core/str/
error.rs

1//! Defines utf8 error type.
2
3use crate::error::Error;
4use 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")]
47pub struct Utf8Error {
48    pub(super) valid_up_to: usize,
49    pub(super) error_len: Option<u8>,
50}
51
52impl 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(const-hack): 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")]
112impl 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")]
127impl 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")]
140pub struct ParseBoolError;
141
142#[stable(feature = "rust1", since = "1.0.0")]
143impl 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")]
150impl Error for ParseBoolError {
151    #[allow(deprecated)]
152    fn description(&self) -> &str {
153        "failed to parse bool"
154    }
155}