library/core/src/str/error.rs

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