src/libstd/io/error.rs

   1 use crate::convert::From;
   2 use crate::error;
   3 use crate::fmt;
   4 use crate::result;
   5 use crate::sys;
   6
   7 /// A specialized [`Result`](../result/enum.Result.html) type for I/O
   8 /// operations.
   9 ///
  10 /// This type is broadly used across [`std::io`] for any operation which may
  11 /// produce an error.
  12 ///
  13 /// This typedef is generally used to avoid writing out [`io::Error`] directly and
  14 /// is otherwise a direct mapping to [`Result`].
  15 ///
  16 /// While usual Rust style is to import types directly, aliases of [`Result`]
  17 /// often are not, to make it easier to distinguish between them. [`Result`] is
  18 /// generally assumed to be [`std::result::Result`][`Result`], and so users of this alias
  19 /// will generally use `io::Result` instead of shadowing the prelude's import
  20 /// of [`std::result::Result`][`Result`].
  21 ///
  22 /// [`std::io`]: ../io/index.html
  23 /// [`io::Error`]: ../io/struct.Error.html
  24 /// [`Result`]: ../result/enum.Result.html
  25 ///
  26 /// # Examples
  27 ///
  28 /// A convenience function that bubbles an `io::Result` to its caller:
  29 ///
  30 /// ```
  31 /// use std::io;
  32 ///
  33 /// fn get_string() -> io::Result<String> {
  34 ///     let mut buffer = String::new();
  35 ///
  36 ///     io::stdin().read_line(&mut buffer)?;
  37 ///
  38 ///     Ok(buffer)
  39 /// }
  40 /// ```
  41 #[stable(feature = "rust1", since = "1.0.0")]
  42 pub type Result<T> = result::Result<T, Error>;
  43
  44 /// The error type for I/O operations of the [`Read`], [`Write`], [`Seek`], and
  45 /// associated traits.
  46 ///
  47 /// Errors mostly originate from the underlying OS, but custom instances of
  48 /// `Error` can be created with crafted error messages and a particular value of
  49 /// [`ErrorKind`].
  50 ///
  51 /// [`Read`]: ../io/trait.Read.html
  52 /// [`Write`]: ../io/trait.Write.html
  53 /// [`Seek`]: ../io/trait.Seek.html
  54 /// [`ErrorKind`]: enum.ErrorKind.html
  55 #[stable(feature = "rust1", since = "1.0.0")]
  56 pub struct Error {
  57     repr: Repr,
  58 }
  59
  60 #[stable(feature = "rust1", since = "1.0.0")]
  61 impl fmt::Debug for Error {
  62     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  63         fmt::Debug::fmt(&self.repr, f)
  64     }
  65 }
  66
  67 enum Repr {
  68     Os(i32),
  69     Simple(ErrorKind),
  70     Custom(Box<Custom>),
  71 }
  72
  73 #[derive(Debug)]
  74 struct Custom {
  75     kind: ErrorKind,
  76     error: Box<dyn error::Error + Send + Sync>,
  77 }
  78
  79 /// A list specifying general categories of I/O error.
  80 ///
  81 /// This list is intended to grow over time and it is not recommended to
  82 /// exhaustively match against it.
  83 ///
  84 /// It is used with the [`io::Error`] type.
  85 ///
  86 /// [`io::Error`]: struct.Error.html
  87 #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
  88 #[stable(feature = "rust1", since = "1.0.0")]
  89 #[allow(deprecated)]
  90 #[non_exhaustive]
  91 pub enum ErrorKind {
  92     /// An entity was not found, often a file.
  93     #[stable(feature = "rust1", since = "1.0.0")]
  94     NotFound,
  95     /// The operation lacked the necessary privileges to complete.
  96     #[stable(feature = "rust1", since = "1.0.0")]
  97     PermissionDenied,
  98     /// The connection was refused by the remote server.
  99     #[stable(feature = "rust1", since = "1.0.0")]
 100     ConnectionRefused,
 101     /// The connection was reset by the remote server.
 102     #[stable(feature = "rust1", since = "1.0.0")]
 103     ConnectionReset,
 104     /// The connection was aborted (terminated) by the remote server.
 105     #[stable(feature = "rust1", since = "1.0.0")]
 106     ConnectionAborted,
 107     /// The network operation failed because it was not connected yet.
 108     #[stable(feature = "rust1", since = "1.0.0")]
 109     NotConnected,
 110     /// A socket address could not be bound because the address is already in
 111     /// use elsewhere.
 112     #[stable(feature = "rust1", since = "1.0.0")]
 113     AddrInUse,
 114     /// A nonexistent interface was requested or the requested address was not
 115     /// local.
 116     #[stable(feature = "rust1", since = "1.0.0")]
 117     AddrNotAvailable,
 118     /// The operation failed because a pipe was closed.
 119     #[stable(feature = "rust1", since = "1.0.0")]
 120     BrokenPipe,
 121     /// An entity already exists, often a file.
 122     #[stable(feature = "rust1", since = "1.0.0")]
 123     AlreadyExists,
 124     /// The operation needs to block to complete, but the blocking operation was
 125     /// requested to not occur.
 126     #[stable(feature = "rust1", since = "1.0.0")]
 127     WouldBlock,
 128     /// A parameter was incorrect.
 129     #[stable(feature = "rust1", since = "1.0.0")]
 130     InvalidInput,
 131     /// Data not valid for the operation were encountered.
 132     ///
 133     /// Unlike [`InvalidInput`], this typically means that the operation
 134     /// parameters were valid, however the error was caused by malformed
 135     /// input data.
 136     ///
 137     /// For example, a function that reads a file into a string will error with
 138     /// `InvalidData` if the file's contents are not valid UTF-8.
 139     ///
 140     /// [`InvalidInput`]: #variant.InvalidInput
 141     #[stable(feature = "io_invalid_data", since = "1.2.0")]
 142     InvalidData,
 143     /// The I/O operation's timeout expired, causing it to be canceled.
 144     #[stable(feature = "rust1", since = "1.0.0")]
 145     TimedOut,
 146     /// An error returned when an operation could not be completed because a
 147     /// call to [`write`] returned [`Ok(0)`].
 148     ///
 149     /// This typically means that an operation could only succeed if it wrote a
 150     /// particular number of bytes but only a smaller number of bytes could be
 151     /// written.
 152     ///
 153     /// [`write`]: ../../std/io/trait.Write.html#tymethod.write
 154     /// [`Ok(0)`]: ../../std/io/type.Result.html
 155     #[stable(feature = "rust1", since = "1.0.0")]
 156     WriteZero,
 157     /// This operation was interrupted.
 158     ///
 159     /// Interrupted operations can typically be retried.
 160     #[stable(feature = "rust1", since = "1.0.0")]
 161     Interrupted,
 162     /// Any I/O error not part of this list.
 163     #[stable(feature = "rust1", since = "1.0.0")]
 164     Other,
 165
 166     /// An error returned when an operation could not be completed because an
 167     /// "end of file" was reached prematurely.
 168     ///
 169     /// This typically means that an operation could only succeed if it read a
 170     /// particular number of bytes but only a smaller number of bytes could be
 171     /// read.
 172     #[stable(feature = "read_exact", since = "1.6.0")]
 173     UnexpectedEof,
 174 }
 175
 176 impl ErrorKind {
 177     pub(crate) fn as_str(&self) -> &'static str {
 178         match *self {
 179             ErrorKind::NotFound => "entity not found",
 180             ErrorKind::PermissionDenied => "permission denied",
 181             ErrorKind::ConnectionRefused => "connection refused",
 182             ErrorKind::ConnectionReset => "connection reset",
 183             ErrorKind::ConnectionAborted => "connection aborted",
 184             ErrorKind::NotConnected => "not connected",
 185             ErrorKind::AddrInUse => "address in use",
 186             ErrorKind::AddrNotAvailable => "address not available",
 187             ErrorKind::BrokenPipe => "broken pipe",
 188             ErrorKind::AlreadyExists => "entity already exists",
 189             ErrorKind::WouldBlock => "operation would block",
 190             ErrorKind::InvalidInput => "invalid input parameter",
 191             ErrorKind::InvalidData => "invalid data",
 192             ErrorKind::TimedOut => "timed out",
 193             ErrorKind::WriteZero => "write zero",
 194             ErrorKind::Interrupted => "operation interrupted",
 195             ErrorKind::Other => "other os error",
 196             ErrorKind::UnexpectedEof => "unexpected end of file",
 197         }
 198     }
 199 }
 200
 201 /// Intended for use for errors not exposed to the user, where allocating onto
 202 /// the heap (for normal construction via Error::new) is too costly.
 203 #[stable(feature = "io_error_from_errorkind", since = "1.14.0")]
 204 impl From<ErrorKind> for Error {
 205     /// Converts an [`ErrorKind`] into an [`Error`].
 206     ///
 207     /// This conversion allocates a new error with a simple representation of error kind.
 208     ///
 209     /// # Examples
 210     ///
 211     /// ```
 212     /// use std::io::{Error, ErrorKind};
 213     ///
 214     /// let not_found = ErrorKind::NotFound;
 215     /// let error = Error::from(not_found);
 216     /// assert_eq!("entity not found", format!("{}", error));
 217     /// ```
 218     ///
 219     /// [`ErrorKind`]: ../../std/io/enum.ErrorKind.html
 220     /// [`Error`]: ../../std/io/struct.Error.html
 221     #[inline]
 222     fn from(kind: ErrorKind) -> Error {
 223         Error { repr: Repr::Simple(kind) }
 224     }
 225 }
 226
 227 impl Error {
 228     /// Creates a new I/O error from a known kind of error as well as an
 229     /// arbitrary error payload.
 230     ///
 231     /// This function is used to generically create I/O errors which do not
 232     /// originate from the OS itself. The `error` argument is an arbitrary
 233     /// payload which will be contained in this `Error`.
 234     ///
 235     /// # Examples
 236     ///
 237     /// ```
 238     /// use std::io::{Error, ErrorKind};
 239     ///
 240     /// // errors can be created from strings
 241     /// let custom_error = Error::new(ErrorKind::Other, "oh no!");
 242     ///
 243     /// // errors can also be created from other errors
 244     /// let custom_error2 = Error::new(ErrorKind::Interrupted, custom_error);
 245     /// ```
 246     #[stable(feature = "rust1", since = "1.0.0")]
 247     pub fn new<E>(kind: ErrorKind, error: E) -> Error
 248     where
 249         E: Into<Box<dyn error::Error + Send + Sync>>,
 250     {
 251         Self::_new(kind, error.into())
 252     }
 253
 254     fn _new(kind: ErrorKind, error: Box<dyn error::Error + Send + Sync>) -> Error {
 255         Error { repr: Repr::Custom(Box::new(Custom { kind, error })) }
 256     }
 257
 258     /// Returns an error representing the last OS error which occurred.
 259     ///
 260     /// This function reads the value of `errno` for the target platform (e.g.
 261     /// `GetLastError` on Windows) and will return a corresponding instance of
 262     /// `Error` for the error code.
 263     ///
 264     /// # Examples
 265     ///
 266     /// ```
 267     /// use std::io::Error;
 268     ///
 269     /// println!("last OS error: {:?}", Error::last_os_error());
 270     /// ```
 271     #[stable(feature = "rust1", since = "1.0.0")]
 272     pub fn last_os_error() -> Error {
 273         Error::from_raw_os_error(sys::os::errno() as i32)
 274     }
 275
 276     /// Creates a new instance of an `Error` from a particular OS error code.
 277     ///
 278     /// # Examples
 279     ///
 280     /// On Linux:
 281     ///
 282     /// ```
 283     /// # if cfg!(target_os = "linux") {
 284     /// use std::io;
 285     ///
 286     /// let error = io::Error::from_raw_os_error(22);
 287     /// assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
 288     /// # }
 289     /// ```
 290     ///
 291     /// On Windows:
 292     ///
 293     /// ```
 294     /// # if cfg!(windows) {
 295     /// use std::io;
 296     ///
 297     /// let error = io::Error::from_raw_os_error(10022);
 298     /// assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
 299     /// # }
 300     /// ```
 301     #[stable(feature = "rust1", since = "1.0.0")]
 302     pub fn from_raw_os_error(code: i32) -> Error {
 303         Error { repr: Repr::Os(code) }
 304     }
 305
 306     /// Returns the OS error that this error represents (if any).
 307     ///
 308     /// If this `Error` was constructed via `last_os_error` or
 309     /// `from_raw_os_error`, then this function will return `Some`, otherwise
 310     /// it will return `None`.
 311     ///
 312     /// # Examples
 313     ///
 314     /// ```
 315     /// use std::io::{Error, ErrorKind};
 316     ///
 317     /// fn print_os_error(err: &Error) {
 318     ///     if let Some(raw_os_err) = err.raw_os_error() {
 319     ///         println!("raw OS error: {:?}", raw_os_err);
 320     ///     } else {
 321     ///         println!("Not an OS error");
 322     ///     }
 323     /// }
 324     ///
 325     /// fn main() {
 326     ///     // Will print "raw OS error: ...".
 327     ///     print_os_error(&Error::last_os_error());
 328     ///     // Will print "Not an OS error".
 329     ///     print_os_error(&Error::new(ErrorKind::Other, "oh no!"));
 330     /// }
 331     /// ```
 332     #[stable(feature = "rust1", since = "1.0.0")]
 333     pub fn raw_os_error(&self) -> Option<i32> {
 334         match self.repr {
 335             Repr::Os(i) => Some(i),
 336             Repr::Custom(..) => None,
 337             Repr::Simple(..) => None,
 338         }
 339     }
 340
 341     /// Returns a reference to the inner error wrapped by this error (if any).
 342     ///
 343     /// If this `Error` was constructed via `new` then this function will
 344     /// return `Some`, otherwise it will return `None`.
 345     ///
 346     /// # Examples
 347     ///
 348     /// ```
 349     /// use std::io::{Error, ErrorKind};
 350     ///
 351     /// fn print_error(err: &Error) {
 352     ///     if let Some(inner_err) = err.get_ref() {
 353     ///         println!("Inner error: {:?}", inner_err);
 354     ///     } else {
 355     ///         println!("No inner error");
 356     ///     }
 357     /// }
 358     ///
 359     /// fn main() {
 360     ///     // Will print "No inner error".
 361     ///     print_error(&Error::last_os_error());
 362     ///     // Will print "Inner error: ...".
 363     ///     print_error(&Error::new(ErrorKind::Other, "oh no!"));
 364     /// }
 365     /// ```
 366     #[stable(feature = "io_error_inner", since = "1.3.0")]
 367     pub fn get_ref(&self) -> Option<&(dyn error::Error + Send + Sync + 'static)> {
 368         match self.repr {
 369             Repr::Os(..) => None,
 370             Repr::Simple(..) => None,
 371             Repr::Custom(ref c) => Some(&*c.error),
 372         }
 373     }
 374
 375     /// Returns a mutable reference to the inner error wrapped by this error
 376     /// (if any).
 377     ///
 378     /// If this `Error` was constructed via `new` then this function will
 379     /// return `Some`, otherwise it will return `None`.
 380     ///
 381     /// # Examples
 382     ///
 383     /// ```
 384     /// use std::io::{Error, ErrorKind};
 385     /// use std::{error, fmt};
 386     /// use std::fmt::Display;
 387     ///
 388     /// #[derive(Debug)]
 389     /// struct MyError {
 390     ///     v: String,
 391     /// }
 392     ///
 393     /// impl MyError {
 394     ///     fn new() -> MyError {
 395     ///         MyError {
 396     ///             v: "oh no!".to_string()
 397     ///         }
 398     ///     }
 399     ///
 400     ///     fn change_message(&mut self, new_message: &str) {
 401     ///         self.v = new_message.to_string();
 402     ///     }
 403     /// }
 404     ///
 405     /// impl error::Error for MyError {
 406     ///     fn description(&self) -> &str { &self.v }
 407     /// }
 408     ///
 409     /// impl Display for MyError {
 410     ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 411     ///         write!(f, "MyError: {}", &self.v)
 412     ///     }
 413     /// }
 414     ///
 415     /// fn change_error(mut err: Error) -> Error {
 416     ///     if let Some(inner_err) = err.get_mut() {
 417     ///         inner_err.downcast_mut::<MyError>().unwrap().change_message("I've been changed!");
 418     ///     }
 419     ///     err
 420     /// }
 421     ///
 422     /// fn print_error(err: &Error) {
 423     ///     if let Some(inner_err) = err.get_ref() {
 424     ///         println!("Inner error: {}", inner_err);
 425     ///     } else {
 426     ///         println!("No inner error");
 427     ///     }
 428     /// }
 429     ///
 430     /// fn main() {
 431     ///     // Will print "No inner error".
 432     ///     print_error(&change_error(Error::last_os_error()));
 433     ///     // Will print "Inner error: ...".
 434     ///     print_error(&change_error(Error::new(ErrorKind::Other, MyError::new())));
 435     /// }
 436     /// ```
 437     #[stable(feature = "io_error_inner", since = "1.3.0")]
 438     pub fn get_mut(&mut self) -> Option<&mut (dyn error::Error + Send + Sync + 'static)> {
 439         match self.repr {
 440             Repr::Os(..) => None,
 441             Repr::Simple(..) => None,
 442             Repr::Custom(ref mut c) => Some(&mut *c.error),
 443         }
 444     }
 445
 446     /// Consumes the `Error`, returning its inner error (if any).
 447     ///
 448     /// If this `Error` was constructed via `new` then this function will
 449     /// return `Some`, otherwise it will return `None`.
 450     ///
 451     /// # Examples
 452     ///
 453     /// ```
 454     /// use std::io::{Error, ErrorKind};
 455     ///
 456     /// fn print_error(err: Error) {
 457     ///     if let Some(inner_err) = err.into_inner() {
 458     ///         println!("Inner error: {}", inner_err);
 459     ///     } else {
 460     ///         println!("No inner error");
 461     ///     }
 462     /// }
 463     ///
 464     /// fn main() {
 465     ///     // Will print "No inner error".
 466     ///     print_error(Error::last_os_error());
 467     ///     // Will print "Inner error: ...".
 468     ///     print_error(Error::new(ErrorKind::Other, "oh no!"));
 469     /// }
 470     /// ```
 471     #[stable(feature = "io_error_inner", since = "1.3.0")]
 472     pub fn into_inner(self) -> Option<Box<dyn error::Error + Send + Sync>> {
 473         match self.repr {
 474             Repr::Os(..) => None,
 475             Repr::Simple(..) => None,
 476             Repr::Custom(c) => Some(c.error),
 477         }
 478     }
 479
 480     /// Returns the corresponding `ErrorKind` for this error.
 481     ///
 482     /// # Examples
 483     ///
 484     /// ```
 485     /// use std::io::{Error, ErrorKind};
 486     ///
 487     /// fn print_error(err: Error) {
 488     ///     println!("{:?}", err.kind());
 489     /// }
 490     ///
 491     /// fn main() {
 492     ///     // Will print "No inner error".
 493     ///     print_error(Error::last_os_error());
 494     ///     // Will print "Inner error: ...".
 495     ///     print_error(Error::new(ErrorKind::AddrInUse, "oh no!"));
 496     /// }
 497     /// ```
 498     #[stable(feature = "rust1", since = "1.0.0")]
 499     pub fn kind(&self) -> ErrorKind {
 500         match self.repr {
 501             Repr::Os(code) => sys::decode_error_kind(code),
 502             Repr::Custom(ref c) => c.kind,
 503             Repr::Simple(kind) => kind,
 504         }
 505     }
 506 }
 507
 508 impl fmt::Debug for Repr {
 509     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
 510         match *self {
 511             Repr::Os(code) => fmt
 512                 .debug_struct("Os")
 513                 .field("code", &code)
 514                 .field("kind", &sys::decode_error_kind(code))
 515                 .field("message", &sys::os::error_string(code))
 516                 .finish(),
 517             Repr::Custom(ref c) => fmt::Debug::fmt(&c, fmt),
 518             Repr::Simple(kind) => fmt.debug_tuple("Kind").field(&kind).finish(),
 519         }
 520     }
 521 }
 522
 523 #[stable(feature = "rust1", since = "1.0.0")]
 524 impl fmt::Display for Error {
 525     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
 526         match self.repr {
 527             Repr::Os(code) => {
 528                 let detail = sys::os::error_string(code);
 529                 write!(fmt, "{} (os error {})", detail, code)
 530             }
 531             Repr::Custom(ref c) => c.error.fmt(fmt),
 532             Repr::Simple(kind) => write!(fmt, "{}", kind.as_str()),
 533         }
 534     }
 535 }
 536
 537 #[stable(feature = "rust1", since = "1.0.0")]
 538 impl error::Error for Error {
 539     fn description(&self) -> &str {
 540         match self.repr {
 541             Repr::Os(..) | Repr::Simple(..) => self.kind().as_str(),
 542             Repr::Custom(ref c) => c.error.description(),
 543         }
 544     }
 545
 546     #[allow(deprecated)]
 547     fn cause(&self) -> Option<&dyn error::Error> {
 548         match self.repr {
 549             Repr::Os(..) => None,
 550             Repr::Simple(..) => None,
 551             Repr::Custom(ref c) => c.error.cause(),
 552         }
 553     }
 554
 555     fn source(&self) -> Option<&(dyn error::Error + 'static)> {
 556         match self.repr {
 557             Repr::Os(..) => None,
 558             Repr::Simple(..) => None,
 559             Repr::Custom(ref c) => c.error.source(),
 560         }
 561     }
 562 }
 563
 564 fn _assert_error_is_sync_send() {
 565     fn _is_sync_send<T: Sync + Send>() {}
 566     _is_sync_send::<Error>();
 567 }
 568
 569 #[cfg(test)]
 570 mod test {
 571     use super::{Custom, Error, ErrorKind, Repr};
 572     use crate::error;
 573     use crate::fmt;
 574     use crate::sys::decode_error_kind;
 575     use crate::sys::os::error_string;
 576
 577     #[test]
 578     fn test_debug_error() {
 579         let code = 6;
 580         let msg = error_string(code);
 581         let kind = decode_error_kind(code);
 582         let err = Error {
 583             repr: Repr::Custom(box Custom {
 584                 kind: ErrorKind::InvalidInput,
 585                 error: box Error { repr: super::Repr::Os(code) },
 586             }),
 587         };
 588         let expected = format!(
 589             "Custom {{ \
 590              kind: InvalidInput, \
 591              error: Os {{ \
 592              code: {:?}, \
 593              kind: {:?}, \
 594              message: {:?} \
 595              }} \
 596              }}",
 597             code, kind, msg
 598         );
 599         assert_eq!(format!("{:?}", err), expected);
 600     }
 601
 602     #[test]
 603     fn test_downcasting() {
 604         #[derive(Debug)]
 605         struct TestError;
 606
 607         impl fmt::Display for TestError {
 608             fn fmt(&self, _: &mut fmt::Formatter<'_>) -> fmt::Result {
 609                 Ok(())
 610             }
 611         }
 612
 613         impl error::Error for TestError {
 614             fn description(&self) -> &str {
 615                 "asdf"
 616             }
 617         }
 618
 619         // we have to call all of these UFCS style right now since method
 620         // resolution won't implicitly drop the Send+Sync bounds
 621         let mut err = Error::new(ErrorKind::Other, TestError);
 622         assert!(err.get_ref().unwrap().is::<TestError>());
 623         assert_eq!("asdf", err.get_ref().unwrap().description());
 624         assert!(err.get_mut().unwrap().is::<TestError>());
 625         let extracted = err.into_inner().unwrap();
 626         extracted.downcast::<TestError>().unwrap();
 627     }
 628 }