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// Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#![warn(missing_docs)]
//! Manipulate Unix file mode bits.
//!
//! Every filesystem entry (or inode) on Unix has a bit field of
//! [mode bits](https://en.wikipedia.org/wiki/Modes_(Unix))
//! that describe both the type of the file and its permissions.
//!
//! These are classically displayed in the left of `ls` output, and the permissions
//! can be changed with `chmod`. For example:
//!
//! ```
//! assert_eq!(unix_mode::to_string(0o0040755), "drwxr-xr-x");
//! assert_eq!(unix_mode::to_string(0o0100640), "-rw-r-----");
//! ```
//!
//! The encoding is fairly standard across unices, and occurs in some file
//! formats and network protocols that might be seen on non-Unix platforms, including that of
//! `rsync`.
//!
//! This library isn't Unix-specific and doesn't depend on the underlying OS to
//! interpret the bits.
//!
//! For example, this can be used with the return value from
//! [std::os::unix::fs::MetadataExt::mode].
//!
//! The names of the predicate functions match [std::fs::FileType] and
//! [std::os::unix::fs::FileTypeExt].
//!
//! # Changelog
//!
//! ## 0.1.3
//!
//! * Add [Type] enum for matching the file type.
//! * Add [Access], and [Accessor] enums for testing permissions.
//! * More tests.
//! * Move changelog into Rustdoc.
//!
//! ## 0.1.2
//!
//! * Add [is_setuid], [is_setgid], [is_sticky].
//!
//! ## 0.1.1
//!
//! * Fix tests on Windows.
//!
//! ## 0.1.0
//!
//! * Initial release.
/// Return just the bits representing the type of file.
fn type_bits(mode: u32) -> u32 {
(mode >> 12) & 0o17
}
/// The different types of files known to this library
///
/// Can be constructed `From<u32>`.
/// ```
/// assert_eq!(unix_mode::Type::from(0o0100640), unix_mode::Type::File);
/// ```
#[derive(Debug, PartialEq, Eq, Clone, Copy)]
#[non_exhaustive]
pub enum Type {
/// A plain file.
File,
/// A directory.
Dir,
/// A symbolic link.
Symlink,
/// A Unix-domain socket.
Socket,
/// A named pipe / FIFO.
Fifo,
/// A block device, such as a disk.
BlockDevice,
/// A character device, such as a `/dev/null`.
CharDevice,
/// A removed file in union filesystems.
Whiteout,
/// File type not recognized by this version of this library
///
/// More types might be added in the future, so the semantics of this variant may change.
Unknown,
}
impl From<u32> for Type {
/// Parse type from mode
///
fn from(mode: u32) -> Type {
use Type::*;
match type_bits(mode) {
0o001 => Fifo,
0o002 => CharDevice,
0o004 => Dir,
0o006 => BlockDevice,
0o010 => File,
0o012 => Symlink,
0o014 => Socket,
0o016 => Whiteout,
_ => Unknown,
}
}
}
/// Enum for specifying the context / "who" accesses in [is_allowed]
#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub enum Accessor {
/// Access by anyone other than the user or group.
Other,
/// Access by the group of the file.
Group,
/// Access by the owner of the file.
User,
}
/// Enum for specifying the type of access in [is_allowed]
#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub enum Access {
/// Permission to "execute", broadly.
///
/// For plain files, this does mean permission to execute. For directories, this grants
/// permission to open files within the directory whose name is known.
Execute,
/// Permission to write the file.
Write,
/// Permission to read the file, or to read the names of files in a directory.
Read,
}
/// Check whether `mode` represents an allowed (`true`) or denied (`false`) access
pub fn is_allowed(by: Accessor, ty: Access, mode: u32) -> bool {
use Access::*;
use Accessor::*;
let by = match by {
User => 2,
Group => 1,
Other => 0,
};
let bits = (mode >> (3 * by)) & 0o7;
let ty = match ty {
Read => 2,
Write => 1,
Execute => 0,
};
bits & (1 << ty) != 0
}
/// Returns true if this mode represents a regular file.
///
/// ```
/// assert_eq!(unix_mode::is_file(0o0041777), false);
/// assert_eq!(unix_mode::is_file(0o0100640), true);
/// ```
pub fn is_file(mode: u32) -> bool {
Type::from(mode) == Type::File
}
/// Returns true if this mode represents a directory.
///
/// ```
/// assert_eq!(unix_mode::is_dir(0o0041777), true);
/// assert_eq!(unix_mode::is_dir(0o0100640), false);
/// ```
pub fn is_dir(mode: u32) -> bool {
Type::from(mode) == Type::Dir
}
/// Returns true if this mode represents a symlink.
///
/// ```
/// assert_eq!(unix_mode::is_symlink(0o0040755), false);
/// assert_eq!(unix_mode::is_symlink(0o0120755), true);
/// ```
pub fn is_symlink(mode: u32) -> bool {
Type::from(mode) == Type::Symlink
}
/// Returns true if this mode represents a fifo, also known as a named pipe.
pub fn is_fifo(mode: u32) -> bool {
Type::from(mode) == Type::Fifo
}
/// Returns true if this mode represents a character device.
pub fn is_char_device(mode: u32) -> bool {
Type::from(mode) == Type::CharDevice
}
/// Returns true if this mode represents a block device.
pub fn is_block_device(mode: u32) -> bool {
Type::from(mode) == Type::BlockDevice
}
/// Returns true if this mode represents a Unix-domain socket.
pub fn is_socket(mode: u32) -> bool {
Type::from(mode) == Type::Socket
}
/// Returns true if the set-user-ID bit is set
pub fn is_setuid(mode: u32) -> bool {
mode & 0o4000 != 0
}
/// Returns true if the set-group-ID bit is set
pub fn is_setgid(mode: u32) -> bool {
mode & 0o2000 != 0
}
/// Returns true if the sticky bit is set
pub fn is_sticky(mode: u32) -> bool {
mode & 0o1000 != 0
}
/// Convert Unix mode bits to a text string describing type and permissions,
/// as shown in `ls`.
///
/// Examples:
/// ```
/// assert_eq!(unix_mode::to_string(0o0040755), "drwxr-xr-x");
/// assert_eq!(unix_mode::to_string(0o0100640), "-rw-r-----");
///
/// // Classic "sticky" directory
/// assert_eq!(unix_mode::to_string(0o0041777), "drwxrwxrwt");
///
/// // Char and block devices
/// assert_eq!(unix_mode::to_string(0o0020600), "crw-------");
/// assert_eq!(unix_mode::to_string(0o0060600), "brw-------");
///
/// // Symlink
/// assert_eq!(unix_mode::to_string(0o0120777), "lrwxrwxrwx");
///
/// ```
pub fn to_string(mode: u32) -> String {
// This is decoded "by hand" here so that it'll work
// on non-Unix platforms.
use Access::*;
use Accessor::*;
use Type::*;
let setuid = is_setuid(mode);
let setgid = is_setgid(mode);
let sticky = is_sticky(mode);
let mut s = String::with_capacity(10);
s.push(match Type::from(mode) {
Fifo => 'p',
CharDevice => 'c',
Dir => 'd',
BlockDevice => 'b',
File => '-',
Symlink => 'l',
Socket => 's',
Whiteout => 'w',
Unknown => '?',
});
for accessor in [User, Group, Other] {
for access in [Read, Write, Execute] {
s.push(
match (access, accessor, is_allowed(accessor, access, mode)) {
(Execute, User, true) if setuid => 's',
(Execute, User, false) if setuid => 'S',
(Execute, Group, true) if setgid => 's',
(Execute, Group, false) if setgid => 'S',
(Execute, Other, true) if sticky => 't',
(Execute, Other, false) if sticky => 'T',
(Execute, _, true) => 'x',
(Write, _, true) => 'w',
(Read, _, true) => 'r',
(_, _, false) => '-',
},
);
}
}
s
}
#[cfg(unix)]
#[cfg(test)]
mod unix_tests {
use super::*;
use nix::sys::stat;
use nix::unistd;
use std::os::unix::fs::MetadataExt;
use std::os::unix::net::UnixListener;
use std::path::Path;
use tempfile::tempdir;
fn file_mode<S: AsRef<Path>>(s: S) -> u32 {
let mode = std::fs::symlink_metadata(s.as_ref()).unwrap().mode();
println!("Mode of {:?} is 0o{:07o}", s.as_ref(), mode);
mode
}
/// Test predicates against files likely to already exist on a Unix system.
#[test]
fn stat_existing_files() {
assert!(is_dir(file_mode("/")));
assert!(!is_file(file_mode("/")));
assert!(is_file(file_mode("/etc/passwd")));
assert!(is_char_device(file_mode("/dev/null")));
assert!(is_sticky(file_mode("/tmp/")));
// I don't know how to reliably find a block device across OSes, and
// we can't make one (without root.)
}
/// Test [is_allowed] against files likely to already exist on a Unix system.
#[test]
fn existing_file_perms() {
use Access::*;
use Accessor::*;
for by in [User, Group, Other] {
assert!(is_allowed(by, Read, file_mode("/")));
assert!(is_allowed(by, Execute, file_mode("/")));
assert!(is_allowed(by, Write, file_mode("/dev/null")));
}
assert!(!is_allowed(Other, Write, file_mode("/dev/")));
assert!(!is_allowed(Other, Execute, file_mode("/dev/null")));
}
#[test]
fn stat_created_symlink() {
let tmp_dir = tempdir().unwrap();
let link_path = tmp_dir.path().join("sym");
unistd::symlinkat(".", None, &link_path).unwrap();
assert!(is_symlink(file_mode(link_path)));
}
#[test]
fn stat_created_fifo() {
let tmp_dir = tempdir().unwrap();
let fifo_path = tmp_dir.path().join("fifo");
unistd::mkfifo(&fifo_path, stat::Mode::S_IRWXU).unwrap();
assert!(is_fifo(file_mode(fifo_path)));
}
#[test]
fn stat_created_socket() {
let tmp_dir = tempdir().unwrap();
let sock_path = tmp_dir.path().join("sock");
let _ = UnixListener::bind(&sock_path).unwrap();
assert!(is_socket(file_mode(sock_path)));
}
mod to_string {
use super::*;
use std::fs::Permissions;
use std::os::unix::fs::PermissionsExt;
use std::process::Command;
fn shells(chmod_to: &str, expect_mode: &str) {
let tmp_dir = tempdir().unwrap();
// We're gonna be mucking around with setuid files, so exercise a little bit of caution
std::fs::set_permissions(tmp_dir.path(), Permissions::from_mode(0o700)).unwrap();
let f = &tmp_dir.path().join("f");
std::fs::write(f, &[0]).unwrap();
std::fs::set_permissions(f, Permissions::from_mode(0)).unwrap();
let chmod = Command::new("chmod").arg(chmod_to).arg(f).output().unwrap();
println!("chmod {:#?}", chmod);
assert_eq!(to_string(file_mode(f)), expect_mode);
// For good measure, also compare against ls
let ls = Command::new("ls").arg("-l").arg(f).output().unwrap();
println!("{:#?}", ls);
assert_eq!(std::str::from_utf8(&ls.stdout[0..10]), Ok(expect_mode));
}
#[test]
fn rwx() {
shells("a+r", "-r--r--r--");
shells("a+w", "--w--w--w-");
shells("a+x", "---x--x--x");
}
#[test]
fn extrabits() {
shells("+t", "---------T");
shells("+xt", "---x--x--t");
shells("+s", "---S--S---");
shells("+xs", "---s--s--x");
}
#[test]
fn nothing_with_left_beef() {
shells("u+wx,g+r", "--wxr-----");
}
}
}