4 #[cfg(target_pointer_width = "64")]
6 #[cfg(target_pointer_width = "64")]
7 use repr_bitpacked::Repr;
9 #[cfg(not(target_pointer_width = "64"))]
11 #[cfg(not(target_pointer_width = "64"))]
12 use repr_unpacked::Repr;
14 use crate::convert::From;
20 /// A specialized [`Result`] type for I/O operations.
22 /// This type is broadly used across [`std::io`] for any operation which may
25 /// This typedef is generally used to avoid writing out [`io::Error`] directly and
26 /// is otherwise a direct mapping to [`Result`].
28 /// While usual Rust style is to import types directly, aliases of [`Result`]
29 /// often are not, to make it easier to distinguish between them. [`Result`] is
30 /// generally assumed to be [`std::result::Result`][`Result`], and so users of this alias
31 /// will generally use `io::Result` instead of shadowing the [prelude]'s import
32 /// of [`std::result::Result`][`Result`].
34 /// [`std::io`]: crate::io
35 /// [`io::Error`]: Error
36 /// [`Result`]: crate::result::Result
37 /// [prelude]: crate::prelude
41 /// A convenience function that bubbles an `io::Result` to its caller:
46 /// fn get_string() -> io::Result<String> {
47 /// let mut buffer = String::new();
49 /// io::stdin().read_line(&mut buffer)?;
54 #[stable(feature = "rust1", since = "1.0.0")]
55 pub type Result<T> = result::Result<T, Error>;
57 /// The error type for I/O operations of the [`Read`], [`Write`], [`Seek`], and
58 /// associated traits.
60 /// Errors mostly originate from the underlying OS, but custom instances of
61 /// `Error` can be created with crafted error messages and a particular value of
64 /// [`Read`]: crate::io::Read
65 /// [`Write`]: crate::io::Write
66 /// [`Seek`]: crate::io::Seek
67 #[stable(feature = "rust1", since = "1.0.0")]
72 #[stable(feature = "rust1", since = "1.0.0")]
73 impl fmt::Debug for Error {
74 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
75 fmt::Debug::fmt(&self.repr, f)
79 // Only derive debug in tests, to make sure it
80 // doesn't accidentally get printed.
81 #[cfg_attr(test, derive(Debug))]
85 SimpleMessage(&'static SimpleMessage),
89 // `#[repr(align(4))]` is probably redundant, it should have that value or
90 // higher already. We include it just because repr_bitpacked.rs's encoding
91 // requires an alignment >= 4 (note that `#[repr(align)]` will not reduce the
92 // alignment required by the struct, only increase it).
94 // If we add more variants to ErrorData, this can be increased to 8, but it
95 // should probably be behind `#[cfg_attr(target_pointer_width = "64", ...)]` or
96 // whatever cfg we're using to enable the `repr_bitpacked` code, since only the
97 // that version needs the alignment, and 8 is higher than the alignment we'll
98 // have on 32 bit platforms.
100 // (For the sake of being explicit: the alignment requirement here only matters
101 // if `error/repr_bitpacked.rs` is in use — for the unpacked repr it doesn't
105 pub(crate) struct SimpleMessage {
107 message: &'static str,
111 pub(crate) const fn new(kind: ErrorKind, message: &'static str) -> Self {
112 Self { kind, message }
116 /// Create and return an `io::Error` for a given `ErrorKind` and constant
117 /// message. This doesn't allocate.
118 pub(crate) macro const_io_error($kind:expr, $message:expr $(,)?) {
119 $crate::io::error::Error::from_static_message({
120 const MESSAGE_DATA: $crate::io::error::SimpleMessage =
121 $crate::io::error::SimpleMessage::new($kind, $message);
126 // As with `SimpleMessage`: `#[repr(align(4))]` here is just because
127 // repr_bitpacked's encoding requires it. In practice it almost certainly be
128 // already be this high or higher.
133 error: Box<dyn error::Error + Send + Sync>,
136 /// A list specifying general categories of I/O error.
138 /// This list is intended to grow over time and it is not recommended to
139 /// exhaustively match against it.
141 /// It is used with the [`io::Error`] type.
143 /// [`io::Error`]: Error
145 /// # Handling errors and matching on `ErrorKind`
147 /// In application code, use `match` for the `ErrorKind` values you are
148 /// expecting; use `_` to match "all other errors".
150 /// In comprehensive and thorough tests that want to verify that a test doesn't
151 /// return any known incorrect error kind, you may want to cut-and-paste the
152 /// current full list of errors from here into your test code, and then match
153 /// `_` as the correct case. This seems counterintuitive, but it will make your
154 /// tests more robust. In particular, if you want to verify that your code does
155 /// produce an unrecognized error kind, the robust solution is to check for all
156 /// the recognized error kinds and fail in those cases.
157 #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
158 #[stable(feature = "rust1", since = "1.0.0")]
162 /// An entity was not found, often a file.
163 #[stable(feature = "rust1", since = "1.0.0")]
165 /// The operation lacked the necessary privileges to complete.
166 #[stable(feature = "rust1", since = "1.0.0")]
168 /// The connection was refused by the remote server.
169 #[stable(feature = "rust1", since = "1.0.0")]
171 /// The connection was reset by the remote server.
172 #[stable(feature = "rust1", since = "1.0.0")]
174 /// The remote host is not reachable.
175 #[unstable(feature = "io_error_more", issue = "86442")]
177 /// The network containing the remote host is not reachable.
178 #[unstable(feature = "io_error_more", issue = "86442")]
180 /// The connection was aborted (terminated) by the remote server.
181 #[stable(feature = "rust1", since = "1.0.0")]
183 /// The network operation failed because it was not connected yet.
184 #[stable(feature = "rust1", since = "1.0.0")]
186 /// A socket address could not be bound because the address is already in
188 #[stable(feature = "rust1", since = "1.0.0")]
190 /// A nonexistent interface was requested or the requested address was not
192 #[stable(feature = "rust1", since = "1.0.0")]
194 /// The system's networking is down.
195 #[unstable(feature = "io_error_more", issue = "86442")]
197 /// The operation failed because a pipe was closed.
198 #[stable(feature = "rust1", since = "1.0.0")]
200 /// An entity already exists, often a file.
201 #[stable(feature = "rust1", since = "1.0.0")]
203 /// The operation needs to block to complete, but the blocking operation was
204 /// requested to not occur.
205 #[stable(feature = "rust1", since = "1.0.0")]
207 /// A filesystem object is, unexpectedly, not a directory.
209 /// For example, a filesystem path was specified where one of the intermediate directory
210 /// components was, in fact, a plain file.
211 #[unstable(feature = "io_error_more", issue = "86442")]
213 /// The filesystem object is, unexpectedly, a directory.
215 /// A directory was specified when a non-directory was expected.
216 #[unstable(feature = "io_error_more", issue = "86442")]
218 /// A non-empty directory was specified where an empty directory was expected.
219 #[unstable(feature = "io_error_more", issue = "86442")]
221 /// The filesystem or storage medium is read-only, but a write operation was attempted.
222 #[unstable(feature = "io_error_more", issue = "86442")]
224 /// Loop in the filesystem or IO subsystem; often, too many levels of symbolic links.
226 /// There was a loop (or excessively long chain) resolving a filesystem object
227 /// or file IO object.
229 /// On Unix this is usually the result of a symbolic link loop; or, of exceeding the
230 /// system-specific limit on the depth of symlink traversal.
231 #[unstable(feature = "io_error_more", issue = "86442")]
233 /// Stale network file handle.
235 /// With some network filesystems, notably NFS, an open file (or directory) can be invalidated
236 /// by problems with the network or server.
237 #[unstable(feature = "io_error_more", issue = "86442")]
238 StaleNetworkFileHandle,
239 /// A parameter was incorrect.
240 #[stable(feature = "rust1", since = "1.0.0")]
242 /// Data not valid for the operation were encountered.
244 /// Unlike [`InvalidInput`], this typically means that the operation
245 /// parameters were valid, however the error was caused by malformed
248 /// For example, a function that reads a file into a string will error with
249 /// `InvalidData` if the file's contents are not valid UTF-8.
251 /// [`InvalidInput`]: ErrorKind::InvalidInput
252 #[stable(feature = "io_invalid_data", since = "1.2.0")]
254 /// The I/O operation's timeout expired, causing it to be canceled.
255 #[stable(feature = "rust1", since = "1.0.0")]
257 /// An error returned when an operation could not be completed because a
258 /// call to [`write`] returned [`Ok(0)`].
260 /// This typically means that an operation could only succeed if it wrote a
261 /// particular number of bytes but only a smaller number of bytes could be
264 /// [`write`]: crate::io::Write::write
266 #[stable(feature = "rust1", since = "1.0.0")]
268 /// The underlying storage (typically, a filesystem) is full.
270 /// This does not include out of quota errors.
271 #[unstable(feature = "io_error_more", issue = "86442")]
273 /// Seek on unseekable file.
275 /// Seeking was attempted on an open file handle which is not suitable for seeking - for
276 /// example, on Unix, a named pipe opened with `File::open`.
277 #[unstable(feature = "io_error_more", issue = "86442")]
279 /// Filesystem quota was exceeded.
280 #[unstable(feature = "io_error_more", issue = "86442")]
281 FilesystemQuotaExceeded,
282 /// File larger than allowed or supported.
284 /// This might arise from a hard limit of the underlying filesystem or file access API, or from
285 /// an administratively imposed resource limitation. Simple disk full, and out of quota, have
286 /// their own errors.
287 #[unstable(feature = "io_error_more", issue = "86442")]
289 /// Resource is busy.
290 #[unstable(feature = "io_error_more", issue = "86442")]
292 /// Executable file is busy.
294 /// An attempt was made to write to a file which is also in use as a running program. (Not all
295 /// operating systems detect this situation.)
296 #[unstable(feature = "io_error_more", issue = "86442")]
298 /// Deadlock (avoided).
300 /// A file locking operation would result in deadlock. This situation is typically detected, if
301 /// at all, on a best-effort basis.
302 #[unstable(feature = "io_error_more", issue = "86442")]
304 /// Cross-device or cross-filesystem (hard) link or rename.
305 #[unstable(feature = "io_error_more", issue = "86442")]
307 /// Too many (hard) links to the same filesystem object.
309 /// The filesystem does not support making so many hardlinks to the same file.
310 #[unstable(feature = "io_error_more", issue = "86442")]
312 /// A filename was invalid.
314 /// This error can also cause if it exceeded the filename length limit.
315 #[unstable(feature = "io_error_more", issue = "86442")]
317 /// Program argument list too long.
319 /// When trying to run an external program, a system or process limit on the size of the
320 /// arguments would have been exceeded.
321 #[unstable(feature = "io_error_more", issue = "86442")]
323 /// This operation was interrupted.
325 /// Interrupted operations can typically be retried.
326 #[stable(feature = "rust1", since = "1.0.0")]
329 /// This operation is unsupported on this platform.
331 /// This means that the operation can never succeed.
332 #[stable(feature = "unsupported_error", since = "1.53.0")]
335 // ErrorKinds which are primarily categorisations for OS error
336 // codes should be added above.
338 /// An error returned when an operation could not be completed because an
339 /// "end of file" was reached prematurely.
341 /// This typically means that an operation could only succeed if it read a
342 /// particular number of bytes but only a smaller number of bytes could be
344 #[stable(feature = "read_exact", since = "1.6.0")]
347 /// An operation could not be completed, because it failed
348 /// to allocate enough memory.
349 #[stable(feature = "out_of_memory_error", since = "1.54.0")]
352 // "Unusual" error kinds which do not correspond simply to (sets
353 // of) OS error codes, should be added just above this comment.
354 // `Other` and `Uncategorised` should remain at the end:
356 /// A custom error that does not fall under any other I/O error kind.
358 /// This can be used to construct your own [`Error`]s that do not match any
361 /// This [`ErrorKind`] is not used by the standard library.
363 /// Errors from the standard library that do not fall under any of the I/O
364 /// error kinds cannot be `match`ed on, and will only match a wildcard (`_`) pattern.
365 /// New [`ErrorKind`]s might be added in the future for some of those.
366 #[stable(feature = "rust1", since = "1.0.0")]
369 /// Any I/O error from the standard library that's not part of this list.
371 /// Errors that are `Uncategorized` now may move to a different or a new
372 /// [`ErrorKind`] variant in the future. It is not recommended to match
373 /// an error against `Uncategorized`; use a wildcard match (`_`) instead.
374 #[unstable(feature = "io_error_uncategorized", issue = "none")]
380 pub(crate) fn as_str(&self) -> &'static str {
382 // Strictly alphabetical, please. (Sadly rustfmt cannot do this yet.)
384 AddrInUse => "address in use",
385 AddrNotAvailable => "address not available",
386 AlreadyExists => "entity already exists",
387 ArgumentListTooLong => "argument list too long",
388 BrokenPipe => "broken pipe",
389 ConnectionAborted => "connection aborted",
390 ConnectionRefused => "connection refused",
391 ConnectionReset => "connection reset",
392 CrossesDevices => "cross-device link or rename",
393 Deadlock => "deadlock",
394 DirectoryNotEmpty => "directory not empty",
395 ExecutableFileBusy => "executable file busy",
396 FileTooLarge => "file too large",
397 FilesystemLoop => "filesystem loop or indirection limit (e.g. symlink loop)",
398 FilesystemQuotaExceeded => "filesystem quota exceeded",
399 HostUnreachable => "host unreachable",
400 Interrupted => "operation interrupted",
401 InvalidData => "invalid data",
402 InvalidFilename => "invalid filename",
403 InvalidInput => "invalid input parameter",
404 IsADirectory => "is a directory",
405 NetworkDown => "network down",
406 NetworkUnreachable => "network unreachable",
407 NotADirectory => "not a directory",
408 NotConnected => "not connected",
409 NotFound => "entity not found",
410 NotSeekable => "seek on unseekable file",
411 Other => "other error",
412 OutOfMemory => "out of memory",
413 PermissionDenied => "permission denied",
414 ReadOnlyFilesystem => "read-only filesystem or storage medium",
415 ResourceBusy => "resource busy",
416 StaleNetworkFileHandle => "stale network file handle",
417 StorageFull => "no storage space",
418 TimedOut => "timed out",
419 TooManyLinks => "too many links",
420 Uncategorized => "uncategorized error",
421 UnexpectedEof => "unexpected end of file",
422 Unsupported => "unsupported",
423 WouldBlock => "operation would block",
424 WriteZero => "write zero",
429 #[stable(feature = "io_errorkind_display", since = "1.60.0")]
430 impl fmt::Display for ErrorKind {
431 /// Shows a human-readable description of the `ErrorKind`.
433 /// This is similar to `impl Display for Error`, but doesn't require first converting to Error.
437 /// use std::io::ErrorKind;
438 /// assert_eq!("entity not found", ErrorKind::NotFound.to_string());
440 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
441 fmt.write_str(self.as_str())
445 /// Intended for use for errors not exposed to the user, where allocating onto
446 /// the heap (for normal construction via Error::new) is too costly.
447 #[stable(feature = "io_error_from_errorkind", since = "1.14.0")]
448 impl From<ErrorKind> for Error {
449 /// Converts an [`ErrorKind`] into an [`Error`].
451 /// This conversion creates a new error with a simple representation of error kind.
456 /// use std::io::{Error, ErrorKind};
458 /// let not_found = ErrorKind::NotFound;
459 /// let error = Error::from(not_found);
460 /// assert_eq!("entity not found", format!("{error}"));
463 fn from(kind: ErrorKind) -> Error {
464 Error { repr: Repr::new_simple(kind) }
469 /// Creates a new I/O error from a known kind of error as well as an
470 /// arbitrary error payload.
472 /// This function is used to generically create I/O errors which do not
473 /// originate from the OS itself. The `error` argument is an arbitrary
474 /// payload which will be contained in this [`Error`].
476 /// If no extra payload is required, use the `From` conversion from
482 /// use std::io::{Error, ErrorKind};
484 /// // errors can be created from strings
485 /// let custom_error = Error::new(ErrorKind::Other, "oh no!");
487 /// // errors can also be created from other errors
488 /// let custom_error2 = Error::new(ErrorKind::Interrupted, custom_error);
490 /// // creating an error without payload
491 /// let eof_error = Error::from(ErrorKind::UnexpectedEof);
493 #[stable(feature = "rust1", since = "1.0.0")]
494 pub fn new<E>(kind: ErrorKind, error: E) -> Error
496 E: Into<Box<dyn error::Error + Send + Sync>>,
498 Self::_new(kind, error.into())
501 /// Creates a new I/O error from an arbitrary error payload.
503 /// This function is used to generically create I/O errors which do not
504 /// originate from the OS itself. It is a shortcut for [`Error::new`]
505 /// with [`ErrorKind::Other`].
510 /// #![feature(io_error_other)]
512 /// use std::io::Error;
514 /// // errors can be created from strings
515 /// let custom_error = Error::other("oh no!");
517 /// // errors can also be created from other errors
518 /// let custom_error2 = Error::other(custom_error);
520 #[unstable(feature = "io_error_other", issue = "91946")]
521 pub fn other<E>(error: E) -> Error
523 E: Into<Box<dyn error::Error + Send + Sync>>,
525 Self::_new(ErrorKind::Other, error.into())
528 fn _new(kind: ErrorKind, error: Box<dyn error::Error + Send + Sync>) -> Error {
529 Error { repr: Repr::new_custom(Box::new(Custom { kind, error })) }
532 /// Creates a new I/O error from a known kind of error as well as a constant
535 /// This function does not allocate.
537 /// You should not use this directly, and instead use the `const_io_error!`
538 /// macro: `io::const_io_error!(ErrorKind::Something, "some_message")`.
540 /// This function should maybe change to `from_static_message<const MSG: &'static
541 /// str>(kind: ErrorKind)` in the future, when const generics allow that.
543 pub(crate) const fn from_static_message(msg: &'static SimpleMessage) -> Error {
544 Self { repr: Repr::new_simple_message(msg) }
547 /// Returns an error representing the last OS error which occurred.
549 /// This function reads the value of `errno` for the target platform (e.g.
550 /// `GetLastError` on Windows) and will return a corresponding instance of
551 /// [`Error`] for the error code.
553 /// This should be called immediately after a call to a platform function,
554 /// otherwise the state of the error value is indeterminate. In particular,
555 /// other standard library functions may call platform functions that may
556 /// (or may not) reset the error value even if they succeed.
561 /// use std::io::Error;
563 /// let os_error = Error::last_os_error();
564 /// println!("last OS error: {os_error:?}");
566 #[stable(feature = "rust1", since = "1.0.0")]
569 pub fn last_os_error() -> Error {
570 Error::from_raw_os_error(sys::os::errno() as i32)
573 /// Creates a new instance of an [`Error`] from a particular OS error code.
580 /// # if cfg!(target_os = "linux") {
583 /// let error = io::Error::from_raw_os_error(22);
584 /// assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
591 /// # if cfg!(windows) {
594 /// let error = io::Error::from_raw_os_error(10022);
595 /// assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
598 #[stable(feature = "rust1", since = "1.0.0")]
601 pub fn from_raw_os_error(code: i32) -> Error {
602 Error { repr: Repr::new_os(code) }
605 /// Returns the OS error that this error represents (if any).
607 /// If this [`Error`] was constructed via [`last_os_error`] or
608 /// [`from_raw_os_error`], then this function will return [`Some`], otherwise
609 /// it will return [`None`].
611 /// [`last_os_error`]: Error::last_os_error
612 /// [`from_raw_os_error`]: Error::from_raw_os_error
617 /// use std::io::{Error, ErrorKind};
619 /// fn print_os_error(err: &Error) {
620 /// if let Some(raw_os_err) = err.raw_os_error() {
621 /// println!("raw OS error: {raw_os_err:?}");
623 /// println!("Not an OS error");
628 /// // Will print "raw OS error: ...".
629 /// print_os_error(&Error::last_os_error());
630 /// // Will print "Not an OS error".
631 /// print_os_error(&Error::new(ErrorKind::Other, "oh no!"));
634 #[stable(feature = "rust1", since = "1.0.0")]
637 pub fn raw_os_error(&self) -> Option<i32> {
638 match self.repr.data() {
639 ErrorData::Os(i) => Some(i),
640 ErrorData::Custom(..) => None,
641 ErrorData::Simple(..) => None,
642 ErrorData::SimpleMessage(..) => None,
646 /// Returns a reference to the inner error wrapped by this error (if any).
648 /// If this [`Error`] was constructed via [`new`] then this function will
649 /// return [`Some`], otherwise it will return [`None`].
651 /// [`new`]: Error::new
656 /// use std::io::{Error, ErrorKind};
658 /// fn print_error(err: &Error) {
659 /// if let Some(inner_err) = err.get_ref() {
660 /// println!("Inner error: {inner_err:?}");
662 /// println!("No inner error");
667 /// // Will print "No inner error".
668 /// print_error(&Error::last_os_error());
669 /// // Will print "Inner error: ...".
670 /// print_error(&Error::new(ErrorKind::Other, "oh no!"));
673 #[stable(feature = "io_error_inner", since = "1.3.0")]
676 pub fn get_ref(&self) -> Option<&(dyn error::Error + Send + Sync + 'static)> {
677 match self.repr.data() {
678 ErrorData::Os(..) => None,
679 ErrorData::Simple(..) => None,
680 ErrorData::SimpleMessage(..) => None,
681 ErrorData::Custom(c) => Some(&*c.error),
685 /// Returns a mutable reference to the inner error wrapped by this error
688 /// If this [`Error`] was constructed via [`new`] then this function will
689 /// return [`Some`], otherwise it will return [`None`].
691 /// [`new`]: Error::new
696 /// use std::io::{Error, ErrorKind};
697 /// use std::{error, fmt};
698 /// use std::fmt::Display;
706 /// fn new() -> MyError {
708 /// v: "oh no!".to_string()
712 /// fn change_message(&mut self, new_message: &str) {
713 /// self.v = new_message.to_string();
717 /// impl error::Error for MyError {}
719 /// impl Display for MyError {
720 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
721 /// write!(f, "MyError: {}", &self.v)
725 /// fn change_error(mut err: Error) -> Error {
726 /// if let Some(inner_err) = err.get_mut() {
727 /// inner_err.downcast_mut::<MyError>().unwrap().change_message("I've been changed!");
732 /// fn print_error(err: &Error) {
733 /// if let Some(inner_err) = err.get_ref() {
734 /// println!("Inner error: {inner_err}");
736 /// println!("No inner error");
741 /// // Will print "No inner error".
742 /// print_error(&change_error(Error::last_os_error()));
743 /// // Will print "Inner error: ...".
744 /// print_error(&change_error(Error::new(ErrorKind::Other, MyError::new())));
747 #[stable(feature = "io_error_inner", since = "1.3.0")]
750 pub fn get_mut(&mut self) -> Option<&mut (dyn error::Error + Send + Sync + 'static)> {
751 match self.repr.data_mut() {
752 ErrorData::Os(..) => None,
753 ErrorData::Simple(..) => None,
754 ErrorData::SimpleMessage(..) => None,
755 ErrorData::Custom(c) => Some(&mut *c.error),
759 /// Consumes the `Error`, returning its inner error (if any).
761 /// If this [`Error`] was constructed via [`new`] then this function will
762 /// return [`Some`], otherwise it will return [`None`].
764 /// [`new`]: Error::new
769 /// use std::io::{Error, ErrorKind};
771 /// fn print_error(err: Error) {
772 /// if let Some(inner_err) = err.into_inner() {
773 /// println!("Inner error: {inner_err}");
775 /// println!("No inner error");
780 /// // Will print "No inner error".
781 /// print_error(Error::last_os_error());
782 /// // Will print "Inner error: ...".
783 /// print_error(Error::new(ErrorKind::Other, "oh no!"));
786 #[stable(feature = "io_error_inner", since = "1.3.0")]
787 #[must_use = "`self` will be dropped if the result is not used"]
789 pub fn into_inner(self) -> Option<Box<dyn error::Error + Send + Sync>> {
790 match self.repr.into_data() {
791 ErrorData::Os(..) => None,
792 ErrorData::Simple(..) => None,
793 ErrorData::SimpleMessage(..) => None,
794 ErrorData::Custom(c) => Some(c.error),
798 /// Attempt to downgrade the inner error to `E` if any.
800 /// If this [`Error`] was constructed via [`new`] then this function will
801 /// attempt to perform downgrade on it, otherwise it will return [`Err`].
803 /// If downgrade succeeds, it will return [`Ok`], otherwise it will also
806 /// [`new`]: Error::new
811 /// #![feature(io_error_downcast)]
815 /// use std::error::Error;
820 /// SomeOtherVariant,
823 /// impl fmt::Display for E {
825 /// # fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
829 /// impl Error for E {}
831 /// impl From<io::Error> for E {
832 /// fn from(err: io::Error) -> E {
833 /// err.downcast::<E>()
835 /// .unwrap_or_else(E::Io)
839 #[unstable(feature = "io_error_downcast", issue = "99262")]
840 pub fn downcast<E>(self) -> result::Result<Box<E>, Self>
842 E: error::Error + Send + Sync + 'static,
844 match self.repr.into_data() {
845 ErrorData::Custom(b) if b.error.is::<E>() => {
846 let res = (*b).error.downcast::<E>();
848 // downcast is a really trivial and is marked as inline, so
849 // it's likely be inlined here.
851 // And the compiler should be able to eliminate the branch
852 // that produces `Err` here since b.error.is::<E>()
856 repr_data => Err(Self { repr: Repr::new(repr_data) }),
860 /// Returns the corresponding [`ErrorKind`] for this error.
865 /// use std::io::{Error, ErrorKind};
867 /// fn print_error(err: Error) {
868 /// println!("{:?}", err.kind());
872 /// // Will print "Uncategorized".
873 /// print_error(Error::last_os_error());
874 /// // Will print "AddrInUse".
875 /// print_error(Error::new(ErrorKind::AddrInUse, "oh no!"));
878 #[stable(feature = "rust1", since = "1.0.0")]
881 pub fn kind(&self) -> ErrorKind {
882 match self.repr.data() {
883 ErrorData::Os(code) => sys::decode_error_kind(code),
884 ErrorData::Custom(c) => c.kind,
885 ErrorData::Simple(kind) => kind,
886 ErrorData::SimpleMessage(m) => m.kind,
891 impl fmt::Debug for Repr {
892 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
894 ErrorData::Os(code) => fmt
896 .field("code", &code)
897 .field("kind", &sys::decode_error_kind(code))
898 .field("message", &sys::os::error_string(code))
900 ErrorData::Custom(c) => fmt::Debug::fmt(&c, fmt),
901 ErrorData::Simple(kind) => fmt.debug_tuple("Kind").field(&kind).finish(),
902 ErrorData::SimpleMessage(msg) => fmt
903 .debug_struct("Error")
904 .field("kind", &msg.kind)
905 .field("message", &msg.message)
911 #[stable(feature = "rust1", since = "1.0.0")]
912 impl fmt::Display for Error {
913 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
914 match self.repr.data() {
915 ErrorData::Os(code) => {
916 let detail = sys::os::error_string(code);
917 write!(fmt, "{detail} (os error {code})")
919 ErrorData::Custom(ref c) => c.error.fmt(fmt),
920 ErrorData::Simple(kind) => write!(fmt, "{}", kind.as_str()),
921 ErrorData::SimpleMessage(msg) => msg.message.fmt(fmt),
926 #[stable(feature = "rust1", since = "1.0.0")]
927 impl error::Error for Error {
928 #[allow(deprecated, deprecated_in_future)]
929 fn description(&self) -> &str {
930 match self.repr.data() {
931 ErrorData::Os(..) | ErrorData::Simple(..) => self.kind().as_str(),
932 ErrorData::SimpleMessage(msg) => msg.message,
933 ErrorData::Custom(c) => c.error.description(),
938 fn cause(&self) -> Option<&dyn error::Error> {
939 match self.repr.data() {
940 ErrorData::Os(..) => None,
941 ErrorData::Simple(..) => None,
942 ErrorData::SimpleMessage(..) => None,
943 ErrorData::Custom(c) => c.error.cause(),
947 fn source(&self) -> Option<&(dyn error::Error + 'static)> {
948 match self.repr.data() {
949 ErrorData::Os(..) => None,
950 ErrorData::Simple(..) => None,
951 ErrorData::SimpleMessage(..) => None,
952 ErrorData::Custom(c) => c.error.source(),
957 fn _assert_error_is_sync_send() {
958 fn _is_sync_send<T: Sync + Send>() {}
959 _is_sync_send::<Error>();