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Implement feature string_from_utf8_lossy_owned for lossy conversion from Vec<u8> to String methods #129439

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Sep 15, 2024
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Implement feature string_from_utf8_lossy_owned for lossy conversion from Vec<u8> to String methods #129439

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74 changes: 74 additions & 0 deletions library/alloc/src/string.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -662,6 +662,56 @@ impl String {
Cow::Owned(res)
}

/// Converts a [`Vec<u8>`] to a `String`, substituting invalid UTF-8
/// sequences with replacement characters.
///
/// See [`from_utf8_lossy`] for more details.
///
/// [`from_utf8_lossy`]: String::from_utf8_lossy
///
/// Note that this function does not guarantee reuse of the original `Vec`
/// allocation.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// #![feature(string_from_utf8_lossy_owned)]
/// // some bytes, in a vector
/// let sparkle_heart = vec![240, 159, 146, 150];
///
/// let sparkle_heart = String::from_utf8_lossy_owned(sparkle_heart);
///
/// assert_eq!(String::from("💖"), sparkle_heart);
/// ```
///
/// Incorrect bytes:
///
/// ```
/// #![feature(string_from_utf8_lossy_owned)]
/// // some invalid bytes
/// let input: Vec<u8> = b"Hello \xF0\x90\x80World".into();
/// let output = String::from_utf8_lossy_owned(input);
///
/// assert_eq!(String::from("Hello �World"), output);
/// ```
#[must_use]
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "string_from_utf8_lossy_owned", issue = "129436")]
pub fn from_utf8_lossy_owned(v: Vec<u8>) -> String {
if let Cow::Owned(string) = String::from_utf8_lossy(&v) {
string
} else {
// SAFETY: `String::from_utf8_lossy`'s contract ensures that if
// it returns a `Cow::Borrowed`, it is a valid UTF-8 string.
// Otherwise, it returns a new allocation of an owned `String`, with
// replacement characters for invalid sequences, which is returned
// above.
unsafe { String::from_utf8_unchecked(v) }
}
}

/// Decode a UTF-16–encoded vector `v` into a `String`, returning [`Err`]
/// if `v` contains any invalid data.
///
Expand Down Expand Up @@ -2012,6 +2062,30 @@ impl FromUtf8Error {
&self.bytes[..]
}

/// Converts the bytes into a `String` lossily, substituting invalid UTF-8
/// sequences with replacement characters.
///
/// See [`String::from_utf8_lossy`] for more details on replacement of
/// invalid sequences, and [`String::from_utf8_lossy_owned`] for the
/// `String` function which corresponds to this function.
///
/// # Examples
///
/// ```
/// #![feature(string_from_utf8_lossy_owned)]
/// // some invalid bytes
/// let input: Vec<u8> = b"Hello \xF0\x90\x80World".into();
/// let output = String::from_utf8(input).unwrap_or_else(|e| e.into_utf8_lossy());
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this example isn't great, since it's just String::from_utf8_lossy_owned(input) but with more characters. I can't think of any better one though, so it's fine.

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I agree.

After some thinking, something more illustrative could be matching on the result of String::from_utf8

// some invalid bytes
let input: Vec<u8> = b"Hello \xF0\x90\x80World".into();

let output = match String::from_utf8(input) {
    Ok(s) => s,
    Err(e) => {
        // Log invalid UTF-8 error
        // ...
        
        // Lossily convert the bytes to a `String`
        e.into_utf8_lossy()
    }
};

assert_eq!(String::from("Hello �World"), output);

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that sounds better

///
/// assert_eq!(String::from("Hello �World"), output);
/// ```
#[must_use]
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "string_from_utf8_lossy_owned", issue = "129436")]
pub fn into_utf8_lossy(self) -> String {
String::from_utf8_lossy_owned(self.bytes)
}

/// Returns the bytes that were attempted to convert to a `String`.
///
/// This method is carefully constructed to avoid allocation. It will
Expand Down
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