core/str/
error.rs

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

core/str/
error.rs
