bytes2chars 0.2.1

lazy utf-8 decoder iterator with rich errors
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<!-- cargo-rdme start -->

# bytes2chars

lazily decodes utf-8 [`char`][char]s from bytes

provides lazy, fallible analogs to [`str::Chars`][str-chars] ([`Utf8Chars`][utf8-chars]) and [`str::CharIndices`][str-char-indices] ([`Utf8CharIndices`][utf8-char-indices]), as well as a lower-level push-based [`Utf8Decoder`][utf8-decoder]

[char]: https://doc.rust-lang.org/stable/std/primitive.char.html
[str-chars]: https://doc.rust-lang.org/stable/std/str/struct.Chars.html
[str-char-indices]: https://doc.rust-lang.org/stable/std/str/struct.CharIndices.html
[utf8-chars]: https://docs.rs/bytes2chars/latest/bytes2chars/struct.Utf8Chars.html
[utf8-char-indices]: https://docs.rs/bytes2chars/latest/bytes2chars/struct.Utf8CharIndices.html
[utf8-decoder]: https://docs.rs/bytes2chars/latest/bytes2chars/struct.Utf8Decoder.html
## installation

```shell
cargo add bytes2chars
```

## design goals

- rich errors—what went wrong and where
- lazy
- `no-std`
- performance

## quick start

prefer iterators like [`Utf8CharIndices`][utf8-char-indices] or [`Utf8Chars`][utf8-chars] if you have access to a byte iterator. [`Utf8Chars`][utf8-chars] still tracks bytes for error context, so it's purely a convenience wrapper

if you receive bytes in chunks, use the push-based [`Utf8Decoder`][utf8-decoder]

## examples

### iterator api

```rust
let input = b"\xF0\x9F\xA6\x80 rust".iter().copied();

// decode into an iterator of chars and their positions
let indexed = Utf8CharIndices::from(input.clone()).collect::<Result<Vec<_>>>()?;
let expected = vec![(0, '🦀'), (4, ' '), (5, 'r'), (6, 'u'), (7, 's'), (8, 't')];
assert_eq!(indexed, expected);

// convenience wrapper to decode into an iterator of chars
let chars = Utf8Chars::from(input).collect::<Result<String>>()?;
assert_eq!(chars, "🦀 rust");
```


### push based decoder

```rust
let mut decoder = Utf8Decoder::new(0);
assert_eq!(decoder.push(0xF0), None); // accumulating
assert_eq!(decoder.push(0x9F), None);
assert_eq!(decoder.push(0xA6), None);
assert_eq!(decoder.push(0x80), Some(Ok((0, '🦀')))); // complete
assert_eq!(decoder.push(0xF0), None); // start new sequence
let err = Error {
    range: 4..5,
    kind: ErrorKind::UnfinishedSequence,
};
assert_eq!(decoder.finish(), Err(err)); // check for truncated sequence

```

## rfc 3629 conformance

decoding requirements are formally specified in [`spec/utf8.md`][spec],
derived from [RFC 3629](https://datatracker.ietf.org/doc/html/rfc3629). requirements are linked to implementation and tests using [Tracey][tracey]

conformance is validated against the [flenniken utf-8 test suite][utf8tests]

[spec]: ../../spec/utf8.md
[tracey]: https://tracey.bearcove.eu/
[utf8tests]: https://github.com/flenniken/utf8tests



## comparison with alternatives

the unique benefit `bytes2chars` provides is rich error context

see [BENCHMARKS.md](../BENCHMARKS.md) for throughput comparisons. `bytes2chars` still has a ways to go with perf!

### [`std::str::from_utf8`](https://doc.rust-lang.org/std/str/fn.from_utf8.html)

eager and error context provides a range but not a particular cause

### [`utf8-decode`](https://docs.rs/utf8-decode/latest/utf8_decode/index.html)

also lazy. error provides a range but not a particular cause. does not provide a push based decoder

### [`bstr::ByteSlice::chars`](https://docs.rs/utf8-decode/latest/utf8_decode/index.html)

also lazy. swallows errors. does not provide a push based decoder. really fast

<!-- cargo-rdme end -->