[][src]Crate circbuf

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 (e.g. read and write) as well as vector IO (readv and writev).

Feature flags

  • bytes: Adds a dependency on the bytes crate and implements the Buf and BufMut traits from that crate.


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 and writev 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) => {
                    // update read cursor past '|' and reset num_bytes since last '|'
                    buf.advance_read(i + 1);
                    num_bytes = 0;
                    num_messages += 1;

                    let response = format!("Message {} contained {} bytes\n", num_messages, i - 1); // don't inclue '|' in num_bytes
                    match stream.write(&response.as_bytes()) {
                        Ok(n) => {
                            println!("wrote {} bytes to the client", n);
                        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),



Circular Buffer



Circular Buffer Error



Default size of the circular buffer is 1 page


Double the size of the buffer by default when growing it