#buffer #bytes #circular #ring


A growable circular buffer for working with bytes

6 releases

0.2.0 Jun 29, 2020
0.1.4 Mar 26, 2018
0.1.3 Nov 13, 2016

#30 in Memory management

28 downloads per month

MIT license

752 lines


Build Status codecov crates.io docs.rs License


An implementation of a growable circular buffer of bytes. The CircBuf struct manages a buffer of bytes allocated on the heap. The buffer can be grown when needed and can return slices into its internal buffer that can be used for both normal IO (read and write) as well as vector IO (readv and writev).

bytes support

If the bytes feature flag is enabled, then the bytes crate will be added as a dependency and the Buf and BufMut traits implemented for CircBuf. The optional vectored read/write functions are implemented, allowing you to use the CircBuf for efficient vectored IO operations with libraries such as tokio. See for example the read_buf and write_buf methods, which can accept a CircBuf when the bytes feature flag is enabled.


Below is a simple example of a server which makes use of a CircBuf to read messages from a client. It uses the vecio crate to call readv on the socket. Messages are seperated by a vertical bar | and the server returns to the client the number of bytes in each message it receives.

extern crate vecio;
extern crate circbuf;

use std::thread;
use std::net::{TcpListener, TcpStream};
use std::io::Write;
use vecio::Rawv;
use circbuf::CircBuf;

fn handle_client(mut stream: TcpStream) {
    let mut buf = CircBuf::new();
    let mut num_messages = 0; // number of messages from the client
    let mut num_bytes = 0; // number of bytes read since last '|'

    loop {
        // grow the buffer if it is less than half full
        if buf.len() > buf.avail() {

        let n;
            n = match stream.readv(&buf.get_avail()) {
                Ok(n) => {
                    if n == 0 {
                        // EOF
                        println!("client closed connection");
                Err(e) => panic!("got an error reading from a connection: {}", e),

        println!("read {} bytes from the client", n);

        // update write cursor

        // parse request from client for messages seperated by '|'
        loop {
            match buf.find_from_index(b'|', num_bytes) {
                Some(i) => {
                    let response = format!("Message {} contained {} bytes\n", num_messages, num_bytes + i - 1); // don't include '|' in number of bytes
                    match stream.write(&response.as_bytes()) {
                        Ok(n) => {
                            println!("wrote {} bytes to the client", n);

                            // update read cursor past '|' and reset num_bytes since last '|'
                            buf.advance_read(i + 1);
                            num_bytes = 0;
                            num_messages += 1;
                        Err(e) => panic!("got an error writing to connection: {}", e),
                None => break,

fn main() {
    let listener = TcpListener::bind("").unwrap();
    for stream in listener.incoming() {
        match stream {
            Ok(stream) => {
                thread::spawn(move || handle_client(stream));
            Err(e) => panic!("got an error accepting connection: {}", e),