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}