error.rs - source
Description: Source of the Rust file `library/std/src/io/error.rs`.
Keywords: rust, rustlang, rust-lang

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    #[cfg(test)]
    mod tests;

    use crate::convert::From;
    use crate::error;
    use crate::fmt;
    use crate::result;
    use crate::sys;

    /// A specialized [`Result`] type for I/O operations.
    ///
    /// This type is broadly used across [`std::io`] for any operation which may
    /// produce an error.
    ///
    /// This typedef is generally used to avoid writing out [`io::Error`] directly and
    /// is otherwise a direct mapping to [`Result`].
    ///
    /// While usual Rust style is to import types directly, aliases of [`Result`]
    /// often are not, to make it easier to distinguish between them. [`Result`] is
    /// generally assumed to be [`std::result::Result`][`Result`], and so users of this alias
    /// will generally use `io::Result` instead of shadowing the [prelude]'s import
    /// of [`std::result::Result`][`Result`].
    ///
    /// [`std::io`]: crate::io
    /// [`io::Error`]: Error
    /// [`Result`]: crate::result::Result
    /// [prelude]: crate::prelude
    ///
    /// # Examples
    ///
    /// A convenience function that bubbles an `io::Result` to its caller:
    ///
    /// ```
    /// use std::io;
    ///
    /// fn get_string() -> io::Result<String> {
    ///     let mut buffer = String::new();
    ///
    ///     io::stdin().read_line(&mut buffer)?;
    ///
    ///     Ok(buffer)
    /// }
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub type Result<T> = result::Result<T, Error>;

    /// The error type for I/O operations of the [`Read`], [`Write`], [`Seek`], and
    /// associated traits.
    ///
    /// Errors mostly originate from the underlying OS, but custom instances of
    /// `Error` can be created with crafted error messages and a particular value of
    /// [`ErrorKind`].
    ///
    /// [`Read`]: crate::io::Read
    /// [`Write`]: crate::io::Write
    /// [`Seek`]: crate::io::Seek
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct Error {
        repr: Repr,
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl fmt::Debug for Error {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            fmt::Debug::fmt(&self.repr, f)
        }
    }

    enum Repr {
        Os(i32),
        Simple(ErrorKind),
        Custom(Box<Custom>),
    }

    #[derive(Debug)]
    struct Custom {
        kind: ErrorKind,
        error: Box<dyn error::Error + Send + Sync>,
    }

    /// A list specifying general categories of I/O error.
    ///
    /// This list is intended to grow over time and it is not recommended to
    /// exhaustively match against it.
    ///
    /// It is used with the [`io::Error`] type.
    ///
    /// [`io::Error`]: Error
    #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
    #[stable(feature = "rust1", since = "1.0.0")]
    #[allow(deprecated)]
    #[non_exhaustive]
    pub enum ErrorKind {
        /// An entity was not found, often a file.
        #[stable(feature = "rust1", since = "1.0.0")]
        NotFound,
        /// The operation lacked the necessary privileges to complete.
        #[stable(feature = "rust1", since = "1.0.0")]
        PermissionDenied,
        /// The connection was refused by the remote server.
        #[stable(feature = "rust1", since = "1.0.0")]
        ConnectionRefused,
        /// The connection was reset by the remote server.
        #[stable(feature = "rust1", since = "1.0.0")]
        ConnectionReset,
        /// The connection was aborted (terminated) by the remote server.
        #[stable(feature = "rust1", since = "1.0.0")]
        ConnectionAborted,
        /// The network operation failed because it was not connected yet.
        #[stable(feature = "rust1", since = "1.0.0")]
        NotConnected,
        /// A socket address could not be bound because the address is already in
        /// use elsewhere.
        #[stable(feature = "rust1", since = "1.0.0")]
        AddrInUse,
        /// A nonexistent interface was requested or the requested address was not
        /// local.
        #[stable(feature = "rust1", since = "1.0.0")]
        AddrNotAvailable,
        /// The operation failed because a pipe was closed.
        #[stable(feature = "rust1", since = "1.0.0")]
        BrokenPipe,
        /// An entity already exists, often a file.
        #[stable(feature = "rust1", since = "1.0.0")]
        AlreadyExists,
        /// The operation needs to block to complete, but the blocking operation was
        /// requested to not occur.
        #[stable(feature = "rust1", since = "1.0.0")]
        WouldBlock,
        /// A parameter was incorrect.
        #[stable(feature = "rust1", since = "1.0.0")]
        InvalidInput,
        /// Data not valid for the operation were encountered.
        ///
        /// Unlike [`InvalidInput`], this typically means that the operation
        /// parameters were valid, however the error was caused by malformed
        /// input data.
        ///
        /// For example, a function that reads a file into a string will error with
        /// `InvalidData` if the file's contents are not valid UTF-8.
        ///
        /// [`InvalidInput`]: ErrorKind::InvalidInput
        #[stable(feature = "io_invalid_data", since = "1.2.0")]
        InvalidData,
        /// The I/O operation's timeout expired, causing it to be canceled.
        #[stable(feature = "rust1", since = "1.0.0")]
        TimedOut,
        /// An error returned when an operation could not be completed because a
        /// call to [`write`] returned [`Ok(0)`].
        ///
        /// This typically means that an operation could only succeed if it wrote a
        /// particular number of bytes but only a smaller number of bytes could be
        /// written.
        ///
        /// [`write`]: crate::io::Write::write
        /// [`Ok(0)`]: Ok
        #[stable(feature = "rust1", since = "1.0.0")]
        WriteZero,
        /// This operation was interrupted.
        ///
        /// Interrupted operations can typically be retried.
        #[stable(feature = "rust1", since = "1.0.0")]
        Interrupted,
        /// Any I/O error not part of this list.
        ///
        /// Errors that are `Other` now may move to a different or a new
        /// [`ErrorKind`] variant in the future. It is not recommended to match
        /// an error against `Other` and to expect any additional characteristics,
        /// e.g., a specific [`Error::raw_os_error`] return value.
        #[stable(feature = "rust1", since = "1.0.0")]
        Other,

        /// An error returned when an operation could not be completed because an
        /// "end of file" was reached prematurely.
        ///
        /// This typically means that an operation could only succeed if it read a
        /// particular number of bytes but only a smaller number of bytes could be
        /// read.
        #[stable(feature = "read_exact", since = "1.6.0")]
        UnexpectedEof,
    }

    impl ErrorKind {
        pub(crate) fn as_str(&self) -> &'static str {
            match *self {
                ErrorKind::NotFound => "entity not found",
                ErrorKind::PermissionDenied => "permission denied",
                ErrorKind::ConnectionRefused => "connection refused",
                ErrorKind::ConnectionReset => "connection reset",
                ErrorKind::ConnectionAborted => "connection aborted",
                ErrorKind::NotConnected => "not connected",
                ErrorKind::AddrInUse => "address in use",
                ErrorKind::AddrNotAvailable => "address not available",
                ErrorKind::BrokenPipe => "broken pipe",
                ErrorKind::AlreadyExists => "entity already exists",
                ErrorKind::WouldBlock => "operation would block",
                ErrorKind::InvalidInput => "invalid input parameter",
                ErrorKind::InvalidData => "invalid data",
                ErrorKind::TimedOut => "timed out",
                ErrorKind::WriteZero => "write zero",
                ErrorKind::Interrupted => "operation interrupted",
                ErrorKind::Other => "other os error",
                ErrorKind::UnexpectedEof => "unexpected end of file",
            }
        }
    }

    /// Intended for use for errors not exposed to the user, where allocating onto
    /// the heap (for normal construction via Error::new) is too costly.
    #[stable(feature = "io_error_from_errorkind", since = "1.14.0")]
    impl From<ErrorKind> for Error {
        /// Converts an [`ErrorKind`] into an [`Error`].
        ///
        /// This conversion allocates a new error with a simple representation of error kind.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::io::{Error, ErrorKind};
        ///
        /// let not_found = ErrorKind::NotFound;
        /// let error = Error::from(not_found);
        /// assert_eq!("entity not found", format!("{}", error));
        /// ```
        #[inline]
        fn from(kind: ErrorKind) -> Error {
            Error { repr: Repr::Simple(kind) }
        }
    }

    impl Error {
        /// Creates a new I/O error from a known kind of error as well as an
        /// arbitrary error payload.
        ///
        /// This function is used to generically create I/O errors which do not
        /// originate from the OS itself. The `error` argument is an arbitrary
        /// payload which will be contained in this [`Error`].
        ///
        /// # Examples
        ///
        /// ```
        /// use std::io::{Error, ErrorKind};
        ///
        /// // errors can be created from strings
        /// let custom_error = Error::new(ErrorKind::Other, "oh no!");
        ///
        /// // errors can also be created from other errors
        /// let custom_error2 = Error::new(ErrorKind::Interrupted, custom_error);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn new<E>(kind: ErrorKind, error: E) -> Error
        where
            E: Into<Box<dyn error::Error + Send + Sync>>,
        {
            Self::_new(kind, error.into())
        }

        fn _new(kind: ErrorKind, error: Box<dyn error::Error + Send + Sync>) -> Error {
            Error { repr: Repr::Custom(Box::new(Custom { kind, error })) }
        }

        /// Returns an error representing the last OS error which occurred.
        ///
        /// This function reads the value of `errno` for the target platform (e.g.
        /// `GetLastError` on Windows) and will return a corresponding instance of
        /// [`Error`] for the error code.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::io::Error;
        ///
        /// println!("last OS error: {:?}", Error::last_os_error());
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn last_os_error() -> Error {
            Error::from_raw_os_error(sys::os::errno() as i32)
        }

        /// Creates a new instance of an [`Error`] from a particular OS error code.
        ///
        /// # Examples
        ///
        /// On Linux:
        ///
        /// ```
        /// # if cfg!(target_os = "linux") {
        /// use std::io;
        ///
        /// let error = io::Error::from_raw_os_error(22);
        /// assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
        /// # }
        /// ```
        ///
        /// On Windows:
        ///
        /// ```
        /// # if cfg!(windows) {
        /// use std::io;
        ///
        /// let error = io::Error::from_raw_os_error(10022);
        /// assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
        /// # }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn from_raw_os_error(code: i32) -> Error {
            Error { repr: Repr::Os(code) }
        }

        /// Returns the OS error that this error represents (if any).
        ///
        /// If this [`Error`] was constructed via [`last_os_error`] or
        /// [`from_raw_os_error`], then this function will return [`Some`], otherwise
        /// it will return [`None`].
        ///
        /// [`last_os_error`]: Error::last_os_error
        /// [`from_raw_os_error`]: Error::from_raw_os_error
        ///
        /// # Examples
        ///
        /// ```
        /// use std::io::{Error, ErrorKind};
        ///
        /// fn print_os_error(err: &Error) {
        ///     if let Some(raw_os_err) = err.raw_os_error() {
        ///         println!("raw OS error: {:?}", raw_os_err);
        ///     } else {
        ///         println!("Not an OS error");
        ///     }
        /// }
        ///
        /// fn main() {
        ///     // Will print "raw OS error: ...".
        ///     print_os_error(&Error::last_os_error());
        ///     // Will print "Not an OS error".
        ///     print_os_error(&Error::new(ErrorKind::Other, "oh no!"));
        /// }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn raw_os_error(&self) -> Option<i32> {
            match self.repr {
                Repr::Os(i) => Some(i),
                Repr::Custom(..) => None,
                Repr::Simple(..) => None,
            }
        }

        /// Returns a reference to the inner error wrapped by this error (if any).
        ///
        /// If this [`Error`] was constructed via [`new`] then this function will
        /// return [`Some`], otherwise it will return [`None`].
        ///
        /// [`new`]: Error::new
        ///
        /// # Examples
        ///
        /// ```
        /// use std::io::{Error, ErrorKind};
        ///
        /// fn print_error(err: &Error) {
        ///     if let Some(inner_err) = err.get_ref() {
        ///         println!("Inner error: {:?}", inner_err);
        ///     } else {
        ///         println!("No inner error");
        ///     }
        /// }
        ///
        /// fn main() {
        ///     // Will print "No inner error".
        ///     print_error(&Error::last_os_error());
        ///     // Will print "Inner error: ...".
        ///     print_error(&Error::new(ErrorKind::Other, "oh no!"));
        /// }
        /// ```
        #[stable(feature = "io_error_inner", since = "1.3.0")]
        pub fn get_ref(&self) -> Option<&(dyn error::Error + Send + Sync + 'static)> {
            match self.repr {
                Repr::Os(..) => None,
                Repr::Simple(..) => None,
                Repr::Custom(ref c) => Some(&*c.error),
            }
        }

        /// Returns a mutable reference to the inner error wrapped by this error
        /// (if any).
        ///
        /// If this [`Error`] was constructed via [`new`] then this function will
        /// return [`Some`], otherwise it will return [`None`].
        ///
        /// [`new`]: Error::new
        ///
        /// # Examples
        ///
        /// ```
        /// use std::io::{Error, ErrorKind};
        /// use std::{error, fmt};
        /// use std::fmt::Display;
        ///
        /// #[derive(Debug)]
        /// struct MyError {
        ///     v: String,
        /// }
        ///
        /// impl MyError {
        ///     fn new() -> MyError {
        ///         MyError {
        ///             v: "oh no!".to_string()
        ///         }
        ///     }
        ///
        ///     fn change_message(&mut self, new_message: &str) {
        ///         self.v = new_message.to_string();
        ///     }
        /// }
        ///
        /// impl error::Error for MyError {}
        ///
        /// impl Display for MyError {
        ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        ///         write!(f, "MyError: {}", &self.v)
        ///     }
        /// }
        ///
        /// fn change_error(mut err: Error) -> Error {
        ///     if let Some(inner_err) = err.get_mut() {
        ///         inner_err.downcast_mut::<MyError>().unwrap().change_message("I've been changed!");
        ///     }
        ///     err
        /// }
        ///
        /// fn print_error(err: &Error) {
        ///     if let Some(inner_err) = err.get_ref() {
        ///         println!("Inner error: {}", inner_err);
        ///     } else {
        ///         println!("No inner error");
        ///     }
        /// }
        ///
        /// fn main() {
        ///     // Will print "No inner error".
        ///     print_error(&change_error(Error::last_os_error()));
        ///     // Will print "Inner error: ...".
        ///     print_error(&change_error(Error::new(ErrorKind::Other, MyError::new())));
        /// }
        /// ```
        #[stable(feature = "io_error_inner", since = "1.3.0")]
        pub fn get_mut(&mut self) -> Option<&mut (dyn error::Error + Send + Sync + 'static)> {
            match self.repr {
                Repr::Os(..) => None,
                Repr::Simple(..) => None,
                Repr::Custom(ref mut c) => Some(&mut *c.error),
            }
        }

        /// Consumes the `Error`, returning its inner error (if any).
        ///
        /// If this [`Error`] was constructed via [`new`] then this function will
        /// return [`Some`], otherwise it will return [`None`].
        ///
        /// [`new`]: Error::new
        ///
        /// # Examples
        ///
        /// ```
        /// use std::io::{Error, ErrorKind};
        ///
        /// fn print_error(err: Error) {
        ///     if let Some(inner_err) = err.into_inner() {
        ///         println!("Inner error: {}", inner_err);
        ///     } else {
        ///         println!("No inner error");
        ///     }
        /// }
        ///
        /// fn main() {
        ///     // Will print "No inner error".
        ///     print_error(Error::last_os_error());
        ///     // Will print "Inner error: ...".
        ///     print_error(Error::new(ErrorKind::Other, "oh no!"));
        /// }
        /// ```
        #[stable(feature = "io_error_inner", since = "1.3.0")]
        pub fn into_inner(self) -> Option<Box<dyn error::Error + Send + Sync>> {
            match self.repr {
                Repr::Os(..) => None,
                Repr::Simple(..) => None,
                Repr::Custom(c) => Some(c.error),
            }
        }

        /// Returns the corresponding [`ErrorKind`] for this error.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::io::{Error, ErrorKind};
        ///
        /// fn print_error(err: Error) {
        ///     println!("{:?}", err.kind());
        /// }
        ///
        /// fn main() {
        ///     // Will print "Other".
        ///     print_error(Error::last_os_error());
        ///     // Will print "AddrInUse".
        ///     print_error(Error::new(ErrorKind::AddrInUse, "oh no!"));
        /// }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn kind(&self) -> ErrorKind {
            match self.repr {
                Repr::Os(code) => sys::decode_error_kind(code),
                Repr::Custom(ref c) => c.kind,
                Repr::Simple(kind) => kind,
            }
        }
    }

    impl fmt::Debug for Repr {
        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
            match *self {
                Repr::Os(code) => fmt
                    .debug_struct("Os")
                    .field("code", &code)
                    .field("kind", &sys::decode_error_kind(code))
                    .field("message", &sys::os::error_string(code))
                    .finish(),
                Repr::Custom(ref c) => fmt::Debug::fmt(&c, fmt),
                Repr::Simple(kind) => fmt.debug_tuple("Kind").field(&kind).finish(),
            }
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl fmt::Display for Error {
        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
            match self.repr {
                Repr::Os(code) => {
                    let detail = sys::os::error_string(code);
                    write!(fmt, "{} (os error {})", detail, code)
                }
                Repr::Custom(ref c) => c.error.fmt(fmt),
                Repr::Simple(kind) => write!(fmt, "{}", kind.as_str()),
            }
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl error::Error for Error {
        #[allow(deprecated, deprecated_in_future)]
        fn description(&self) -> &str {
            match self.repr {
                Repr::Os(..) | Repr::Simple(..) => self.kind().as_str(),
                Repr::Custom(ref c) => c.error.description(),
            }
        }

        #[allow(deprecated)]
        fn cause(&self) -> Option<&dyn error::Error> {
            match self.repr {
                Repr::Os(..) => None,
                Repr::Simple(..) => None,
                Repr::Custom(ref c) => c.error.cause(),
            }
        }

        fn source(&self) -> Option<&(dyn error::Error + 'static)> {
            match self.repr {
                Repr::Os(..) => None,
                Repr::Simple(..) => None,
                Repr::Custom(ref c) => c.error.source(),
            }
        }
    }

    fn _assert_error_is_sync_send() {
        fn _is_sync_send<T: Sync + Send>() {}
        _is_sync_send::<Error>();
    }