1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
#[cfg(test)]
mod tests;

#[cfg(all(target_pointer_width = "64", not(target_os = "uefi")))]
mod repr_bitpacked;
#[cfg(all(target_pointer_width = "64", not(target_os = "uefi")))]
use repr_bitpacked::Repr;

#[cfg(any(not(target_pointer_width = "64"), target_os = "uefi"))]
mod repr_unpacked;
#[cfg(any(not(target_pointer_width = "64"), target_os = "uefi"))]
use repr_unpacked::Repr;

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

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

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

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

/// Common errors constants for use in std
#[allow(dead_code)]
impl Error {
    pub(crate) const INVALID_UTF8: Self =
        const_io_error!(ErrorKind::InvalidData, "stream did not contain valid UTF-8");

    pub(crate) const READ_EXACT_EOF: Self =
        const_io_error!(ErrorKind::UnexpectedEof, "failed to fill whole buffer");

    pub(crate) const UNKNOWN_THREAD_COUNT: Self = const_io_error!(
        ErrorKind::NotFound,
        "The number of hardware threads is not known for the target platform"
    );

    pub(crate) const UNSUPPORTED_PLATFORM: Self =
        const_io_error!(ErrorKind::Unsupported, "operation not supported on this platform");

    pub(crate) const WRITE_ALL_EOF: Self =
        const_io_error!(ErrorKind::WriteZero, "failed to write whole buffer");

    pub(crate) const ZERO_TIMEOUT: Self =
        const_io_error!(ErrorKind::InvalidInput, "cannot set a 0 duration timeout");
}

#[stable(feature = "rust1", since = "1.0.0")]
impl From<alloc::ffi::NulError> for Error {
    /// Converts a [`alloc::ffi::NulError`] into a [`Error`].
    fn from(_: alloc::ffi::NulError) -> Error {
        const_io_error!(ErrorKind::InvalidInput, "data provided contains a nul byte")
    }
}

#[stable(feature = "io_error_from_try_reserve", since = "1.78.0")]
impl From<alloc::collections::TryReserveError> for Error {
    /// Converts `TryReserveError` to an error with [`ErrorKind::OutOfMemory`].
    ///
    /// `TryReserveError` won't be available as the error `source()`,
    /// but this may change in the future.
    fn from(_: alloc::collections::TryReserveError) -> Error {
        // ErrorData::Custom allocates, which isn't great for handling OOM errors.
        ErrorKind::OutOfMemory.into()
    }
}

// Only derive debug in tests, to make sure it
// doesn't accidentally get printed.
#[cfg_attr(test, derive(Debug))]
enum ErrorData<C> {
    Os(RawOsError),
    Simple(ErrorKind),
    SimpleMessage(&'static SimpleMessage),
    Custom(C),
}

/// The type of raw OS error codes returned by [`Error::raw_os_error`].
///
/// This is an [`i32`] on all currently supported platforms, but platforms
/// added in the future (such as UEFI) may use a different primitive type like
/// [`usize`]. Use `as`or [`into`] conversions where applicable to ensure maximum
/// portability.
///
/// [`into`]: Into::into
#[unstable(feature = "raw_os_error_ty", issue = "107792")]
pub type RawOsError = sys::RawOsError;

// `#[repr(align(4))]` is probably redundant, it should have that value or
// higher already. We include it just because repr_bitpacked.rs's encoding
// requires an alignment >= 4 (note that `#[repr(align)]` will not reduce the
// alignment required by the struct, only increase it).
//
// If we add more variants to ErrorData, this can be increased to 8, but it
// should probably be behind `#[cfg_attr(target_pointer_width = "64", ...)]` or
// whatever cfg we're using to enable the `repr_bitpacked` code, since only the
// that version needs the alignment, and 8 is higher than the alignment we'll
// have on 32 bit platforms.
//
// (For the sake of being explicit: the alignment requirement here only matters
// if `error/repr_bitpacked.rs` is in use — for the unpacked repr it doesn't
// matter at all)
#[repr(align(4))]
#[derive(Debug)]
pub(crate) struct SimpleMessage {
    kind: ErrorKind,
    message: &'static str,
}

impl SimpleMessage {
    pub(crate) const fn new(kind: ErrorKind, message: &'static str) -> Self {
        Self { kind, message }
    }
}

/// Create and return an `io::Error` for a given `ErrorKind` and constant
/// message. This doesn't allocate.
pub(crate) macro const_io_error($kind:expr, $message:expr $(,)?) {
    $crate::io::error::Error::from_static_message({
        const MESSAGE_DATA: $crate::io::error::SimpleMessage =
            $crate::io::error::SimpleMessage::new($kind, $message);
        &MESSAGE_DATA
    })
}

// As with `SimpleMessage`: `#[repr(align(4))]` here is just because
// repr_bitpacked's encoding requires it. In practice it almost certainly be
// already be this high or higher.
#[derive(Debug)]
#[repr(align(4))]
struct Custom {
    kind: ErrorKind,
    error: Box<dyn error::Error + Send + Sync>,
}

/// A list specifying general categories of I/O error.
///
/// This list is intended to grow over time and it is not recommended to
/// exhaustively match against it.
///
/// It is used with the [`io::Error`] type.
///
/// [`io::Error`]: Error
///
/// # Handling errors and matching on `ErrorKind`
///
/// In application code, use `match` for the `ErrorKind` values you are
/// expecting; use `_` to match "all other errors".
///
/// In comprehensive and thorough tests that want to verify that a test doesn't
/// return any known incorrect error kind, you may want to cut-and-paste the
/// current full list of errors from here into your test code, and then match
/// `_` as the correct case. This seems counterintuitive, but it will make your
/// tests more robust. In particular, if you want to verify that your code does
/// produce an unrecognized error kind, the robust solution is to check for all
/// the recognized error kinds and fail in those cases.
#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
#[stable(feature = "rust1", since = "1.0.0")]
#[allow(deprecated)]
#[non_exhaustive]
pub enum ErrorKind {
    /// An entity was not found, often a file.
    #[stable(feature = "rust1", since = "1.0.0")]
    NotFound,
    /// The operation lacked the necessary privileges to complete.
    #[stable(feature = "rust1", since = "1.0.0")]
    PermissionDenied,
    /// The connection was refused by the remote server.
    #[stable(feature = "rust1", since = "1.0.0")]
    ConnectionRefused,
    /// The connection was reset by the remote server.
    #[stable(feature = "rust1", since = "1.0.0")]
    ConnectionReset,
    /// The remote host is not reachable.
    #[unstable(feature = "io_error_more", issue = "86442")]
    HostUnreachable,
    /// The network containing the remote host is not reachable.
    #[unstable(feature = "io_error_more", issue = "86442")]
    NetworkUnreachable,
    /// The connection was aborted (terminated) by the remote server.
    #[stable(feature = "rust1", since = "1.0.0")]
    ConnectionAborted,
    /// The network operation failed because it was not connected yet.
    #[stable(feature = "rust1", since = "1.0.0")]
    NotConnected,
    /// A socket address could not be bound because the address is already in
    /// use elsewhere.
    #[stable(feature = "rust1", since = "1.0.0")]
    AddrInUse,
    /// A nonexistent interface was requested or the requested address was not
    /// local.
    #[stable(feature = "rust1", since = "1.0.0")]
    AddrNotAvailable,
    /// The system's networking is down.
    #[unstable(feature = "io_error_more", issue = "86442")]
    NetworkDown,
    /// The operation failed because a pipe was closed.
    #[stable(feature = "rust1", since = "1.0.0")]
    BrokenPipe,
    /// An entity already exists, often a file.
    #[stable(feature = "rust1", since = "1.0.0")]
    AlreadyExists,
    /// The operation needs to block to complete, but the blocking operation was
    /// requested to not occur.
    #[stable(feature = "rust1", since = "1.0.0")]
    WouldBlock,
    /// A filesystem object is, unexpectedly, not a directory.
    ///
    /// For example, a filesystem path was specified where one of the intermediate directory
    /// components was, in fact, a plain file.
    #[unstable(feature = "io_error_more", issue = "86442")]
    NotADirectory,
    /// The filesystem object is, unexpectedly, a directory.
    ///
    /// A directory was specified when a non-directory was expected.
    #[unstable(feature = "io_error_more", issue = "86442")]
    IsADirectory,
    /// A non-empty directory was specified where an empty directory was expected.
    #[unstable(feature = "io_error_more", issue = "86442")]
    DirectoryNotEmpty,
    /// The filesystem or storage medium is read-only, but a write operation was attempted.
    #[unstable(feature = "io_error_more", issue = "86442")]
    ReadOnlyFilesystem,
    /// Loop in the filesystem or IO subsystem; often, too many levels of symbolic links.
    ///
    /// There was a loop (or excessively long chain) resolving a filesystem object
    /// or file IO object.
    ///
    /// On Unix this is usually the result of a symbolic link loop; or, of exceeding the
    /// system-specific limit on the depth of symlink traversal.
    #[unstable(feature = "io_error_more", issue = "86442")]
    FilesystemLoop,
    /// Stale network file handle.
    ///
    /// With some network filesystems, notably NFS, an open file (or directory) can be invalidated
    /// by problems with the network or server.
    #[unstable(feature = "io_error_more", issue = "86442")]
    StaleNetworkFileHandle,
    /// A parameter was incorrect.
    #[stable(feature = "rust1", since = "1.0.0")]
    InvalidInput,
    /// Data not valid for the operation were encountered.
    ///
    /// Unlike [`InvalidInput`], this typically means that the operation
    /// parameters were valid, however the error was caused by malformed
    /// input data.
    ///
    /// For example, a function that reads a file into a string will error with
    /// `InvalidData` if the file's contents are not valid UTF-8.
    ///
    /// [`InvalidInput`]: ErrorKind::InvalidInput
    #[stable(feature = "io_invalid_data", since = "1.2.0")]
    InvalidData,
    /// The I/O operation's timeout expired, causing it to be canceled.
    #[stable(feature = "rust1", since = "1.0.0")]
    TimedOut,
    /// An error returned when an operation could not be completed because a
    /// call to [`write`] returned [`Ok(0)`].
    ///
    /// This typically means that an operation could only succeed if it wrote a
    /// particular number of bytes but only a smaller number of bytes could be
    /// written.
    ///
    /// [`write`]: crate::io::Write::write
    /// [`Ok(0)`]: Ok
    #[stable(feature = "rust1", since = "1.0.0")]
    WriteZero,
    /// The underlying storage (typically, a filesystem) is full.
    ///
    /// This does not include out of quota errors.
    #[unstable(feature = "io_error_more", issue = "86442")]
    StorageFull,
    /// Seek on unseekable file.
    ///
    /// Seeking was attempted on an open file handle which is not suitable for seeking - for
    /// example, on Unix, a named pipe opened with `File::open`.
    #[unstable(feature = "io_error_more", issue = "86442")]
    NotSeekable,
    /// Filesystem quota was exceeded.
    #[unstable(feature = "io_error_more", issue = "86442")]
    FilesystemQuotaExceeded,
    /// File larger than allowed or supported.
    ///
    /// This might arise from a hard limit of the underlying filesystem or file access API, or from
    /// an administratively imposed resource limitation.  Simple disk full, and out of quota, have
    /// their own errors.
    #[unstable(feature = "io_error_more", issue = "86442")]
    FileTooLarge,
    /// Resource is busy.
    #[unstable(feature = "io_error_more", issue = "86442")]
    ResourceBusy,
    /// Executable file is busy.
    ///
    /// An attempt was made to write to a file which is also in use as a running program.  (Not all
    /// operating systems detect this situation.)
    #[unstable(feature = "io_error_more", issue = "86442")]
    ExecutableFileBusy,
    /// Deadlock (avoided).
    ///
    /// A file locking operation would result in deadlock.  This situation is typically detected, if
    /// at all, on a best-effort basis.
    #[unstable(feature = "io_error_more", issue = "86442")]
    Deadlock,
    /// Cross-device or cross-filesystem (hard) link or rename.
    #[unstable(feature = "io_error_more", issue = "86442")]
    CrossesDevices,
    /// Too many (hard) links to the same filesystem object.
    ///
    /// The filesystem does not support making so many hardlinks to the same file.
    #[unstable(feature = "io_error_more", issue = "86442")]
    TooManyLinks,
    /// A filename was invalid.
    ///
    /// This error can also cause if it exceeded the filename length limit.
    #[unstable(feature = "io_error_more", issue = "86442")]
    InvalidFilename,
    /// Program argument list too long.
    ///
    /// When trying to run an external program, a system or process limit on the size of the
    /// arguments would have been exceeded.
    #[unstable(feature = "io_error_more", issue = "86442")]
    ArgumentListTooLong,
    /// This operation was interrupted.
    ///
    /// Interrupted operations can typically be retried.
    #[stable(feature = "rust1", since = "1.0.0")]
    Interrupted,

    /// This operation is unsupported on this platform.
    ///
    /// This means that the operation can never succeed.
    #[stable(feature = "unsupported_error", since = "1.53.0")]
    Unsupported,

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

    /// An operation could not be completed, because it failed
    /// to allocate enough memory.
    #[stable(feature = "out_of_memory_error", since = "1.54.0")]
    OutOfMemory,

    // "Unusual" error kinds which do not correspond simply to (sets
    // of) OS error codes, should be added just above this comment.
    // `Other` and `Uncategorized` should remain at the end:
    //
    /// A custom error that does not fall under any other I/O error kind.
    ///
    /// This can be used to construct your own [`Error`]s that do not match any
    /// [`ErrorKind`].
    ///
    /// This [`ErrorKind`] is not used by the standard library.
    ///
    /// Errors from the standard library that do not fall under any of the I/O
    /// error kinds cannot be `match`ed on, and will only match a wildcard (`_`) pattern.
    /// New [`ErrorKind`]s might be added in the future for some of those.
    #[stable(feature = "rust1", since = "1.0.0")]
    Other,

    /// Any I/O error from the standard library that's not part of this list.
    ///
    /// Errors that are `Uncategorized` now may move to a different or a new
    /// [`ErrorKind`] variant in the future. It is not recommended to match
    /// an error against `Uncategorized`; use a wildcard match (`_`) instead.
    #[unstable(feature = "io_error_uncategorized", issue = "none")]
    #[doc(hidden)]
    Uncategorized,
}

impl ErrorKind {
    pub(crate) fn as_str(&self) -> &'static str {
        use ErrorKind::*;
        // tidy-alphabetical-start
        match *self {
            AddrInUse => "address in use",
            AddrNotAvailable => "address not available",
            AlreadyExists => "entity already exists",
            ArgumentListTooLong => "argument list too long",
            BrokenPipe => "broken pipe",
            ConnectionAborted => "connection aborted",
            ConnectionRefused => "connection refused",
            ConnectionReset => "connection reset",
            CrossesDevices => "cross-device link or rename",
            Deadlock => "deadlock",
            DirectoryNotEmpty => "directory not empty",
            ExecutableFileBusy => "executable file busy",
            FileTooLarge => "file too large",
            FilesystemLoop => "filesystem loop or indirection limit (e.g. symlink loop)",
            FilesystemQuotaExceeded => "filesystem quota exceeded",
            HostUnreachable => "host unreachable",
            Interrupted => "operation interrupted",
            InvalidData => "invalid data",
            InvalidFilename => "invalid filename",
            InvalidInput => "invalid input parameter",
            IsADirectory => "is a directory",
            NetworkDown => "network down",
            NetworkUnreachable => "network unreachable",
            NotADirectory => "not a directory",
            NotConnected => "not connected",
            NotFound => "entity not found",
            NotSeekable => "seek on unseekable file",
            Other => "other error",
            OutOfMemory => "out of memory",
            PermissionDenied => "permission denied",
            ReadOnlyFilesystem => "read-only filesystem or storage medium",
            ResourceBusy => "resource busy",
            StaleNetworkFileHandle => "stale network file handle",
            StorageFull => "no storage space",
            TimedOut => "timed out",
            TooManyLinks => "too many links",
            Uncategorized => "uncategorized error",
            UnexpectedEof => "unexpected end of file",
            Unsupported => "unsupported",
            WouldBlock => "operation would block",
            WriteZero => "write zero",
        }
        // tidy-alphabetical-end
    }
}

#[stable(feature = "io_errorkind_display", since = "1.60.0")]
impl fmt::Display for ErrorKind {
    /// Shows a human-readable description of the `ErrorKind`.
    ///
    /// This is similar to `impl Display for Error`, but doesn't require first converting to Error.
    ///
    /// # Examples
    /// ```
    /// use std::io::ErrorKind;
    /// assert_eq!("entity not found", ErrorKind::NotFound.to_string());
    /// ```
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt.write_str(self.as_str())
    }
}

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

impl Error {
    /// Creates a new I/O error from a known kind of error as well as an
    /// arbitrary error payload.
    ///
    /// This function is used to generically create I/O errors which do not
    /// originate from the OS itself. The `error` argument is an arbitrary
    /// payload which will be contained in this [`Error`].
    ///
    /// Note that this function allocates memory on the heap.
    /// If no extra payload is required, use the `From` conversion from
    /// `ErrorKind`.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::io::{Error, ErrorKind};
    ///
    /// // errors can be created from strings
    /// let custom_error = Error::new(ErrorKind::Other, "oh no!");
    ///
    /// // errors can also be created from other errors
    /// let custom_error2 = Error::new(ErrorKind::Interrupted, custom_error);
    ///
    /// // creating an error without payload (and without memory allocation)
    /// let eof_error = Error::from(ErrorKind::UnexpectedEof);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[inline(never)]
    pub fn new<E>(kind: ErrorKind, error: E) -> Error
    where
        E: Into<Box<dyn error::Error + Send + Sync>>,
    {
        Self::_new(kind, error.into())
    }

    /// Creates a new I/O error from an arbitrary error payload.
    ///
    /// This function is used to generically create I/O errors which do not
    /// originate from the OS itself. It is a shortcut for [`Error::new`]
    /// with [`ErrorKind::Other`].
    ///
    /// # Examples
    ///
    /// ```
    /// use std::io::Error;
    ///
    /// // errors can be created from strings
    /// let custom_error = Error::other("oh no!");
    ///
    /// // errors can also be created from other errors
    /// let custom_error2 = Error::other(custom_error);
    /// ```
    #[stable(feature = "io_error_other", since = "1.74.0")]
    pub fn other<E>(error: E) -> Error
    where
        E: Into<Box<dyn error::Error + Send + Sync>>,
    {
        Self::_new(ErrorKind::Other, error.into())
    }

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

    /// Creates a new I/O error from a known kind of error as well as a constant
    /// message.
    ///
    /// This function does not allocate.
    ///
    /// You should not use this directly, and instead use the `const_io_error!`
    /// macro: `io::const_io_error!(ErrorKind::Something, "some_message")`.
    ///
    /// This function should maybe change to `from_static_message<const MSG: &'static
    /// str>(kind: ErrorKind)` in the future, when const generics allow that.
    #[inline]
    pub(crate) const fn from_static_message(msg: &'static SimpleMessage) -> Error {
        Self { repr: Repr::new_simple_message(msg) }
    }

    /// Returns an error representing the last OS error which occurred.
    ///
    /// This function reads the value of `errno` for the target platform (e.g.
    /// `GetLastError` on Windows) and will return a corresponding instance of
    /// [`Error`] for the error code.
    ///
    /// This should be called immediately after a call to a platform function,
    /// otherwise the state of the error value is indeterminate. In particular,
    /// other standard library functions may call platform functions that may
    /// (or may not) reset the error value even if they succeed.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::io::Error;
    ///
    /// let os_error = Error::last_os_error();
    /// println!("last OS error: {os_error:?}");
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[doc(alias = "GetLastError")]
    #[doc(alias = "errno")]
    #[must_use]
    #[inline]
    pub fn last_os_error() -> Error {
        Error::from_raw_os_error(sys::os::errno())
    }

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

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

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

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

    /// Consumes the `Error`, returning its inner error (if any).
    ///
    /// If this [`Error`] was constructed via [`new`] then this function will
    /// return [`Some`], otherwise it will return [`None`].
    ///
    /// [`new`]: Error::new
    ///
    /// # Examples
    ///
    /// ```
    /// use std::io::{Error, ErrorKind};
    ///
    /// fn print_error(err: Error) {
    ///     if let Some(inner_err) = err.into_inner() {
    ///         println!("Inner error: {inner_err}");
    ///     } else {
    ///         println!("No inner error");
    ///     }
    /// }
    ///
    /// fn main() {
    ///     // Will print "No inner error".
    ///     print_error(Error::last_os_error());
    ///     // Will print "Inner error: ...".
    ///     print_error(Error::new(ErrorKind::Other, "oh no!"));
    /// }
    /// ```
    #[stable(feature = "io_error_inner", since = "1.3.0")]
    #[must_use = "`self` will be dropped if the result is not used"]
    #[inline]
    pub fn into_inner(self) -> Option<Box<dyn error::Error + Send + Sync>> {
        match self.repr.into_data() {
            ErrorData::Os(..) => None,
            ErrorData::Simple(..) => None,
            ErrorData::SimpleMessage(..) => None,
            ErrorData::Custom(c) => Some(c.error),
        }
    }

    /// Attempt to downcast the custom boxed error to `E`.
    ///
    /// If this [`Error`] contains a custom boxed error,
    /// then it would attempt downcasting on the boxed error,
    /// otherwise it will return [`Err`].
    ///
    /// If the custom boxed error has the same type as `E`, it will return [`Ok`],
    /// otherwise it will also return [`Err`].
    ///
    /// This method is meant to be a convenience routine for calling
    /// `Box<dyn Error + Sync + Send>::downcast` on the custom boxed error, returned by
    /// [`Error::into_inner`].
    ///
    ///
    /// # Examples
    ///
    /// ```
    /// #![feature(io_error_downcast)]
    ///
    /// use std::fmt;
    /// use std::io;
    /// use std::error::Error;
    ///
    /// #[derive(Debug)]
    /// enum E {
    ///     Io(io::Error),
    ///     SomeOtherVariant,
    /// }
    ///
    /// impl fmt::Display for E {
    ///    // ...
    /// #    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
    /// #        todo!()
    /// #    }
    /// }
    /// impl Error for E {}
    ///
    /// impl From<io::Error> for E {
    ///     fn from(err: io::Error) -> E {
    ///         err.downcast::<E>()
    ///             .unwrap_or_else(E::Io)
    ///     }
    /// }
    ///
    /// impl From<E> for io::Error {
    ///     fn from(err: E) -> io::Error {
    ///         match err {
    ///             E::Io(io_error) => io_error,
    ///             e => io::Error::new(io::ErrorKind::Other, e),
    ///         }
    ///     }
    /// }
    ///
    /// # fn main() {
    /// let e = E::SomeOtherVariant;
    /// // Convert it to an io::Error
    /// let io_error = io::Error::from(e);
    /// // Cast it back to the original variant
    /// let e = E::from(io_error);
    /// assert!(matches!(e, E::SomeOtherVariant));
    ///
    /// let io_error = io::Error::from(io::ErrorKind::AlreadyExists);
    /// // Convert it to E
    /// let e = E::from(io_error);
    /// // Cast it back to the original variant
    /// let io_error = io::Error::from(e);
    /// assert_eq!(io_error.kind(), io::ErrorKind::AlreadyExists);
    /// assert!(io_error.get_ref().is_none());
    /// assert!(io_error.raw_os_error().is_none());
    /// # }
    /// ```
    #[unstable(feature = "io_error_downcast", issue = "99262")]
    pub fn downcast<E>(self) -> result::Result<E, Self>
    where
        E: error::Error + Send + Sync + 'static,
    {
        match self.repr.into_data() {
            ErrorData::Custom(b) if b.error.is::<E>() => {
                let res = (*b).error.downcast::<E>();

                // downcast is a really trivial and is marked as inline, so
                // it's likely be inlined here.
                //
                // And the compiler should be able to eliminate the branch
                // that produces `Err` here since b.error.is::<E>()
                // returns true.
                Ok(*res.unwrap())
            }
            repr_data => Err(Self { repr: Repr::new(repr_data) }),
        }
    }

    /// Returns the corresponding [`ErrorKind`] for this error.
    ///
    /// This may be a value set by Rust code constructing custom `io::Error`s,
    /// or if this `io::Error` was sourced from the operating system,
    /// it will be a value inferred from the system's error encoding.
    /// See [`last_os_error`] for more details.
    ///
    /// [`last_os_error`]: Error::last_os_error
    ///
    /// # Examples
    ///
    /// ```
    /// use std::io::{Error, ErrorKind};
    ///
    /// fn print_error(err: Error) {
    ///     println!("{:?}", err.kind());
    /// }
    ///
    /// fn main() {
    ///     // As no error has (visibly) occurred, this may print anything!
    ///     // It likely prints a placeholder for unidentified (non-)errors.
    ///     print_error(Error::last_os_error());
    ///     // Will print "AddrInUse".
    ///     print_error(Error::new(ErrorKind::AddrInUse, "oh no!"));
    /// }
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[must_use]
    #[inline]
    pub fn kind(&self) -> ErrorKind {
        match self.repr.data() {
            ErrorData::Os(code) => sys::decode_error_kind(code),
            ErrorData::Custom(c) => c.kind,
            ErrorData::Simple(kind) => kind,
            ErrorData::SimpleMessage(m) => m.kind,
        }
    }

    #[inline]
    pub(crate) fn is_interrupted(&self) -> bool {
        match self.repr.data() {
            ErrorData::Os(code) => sys::is_interrupted(code),
            ErrorData::Custom(c) => c.kind == ErrorKind::Interrupted,
            ErrorData::Simple(kind) => kind == ErrorKind::Interrupted,
            ErrorData::SimpleMessage(m) => m.kind == ErrorKind::Interrupted,
        }
    }
}

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

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

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

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

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

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