Struct alloc::str::Utf8Error

pub struct Utf8Error { /* private fields */ }

Errors which can occur when attempting to interpret a sequence of u8 as a string.

As such, the from_utf8 family of functions and methods for both Strings and &strs make use of this error, for example.

Examples

This error type’s methods can be used to create functionality similar to String::from_utf8_lossy without allocating heap memory:

fn from_utf8_lossy<F>(mut input: &[u8], mut push: F) where F: FnMut(&str) {
    loop {
        match std::str::from_utf8(input) {
            Ok(valid) => {
                push(valid);
                break
            }
            Err(error) => {
                let (valid, after_valid) = input.split_at(error.valid_up_to());
                unsafe {
                    push(std::str::from_utf8_unchecked(valid))
                }
                push("\u{FFFD}");

                if let Some(invalid_sequence_length) = error.error_len() {
                    input = &after_valid[invalid_sequence_length..]
                } else {
                    break
                }
            }
        }
    }
}

Implementations

impl Utf8Error

pub const fn valid_up_to(&self) -> usize

Returns the index in the given string up to which valid UTF-8 was verified.

It is the maximum index such that from_utf8(&input[..index]) would return Ok(_).

Examples

Basic usage:

use std::str;

// some invalid bytes, in a vector
let sparkle_heart = vec![0, 159, 146, 150];

// std::str::from_utf8 returns a Utf8Error
let error = str::from_utf8(&sparkle_heart).unwrap_err();

// the second byte is invalid here
assert_eq!(1, error.valid_up_to());

pub const fn error_len(&self) -> Option<usize>

Provides more information about the failure:

• None: the end of the input was reached unexpectedly. self.valid_up_to() is 1 to 3 bytes from the end of the input. If a byte stream (such as a file or a network socket) is being decoded incrementally, this could be a valid char whose UTF-8 byte sequence is spanning multiple chunks.

• Some(len): an unexpected byte was encountered. The length provided is that of the invalid byte sequence that starts at the index given by valid_up_to(). Decoding should resume after that sequence (after inserting a U+FFFD REPLACEMENT CHARACTER) in case of lossy decoding.

Trait Implementations

impl Clone for Utf8Error

fn clone(&self) -> Utf8Error

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Utf8Error

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Display for Utf8Error

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Error for Utf8Error

fn description(&self) -> &str

👎Deprecated since 1.42.0: use the Display impl or to_string()

fn source(&self) -> Option<&(dyn Error + 'static)>

The lower-level source of this error, if any.

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting

fn provide(&'a self, demand: &mut Demand<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access #99301)

Provides type based access to context intended for error reports.

impl PartialEq<Utf8Error> for Utf8Error

fn eq(&self, other: &Utf8Error) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for Utf8Error

impl Eq for Utf8Error

impl StructuralEq for Utf8Error

impl StructuralPartialEq for Utf8Error