core/str/
error.rs

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

core/str/
error.rs
