        assert_eq!(mode, Mode::new(0o777, 0o777)); // according to chmod behaviour

        let mut mode = Mode::new(0o604, 0o777); // file is rw-rw-r--
        mode.set_str("u+r,g+u").unwrap();
        assert_eq!(mode.apply_to(0o664), 0o664); // according to chmod behaviour

        let mut mode = Mode::new(0o664, 0o777); // file is rw-rw-r--
        mode.set_str("u+r,g-u").unwrap(); // g-u will copy rw- from u and unset bot bits
        assert_eq!(mode.apply_to(0o664), 0o604); // according to chmod behaviour

        let dir = 0o040664; // no exec/search
        let file = 0o100664; // no exec/search

        let mut mode = Mode::empty();
        mode.set_str("u+x,g+X").unwrap();

        assert_eq!(mode.apply_to(dir), 0o040774);
        assert_eq!(mode.apply_to(file), 0o100764);
    }

    #[test]
    fn test_set_str_umask_octal() {
        let mut mode = Mode::new(0o000,0o000);
        mode.set_str_umask("=777", 0o002).unwrap();
        assert_eq!(mode, Mode::new(0o777, 0o7777));

        let mut mode = Mode::new(0o000,0o000);
        mode.set_str_umask("+777,-111", 0o002).unwrap();
        assert_eq!(mode, Mode::new(0o666, 0o7777));

        let mut mode = Mode::new(0o000,0o000);
        mode.set_str_umask("=0,+7,-1", 0o002).unwrap();
        assert_eq!(mode, Mode::new(0o006, 0o7777));

        let mut mode = Mode::new(0o000,0o000);
        mode.set_str_umask("a=t,ug=s,+7,-1", 0o002).unwrap();
        assert_eq!(mode, Mode::new(0o7006, 0o7777));
    }

    #[test]
    fn test_from_str() {
        let lock = UMASK_LOCK;
        let guard = lock.lock();
        let umask = umask();

        set_umask(0o002);
        let mut mode = Mode::empty();
        mode.set_str("=rwx").unwrap();
        assert_eq!(mode, Mode::new(0o0775, 0o0777)); // according to chmod behaviour; with umask 0o002

        set_umask(0o022);
        let mut mode = Mode::empty();
        mode.set_str("=rwx").unwrap();
        assert_eq!(mode, Mode::new(0o0755, 0o0777));

        set_umask(0o002);
        let mut mode = Mode::empty();
        mode.set_str("+w").unwrap();
        assert_eq!(mode, Mode::new(0o0220, 0o0222)); // according to chmod behaviour; with umask 0o002

        set_umask(umask);
        drop(guard);
    }

    #[test]
    fn test_file_type() {
        // originally taken with from_path assuming umask 0o002
        assert_eq!(Mode::new(0o040775, 0o177777).file_type(), Some(FileType::Directory)); // from_path("src")
        assert_eq!(Mode::new(0o020666, 0o177777).file_type(), Some(FileType::CharacterDevice)); // from_path("/dev/null")
        assert_eq!(Mode::new(0o060660, 0o177777).file_type(), Some(FileType::BlockDevice)); // from_path("/dev/loop0")
        assert_eq!(Mode::new(0o100644, 0o177777).file_type(), Some(FileType::RegularFile)); // from_path(".gitignore")
        assert_eq!(Mode::new(0o010664, 0o177777).file_type(), Some(FileType::FIFO));
        assert_eq!(Mode::new(0o120777, 0o177777).file_type(), Some(FileType::SymbolicLink)); // from_path("/etc/localtime")
        assert_eq!(Mode::new(0o140777, 0o177777).file_type(), Some(FileType::Socket)); // from_path("/dev/log")
    }

    #[test]
    fn test_apply_to() {
        let dir = 0o040664; // no exec/search
        let file = 0o100664; // no exec/search

        let mut search = Mode::empty();
        search.set_protection(User::Owner, &ProtectionBit::Execute.into());
        search.set_protection(User::Group, &ProtectionBit::Search.into());

        assert_eq!(search.apply_to(dir), 0o040774);
        assert_eq!(search.apply_to(file), 0o100764);
    }

    #[test]
    fn test_to_string() {
        // originally taken with from_path assuming umask 0o002
        assert_eq!(&Mode::new(0o040775, 0o177777).to_string(), "drwxrwxr-x"); // from_path("src")
        assert_eq!(&Mode::new(0o100644, 0o177777).to_string(), "-rw-r--r--"); // from_path(".gitignore")
        assert_eq!(&Mode::new(0o104755, 0o177777).to_string(), "-rwsr-xr-x"); // from_path("/sbin/sudo")
        assert_eq!(&Mode::new(0o041777, 0o177777).to_string(), "drwxrwxrwt"); // from_path("/tmp")

        assert_eq!(&Mode::new(0o7000, 0o7777).to_string(), "?--S--S--T");

        let mut mode = Mode::new(0o7000, 0o7777);
        mode.set_file_type(FileType::Directory);
        assert_eq!(&mode.to_string(), "d--S--S--T");

        let mut mode = Mode::empty();
        mode.set_str("u+x,g+X").unwrap();
        assert_eq!(&mode.to_string(), "?--x--X---");
    }

    #[test]
    fn test_mode_debug() {
        let mode = Mode::new(0o040775, 0o177777); // from_path("src")
        eprintln!("{}", mode);
        eprintln!("{:?}", mode);
        eprintln!("{:#?}", mode);
    }

    #[test]
    #[cfg(target_family = "unix")]
    fn test_set_mode_traits() {
        //TODO: use temp file
        let file = Path::new("LICENSE");
        file.set_mode(0o600).unwrap();
        assert_eq!(file.set_mode("+r").unwrap() & 0o777, 0o644);

        let file = File::open(file).unwrap();
        file.set_mode(0o600).unwrap();
        assert_eq!(file.set_mode("+r").unwrap() & 0o777, 0o644);
        assert_eq!(file.set_mode("g-u").unwrap() & 0o777, 0o604);
        assert_eq!(file.set_mode("g+u").unwrap() & 0o777, 0o664);
    }
}