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
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 asVec<u8>
andPathBuf
. Enabling this feature also enables thealloc
feature.alloc
- Enabled by default. This provides APIs that require allocations via thealloc
crate, such asVec<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 thestd
feature. It is expected that this limitation will be lifted at some point.serde
- Enables implementations of serde traits forBStr
, and alsoBString
whenalloc
is enabled.
Minimum Rust version policy
This crate's minimum supported rustc
version (MSRV) is 1.60.0
.
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
andunicase
.
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 useUtf8Error
above to implement grapheme iteration with the same semantics as whatbstr
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.