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| 1 | +//! Ways to create a `str` from bytes slice. |
| 2 | +
|
| 3 | +use crate::mem; |
| 4 | + |
| 5 | +use super::validations::run_utf8_validation; |
| 6 | +use super::Utf8Error; |
| 7 | + |
| 8 | +/// Converts a slice of bytes to a string slice. |
| 9 | +/// |
| 10 | +/// A string slice ([`&str`]) is made of bytes ([`u8`]), and a byte slice |
| 11 | +/// ([`&[u8]`][byteslice]) is made of bytes, so this function converts between |
| 12 | +/// the two. Not all byte slices are valid string slices, however: [`&str`] requires |
| 13 | +/// that it is valid UTF-8. `from_utf8()` checks to ensure that the bytes are valid |
| 14 | +/// UTF-8, and then does the conversion. |
| 15 | +/// |
| 16 | +/// [`&str`]: str |
| 17 | +/// [byteslice]: ../../std/primitive.slice.html |
| 18 | +/// |
| 19 | +/// If you are sure that the byte slice is valid UTF-8, and you don't want to |
| 20 | +/// incur the overhead of the validity check, there is an unsafe version of |
| 21 | +/// this function, [`from_utf8_unchecked`], which has the same |
| 22 | +/// behavior but skips the check. |
| 23 | +/// |
| 24 | +/// If you need a `String` instead of a `&str`, consider |
| 25 | +/// [`String::from_utf8`][string]. |
| 26 | +/// |
| 27 | +/// [string]: ../../std/string/struct.String.html#method.from_utf8 |
| 28 | +/// |
| 29 | +/// Because you can stack-allocate a `[u8; N]`, and you can take a |
| 30 | +/// [`&[u8]`][byteslice] of it, this function is one way to have a |
| 31 | +/// stack-allocated string. There is an example of this in the |
| 32 | +/// examples section below. |
| 33 | +/// |
| 34 | +/// [byteslice]: ../../std/primitive.slice.html |
| 35 | +/// |
| 36 | +/// # Errors |
| 37 | +/// |
| 38 | +/// Returns `Err` if the slice is not UTF-8 with a description as to why the |
| 39 | +/// provided slice is not UTF-8. |
| 40 | +/// |
| 41 | +/// # Examples |
| 42 | +/// |
| 43 | +/// Basic usage: |
| 44 | +/// |
| 45 | +/// ``` |
| 46 | +/// use std::str; |
| 47 | +/// |
| 48 | +/// // some bytes, in a vector |
| 49 | +/// let sparkle_heart = vec![240, 159, 146, 150]; |
| 50 | +/// |
| 51 | +/// // We know these bytes are valid, so just use `unwrap()`. |
| 52 | +/// let sparkle_heart = str::from_utf8(&sparkle_heart).unwrap(); |
| 53 | +/// |
| 54 | +/// assert_eq!("💖", sparkle_heart); |
| 55 | +/// ``` |
| 56 | +/// |
| 57 | +/// Incorrect bytes: |
| 58 | +/// |
| 59 | +/// ``` |
| 60 | +/// use std::str; |
| 61 | +/// |
| 62 | +/// // some invalid bytes, in a vector |
| 63 | +/// let sparkle_heart = vec![0, 159, 146, 150]; |
| 64 | +/// |
| 65 | +/// assert!(str::from_utf8(&sparkle_heart).is_err()); |
| 66 | +/// ``` |
| 67 | +/// |
| 68 | +/// See the docs for [`Utf8Error`] for more details on the kinds of |
| 69 | +/// errors that can be returned. |
| 70 | +/// |
| 71 | +/// A "stack allocated string": |
| 72 | +/// |
| 73 | +/// ``` |
| 74 | +/// use std::str; |
| 75 | +/// |
| 76 | +/// // some bytes, in a stack-allocated array |
| 77 | +/// let sparkle_heart = [240, 159, 146, 150]; |
| 78 | +/// |
| 79 | +/// // We know these bytes are valid, so just use `unwrap()`. |
| 80 | +/// let sparkle_heart = str::from_utf8(&sparkle_heart).unwrap(); |
| 81 | +/// |
| 82 | +/// assert_eq!("💖", sparkle_heart); |
| 83 | +/// ``` |
| 84 | +#[stable(feature = "rust1", since = "1.0.0")] |
| 85 | +pub fn from_utf8(v: &[u8]) -> Result<&str, Utf8Error> { |
| 86 | + run_utf8_validation(v)?; |
| 87 | + // SAFETY: Just ran validation. |
| 88 | + Ok(unsafe { from_utf8_unchecked(v) }) |
| 89 | +} |
| 90 | + |
| 91 | +/// Converts a mutable slice of bytes to a mutable string slice. |
| 92 | +/// |
| 93 | +/// # Examples |
| 94 | +/// |
| 95 | +/// Basic usage: |
| 96 | +/// |
| 97 | +/// ``` |
| 98 | +/// use std::str; |
| 99 | +/// |
| 100 | +/// // "Hello, Rust!" as a mutable vector |
| 101 | +/// let mut hellorust = vec![72, 101, 108, 108, 111, 44, 32, 82, 117, 115, 116, 33]; |
| 102 | +/// |
| 103 | +/// // As we know these bytes are valid, we can use `unwrap()` |
| 104 | +/// let outstr = str::from_utf8_mut(&mut hellorust).unwrap(); |
| 105 | +/// |
| 106 | +/// assert_eq!("Hello, Rust!", outstr); |
| 107 | +/// ``` |
| 108 | +/// |
| 109 | +/// Incorrect bytes: |
| 110 | +/// |
| 111 | +/// ``` |
| 112 | +/// use std::str; |
| 113 | +/// |
| 114 | +/// // Some invalid bytes in a mutable vector |
| 115 | +/// let mut invalid = vec![128, 223]; |
| 116 | +/// |
| 117 | +/// assert!(str::from_utf8_mut(&mut invalid).is_err()); |
| 118 | +/// ``` |
| 119 | +/// See the docs for [`Utf8Error`] for more details on the kinds of |
| 120 | +/// errors that can be returned. |
| 121 | +#[stable(feature = "str_mut_extras", since = "1.20.0")] |
| 122 | +pub fn from_utf8_mut(v: &mut [u8]) -> Result<&mut str, Utf8Error> { |
| 123 | + run_utf8_validation(v)?; |
| 124 | + // SAFETY: Just ran validation. |
| 125 | + Ok(unsafe { from_utf8_unchecked_mut(v) }) |
| 126 | +} |
| 127 | + |
| 128 | +/// Converts a slice of bytes to a string slice without checking |
| 129 | +/// that the string contains valid UTF-8. |
| 130 | +/// |
| 131 | +/// See the safe version, [`from_utf8`], for more information. |
| 132 | +/// |
| 133 | +/// # Safety |
| 134 | +/// |
| 135 | +/// This function is unsafe because it does not check that the bytes passed to |
| 136 | +/// it are valid UTF-8. If this constraint is violated, undefined behavior |
| 137 | +/// results, as the rest of Rust assumes that [`&str`]s are valid UTF-8. |
| 138 | +/// |
| 139 | +/// [`&str`]: str |
| 140 | +/// |
| 141 | +/// # Examples |
| 142 | +/// |
| 143 | +/// Basic usage: |
| 144 | +/// |
| 145 | +/// ``` |
| 146 | +/// use std::str; |
| 147 | +/// |
| 148 | +/// // some bytes, in a vector |
| 149 | +/// let sparkle_heart = vec![240, 159, 146, 150]; |
| 150 | +/// |
| 151 | +/// let sparkle_heart = unsafe { |
| 152 | +/// str::from_utf8_unchecked(&sparkle_heart) |
| 153 | +/// }; |
| 154 | +/// |
| 155 | +/// assert_eq!("💖", sparkle_heart); |
| 156 | +/// ``` |
| 157 | +#[inline] |
| 158 | +#[stable(feature = "rust1", since = "1.0.0")] |
| 159 | +#[rustc_const_unstable(feature = "const_str_from_utf8_unchecked", issue = "75196")] |
| 160 | +#[allow_internal_unstable(const_fn_transmute)] |
| 161 | +pub const unsafe fn from_utf8_unchecked(v: &[u8]) -> &str { |
| 162 | + // SAFETY: the caller must guarantee that the bytes `v` are valid UTF-8. |
| 163 | + // Also relies on `&str` and `&[u8]` having the same layout. |
| 164 | + unsafe { mem::transmute(v) } |
| 165 | +} |
| 166 | + |
| 167 | +/// Converts a slice of bytes to a string slice without checking |
| 168 | +/// that the string contains valid UTF-8; mutable version. |
| 169 | +/// |
| 170 | +/// See the immutable version, [`from_utf8_unchecked()`] for more information. |
| 171 | +/// |
| 172 | +/// # Examples |
| 173 | +/// |
| 174 | +/// Basic usage: |
| 175 | +/// |
| 176 | +/// ``` |
| 177 | +/// use std::str; |
| 178 | +/// |
| 179 | +/// let mut heart = vec![240, 159, 146, 150]; |
| 180 | +/// let heart = unsafe { str::from_utf8_unchecked_mut(&mut heart) }; |
| 181 | +/// |
| 182 | +/// assert_eq!("💖", heart); |
| 183 | +/// ``` |
| 184 | +#[inline] |
| 185 | +#[stable(feature = "str_mut_extras", since = "1.20.0")] |
| 186 | +pub unsafe fn from_utf8_unchecked_mut(v: &mut [u8]) -> &mut str { |
| 187 | + // SAFETY: the caller must guarantee that the bytes `v` |
| 188 | + // are valid UTF-8, thus the cast to `*mut str` is safe. |
| 189 | + // Also, the pointer dereference is safe because that pointer |
| 190 | + // comes from a reference which is guaranteed to be valid for writes. |
| 191 | + unsafe { &mut *(v as *mut [u8] as *mut str) } |
| 192 | +} |
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