library/std/src/io/error.rs

   1 #[cfg(test)]
   2 mod tests;
   3
   4 use crate::convert::From;
   5 use crate::error;
   6 use crate::fmt;
   7 use crate::result;
   8 use crate::sys;
   9
  10 /// A specialized [`Result`] type for I/O operations.
  11 ///
  12 /// This type is broadly used across [`std::io`] for any operation which may
  13 /// produce an error.
  14 ///
  15 /// This typedef is generally used to avoid writing out [`io::Error`] directly and
  16 /// is otherwise a direct mapping to [`Result`].
  17 ///
  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`].
  23 ///
  24 /// [`std::io`]: crate::io
  25 /// [`io::Error`]: Error
  26 /// [`Result`]: crate::result::Result
  27 /// [prelude]: crate::prelude
  28 ///
  29 /// # Examples
  30 ///
  31 /// A convenience function that bubbles an `io::Result` to its caller:
  32 ///
  33 /// ```
  34 /// use std::io;
  35 ///
  36 /// fn get_string() -> io::Result<String> {
  37 ///     let mut buffer = String::new();
  38 ///
  39 ///     io::stdin().read_line(&mut buffer)?;
  40 ///
  41 ///     Ok(buffer)
  42 /// }
  43 /// ```
  44 #[stable(feature = "rust1", since = "1.0.0")]
  45 pub type Result<T> = result::Result<T, Error>;
  46
  47 /// The error type for I/O operations of the [`Read`], [`Write`], [`Seek`], and
  48 /// associated traits.
  49 ///
  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
  52 /// [`ErrorKind`].
  53 ///
  54 /// [`Read`]: crate::io::Read
  55 /// [`Write`]: crate::io::Write
  56 /// [`Seek`]: crate::io::Seek
  57 #[stable(feature = "rust1", since = "1.0.0")]
  58 pub struct Error {
  59     repr: Repr,
  60 }
  61
  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)
  66     }
  67 }
  68
  69 enum Repr {
  70     Os(i32),
  71     Simple(ErrorKind),
  72     // &str is a fat pointer, but &&str is a thin pointer.
  73     SimpleMessage(ErrorKind, &'static &'static str),
  74     Custom(Box<Custom>),
  75 }
  76
  77 #[derive(Debug)]
  78 struct Custom {
  79     kind: ErrorKind,
  80     error: Box<dyn error::Error + Send + Sync>,
  81 }
  82
  83 /// A list specifying general categories of I/O error.
  84 ///
  85 /// This list is intended to grow over time and it is not recommended to
  86 /// exhaustively match against it.
  87 ///
  88 /// It is used with the [`io::Error`] type.
  89 ///
  90 /// [`io::Error`]: Error
  91 #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
  92 #[stable(feature = "rust1", since = "1.0.0")]
  93 #[allow(deprecated)]
  94 #[non_exhaustive]
  95 pub enum ErrorKind {
  96     /// An entity was not found, often a file.
  97     #[stable(feature = "rust1", since = "1.0.0")]
  98     NotFound,
  99     /// The operation lacked the necessary privileges to complete.
 100     #[stable(feature = "rust1", since = "1.0.0")]
 101     PermissionDenied,
 102     /// The connection was refused by the remote server.
 103     #[stable(feature = "rust1", since = "1.0.0")]
 104     ConnectionRefused,
 105     /// The connection was reset by the remote server.
 106     #[stable(feature = "rust1", since = "1.0.0")]
 107     ConnectionReset,
 108     /// The connection was aborted (terminated) by the remote server.
 109     #[stable(feature = "rust1", since = "1.0.0")]
 110     ConnectionAborted,
 111     /// The network operation failed because it was not connected yet.
 112     #[stable(feature = "rust1", since = "1.0.0")]
 113     NotConnected,
 114     /// A socket address could not be bound because the address is already in
 115     /// use elsewhere.
 116     #[stable(feature = "rust1", since = "1.0.0")]
 117     AddrInUse,
 118     /// A nonexistent interface was requested or the requested address was not
 119     /// local.
 120     #[stable(feature = "rust1", since = "1.0.0")]
 121     AddrNotAvailable,
 122     /// The operation failed because a pipe was closed.
 123     #[stable(feature = "rust1", since = "1.0.0")]
 124     BrokenPipe,
 125     /// An entity already exists, often a file.
 126     #[stable(feature = "rust1", since = "1.0.0")]
 127     AlreadyExists,
 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")]
 131     WouldBlock,
 132     /// A parameter was incorrect.
 133     #[stable(feature = "rust1", since = "1.0.0")]
 134     InvalidInput,
 135     /// Data not valid for the operation were encountered.
 136     ///
 137     /// Unlike [`InvalidInput`], this typically means that the operation
 138     /// parameters were valid, however the error was caused by malformed
 139     /// input data.
 140     ///
 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.
 143     ///
 144     /// [`InvalidInput`]: ErrorKind::InvalidInput
 145     #[stable(feature = "io_invalid_data", since = "1.2.0")]
 146     InvalidData,
 147     /// The I/O operation's timeout expired, causing it to be canceled.
 148     #[stable(feature = "rust1", since = "1.0.0")]
 149     TimedOut,
 150     /// An error returned when an operation could not be completed because a
 151     /// call to [`write`] returned [`Ok(0)`].
 152     ///
 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
 155     /// written.
 156     ///
 157     /// [`write`]: crate::io::Write::write
 158     /// [`Ok(0)`]: Ok
 159     #[stable(feature = "rust1", since = "1.0.0")]
 160     WriteZero,
 161     /// This operation was interrupted.
 162     ///
 163     /// Interrupted operations can typically be retried.
 164     #[stable(feature = "rust1", since = "1.0.0")]
 165     Interrupted,
 166     /// Any I/O error not part of this list.
 167     ///
 168     /// Errors that are `Other` now may move to a different or a new
 169     /// [`ErrorKind`] variant in the future. It is not recommended to match
 170     /// an error against `Other` and to expect any additional characteristics,
 171     /// e.g., a specific [`Error::raw_os_error`] return value.
 172     #[stable(feature = "rust1", since = "1.0.0")]
 173     Other,
 174
 175     /// An error returned when an operation could not be completed because an
 176     /// "end of file" was reached prematurely.
 177     ///
 178     /// This typically means that an operation could only succeed if it read a
 179     /// particular number of bytes but only a smaller number of bytes could be
 180     /// read.
 181     #[stable(feature = "read_exact", since = "1.6.0")]
 182     UnexpectedEof,
 183
 184     /// This operation is unsupported on this platform.
 185     ///
 186     /// This means that the operation can never succeed.
 187     #[stable(feature = "unsupported_error", since = "1.53.0")]
 188     Unsupported,
 189
 190     /// An operation could not be completed, because it failed
 191     /// to allocate enough memory.
 192     #[stable(feature = "out_of_memory_error", since = "1.54.0")]
 193     OutOfMemory,
 194 }
 195
 196 impl ErrorKind {
 197     pub(crate) fn as_str(&self) -> &'static str {
 198         match *self {
 199             ErrorKind::NotFound => "entity not found",
 200             ErrorKind::PermissionDenied => "permission denied",
 201             ErrorKind::ConnectionRefused => "connection refused",
 202             ErrorKind::ConnectionReset => "connection reset",
 203             ErrorKind::ConnectionAborted => "connection aborted",
 204             ErrorKind::NotConnected => "not connected",
 205             ErrorKind::AddrInUse => "address in use",
 206             ErrorKind::AddrNotAvailable => "address not available",
 207             ErrorKind::BrokenPipe => "broken pipe",
 208             ErrorKind::AlreadyExists => "entity already exists",
 209             ErrorKind::WouldBlock => "operation would block",
 210             ErrorKind::InvalidInput => "invalid input parameter",
 211             ErrorKind::InvalidData => "invalid data",
 212             ErrorKind::TimedOut => "timed out",
 213             ErrorKind::WriteZero => "write zero",
 214             ErrorKind::Interrupted => "operation interrupted",
 215             ErrorKind::Other => "other os error",
 216             ErrorKind::UnexpectedEof => "unexpected end of file",
 217             ErrorKind::Unsupported => "unsupported",
 218             ErrorKind::OutOfMemory => "out of memory",
 219         }
 220     }
 221 }
 222
 223 /// Intended for use for errors not exposed to the user, where allocating onto
 224 /// the heap (for normal construction via Error::new) is too costly.
 225 #[stable(feature = "io_error_from_errorkind", since = "1.14.0")]
 226 impl From<ErrorKind> for Error {
 227     /// Converts an [`ErrorKind`] into an [`Error`].
 228     ///
 229     /// This conversion allocates a new error with a simple representation of error kind.
 230     ///
 231     /// # Examples
 232     ///
 233     /// ```
 234     /// use std::io::{Error, ErrorKind};
 235     ///
 236     /// let not_found = ErrorKind::NotFound;
 237     /// let error = Error::from(not_found);
 238     /// assert_eq!("entity not found", format!("{}", error));
 239     /// ```
 240     #[inline]
 241     fn from(kind: ErrorKind) -> Error {
 242         Error { repr: Repr::Simple(kind) }
 243     }
 244 }
 245
 246 impl Error {
 247     /// Creates a new I/O error from a known kind of error as well as an
 248     /// arbitrary error payload.
 249     ///
 250     /// This function is used to generically create I/O errors which do not
 251     /// originate from the OS itself. The `error` argument is an arbitrary
 252     /// payload which will be contained in this [`Error`].
 253     ///
 254     /// # Examples
 255     ///
 256     /// ```
 257     /// use std::io::{Error, ErrorKind};
 258     ///
 259     /// // errors can be created from strings
 260     /// let custom_error = Error::new(ErrorKind::Other, "oh no!");
 261     ///
 262     /// // errors can also be created from other errors
 263     /// let custom_error2 = Error::new(ErrorKind::Interrupted, custom_error);
 264     /// ```
 265     #[stable(feature = "rust1", since = "1.0.0")]
 266     pub fn new<E>(kind: ErrorKind, error: E) -> Error
 267     where
 268         E: Into<Box<dyn error::Error + Send + Sync>>,
 269     {
 270         Self::_new(kind, error.into())
 271     }
 272
 273     fn _new(kind: ErrorKind, error: Box<dyn error::Error + Send + Sync>) -> Error {
 274         Error { repr: Repr::Custom(Box::new(Custom { kind, error })) }
 275     }
 276
 277     /// Creates a new I/O error from a known kind of error as well as a
 278     /// constant message.
 279     ///
 280     /// This function does not allocate.
 281     ///
 282     /// This function should maybe change to
 283     /// `new_const<const MSG: &'static str>(kind: ErrorKind)`
 284     /// in the future, when const generics allow that.
 285     #[inline]
 286     pub(crate) const fn new_const(kind: ErrorKind, message: &'static &'static str) -> Error {
 287         Self { repr: Repr::SimpleMessage(kind, message) }
 288     }
 289
 290     /// Returns an error representing the last OS error which occurred.
 291     ///
 292     /// This function reads the value of `errno` for the target platform (e.g.
 293     /// `GetLastError` on Windows) and will return a corresponding instance of
 294     /// [`Error`] for the error code.
 295     ///
 296     /// # Examples
 297     ///
 298     /// ```
 299     /// use std::io::Error;
 300     ///
 301     /// println!("last OS error: {:?}", Error::last_os_error());
 302     /// ```
 303     #[stable(feature = "rust1", since = "1.0.0")]
 304     #[inline]
 305     pub fn last_os_error() -> Error {
 306         Error::from_raw_os_error(sys::os::errno() as i32)
 307     }
 308
 309     /// Creates a new instance of an [`Error`] from a particular OS error code.
 310     ///
 311     /// # Examples
 312     ///
 313     /// On Linux:
 314     ///
 315     /// ```
 316     /// # if cfg!(target_os = "linux") {
 317     /// use std::io;
 318     ///
 319     /// let error = io::Error::from_raw_os_error(22);
 320     /// assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
 321     /// # }
 322     /// ```
 323     ///
 324     /// On Windows:
 325     ///
 326     /// ```
 327     /// # if cfg!(windows) {
 328     /// use std::io;
 329     ///
 330     /// let error = io::Error::from_raw_os_error(10022);
 331     /// assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
 332     /// # }
 333     /// ```
 334     #[stable(feature = "rust1", since = "1.0.0")]
 335     #[inline]
 336     pub fn from_raw_os_error(code: i32) -> Error {
 337         Error { repr: Repr::Os(code) }
 338     }
 339
 340     /// Returns the OS error that this error represents (if any).
 341     ///
 342     /// If this [`Error`] was constructed via [`last_os_error`] or
 343     /// [`from_raw_os_error`], then this function will return [`Some`], otherwise
 344     /// it will return [`None`].
 345     ///
 346     /// [`last_os_error`]: Error::last_os_error
 347     /// [`from_raw_os_error`]: Error::from_raw_os_error
 348     ///
 349     /// # Examples
 350     ///
 351     /// ```
 352     /// use std::io::{Error, ErrorKind};
 353     ///
 354     /// fn print_os_error(err: &Error) {
 355     ///     if let Some(raw_os_err) = err.raw_os_error() {
 356     ///         println!("raw OS error: {:?}", raw_os_err);
 357     ///     } else {
 358     ///         println!("Not an OS error");
 359     ///     }
 360     /// }
 361     ///
 362     /// fn main() {
 363     ///     // Will print "raw OS error: ...".
 364     ///     print_os_error(&Error::last_os_error());
 365     ///     // Will print "Not an OS error".
 366     ///     print_os_error(&Error::new(ErrorKind::Other, "oh no!"));
 367     /// }
 368     /// ```
 369     #[stable(feature = "rust1", since = "1.0.0")]
 370     #[inline]
 371     pub fn raw_os_error(&self) -> Option<i32> {
 372         match self.repr {
 373             Repr::Os(i) => Some(i),
 374             Repr::Custom(..) => None,
 375             Repr::Simple(..) => None,
 376             Repr::SimpleMessage(..) => None,
 377         }
 378     }
 379
 380     /// Returns a reference to the inner error wrapped by this error (if any).
 381     ///
 382     /// If this [`Error`] was constructed via [`new`] then this function will
 383     /// return [`Some`], otherwise it will return [`None`].
 384     ///
 385     /// [`new`]: Error::new
 386     ///
 387     /// # Examples
 388     ///
 389     /// ```
 390     /// use std::io::{Error, ErrorKind};
 391     ///
 392     /// fn print_error(err: &Error) {
 393     ///     if let Some(inner_err) = err.get_ref() {
 394     ///         println!("Inner error: {:?}", inner_err);
 395     ///     } else {
 396     ///         println!("No inner error");
 397     ///     }
 398     /// }
 399     ///
 400     /// fn main() {
 401     ///     // Will print "No inner error".
 402     ///     print_error(&Error::last_os_error());
 403     ///     // Will print "Inner error: ...".
 404     ///     print_error(&Error::new(ErrorKind::Other, "oh no!"));
 405     /// }
 406     /// ```
 407     #[stable(feature = "io_error_inner", since = "1.3.0")]
 408     #[inline]
 409     pub fn get_ref(&self) -> Option<&(dyn error::Error + Send + Sync + 'static)> {
 410         match self.repr {
 411             Repr::Os(..) => None,
 412             Repr::Simple(..) => None,
 413             Repr::SimpleMessage(..) => None,
 414             Repr::Custom(ref c) => Some(&*c.error),
 415         }
 416     }
 417
 418     /// Returns a mutable reference to the inner error wrapped by this error
 419     /// (if any).
 420     ///
 421     /// If this [`Error`] was constructed via [`new`] then this function will
 422     /// return [`Some`], otherwise it will return [`None`].
 423     ///
 424     /// [`new`]: Error::new
 425     ///
 426     /// # Examples
 427     ///
 428     /// ```
 429     /// use std::io::{Error, ErrorKind};
 430     /// use std::{error, fmt};
 431     /// use std::fmt::Display;
 432     ///
 433     /// #[derive(Debug)]
 434     /// struct MyError {
 435     ///     v: String,
 436     /// }
 437     ///
 438     /// impl MyError {
 439     ///     fn new() -> MyError {
 440     ///         MyError {
 441     ///             v: "oh no!".to_string()
 442     ///         }
 443     ///     }
 444     ///
 445     ///     fn change_message(&mut self, new_message: &str) {
 446     ///         self.v = new_message.to_string();
 447     ///     }
 448     /// }
 449     ///
 450     /// impl error::Error for MyError {}
 451     ///
 452     /// impl Display for MyError {
 453     ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 454     ///         write!(f, "MyError: {}", &self.v)
 455     ///     }
 456     /// }
 457     ///
 458     /// fn change_error(mut err: Error) -> Error {
 459     ///     if let Some(inner_err) = err.get_mut() {
 460     ///         inner_err.downcast_mut::<MyError>().unwrap().change_message("I've been changed!");
 461     ///     }
 462     ///     err
 463     /// }
 464     ///
 465     /// fn print_error(err: &Error) {
 466     ///     if let Some(inner_err) = err.get_ref() {
 467     ///         println!("Inner error: {}", inner_err);
 468     ///     } else {
 469     ///         println!("No inner error");
 470     ///     }
 471     /// }
 472     ///
 473     /// fn main() {
 474     ///     // Will print "No inner error".
 475     ///     print_error(&change_error(Error::last_os_error()));
 476     ///     // Will print "Inner error: ...".
 477     ///     print_error(&change_error(Error::new(ErrorKind::Other, MyError::new())));
 478     /// }
 479     /// ```
 480     #[stable(feature = "io_error_inner", since = "1.3.0")]
 481     #[inline]
 482     pub fn get_mut(&mut self) -> Option<&mut (dyn error::Error + Send + Sync + 'static)> {
 483         match self.repr {
 484             Repr::Os(..) => None,
 485             Repr::Simple(..) => None,
 486             Repr::SimpleMessage(..) => None,
 487             Repr::Custom(ref mut c) => Some(&mut *c.error),
 488         }
 489     }
 490
 491     /// Consumes the `Error`, returning its inner error (if any).
 492     ///
 493     /// If this [`Error`] was constructed via [`new`] then this function will
 494     /// return [`Some`], otherwise it will return [`None`].
 495     ///
 496     /// [`new`]: Error::new
 497     ///
 498     /// # Examples
 499     ///
 500     /// ```
 501     /// use std::io::{Error, ErrorKind};
 502     ///
 503     /// fn print_error(err: Error) {
 504     ///     if let Some(inner_err) = err.into_inner() {
 505     ///         println!("Inner error: {}", inner_err);
 506     ///     } else {
 507     ///         println!("No inner error");
 508     ///     }
 509     /// }
 510     ///
 511     /// fn main() {
 512     ///     // Will print "No inner error".
 513     ///     print_error(Error::last_os_error());
 514     ///     // Will print "Inner error: ...".
 515     ///     print_error(Error::new(ErrorKind::Other, "oh no!"));
 516     /// }
 517     /// ```
 518     #[stable(feature = "io_error_inner", since = "1.3.0")]
 519     #[inline]
 520     pub fn into_inner(self) -> Option<Box<dyn error::Error + Send + Sync>> {
 521         match self.repr {
 522             Repr::Os(..) => None,
 523             Repr::Simple(..) => None,
 524             Repr::SimpleMessage(..) => None,
 525             Repr::Custom(c) => Some(c.error),
 526         }
 527     }
 528
 529     /// Returns the corresponding [`ErrorKind`] for this error.
 530     ///
 531     /// # Examples
 532     ///
 533     /// ```
 534     /// use std::io::{Error, ErrorKind};
 535     ///
 536     /// fn print_error(err: Error) {
 537     ///     println!("{:?}", err.kind());
 538     /// }
 539     ///
 540     /// fn main() {
 541     ///     // Will print "Other".
 542     ///     print_error(Error::last_os_error());
 543     ///     // Will print "AddrInUse".
 544     ///     print_error(Error::new(ErrorKind::AddrInUse, "oh no!"));
 545     /// }
 546     /// ```
 547     #[stable(feature = "rust1", since = "1.0.0")]
 548     #[inline]
 549     pub fn kind(&self) -> ErrorKind {
 550         match self.repr {
 551             Repr::Os(code) => sys::decode_error_kind(code),
 552             Repr::Custom(ref c) => c.kind,
 553             Repr::Simple(kind) => kind,
 554             Repr::SimpleMessage(kind, _) => kind,
 555         }
 556     }
 557 }
 558
 559 impl fmt::Debug for Repr {
 560     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
 561         match *self {
 562             Repr::Os(code) => fmt
 563                 .debug_struct("Os")
 564                 .field("code", &code)
 565                 .field("kind", &sys::decode_error_kind(code))
 566                 .field("message", &sys::os::error_string(code))
 567                 .finish(),
 568             Repr::Custom(ref c) => fmt::Debug::fmt(&c, fmt),
 569             Repr::Simple(kind) => fmt.debug_tuple("Kind").field(&kind).finish(),
 570             Repr::SimpleMessage(kind, &message) => {
 571                 fmt.debug_struct("Error").field("kind", &kind).field("message", &message).finish()
 572             }
 573         }
 574     }
 575 }
 576
 577 #[stable(feature = "rust1", since = "1.0.0")]
 578 impl fmt::Display for Error {
 579     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
 580         match self.repr {
 581             Repr::Os(code) => {
 582                 let detail = sys::os::error_string(code);
 583                 write!(fmt, "{} (os error {})", detail, code)
 584             }
 585             Repr::Custom(ref c) => c.error.fmt(fmt),
 586             Repr::Simple(kind) => write!(fmt, "{}", kind.as_str()),
 587             Repr::SimpleMessage(_, &msg) => msg.fmt(fmt),
 588         }
 589     }
 590 }
 591
 592 #[stable(feature = "rust1", since = "1.0.0")]
 593 impl error::Error for Error {
 594     #[allow(deprecated, deprecated_in_future)]
 595     fn description(&self) -> &str {
 596         match self.repr {
 597             Repr::Os(..) | Repr::Simple(..) => self.kind().as_str(),
 598             Repr::SimpleMessage(_, &msg) => msg,
 599             Repr::Custom(ref c) => c.error.description(),
 600         }
 601     }
 602
 603     #[allow(deprecated)]
 604     fn cause(&self) -> Option<&dyn error::Error> {
 605         match self.repr {
 606             Repr::Os(..) => None,
 607             Repr::Simple(..) => None,
 608             Repr::SimpleMessage(..) => None,
 609             Repr::Custom(ref c) => c.error.cause(),
 610         }
 611     }
 612
 613     fn source(&self) -> Option<&(dyn error::Error + 'static)> {
 614         match self.repr {
 615             Repr::Os(..) => None,
 616             Repr::Simple(..) => None,
 617             Repr::SimpleMessage(..) => None,
 618             Repr::Custom(ref c) => c.error.source(),
 619         }
 620     }
 621 }
 622
 623 fn _assert_error_is_sync_send() {
 624     fn _is_sync_send<T: Sync + Send>() {}
 625     _is_sync_send::<Error>();
 626 }