4 use crate::convert::From;
10 /// A specialized [`Result`] type for I/O operations.
12 /// This type is broadly used across [`std::io`] for any operation which may
15 /// This typedef is generally used to avoid writing out [`io::Error`] directly and
16 /// is otherwise a direct mapping to [`Result`].
18 /// While usual Rust style is to import types directly, aliases of [`Result`]
19 /// often are not, to make it easier to distinguish between them. [`Result`] is
20 /// generally assumed to be [`std::result::Result`][`Result`], and so users of this alias
21 /// will generally use `io::Result` instead of shadowing the [prelude]'s import
22 /// of [`std::result::Result`][`Result`].
24 /// [`std::io`]: crate::io
25 /// [`io::Error`]: Error
26 /// [`Result`]: crate::result::Result
27 /// [prelude]: crate::prelude
31 /// A convenience function that bubbles an `io::Result` to its caller:
36 /// fn get_string() -> io::Result<String> {
37 /// let mut buffer = String::new();
39 /// io::stdin().read_line(&mut buffer)?;
44 #[stable(feature = "rust1", since = "1.0.0")]
45 pub type Result<T> = result::Result<T, Error>;
47 /// The error type for I/O operations of the [`Read`], [`Write`], [`Seek`], and
48 /// associated traits.
50 /// Errors mostly originate from the underlying OS, but custom instances of
51 /// `Error` can be created with crafted error messages and a particular value of
54 /// [`Read`]: crate::io::Read
55 /// [`Write`]: crate::io::Write
56 /// [`Seek`]: crate::io::Seek
57 #[stable(feature = "rust1", since = "1.0.0")]
62 #[stable(feature = "rust1", since = "1.0.0")]
63 impl fmt::Debug for Error {
64 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
65 fmt::Debug::fmt(&self.repr, f)
72 // &str is a fat pointer, but &&str is a thin pointer.
73 SimpleMessage(ErrorKind, &'static &'static str),
80 error: Box<dyn error::Error + Send + Sync>,
83 /// A list specifying general categories of I/O error.
85 /// This list is intended to grow over time and it is not recommended to
86 /// exhaustively match against it.
88 /// It is used with the [`io::Error`] type.
90 /// [`io::Error`]: Error
91 #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
92 #[stable(feature = "rust1", since = "1.0.0")]
96 /// An entity was not found, often a file.
97 #[stable(feature = "rust1", since = "1.0.0")]
99 /// The operation lacked the necessary privileges to complete.
100 #[stable(feature = "rust1", since = "1.0.0")]
102 /// The connection was refused by the remote server.
103 #[stable(feature = "rust1", since = "1.0.0")]
105 /// The connection was reset by the remote server.
106 #[stable(feature = "rust1", since = "1.0.0")]
108 /// The connection was aborted (terminated) by the remote server.
109 #[stable(feature = "rust1", since = "1.0.0")]
111 /// The network operation failed because it was not connected yet.
112 #[stable(feature = "rust1", since = "1.0.0")]
114 /// A socket address could not be bound because the address is already in
116 #[stable(feature = "rust1", since = "1.0.0")]
118 /// A nonexistent interface was requested or the requested address was not
120 #[stable(feature = "rust1", since = "1.0.0")]
122 /// The operation failed because a pipe was closed.
123 #[stable(feature = "rust1", since = "1.0.0")]
125 /// An entity already exists, often a file.
126 #[stable(feature = "rust1", since = "1.0.0")]
128 /// The operation needs to block to complete, but the blocking operation was
129 /// requested to not occur.
130 #[stable(feature = "rust1", since = "1.0.0")]
132 /// A parameter was incorrect.
133 #[stable(feature = "rust1", since = "1.0.0")]
135 /// Data not valid for the operation were encountered.
137 /// Unlike [`InvalidInput`], this typically means that the operation
138 /// parameters were valid, however the error was caused by malformed
141 /// For example, a function that reads a file into a string will error with
142 /// `InvalidData` if the file's contents are not valid UTF-8.
144 /// [`InvalidInput`]: ErrorKind::InvalidInput
145 #[stable(feature = "io_invalid_data", since = "1.2.0")]
147 /// The I/O operation's timeout expired, causing it to be canceled.
148 #[stable(feature = "rust1", since = "1.0.0")]
150 /// An error returned when an operation could not be completed because a
151 /// call to [`write`] returned [`Ok(0)`].
153 /// This typically means that an operation could only succeed if it wrote a
154 /// particular number of bytes but only a smaller number of bytes could be
157 /// [`write`]: crate::io::Write::write
159 #[stable(feature = "rust1", since = "1.0.0")]
161 /// This operation was interrupted.
163 /// Interrupted operations can typically be retried.
164 #[stable(feature = "rust1", since = "1.0.0")]
167 /// An error returned when an operation could not be completed because an
168 /// "end of file" was reached prematurely.
170 /// This typically means that an operation could only succeed if it read a
171 /// particular number of bytes but only a smaller number of bytes could be
173 #[stable(feature = "read_exact", since = "1.6.0")]
175 /// A custom error that does not fall under any other I/O error kind.
177 /// This can be used to construct your own [`Error`]s that do not match any
180 /// This [`ErrorKind`] is not used by the standard library.
182 /// Errors from the standard library that do not fall under any of the I/O
183 /// error kinds cannot be `match`ed on, and will only match a wildcard (`_`) pattern.
184 /// New [`ErrorKind`]s might be added in the future for some of those.
185 #[stable(feature = "rust1", since = "1.0.0")]
188 /// This operation is unsupported on this platform.
190 /// This means that the operation can never succeed.
191 #[stable(feature = "unsupported_error", since = "1.53.0")]
194 /// An operation could not be completed, because it failed
195 /// to allocate enough memory.
196 #[stable(feature = "out_of_memory_error", since = "1.54.0")]
199 /// Any I/O error from the standard library that's not part of this list.
201 /// Errors that are `Uncategorized` now may move to a different or a new
202 /// [`ErrorKind`] variant in the future. It is not recommended to match
203 /// an error against `Uncategorized`; use a wildcard match (`_`) instead.
204 #[unstable(feature = "io_error_uncategorized", issue = "none")]
210 pub(crate) fn as_str(&self) -> &'static str {
212 ErrorKind::NotFound => "entity not found",
213 ErrorKind::PermissionDenied => "permission denied",
214 ErrorKind::ConnectionRefused => "connection refused",
215 ErrorKind::ConnectionReset => "connection reset",
216 ErrorKind::ConnectionAborted => "connection aborted",
217 ErrorKind::NotConnected => "not connected",
218 ErrorKind::AddrInUse => "address in use",
219 ErrorKind::AddrNotAvailable => "address not available",
220 ErrorKind::BrokenPipe => "broken pipe",
221 ErrorKind::AlreadyExists => "entity already exists",
222 ErrorKind::WouldBlock => "operation would block",
223 ErrorKind::InvalidInput => "invalid input parameter",
224 ErrorKind::InvalidData => "invalid data",
225 ErrorKind::TimedOut => "timed out",
226 ErrorKind::WriteZero => "write zero",
227 ErrorKind::Interrupted => "operation interrupted",
228 ErrorKind::UnexpectedEof => "unexpected end of file",
229 ErrorKind::Unsupported => "unsupported",
230 ErrorKind::OutOfMemory => "out of memory",
231 ErrorKind::Other => "other error",
232 ErrorKind::Uncategorized => "uncategorized error",
237 /// Intended for use for errors not exposed to the user, where allocating onto
238 /// the heap (for normal construction via Error::new) is too costly.
239 #[stable(feature = "io_error_from_errorkind", since = "1.14.0")]
240 impl From<ErrorKind> for Error {
241 /// Converts an [`ErrorKind`] into an [`Error`].
243 /// This conversion allocates a new error with a simple representation of error kind.
248 /// use std::io::{Error, ErrorKind};
250 /// let not_found = ErrorKind::NotFound;
251 /// let error = Error::from(not_found);
252 /// assert_eq!("entity not found", format!("{}", error));
255 fn from(kind: ErrorKind) -> Error {
256 Error { repr: Repr::Simple(kind) }
261 /// Creates a new I/O error from a known kind of error as well as an
262 /// arbitrary error payload.
264 /// This function is used to generically create I/O errors which do not
265 /// originate from the OS itself. The `error` argument is an arbitrary
266 /// payload which will be contained in this [`Error`].
271 /// use std::io::{Error, ErrorKind};
273 /// // errors can be created from strings
274 /// let custom_error = Error::new(ErrorKind::Other, "oh no!");
276 /// // errors can also be created from other errors
277 /// let custom_error2 = Error::new(ErrorKind::Interrupted, custom_error);
279 #[stable(feature = "rust1", since = "1.0.0")]
280 pub fn new<E>(kind: ErrorKind, error: E) -> Error
282 E: Into<Box<dyn error::Error + Send + Sync>>,
284 Self::_new(kind, error.into())
287 fn _new(kind: ErrorKind, error: Box<dyn error::Error + Send + Sync>) -> Error {
288 Error { repr: Repr::Custom(Box::new(Custom { kind, error })) }
291 /// Creates a new I/O error from a known kind of error as well as a
292 /// constant message.
294 /// This function does not allocate.
296 /// This function should maybe change to
297 /// `new_const<const MSG: &'static str>(kind: ErrorKind)`
298 /// in the future, when const generics allow that.
300 pub(crate) const fn new_const(kind: ErrorKind, message: &'static &'static str) -> Error {
301 Self { repr: Repr::SimpleMessage(kind, message) }
304 /// Returns an error representing the last OS error which occurred.
306 /// This function reads the value of `errno` for the target platform (e.g.
307 /// `GetLastError` on Windows) and will return a corresponding instance of
308 /// [`Error`] for the error code.
313 /// use std::io::Error;
315 /// println!("last OS error: {:?}", Error::last_os_error());
317 #[stable(feature = "rust1", since = "1.0.0")]
319 pub fn last_os_error() -> Error {
320 Error::from_raw_os_error(sys::os::errno() as i32)
323 /// Creates a new instance of an [`Error`] from a particular OS error code.
330 /// # if cfg!(target_os = "linux") {
333 /// let error = io::Error::from_raw_os_error(22);
334 /// assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
341 /// # if cfg!(windows) {
344 /// let error = io::Error::from_raw_os_error(10022);
345 /// assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
348 #[stable(feature = "rust1", since = "1.0.0")]
350 pub fn from_raw_os_error(code: i32) -> Error {
351 Error { repr: Repr::Os(code) }
354 /// Returns the OS error that this error represents (if any).
356 /// If this [`Error`] was constructed via [`last_os_error`] or
357 /// [`from_raw_os_error`], then this function will return [`Some`], otherwise
358 /// it will return [`None`].
360 /// [`last_os_error`]: Error::last_os_error
361 /// [`from_raw_os_error`]: Error::from_raw_os_error
366 /// use std::io::{Error, ErrorKind};
368 /// fn print_os_error(err: &Error) {
369 /// if let Some(raw_os_err) = err.raw_os_error() {
370 /// println!("raw OS error: {:?}", raw_os_err);
372 /// println!("Not an OS error");
377 /// // Will print "raw OS error: ...".
378 /// print_os_error(&Error::last_os_error());
379 /// // Will print "Not an OS error".
380 /// print_os_error(&Error::new(ErrorKind::Other, "oh no!"));
383 #[stable(feature = "rust1", since = "1.0.0")]
385 pub fn raw_os_error(&self) -> Option<i32> {
387 Repr::Os(i) => Some(i),
388 Repr::Custom(..) => None,
389 Repr::Simple(..) => None,
390 Repr::SimpleMessage(..) => None,
394 /// Returns a reference to the inner error wrapped by this error (if any).
396 /// If this [`Error`] was constructed via [`new`] then this function will
397 /// return [`Some`], otherwise it will return [`None`].
399 /// [`new`]: Error::new
404 /// use std::io::{Error, ErrorKind};
406 /// fn print_error(err: &Error) {
407 /// if let Some(inner_err) = err.get_ref() {
408 /// println!("Inner error: {:?}", inner_err);
410 /// println!("No inner error");
415 /// // Will print "No inner error".
416 /// print_error(&Error::last_os_error());
417 /// // Will print "Inner error: ...".
418 /// print_error(&Error::new(ErrorKind::Other, "oh no!"));
421 #[stable(feature = "io_error_inner", since = "1.3.0")]
423 pub fn get_ref(&self) -> Option<&(dyn error::Error + Send + Sync + 'static)> {
425 Repr::Os(..) => None,
426 Repr::Simple(..) => None,
427 Repr::SimpleMessage(..) => None,
428 Repr::Custom(ref c) => Some(&*c.error),
432 /// Returns a mutable reference to the inner error wrapped by this error
435 /// If this [`Error`] was constructed via [`new`] then this function will
436 /// return [`Some`], otherwise it will return [`None`].
438 /// [`new`]: Error::new
443 /// use std::io::{Error, ErrorKind};
444 /// use std::{error, fmt};
445 /// use std::fmt::Display;
453 /// fn new() -> MyError {
455 /// v: "oh no!".to_string()
459 /// fn change_message(&mut self, new_message: &str) {
460 /// self.v = new_message.to_string();
464 /// impl error::Error for MyError {}
466 /// impl Display for MyError {
467 /// fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
468 /// write!(f, "MyError: {}", &self.v)
472 /// fn change_error(mut err: Error) -> Error {
473 /// if let Some(inner_err) = err.get_mut() {
474 /// inner_err.downcast_mut::<MyError>().unwrap().change_message("I've been changed!");
479 /// fn print_error(err: &Error) {
480 /// if let Some(inner_err) = err.get_ref() {
481 /// println!("Inner error: {}", inner_err);
483 /// println!("No inner error");
488 /// // Will print "No inner error".
489 /// print_error(&change_error(Error::last_os_error()));
490 /// // Will print "Inner error: ...".
491 /// print_error(&change_error(Error::new(ErrorKind::Other, MyError::new())));
494 #[stable(feature = "io_error_inner", since = "1.3.0")]
496 pub fn get_mut(&mut self) -> Option<&mut (dyn error::Error + Send + Sync + 'static)> {
498 Repr::Os(..) => None,
499 Repr::Simple(..) => None,
500 Repr::SimpleMessage(..) => None,
501 Repr::Custom(ref mut c) => Some(&mut *c.error),
505 /// Consumes the `Error`, returning its inner error (if any).
507 /// If this [`Error`] was constructed via [`new`] then this function will
508 /// return [`Some`], otherwise it will return [`None`].
510 /// [`new`]: Error::new
515 /// use std::io::{Error, ErrorKind};
517 /// fn print_error(err: Error) {
518 /// if let Some(inner_err) = err.into_inner() {
519 /// println!("Inner error: {}", inner_err);
521 /// println!("No inner error");
526 /// // Will print "No inner error".
527 /// print_error(Error::last_os_error());
528 /// // Will print "Inner error: ...".
529 /// print_error(Error::new(ErrorKind::Other, "oh no!"));
532 #[stable(feature = "io_error_inner", since = "1.3.0")]
534 pub fn into_inner(self) -> Option<Box<dyn error::Error + Send + Sync>> {
536 Repr::Os(..) => None,
537 Repr::Simple(..) => None,
538 Repr::SimpleMessage(..) => None,
539 Repr::Custom(c) => Some(c.error),
543 /// Returns the corresponding [`ErrorKind`] for this error.
548 /// use std::io::{Error, ErrorKind};
550 /// fn print_error(err: Error) {
551 /// println!("{:?}", err.kind());
555 /// // Will print "Uncategorized".
556 /// print_error(Error::last_os_error());
557 /// // Will print "AddrInUse".
558 /// print_error(Error::new(ErrorKind::AddrInUse, "oh no!"));
561 #[stable(feature = "rust1", since = "1.0.0")]
563 pub fn kind(&self) -> ErrorKind {
565 Repr::Os(code) => sys::decode_error_kind(code),
566 Repr::Custom(ref c) => c.kind,
567 Repr::Simple(kind) => kind,
568 Repr::SimpleMessage(kind, _) => kind,
573 impl fmt::Debug for Repr {
574 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
576 Repr::Os(code) => fmt
578 .field("code", &code)
579 .field("kind", &sys::decode_error_kind(code))
580 .field("message", &sys::os::error_string(code))
582 Repr::Custom(ref c) => fmt::Debug::fmt(&c, fmt),
583 Repr::Simple(kind) => fmt.debug_tuple("Kind").field(&kind).finish(),
584 Repr::SimpleMessage(kind, &message) => {
585 fmt.debug_struct("Error").field("kind", &kind).field("message", &message).finish()
591 #[stable(feature = "rust1", since = "1.0.0")]
592 impl fmt::Display for Error {
593 fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
596 let detail = sys::os::error_string(code);
597 write!(fmt, "{} (os error {})", detail, code)
599 Repr::Custom(ref c) => c.error.fmt(fmt),
600 Repr::Simple(kind) => write!(fmt, "{}", kind.as_str()),
601 Repr::SimpleMessage(_, &msg) => msg.fmt(fmt),
606 #[stable(feature = "rust1", since = "1.0.0")]
607 impl error::Error for Error {
608 #[allow(deprecated, deprecated_in_future)]
609 fn description(&self) -> &str {
611 Repr::Os(..) | Repr::Simple(..) => self.kind().as_str(),
612 Repr::SimpleMessage(_, &msg) => msg,
613 Repr::Custom(ref c) => c.error.description(),
618 fn cause(&self) -> Option<&dyn error::Error> {
620 Repr::Os(..) => None,
621 Repr::Simple(..) => None,
622 Repr::SimpleMessage(..) => None,
623 Repr::Custom(ref c) => c.error.cause(),
627 fn source(&self) -> Option<&(dyn error::Error + 'static)> {
629 Repr::Os(..) => None,
630 Repr::Simple(..) => None,
631 Repr::SimpleMessage(..) => None,
632 Repr::Custom(ref c) => c.error.source(),
637 fn _assert_error_is_sync_send() {
638 fn _is_sync_send<T: Sync + Send>() {}
639 _is_sync_send::<Error>();