yash_env/system/virtual/

file_system.rs

// This file is part of yash, an extended POSIX shell.
// Copyright (C) 2021 WATANABE Yuki
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

//! File system in a virtual system.

use super::super::{Dir, DirEntry, Errno, FileType, Gid, Stat, Uid};
use crate::path::{Component, Path, PathBuf};
use crate::str::UnixStr;
use std::cell::RefCell;
use std::collections::HashMap;
use std::collections::VecDeque;
use std::fmt::Debug;
use std::rc::Rc;

const DEFAULT_DIRECTORY_MODE: Mode = Mode::USER_ALL.union(Mode::ALL_READ).union(Mode::ALL_EXEC);

/// Collection of files.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct FileSystem {
    /// Root directory
    pub root: Rc<RefCell<Inode>>,
}

/// The default file system only contains an empty root directory.
impl Default for FileSystem {
    fn default() -> Self {
        FileSystem {
            root: Rc::new(RefCell::new(Inode {
                body: FileBody::Directory {
                    files: HashMap::new(),
                },
                permissions: DEFAULT_DIRECTORY_MODE,
            })),
        }
    }
}

impl FileSystem {
    /// Saves a file.
    ///
    /// If there is an existing file at the specified path, this function
    /// replaces it the new file and returns the old one, regardless of
    /// permissions.
    ///
    /// TODO Reject relative path
    pub fn save<P: AsRef<Path>>(
        &mut self,
        path: P,
        content: Rc<RefCell<Inode>>,
    ) -> Result<Option<Rc<RefCell<Inode>>>, Errno> {
        fn ensure_dir(body: &mut FileBody) -> &mut HashMap<Rc<UnixStr>, Rc<RefCell<Inode>>> {
            match body {
                FileBody::Directory { files } => files,
                _ => {
                    let files = HashMap::new();
                    *body = FileBody::Directory { files };
                    match body {
                        FileBody::Directory { files } => files,
                        _ => unreachable!(),
                    }
                }
            }
        }

        fn main(
            fs: &mut FileSystem,
            path: &Path,
            content: Rc<RefCell<Inode>>,
        ) -> Result<Option<Rc<RefCell<Inode>>>, Errno> {
            let mut components = path.components();
            let file_name = match components.next_back().ok_or(Errno::ENOENT)? {
                Component::Normal(name) => name,
                _ => return Err(Errno::ENOENT),
            };

            // Create parent directories
            let mut node = Rc::clone(&fs.root);
            for component in components {
                let name = match component {
                    Component::Normal(name) => name,
                    Component::RootDir => continue,
                    _ => return Err(Errno::ENOENT),
                };
                let mut node_ref = node.borrow_mut();
                let children = ensure_dir(&mut node_ref.body);
                use std::collections::hash_map::Entry::*;
                let child = match children.entry(Rc::from(name)) {
                    Occupied(occupied) => Rc::clone(occupied.get()),
                    Vacant(vacant) => {
                        let child = Rc::new(RefCell::new(Inode {
                            body: FileBody::Directory {
                                files: HashMap::new(),
                            },
                            permissions: DEFAULT_DIRECTORY_MODE,
                        }));
                        Rc::clone(vacant.insert(child))
                    }
                };
                drop(node_ref);
                node = child;
            }

            let mut parent_ref = node.borrow_mut();
            let children = ensure_dir(&mut parent_ref.body);
            Ok(children.insert(Rc::from(file_name), content))
        }

        main(self, path.as_ref(), content)
    }

    /// Returns a reference to the existing file at the specified path.
    ///
    /// TODO Reject relative path
    pub fn get<P: AsRef<Path>>(&self, path: P) -> Result<Rc<RefCell<Inode>>, Errno> {
        fn main(fs: &FileSystem, path: &Path) -> Result<Rc<RefCell<Inode>>, Errno> {
            let components = path.components();
            let mut nodes = vec![Rc::clone(&fs.root)];
            for component in components {
                let name = match component {
                    Component::Normal(name) => name,
                    Component::RootDir | Component::CurDir => continue,
                    Component::ParentDir => {
                        if nodes.len() > 1 {
                            nodes.pop();
                        }
                        continue;
                    }
                };

                let node_ref = nodes.last().unwrap().borrow();
                let children = match &node_ref.body {
                    FileBody::Directory { files } => files,
                    _ => return Err(Errno::ENOTDIR),
                };

                if !node_ref.permissions.contains(Mode::USER_EXEC) {
                    return Err(Errno::EACCES);
                }

                let child = Rc::clone(children.get(name).ok_or(Errno::ENOENT)?);
                drop(node_ref);
                nodes.push(child);
            }

            let node = nodes.pop().unwrap();
            if path.as_unix_str().as_bytes().ends_with(b"/")
                && !matches!(&node.borrow().body, FileBody::Directory { .. })
            {
                return Err(Errno::ENOTDIR);
            }
            Ok(node)
        }

        main(self, path.as_ref())
    }
}

/// File on the file system
#[derive(Clone, Debug, Default, Eq, PartialEq)]
pub struct Inode {
    /// File content
    pub body: FileBody,
    /// Access permissions
    pub permissions: Mode,
    // TODO owner user and group, etc.
}

impl Inode {
    /// Create a regular file with the given content.
    pub fn new<T: Into<Vec<u8>>>(bytes: T) -> Self {
        Inode {
            body: FileBody::new(bytes),
            permissions: Mode::default(),
        }
    }

    /// Returns the metadata of the file.
    ///
    /// Currently, only the following fields are filled:
    ///
    /// - `ino`
    /// - `mode`
    /// - `type`
    /// - `size`
    #[must_use]
    pub fn stat(&self) -> Stat {
        Stat {
            dev: 1,
            ino: self as *const Self as u64,
            mode: self.permissions,
            r#type: self.body.r#type(),
            nlink: 1,
            uid: Uid(1),
            gid: Gid(1),
            size: self.body.size() as u64,
        }
    }
}

/// Filetype-specific content of a file
#[derive(Clone, Debug, Eq, PartialEq)]
#[non_exhaustive]
pub enum FileBody {
    /// Regular file
    Regular {
        /// File content
        content: Vec<u8>,
        /// Whether this file is a native binary that can be exec'ed
        is_native_executable: bool,
    },
    /// Directory
    Directory {
        /// Files contained in this directory
        ///
        /// The keys of the hashmap are filenames without any parent directory
        /// components. The hashmap does not contain "." or "..".
        files: HashMap<Rc<UnixStr>, Rc<RefCell<Inode>>>,
        // The hash map contents are reference-counted to allow making cheap
        // copies of them, which is especially handy when traversing entries.
    },
    /// Named pipe
    Fifo {
        /// Content of the pipe
        content: VecDeque<u8>,
        /// Number of open file descriptions reading from this pipe
        readers: usize,
        /// Number of open file descriptions writing to this pipe
        writers: usize,
    },
    /// Symbolic link
    Symlink {
        /// Path to the file referenced by this symlink
        target: PathBuf,
    },
    /// Terminal device
    ///
    /// This is a dummy device that works like a regular file.
    Terminal {
        /// Virtual file content
        content: Vec<u8>,
    },
    // TODO Other filetypes
}

/// The default file body is an empty regular file.
impl Default for FileBody {
    fn default() -> Self {
        FileBody::Regular {
            content: Vec::default(),
            is_native_executable: bool::default(),
        }
    }
}

impl FileBody {
    /// Creates a regular file body with the given content.
    pub fn new<T: Into<Vec<u8>>>(bytes: T) -> Self {
        FileBody::Regular {
            content: bytes.into(),
            is_native_executable: false,
        }
    }

    /// Returns the type of the file.
    #[must_use]
    pub const fn r#type(&self) -> FileType {
        match self {
            Self::Regular { .. } => FileType::Regular,
            Self::Directory { .. } => FileType::Directory,
            Self::Fifo { .. } => FileType::Fifo,
            Self::Symlink { .. } => FileType::Symlink,
            Self::Terminal { .. } => FileType::CharacterDevice,
        }
    }

    /// Returns the size of the file.
    #[must_use]
    pub fn size(&self) -> usize {
        match self {
            Self::Regular { content, .. } => content.len(),
            Self::Directory { files } => files.len(),
            Self::Fifo { content, .. } => content.len(),
            Self::Symlink { target } => target.as_unix_str().len(),
            Self::Terminal { .. } => 0,
        }
    }
}

/// This type alias exists only for historical reasons.
/// Please use `yash_env::system::Mode` instead.
#[deprecated = "use yash_env::system::Mode instead"]
pub use super::super::Mode;

/// Implementor of [`Dir`] for virtual file system
#[derive(Clone, Debug)]
pub struct VirtualDir<I> {
    iter: I,
    current: Rc<UnixStr>,
}

impl<I> VirtualDir<I> {
    /// Creates a `VirtualDir` that yields entries from an iterator.
    #[must_use]
    pub fn new<J>(iter: J) -> Self
    where
        J: IntoIterator<IntoIter = I, Item = Rc<UnixStr>>,
    {
        VirtualDir {
            iter: iter.into_iter(),
            current: Rc::from(UnixStr::new("")),
        }
    }
}

/// Creates a `VirtualDir` that yields entries of a directory.
///
/// This function will fail if the given file body is not a directory.
impl TryFrom<&FileBody> for VirtualDir<std::vec::IntoIter<Rc<UnixStr>>> {
    type Error = Errno;
    fn try_from(file: &FileBody) -> Result<Self, Errno> {
        let FileBody::Directory { files } = file else {
            return Err(Errno::ENOTDIR);
        };

        let mut entries = Vec::with_capacity(files.len() + 2);
        entries.push(Rc::from(UnixStr::new(".")));
        entries.push(Rc::from(UnixStr::new("..")));
        entries.extend(files.keys().cloned());

        // You should not pose any assumption on the order of entries.
        // Here, we deliberately disorder the entries.
        let entry = entries.pop().unwrap();
        let i = entries.len() / 2;
        entries.insert(i, entry);

        Ok(Self::new(entries))
    }
}

impl<I> Dir for VirtualDir<I>
where
    I: Debug,
    I: Iterator<Item = Rc<UnixStr>>,
{
    fn next(&mut self) -> Result<Option<DirEntry<'_>>, Errno> {
        match self.iter.next() {
            Some(name) => {
                self.current = name;
                let name = &self.current;
                Ok(Some(DirEntry { name }))
            }
            None => {
                self.current = Rc::from(UnixStr::new(""));
                Ok(None)
            }
        }
    }
}

// TODO impl Drop for VirtualDir: close backing file descriptor

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

    #[test]
    fn file_system_get_root() {
        let fs = FileSystem::default();
        let result = fs.get("/");
        assert_eq!(result, Ok(fs.root));
    }

    #[test]
    fn file_system_save_and_get_file() {
        let mut fs = FileSystem::default();
        let file_1 = Rc::new(RefCell::new(Inode::new([12, 34, 56])));
        let old = fs.save("/foo/bar", Rc::clone(&file_1));
        assert_eq!(old, Ok(None));

        let file_2 = Rc::new(RefCell::new(Inode::new([98, 76, 54])));
        let old = fs.save("/foo/bar", Rc::clone(&file_2));
        assert_eq!(old, Ok(Some(file_1)));

        let result = fs.get("/foo/bar");
        assert_eq!(result, Ok(file_2));
    }

    #[test]
    fn file_system_save_and_get_directory() {
        let mut fs = FileSystem::default();
        let file = Rc::new(RefCell::new(Inode::new([12, 34, 56])));
        let old = fs.save("/foo/bar", Rc::clone(&file));
        assert_eq!(old, Ok(None));

        let dir = fs.get("/foo").unwrap();
        let dir = dir.borrow();
        assert_eq!(dir.permissions, Mode::from_bits_retain(0o755));
        assert_matches!(&dir.body, FileBody::Directory { files } => {
            let mut i = files.iter();
            let (name, content) = i.next().unwrap();
            assert_eq!(name.as_bytes(), b"bar");
            assert_eq!(content, &file);
            assert_eq!(i.next(), None);
        });
    }

    #[test]
    fn file_system_save_invalid_name() {
        let mut fs = FileSystem::default();
        let old = fs.save("", Rc::default());
        assert_eq!(old, Err(Errno::ENOENT));
    }

    #[test]
    fn file_system_get_parents() {
        let mut fs = FileSystem::default();
        let file = Rc::new(RefCell::new(Inode::new([123])));
        _ = fs.save("/dir/dir1/file", Rc::clone(&file));
        _ = fs.save("/dir/dir2/dir3/file", Rc::default());
        assert_eq!(fs.get("/dir/dir2/dir3/../../dir1/file").unwrap(), file);
        assert_eq!(fs.get("/../dir/dir1/file").unwrap(), file);
    }

    #[test]
    fn file_system_get_non_existent_file() {
        let fs = FileSystem::default();
        let result = fs.get("/no_such_file");
        assert_eq!(result, Err(Errno::ENOENT));
        let result = fs.get("/no_such_directory/foo");
        assert_eq!(result, Err(Errno::ENOENT));
    }

    #[test]
    fn file_system_get_not_directory() {
        let mut fs = FileSystem::default();
        let _ = fs.save("/file", Rc::default());
        let result = fs.get("/file/");
        assert_eq!(result, Err(Errno::ENOTDIR));
        let result = fs.get("/file/foo");
        assert_eq!(result, Err(Errno::ENOTDIR));
    }

    #[test]
    fn file_system_get_no_search_permission() {
        let mut fs = FileSystem::default();
        let _ = fs.save("/dir/file", Rc::default());
        {
            let dir = fs.get("/dir").unwrap();
            dir.borrow_mut().permissions = Mode::from_bits_retain(0o666);
        }
        let result = fs.get("/dir/file");
        assert_eq!(result, Err(Errno::EACCES));
    }

    #[test]
    fn empty_virtual_dir() {
        let mut dir = VirtualDir::new(std::iter::empty());
        assert_matches!(dir.next(), Ok(None));
    }

    #[test]
    fn non_empty_virtual_dir() {
        let iter = ["foo", "bar"]
            .into_iter()
            .map(|s| Rc::from(UnixStr::new(s)));
        let mut dir = VirtualDir::new(iter);
        assert_matches!(dir.next(), Ok(Some(entry)) => {
            assert_eq!(entry.name, "foo");
        });
        assert_matches!(dir.next(), Ok(Some(entry)) => {
            assert_eq!(entry.name, "bar");
        });
        assert_matches!(dir.next(), Ok(None));
    }

    #[test]
    fn virtual_dir_try_from_file_body_directory() {
        let files = ["one", "2", "three"]
            .into_iter()
            .map(|name| (Rc::from(UnixStr::new(name)), Rc::default()))
            .collect();
        let file = FileBody::Directory { files };
        let mut dir = VirtualDir::try_from(&file).unwrap();

        let mut files = Vec::new();
        while let Some(entry) = dir.next().unwrap() {
            files.push(entry.name.to_str().unwrap().to_string());
        }
        files.sort_unstable();
        let files: Vec<&str> = files.iter().map(String::as_str).collect();
        assert_eq!(files, [".", "..", "2", "one", "three"]);
    }

    #[test]
    fn virtual_dir_try_from_file_body_non_directory() {
        let file = FileBody::Regular {
            content: Default::default(),
            is_native_executable: false,
        };
        let result = VirtualDir::try_from(&file);
        assert_eq!(result.unwrap_err(), Errno::ENOTDIR);
    }
}