bstr

This crate provides extension traits for &[u8] and Vec<u8> that enable their use as byte strings, where byte strings are conventionally UTF-8. This differs from the standard library's String and str types in that they are not required to be valid UTF-8, but may be fully or partially valid UTF-8.

Documentation

https://docs.rs/bstr

When should I use byte strings?

See this part of the documentation for more details: https://docs.rs/bstr/1.*/bstr/#when-should-i-use-byte-strings.

The short story is that byte strings are useful when it is inconvenient or incorrect to require valid UTF-8.

Usage

cargo add bstr

Examples

The following two examples exhibit both the API features of byte strings and the I/O convenience functions provided for reading line-by-line quickly.

This first example simply shows how to efficiently iterate over lines in stdin, and print out lines containing a particular substring:

use std::{error::Error, io::{self, Write}};
use bstr::{ByteSlice, io::BufReadExt};

fn main() -> Result<(), Box<dyn Error>> {
    let stdin = io::stdin();
    let mut stdout = io::BufWriter::new(io::stdout());

    stdin.lock().for_byte_line_with_terminator(|line| {
        if line.contains_str("Dimension") {
            stdout.write_all(line)?;
        }
        Ok(true)
    })?;
    Ok(())
}

This example shows how to count all of the words (Unicode-aware) in stdin, line-by-line:

use std::{error::Error, io};
use bstr::{ByteSlice, io::BufReadExt};

fn main() -> Result<(), Box<dyn Error>> {
    let stdin = io::stdin();
    let mut words = 0;
    stdin.lock().for_byte_line_with_terminator(|line| {
        words += line.words().count();
        Ok(true)
    })?;
    println!("{}", words);
    Ok(())
}

This example shows how to convert a stream on stdin to uppercase without performing UTF-8 validation and amortizing allocation. On standard ASCII text, this is quite a bit faster than what you can (easily) do with standard library APIs. (N.B. Any invalid UTF-8 bytes are passed through unchanged.)

use std::{error::Error, io::{self, Write}};
use bstr::{ByteSlice, io::BufReadExt};

fn main() -> Result<(), Box<dyn Error>> {
    let stdin = io::stdin();
    let mut stdout = io::BufWriter::new(io::stdout());

    let mut upper = vec![];
    stdin.lock().for_byte_line_with_terminator(|line| {
        upper.clear();
        line.to_uppercase_into(&mut upper);
        stdout.write_all(&upper)?;
        Ok(true)
    })?;
    Ok(())
}

This example shows how to extract the first 10 visual characters (as grapheme clusters) from each line, where invalid UTF-8 sequences are generally treated as a single character and are passed through correctly:

use std::{error::Error, io::{self, Write}};
use bstr::{ByteSlice, io::BufReadExt};

fn main() -> Result<(), Box<dyn Error>> {
    let stdin = io::stdin();
    let mut stdout = io::BufWriter::new(io::stdout());

    stdin.lock().for_byte_line_with_terminator(|line| {
        let end = line
            .grapheme_indices()
            .map(|(_, end, _)| end)
            .take(10)
            .last()
            .unwrap_or(line.len());
        stdout.write_all(line[..end].trim_end())?;
        stdout.write_all(b"\n")?;
        Ok(true)
    })?;
    Ok(())
}

Cargo features

This crates comes with a few features that control standard library, serde and Unicode support.

• std - Enabled by default. This provides APIs that require the standard library, such as Vec<u8> and PathBuf. Enabling this feature also enables the alloc feature.
• alloc - Enabled by default. This provides APIs that require allocations via the alloc crate, such as Vec<u8>.
• unicode - Enabled by default. This provides APIs that require sizable Unicode data compiled into the binary. This includes, but is not limited to, grapheme/word/sentence segmenters. When this is disabled, basic support such as UTF-8 decoding is still included. Note that currently, enabling this feature also requires enabling the std feature. It is expected that this limitation will be lifted at some point.
• serde - Enables implementations of serde traits for BStr, and also BString when alloc is enabled.

Minimum Rust version policy

This crate's minimum supported rustc version (MSRV) is 1.65.

In general, this crate will be conservative with respect to the minimum supported version of Rust. MSRV may be bumped in minor version releases.

Future work

Since it is plausible that some of the types in this crate might end up in your public API (e.g., BStr and BString), we will commit to being very conservative with respect to new major version releases. It's difficult to say precisely how conservative, but unless there is a major issue with the 1.0 release, I wouldn't expect a 2.0 release to come out any sooner than some period of years.

A large part of the API surface area was taken from the standard library, so from an API design perspective, a good portion of this crate should be on solid ground. The main differences from the standard library are in how the various substring search routines work. The standard library provides generic infrastructure for supporting different types of searches with a single method, where as this library prefers to define new methods for each type of search and drop the generic infrastructure.

Some probable future considerations for APIs include, but are not limited to:

• Unicode normalization.
• More sophisticated support for dealing with Unicode case, perhaps by combining the use cases supported by caseless and unicase.

Here are some examples that are probably out of scope for this crate:

• Regular expressions.
• Unicode collation.

The exact scope isn't quite clear, but I expect we can iterate on it.

In general, as stated below, this crate brings lots of related APIs together into a single crate while simultaneously attempting to keep the total number of dependencies low. Indeed, every dependency of bstr, except for memchr, is optional.

High level motivation

Strictly speaking, the bstr crate provides very little that can't already be achieved with the standard library Vec<u8>/&[u8] APIs and the ecosystem of library crates. For example:

• The standard library's Utf8Error can be used for incremental lossy decoding of &[u8].
• The unicode-segmentation crate can be used for iterating over graphemes (or words), but is only implemented for &str types. One could use Utf8Error above to implement grapheme iteration with the same semantics as what bstr provides (automatic Unicode replacement codepoint substitution).
• The twoway crate can be used for fast substring searching on &[u8].

So why create bstr? Part of the point of the bstr crate is to provide a uniform API of coupled components instead of relying on users to piece together loosely coupled components from the crate ecosystem. For example, if you wanted to perform a search and replace in a Vec<u8>, then writing the code to do that with the twoway crate is not that difficult, but it's still additional glue code you have to write. This work adds up depending on what you're doing. Consider, for example, trimming and splitting, along with their different variants.

In other words, bstr is partially a way of pushing back against the micro-crate ecosystem that appears to be evolving. Namely, it is a goal of bstr to keep its dependency list lightweight. For example, serde is an optional dependency because there is no feasible alternative. In service of this philosophy, currently, the only required dependency of bstr is memchr.

License

This project is licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)

at your option.

The data in src/unicode/data/ is licensed under the Unicode License Agreement (LICENSE-UNICODE), although this data is only used in tests.