Crate fixed_buffer

source · [−]
Expand description

crates.io version license: Apache 2.0 unsafe forbidden pipeline status

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 (99%)
  • 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());

Alternatives

Changelog

  • v0.5.0 - Move ReadWriteChain and ReadWriteTake to new read-write-ext crate.
  • v0.4.0
    • From<&[u8]>
    • 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.
Older changelog entries

TO DO

Release Process

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

Structs

FixedBuf

A fixed-length byte buffer. You can write bytes to it and then read them back.

MalformedInputError
NoWritableSpace

Functions

deframe_crlf

Deframes lines that are terminated by b"\r\n". Ignores solitary b'\n'.

deframe_line

Deframes lines that are terminated by either b'\n' or b"\r\n".

escape_ascii

Convert a byte slice into a string. Includes printable ASCII characters as-is. Converts non-printable or non-ASCII characters to strings like “\n” and “\x19”.