library/core/src/str/error.rs

   1 //! Defines utf8 error type.
   2
   3 use crate::error::Error;
   4 use crate::fmt;
   5
   6 /// Errors which can occur when attempting to interpret a sequence of [`u8`]
   7 /// as a string.
   8 ///
   9 /// As such, the `from_utf8` family of functions and methods for both [`String`]s
  10 /// and [`&str`]s make use of this error, for example.
  11 ///
  12 /// [`String`]: ../../std/string/struct.String.html#method.from_utf8
  13 /// [`&str`]: super::from_utf8
  14 ///
  15 /// # Examples
  16 ///
  17 /// This error type’s methods can be used to create functionality
  18 /// similar to `String::from_utf8_lossy` without allocating heap memory:
  19 ///
  20 /// ```
  21 /// fn from_utf8_lossy<F>(mut input: &[u8], mut push: F) where F: FnMut(&str) {
  22 ///     loop {
  23 ///         match std::str::from_utf8(input) {
  24 ///             Ok(valid) => {
  25 ///                 push(valid);
  26 ///                 break
  27 ///             }
  28 ///             Err(error) => {
  29 ///                 let (valid, after_valid) = input.split_at(error.valid_up_to());
  30 ///                 unsafe {
  31 ///                     push(std::str::from_utf8_unchecked(valid))
  32 ///                 }
  33 ///                 push("\u{FFFD}");
  34 ///
  35 ///                 if let Some(invalid_sequence_length) = error.error_len() {
  36 ///                     input = &after_valid[invalid_sequence_length..]
  37 ///                 } else {
  38 ///                     break
  39 ///                 }
  40 ///             }
  41 ///         }
  42 ///     }
  43 /// }
  44 /// ```
  45 #[derive(Copy, Eq, PartialEq, Clone, Debug)]
  46 #[stable(feature = "rust1", since = "1.0.0")]
  47 pub struct Utf8Error {
  48     pub(super) valid_up_to: usize,
  49     pub(super) error_len: Option<u8>,
  50 }
  51
  52 impl Utf8Error {
  53     /// Returns the index in the given string up to which valid UTF-8 was
  54     /// verified.
  55     ///
  56     /// It is the maximum index such that `from_utf8(&input[..index])`
  57     /// would return `Ok(_)`.
  58     ///
  59     /// # Examples
  60     ///
  61     /// Basic usage:
  62     ///
  63     /// ```
  64     /// use std::str;
  65     ///
  66     /// // some invalid bytes, in a vector
  67     /// let sparkle_heart = vec![0, 159, 146, 150];
  68     ///
  69     /// // std::str::from_utf8 returns a Utf8Error
  70     /// let error = str::from_utf8(&sparkle_heart).unwrap_err();
  71     ///
  72     /// // the second byte is invalid here
  73     /// assert_eq!(1, error.valid_up_to());
  74     /// ```
  75     #[stable(feature = "utf8_error", since = "1.5.0")]
  76     #[rustc_const_stable(feature = "const_str_from_utf8_shared", since = "1.63.0")]
  77     #[must_use]
  78     #[inline]
  79     pub const fn valid_up_to(&self) -> usize {
  80         self.valid_up_to
  81     }
  82
  83     /// Provides more information about the failure:
  84     ///
  85     /// * `None`: the end of the input was reached unexpectedly.
  86     ///   `self.valid_up_to()` is 1 to 3 bytes from the end of the input.
  87     ///   If a byte stream (such as a file or a network socket) is being decoded incrementally,
  88     ///   this could be a valid `char` whose UTF-8 byte sequence is spanning multiple chunks.
  89     ///
  90     /// * `Some(len)`: an unexpected byte was encountered.
  91     ///   The length provided is that of the invalid byte sequence
  92     ///   that starts at the index given by `valid_up_to()`.
  93     ///   Decoding should resume after that sequence
  94     ///   (after inserting a [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD]) in case of
  95     ///   lossy decoding.
  96     ///
  97     /// [U+FFFD]: ../../std/char/constant.REPLACEMENT_CHARACTER.html
  98     #[stable(feature = "utf8_error_error_len", since = "1.20.0")]
  99     #[rustc_const_stable(feature = "const_str_from_utf8_shared", since = "1.63.0")]
 100     #[must_use]
 101     #[inline]
 102     pub const fn error_len(&self) -> Option<usize> {
 103         // FIXME: This should become `map` again, once it's `const`
 104         match self.error_len {
 105             Some(len) => Some(len as usize),
 106             None => None,
 107         }
 108     }
 109 }
 110
 111 #[stable(feature = "rust1", since = "1.0.0")]
 112 impl fmt::Display for Utf8Error {
 113     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 114         if let Some(error_len) = self.error_len {
 115             write!(
 116                 f,
 117                 "invalid utf-8 sequence of {} bytes from index {}",
 118                 error_len, self.valid_up_to
 119             )
 120         } else {
 121             write!(f, "incomplete utf-8 byte sequence from index {}", self.valid_up_to)
 122         }
 123     }
 124 }
 125
 126 #[stable(feature = "rust1", since = "1.0.0")]
 127 impl Error for Utf8Error {
 128     #[allow(deprecated)]
 129     fn description(&self) -> &str {
 130         "invalid utf-8: corrupt contents"
 131     }
 132 }
 133
 134 /// An error returned when parsing a `bool` using [`from_str`] fails
 135 ///
 136 /// [`from_str`]: super::FromStr::from_str
 137 #[derive(Debug, Clone, PartialEq, Eq)]
 138 #[non_exhaustive]
 139 #[stable(feature = "rust1", since = "1.0.0")]
 140 pub struct ParseBoolError;
 141
 142 #[stable(feature = "rust1", since = "1.0.0")]
 143 impl fmt::Display for ParseBoolError {
 144     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 145         "provided string was not `true` or `false`".fmt(f)
 146     }
 147 }
 148
 149 #[stable(feature = "rust1", since = "1.0.0")]
 150 impl Error for ParseBoolError {
 151     #[allow(deprecated)]
 152     fn description(&self) -> &str {
 153         "failed to parse bool"
 154     }
 155 }