fixed-buffer

This is a Rust library with fixed-size buffers, useful for network protocol parsers and file parsers.

Features

forbid(unsafe_code)
Depends only on std
Write bytes to the buffer and read them back
Lives on the stack
Does not allocate
Use it to read a stream, search for a delimiter, and save leftover bytes for the next read.
No macros
Good test coverage (100%)
Async support by enabling cargo features async-std-feature, futures-io, smol-feature, or tokio.

Limitations

Not a circular buffer. You can call shift() periodically to move unread bytes to the front of the buffer.

Examples

Read and handle requests from a remote client:

use fixed_buffer::{deframe_line, FixedBuf};
use std::io::Error;
use std::net::TcpStream;

fn handle_conn(mut tcp_stream: TcpStream) -> Result<(), Error> {
    let mut buf: FixedBuf<4096> = FixedBuf::new();
    loop {
        // Read a line
        // and leave leftover bytes in `buf`.
        let line_bytes = match buf.read_frame(
            &mut tcp_stream, deframe_line)? {
                Some(line_bytes) => line_bytes,
                None => return Ok(()),
            };
        let request = Request::parse(line_bytes)?;
        handle_request(request)?;
    }
}

For a complete example, see tests/server.rs.

Read and process records:

use fixed_buffer::FixedBuf;
use std::io::{Error, ErrorKind, Read};
use std::net::TcpStream;

fn try_process_record(b: &[u8]) -> Result<usize, Error> {
    if b.len() < 2 {
        return Ok(0);
    }
    if b.starts_with("ab".as_bytes()) {
        println!("found record");
        Ok(2)
    } else {
        Err(Error::new(ErrorKind::InvalidData, "bad record"))
    }
}

fn read_and_process<R: Read>(mut input: R) -> Result<(), Error> {
    let mut buf: FixedBuf<1024> = FixedBuf::new();
    loop {
        // Read a chunk into the buffer.
        if buf.copy_once_from(&mut input)? == 0 {
            return if buf.len() == 0 {
                // EOF at record boundary
                Ok(())
            } else {
                // EOF in the middle of a record
                Err(Error::from(
                    ErrorKind::UnexpectedEof))
            };
        }
        // Process records in the buffer.
        loop {
            let num_to_consume =
                try_process_record(buf.readable())?;
            if num_to_consume == 0 {
                break;
            }
            buf.try_read_exact(num_to_consume).unwrap();
        }
        // Shift data in the buffer to free up
        // space at the end for writing.
        buf.shift();
    }
}

The From<&[u8; SIZE]> implementation is useful in tests. Example:

use core::convert::From;
assert_eq!(3, FixedBuf::from(b"abc").len());

Cargo Geiger Safety Report


Metric output format: x/y
    x = unsafe code used by the build
    y = total unsafe code found in the crate

Symbols:
    🔒  = No `unsafe` usage found, declares #![forbid(unsafe_code)]
    ❓  = No `unsafe` usage found, missing #![forbid(unsafe_code)]
    ☢️  = `unsafe` usage found

Functions  Expressions  Impls  Traits  Methods  Dependency

0/0        0/0          0/0    0/0     0/0      🔒  fixed-buffer 1.0.1
0/0        0/0          0/0    0/0     0/0      ❓  ├── futures-io 0.3.31
0/28       0/2662       0/116  0/3     0/108    ❓  └── tokio 1.40.0
0/34       0/814        0/14   0/1     0/20     ❓      ├── bytes 1.7.2
0/90       0/596        0/2    0/0     0/69     ❓      ├── libc 0.2.161
0/0        0/191        0/0    0/0     0/2      ❓      ├── pin-project-lite 0.2.14
0/0        0/12         0/0    0/0     0/0      🔒      ├── signal-hook-registry 1.4.2
0/90       0/596        0/2    0/0     0/69     ❓      │   └── libc 0.2.161
0/0        0/0          0/0    0/0     0/0      ❓      └── tokio-macros 2.4.0
0/0        0/15         0/0    0/0     0/3      ❓          ├── proc-macro2 1.0.88
0/0        0/4          0/0    0/0     0/0      ❓          │   └── unicode-ident 1.0.13
0/0        0/0          0/0    0/0     0/0      ❓          ├── quote 1.0.37
0/0        0/15         0/0    0/0     0/3      ❓          │   └── proc-macro2 1.0.88
0/0        0/88         0/3    0/0     0/2      ❓          └── syn 2.0.82
0/0        0/15         0/0    0/0     0/3      ❓              ├── proc-macro2 1.0.88
0/0        0/0          0/0    0/0     0/0      ❓              ├── quote 1.0.37
0/0        0/4          0/0    0/0     0/0      ❓              └── unicode-ident 1.0.13

0/152      0/4382       0/135  0/4     0/204

Alternatives

bytes, lots of unsafe
buf_redux, circular buffer support, updated in 2019
std::io::BufReader
std::io::BufWriter
static-buffer, updated in 2016
block-buffer, for processing fixed-length blocks of data, some unsafe
arrayvec, vector with fixed capacity, some unsafe

Changelog

v1.0.1 2025-05-30 - Clarify docs.
v1.0.0 2024-10-20 - From<&[u8; SIZE]>, FixedBuffer::from(b"x")
v0.5.0 2022-03-21 - Move ReadWriteChain and ReadWriteTake to new read-write-ext crate.
v0.4.0 2022-03-21
- From<[u8; SIZE]>, FixedBuffer::from([0])
- write_bytes to take AsRef<[u8]>
- Rename try_read_exact to read_and_copy_exact.
- Rename try_read_bytes to try_read_exact.
- Remove empty, filled, read_byte, read_bytes, try_parse, and write_str.
- deframe to allow consuming bytes without returning a frame
- write_bytes to write as many bytes as it can, and return new NoWritableSpace error only when it cannot write any bytes. Remove NotEnoughSpaceError. The method now behaves like std::io::Write::write.

v0.3.1 - Implement From<NotEnoughSpaceError> and From<MalformedInputError> for String.
v0.3.0 - Breaking API changes:
- Change type parameter to const buffer size. Example: FixedBuf<1024>.
- Remove new arg.
- Remove capacity.
- Remove Copy impl.
- Change writable return type to &mut [u8].
v0.2.3
- Add read_byte, try_read_byte, try_read_bytes, try_read_exact, try_parse.
- Implement UnwindSafe
v0.2.2 - Add badges to readme
v0.2.1 - Add deframe and mem, needed by AsyncFixedBuf::read_frame.
v0.2.0
- Move tokio support to fixed_buffer_tokio.
- Add copy_once_from, read_block, ReadWriteChain, and ReadWriteTake.
v0.1.7 - Add FixedBuf::escape_ascii.
v0.1.6 - Add filled constructor.
v0.1.5 - Change read_delimited to return Option<&[u8]>, for clean EOF handling.
v0.1.4 - Add clear().
v0.1.3
- Thanks to freax13 for these changes:
  - Support any buffer size. Now you can make FixedBuf<[u8; 42]>.
  - Support any AsRef<[u8]> + AsMut<[u8]> value for internal memory:
    - [u8; N]
    - Box<[u8; N]>
    - &mut [u8]
    - Vec<u8>
- Renamed new_with_mem to new. Use FixedBuf::default() to construct any FixedBuf<T: Default>, which includes arrays of sizes up to 32.
v0.1.2 - Updated documentation.
v0.1.1 - First published version

TO DO

Change links in docs to standard style. Don't link to docs.rs.
Idea: buf.slice(buf.read_frame(&mut reader, deframe_crlf))
Add an frame_copy_iter function. Because of borrowing rules, this function must return non-borrowed (allocated and copied) data.
Set up CI on:
- DONE - Linux x86 64-bit
- macOS
- Windows
- https://crate-ci.github.io/pr/testing.html#travisci
- Linux ARM 64-bit (Raspberry Pi 3 and newer)
- Linux ARM 32-bit (Raspberry Pi 2)
- RISCV & ESP32 firmware?
DONE - Try to make this crate comply with the Rust API Guidelines.
DONE - Find out how to include Readme.md info in the crate's docs.
DONE - Make the repo public
DONE - Set up continuous integration tests and banner.
- https://github.com/actions-rs/example
- https://alican.codes/rust-github-actions/
DONE - Add some documentation tests
- https://doc.rust-lang.org/rustdoc/documentation-tests.html
- https://doc.rust-lang.org/stable/rust-by-example/testing/doc_testing.html
DONE - Set up public repository on Gitlab.com
DONE - Publish to crates.io
DONE - Read through https://crate-ci.github.io/index.html
DONE - Get a code review from an experienced rustacean
DONE - Add and update a changelog
- Update it manually
- https://crate-ci.github.io/release/changelog.html

Release Process

Edit Cargo.toml and bump version number.
Run ../release.sh

License: Apache-2.0