open_options.rs

use crate::fs::{asyncify, File};

use std::io;
use std::path::Path;

/// Options and flags which can be used to configure how a file is opened.
///
/// This builder exposes the ability to configure how a [`File`] is opened and
/// what operations are permitted on the open file. The [`File::open`] and
/// [`File::create`] methods are aliases for commonly used options using this
/// builder.
///
/// Generally speaking, when using `OpenOptions`, you'll first call [`new`],
/// then chain calls to methods to set each option, then call [`open`], passing
/// the path of the file you're trying to open. This will give you a
/// [`io::Result`][result] with a [`File`] inside that you can further operate
/// on.
///
/// This is a specialized version of [`std::fs::OpenOptions`] for usage from
/// the Tokio runtime.
///
/// `From<std::fs::OpenOptions>` is implemented for more advanced configuration
/// than the methods provided here.
///
/// [`new`]: OpenOptions::new
/// [`open`]: OpenOptions::open
/// [result]: std::io::Result
/// [`File`]: File
/// [`File::open`]: File::open
/// [`File::create`]: File::create
/// [`std::fs::OpenOptions`]: std::fs::OpenOptions
///
/// # Examples
///
/// Opening a file to read:
///
/// ```no_run
/// use tokio::fs::OpenOptions;
/// use std::io;
///
/// #[tokio::main]
/// async fn main() -> io::Result<()> {
///     let file = OpenOptions::new()
///         .read(true)
///         .open("foo.txt")
///         .await?;
///
///     Ok(())
/// }
/// ```
///
/// Opening a file for both reading and writing, as well as creating it if it
/// doesn't exist:
///
/// ```no_run
/// use tokio::fs::OpenOptions;
/// use std::io;
///
/// #[tokio::main]
/// async fn main() -> io::Result<()> {
///     let file = OpenOptions::new()
///         .read(true)
///         .write(true)
///         .create(true)
///         .open("foo.txt")
///         .await?;
///
///     Ok(())
/// }
/// ```
#[derive(Clone, Debug)]
pub struct OpenOptions(std::fs::OpenOptions);

impl OpenOptions {
    /// Creates a blank new set of options ready for configuration.
    ///
    /// All options are initially set to `false`.
    ///
    /// This is an async version of [`std::fs::OpenOptions::new`][std]
    ///
    /// [std]: std::fs::OpenOptions::new
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::fs::OpenOptions;
    ///
    /// let mut options = OpenOptions::new();
    /// let future = options.read(true).open("foo.txt");
    /// ```
    pub fn new() -> OpenOptions {
        OpenOptions(std::fs::OpenOptions::new())
    }

    /// Sets the option for read access.
    ///
    /// This option, when true, will indicate that the file should be
    /// `read`-able if opened.
    ///
    /// This is an async version of [`std::fs::OpenOptions::read`][std]
    ///
    /// [std]: std::fs::OpenOptions::read
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::fs::OpenOptions;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let file = OpenOptions::new()
    ///         .read(true)
    ///         .open("foo.txt")
    ///         .await?;
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn read(&mut self, read: bool) -> &mut OpenOptions {
        self.0.read(read);
        self
    }

    /// Sets the option for write access.
    ///
    /// This option, when true, will indicate that the file should be
    /// `write`-able if opened.
    ///
    /// This is an async version of [`std::fs::OpenOptions::write`][std]
    ///
    /// [std]: std::fs::OpenOptions::write
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::fs::OpenOptions;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let file = OpenOptions::new()
    ///         .write(true)
    ///         .open("foo.txt")
    ///         .await?;
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn write(&mut self, write: bool) -> &mut OpenOptions {
        self.0.write(write);
        self
    }

    /// Sets the option for the append mode.
    ///
    /// This option, when true, means that writes will append to a file instead
    /// of overwriting previous contents.  Note that setting
    /// `.write(true).append(true)` has the same effect as setting only
    /// `.append(true)`.
    ///
    /// For most filesystems, the operating system guarantees that all writes are
    /// atomic: no writes get mangled because another process writes at the same
    /// time.
    ///
    /// One maybe obvious note when using append-mode: make sure that all data
    /// that belongs together is written to the file in one operation. This
    /// can be done by concatenating strings before passing them to [`write()`],
    /// or using a buffered writer (with a buffer of adequate size),
    /// and calling [`flush()`] when the message is complete.
    ///
    /// If a file is opened with both read and append access, beware that after
    /// opening, and after every write, the position for reading may be set at the
    /// end of the file. So, before writing, save the current position (using
    /// [`seek`]`(`[`SeekFrom`]`::`[`Current`]`(0))`), and restore it before the next read.
    ///
    /// This is an async version of [`std::fs::OpenOptions::append`][std]
    ///
    /// [std]: std::fs::OpenOptions::append
    ///
    /// ## Note
    ///
    /// This function doesn't create the file if it doesn't exist. Use the [`create`]
    /// method to do so.
    ///
    /// [`write()`]: crate::io::AsyncWriteExt::write
    /// [`flush()`]: crate::io::AsyncWriteExt::flush
    /// [`seek`]: crate::io::AsyncSeekExt::seek
    /// [`SeekFrom`]: std::io::SeekFrom
    /// [`Current`]: std::io::SeekFrom::Current
    /// [`create`]: OpenOptions::create
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::fs::OpenOptions;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let file = OpenOptions::new()
    ///         .append(true)
    ///         .open("foo.txt")
    ///         .await?;
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn append(&mut self, append: bool) -> &mut OpenOptions {
        self.0.append(append);
        self
    }

    /// Sets the option for truncating a previous file.
    ///
    /// If a file is successfully opened with this option set it will truncate
    /// the file to 0 length if it already exists.
    ///
    /// The file must be opened with write access for truncate to work.
    ///
    /// This is an async version of [`std::fs::OpenOptions::truncate`][std]
    ///
    /// [std]: std::fs::OpenOptions::truncate
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::fs::OpenOptions;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let file = OpenOptions::new()
    ///         .write(true)
    ///         .truncate(true)
    ///         .open("foo.txt")
    ///         .await?;
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn truncate(&mut self, truncate: bool) -> &mut OpenOptions {
        self.0.truncate(truncate);
        self
    }

    /// Sets the option for creating a new file.
    ///
    /// This option indicates whether a new file will be created if the file
    /// does not yet already exist.
    ///
    /// In order for the file to be created, [`write`] or [`append`] access must
    /// be used.
    ///
    /// This is an async version of [`std::fs::OpenOptions::create`][std]
    ///
    /// [std]: std::fs::OpenOptions::create
    /// [`write`]: OpenOptions::write
    /// [`append`]: OpenOptions::append
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::fs::OpenOptions;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let file = OpenOptions::new()
    ///         .write(true)
    ///         .create(true)
    ///         .open("foo.txt")
    ///         .await?;
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn create(&mut self, create: bool) -> &mut OpenOptions {
        self.0.create(create);
        self
    }

    /// Sets the option to always create a new file.
    ///
    /// This option indicates whether a new file will be created.  No file is
    /// allowed to exist at the target location, also no (dangling) symlink.
    ///
    /// This option is useful because it is atomic. Otherwise between checking
    /// whether a file exists and creating a new one, the file may have been
    /// created by another process (a TOCTOU race condition / attack).
    ///
    /// If `.create_new(true)` is set, [`.create()`] and [`.truncate()`] are
    /// ignored.
    ///
    /// The file must be opened with write or append access in order to create a
    /// new file.
    ///
    /// This is an async version of [`std::fs::OpenOptions::create_new`][std]
    ///
    /// [std]: std::fs::OpenOptions::create_new
    /// [`.create()`]: OpenOptions::create
    /// [`.truncate()`]: OpenOptions::truncate
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::fs::OpenOptions;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let file = OpenOptions::new()
    ///         .write(true)
    ///         .create_new(true)
    ///         .open("foo.txt")
    ///         .await?;
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn create_new(&mut self, create_new: bool) -> &mut OpenOptions {
        self.0.create_new(create_new);
        self
    }

    /// Opens a file at `path` with the options specified by `self`.
    ///
    /// This is an async version of [`std::fs::OpenOptions::open`][std]
    ///
    /// [std]: std::fs::OpenOptions::open
    ///
    /// # Errors
    ///
    /// This function will return an error under a number of different
    /// circumstances. Some of these error conditions are listed here, together
    /// with their [`ErrorKind`]. The mapping to [`ErrorKind`]s is not part of
    /// the compatibility contract of the function, especially the `Other` kind
    /// might change to more specific kinds in the future.
    ///
    /// * [`NotFound`]: The specified file does not exist and neither `create`
    ///   or `create_new` is set.
    /// * [`NotFound`]: One of the directory components of the file path does
    ///   not exist.
    /// * [`PermissionDenied`]: The user lacks permission to get the specified
    ///   access rights for the file.
    /// * [`PermissionDenied`]: The user lacks permission to open one of the
    ///   directory components of the specified path.
    /// * [`AlreadyExists`]: `create_new` was specified and the file already
    ///   exists.
    /// * [`InvalidInput`]: Invalid combinations of open options (truncate
    ///   without write access, no access mode set, etc.).
    /// * [`Other`]: One of the directory components of the specified file path
    ///   was not, in fact, a directory.
    /// * [`Other`]: Filesystem-level errors: full disk, write permission
    ///   requested on a read-only file system, exceeded disk quota, too many
    ///   open files, too long filename, too many symbolic links in the
    ///   specified path (Unix-like systems only), etc.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::fs::OpenOptions;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let file = OpenOptions::new().open("foo.txt").await?;
    ///     Ok(())
    /// }
    /// ```
    ///
    /// [`ErrorKind`]: std::io::ErrorKind
    /// [`AlreadyExists`]: std::io::ErrorKind::AlreadyExists
    /// [`InvalidInput`]: std::io::ErrorKind::InvalidInput
    /// [`NotFound`]: std::io::ErrorKind::NotFound
    /// [`Other`]: std::io::ErrorKind::Other
    /// [`PermissionDenied`]: std::io::ErrorKind::PermissionDenied
    pub async fn open(&self, path: impl AsRef<Path>) -> io::Result<File> {
        let path = path.as_ref().to_owned();
        let opts = self.0.clone();

        let std = asyncify(move || opts.open(path)).await?;
        Ok(File::from_std(std))
    }

    /// Returns a mutable reference to the underlying `std::fs::OpenOptions`
    pub(super) fn as_inner_mut(&mut self) -> &mut std::fs::OpenOptions {
        &mut self.0
    }
}

feature! {
    #![unix]

    use std::os::unix::fs::OpenOptionsExt;

    impl OpenOptions {
        /// Sets the mode bits that a new file will be created with.
        ///
        /// If a new file is created as part of an `OpenOptions::open` call then this
        /// specified `mode` will be used as the permission bits for the new file.
        /// If no `mode` is set, the default of `0o666` will be used.
        /// The operating system masks out bits with the system's `umask`, to produce
        /// the final permissions.
        ///
        /// # Examples
        ///
        /// ```no_run
        /// use tokio::fs::OpenOptions;
        /// use std::io;
        ///
        /// #[tokio::main]
        /// async fn main() -> io::Result<()> {
        ///     let mut options = OpenOptions::new();
        ///     options.mode(0o644); // Give read/write for owner and read for others.
        ///     let file = options.open("foo.txt").await?;
        ///
        ///     Ok(())
        /// }
        /// ```
        pub fn mode(&mut self, mode: u32) -> &mut OpenOptions {
            self.as_inner_mut().mode(mode);
            self
        }

        /// Pass custom flags to the `flags` argument of `open`.
        ///
        /// The bits that define the access mode are masked out with `O_ACCMODE`, to
        /// ensure they do not interfere with the access mode set by Rusts options.
        ///
        /// Custom flags can only set flags, not remove flags set by Rusts options.
        /// This options overwrites any previously set custom flags.
        ///
        /// # Examples
        ///
        /// ```no_run
        /// use libc;
        /// use tokio::fs::OpenOptions;
        /// use std::io;
        ///
        /// #[tokio::main]
        /// async fn main() -> io::Result<()> {
        ///     let mut options = OpenOptions::new();
        ///     options.write(true);
        ///     if cfg!(unix) {
        ///         options.custom_flags(libc::O_NOFOLLOW);
        ///     }
        ///     let file = options.open("foo.txt").await?;
        ///
        ///     Ok(())
        /// }
        /// ```
        pub fn custom_flags(&mut self, flags: i32) -> &mut OpenOptions {
            self.as_inner_mut().custom_flags(flags);
            self
        }
    }
}

feature! {
    #![windows]

    use std::os::windows::fs::OpenOptionsExt;

    impl OpenOptions {
        /// Overrides the `dwDesiredAccess` argument to the call to [`CreateFile`]
        /// with the specified value.
        ///
        /// This will override the `read`, `write`, and `append` flags on the
        /// `OpenOptions` structure. This method provides fine-grained control over
        /// the permissions to read, write and append data, attributes (like hidden
        /// and system), and extended attributes.
        ///
        /// # Examples
        ///
        /// ```no_run
        /// use tokio::fs::OpenOptions;
        ///
        /// # #[tokio::main]
        /// # async fn main() -> std::io::Result<()> {
        /// // Open without read and write permission, for example if you only need
        /// // to call `stat` on the file
        /// let file = OpenOptions::new().access_mode(0).open("foo.txt").await?;
        /// # Ok(())
        /// # }
        /// ```
        ///
        /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
        pub fn access_mode(&mut self, access: u32) -> &mut OpenOptions {
            self.as_inner_mut().access_mode(access);
            self
        }

        /// Overrides the `dwShareMode` argument to the call to [`CreateFile`] with
        /// the specified value.
        ///
        /// By default `share_mode` is set to
        /// `FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE`. This allows
        /// other processes to read, write, and delete/rename the same file
        /// while it is open. Removing any of the flags will prevent other
        /// processes from performing the corresponding operation until the file
        /// handle is closed.
        ///
        /// # Examples
        ///
        /// ```no_run
        /// use tokio::fs::OpenOptions;
        ///
        /// # #[tokio::main]
        /// # async fn main() -> std::io::Result<()> {
        /// // Do not allow others to read or modify this file while we have it open
        /// // for writing.
        /// let file = OpenOptions::new()
        ///     .write(true)
        ///     .share_mode(0)
        ///     .open("foo.txt").await?;
        /// # Ok(())
        /// # }
        /// ```
        ///
        /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
        pub fn share_mode(&mut self, share: u32) -> &mut OpenOptions {
            self.as_inner_mut().share_mode(share);
            self
        }

        /// Sets extra flags for the `dwFileFlags` argument to the call to
        /// [`CreateFile2`] to the specified value (or combines it with
        /// `attributes` and `security_qos_flags` to set the `dwFlagsAndAttributes`
        /// for [`CreateFile`]).
        ///
        /// Custom flags can only set flags, not remove flags set by Rust's options.
        /// This option overwrites any previously set custom flags.
        ///
        /// # Examples
        ///
        /// ```no_run
        /// use winapi::um::winbase::FILE_FLAG_DELETE_ON_CLOSE;
        /// use tokio::fs::OpenOptions;
        ///
        /// # #[tokio::main]
        /// # async fn main() -> std::io::Result<()> {
        /// let file = OpenOptions::new()
        ///     .create(true)
        ///     .write(true)
        ///     .custom_flags(FILE_FLAG_DELETE_ON_CLOSE)
        ///     .open("foo.txt").await?;
        /// # Ok(())
        /// # }
        /// ```
        ///
        /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
        /// [`CreateFile2`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfile2
        pub fn custom_flags(&mut self, flags: u32) -> &mut OpenOptions {
            self.as_inner_mut().custom_flags(flags);
            self
        }

        /// Sets the `dwFileAttributes` argument to the call to [`CreateFile2`] to
        /// the specified value (or combines it with `custom_flags` and
        /// `security_qos_flags` to set the `dwFlagsAndAttributes` for
        /// [`CreateFile`]).
        ///
        /// If a _new_ file is created because it does not yet exist and
        /// `.create(true)` or `.create_new(true)` are specified, the new file is
        /// given the attributes declared with `.attributes()`.
        ///
        /// If an _existing_ file is opened with `.create(true).truncate(true)`, its
        /// existing attributes are preserved and combined with the ones declared
        /// with `.attributes()`.
        ///
        /// In all other cases the attributes get ignored.
        ///
        /// # Examples
        ///
        /// ```no_run
        /// use winapi::um::winnt::FILE_ATTRIBUTE_HIDDEN;
        /// use tokio::fs::OpenOptions;
        ///
        /// # #[tokio::main]
        /// # async fn main() -> std::io::Result<()> {
        /// let file = OpenOptions::new()
        ///     .write(true)
        ///     .create(true)
        ///     .attributes(FILE_ATTRIBUTE_HIDDEN)
        ///     .open("foo.txt").await?;
        /// # Ok(())
        /// # }
        /// ```
        ///
        /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
        /// [`CreateFile2`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfile2
        pub fn attributes(&mut self, attributes: u32) -> &mut OpenOptions {
            self.as_inner_mut().attributes(attributes);
            self
        }

        /// Sets the `dwSecurityQosFlags` argument to the call to [`CreateFile2`] to
        /// the specified value (or combines it with `custom_flags` and `attributes`
        /// to set the `dwFlagsAndAttributes` for [`CreateFile`]).
        ///
        /// By default `security_qos_flags` is not set. It should be specified when
        /// opening a named pipe, to control to which degree a server process can
        /// act on behalf of a client process (security impersonation level).
        ///
        /// When `security_qos_flags` is not set, a malicious program can gain the
        /// elevated privileges of a privileged Rust process when it allows opening
        /// user-specified paths, by tricking it into opening a named pipe. So
        /// arguably `security_qos_flags` should also be set when opening arbitrary
        /// paths. However the bits can then conflict with other flags, specifically
        /// `FILE_FLAG_OPEN_NO_RECALL`.
        ///
        /// For information about possible values, see [Impersonation Levels] on the
        /// Windows Dev Center site. The `SECURITY_SQOS_PRESENT` flag is set
        /// automatically when using this method.
        ///
        /// # Examples
        ///
        /// ```no_run
        /// use winapi::um::winbase::SECURITY_IDENTIFICATION;
        /// use tokio::fs::OpenOptions;
        ///
        /// # #[tokio::main]
        /// # async fn main() -> std::io::Result<()> {
        /// let file = OpenOptions::new()
        ///     .write(true)
        ///     .create(true)
        ///
        ///     // Sets the flag value to `SecurityIdentification`.
        ///     .security_qos_flags(SECURITY_IDENTIFICATION)
        ///
        ///     .open(r"\\.\pipe\MyPipe").await?;
        /// # Ok(())
        /// # }
        /// ```
        ///
        /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
        /// [`CreateFile2`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfile2
        /// [Impersonation Levels]:
        ///     https://docs.microsoft.com/en-us/windows/win32/api/winnt/ne-winnt-security_impersonation_level
        pub fn security_qos_flags(&mut self, flags: u32) -> &mut OpenOptions {
            self.as_inner_mut().security_qos_flags(flags);
            self
        }
    }
}

impl From<std::fs::OpenOptions> for OpenOptions {
    fn from(options: std::fs::OpenOptions) -> OpenOptions {
        OpenOptions(options)
    }
}

impl Default for OpenOptions {
    fn default() -> Self {
        Self::new()
    }
}