#io #cursor #alloc #bare

no-std bare-io

The bare essentials of std::io for use in no_std. Alloc support is optional.

4 releases

0.2.1 Oct 11, 2020
0.2.0 Oct 11, 2020
0.1.1 Oct 10, 2020
0.1.0 Oct 10, 2020
0.0.0 Oct 10, 2020

#63 in No standard library

Used in fastvlq

Apache-2.0 OR MIT



Actions Status Documentation

Ever wanted a Cursor in no_std? Well now you can have it. A 'fork' of Rust's std::io module for no_std environments, with the added benefit of not needing alloc.

The goal of this crate is to provide a stable interface for building I/O trait functionality in no_std environments. The current code corresponds to the most recent stable API of Rust 1.47.0. It is also a goal to achieve a true alloc-less experience, with opt-in alloc support.

This crate works on stable with some limitations in functionality, and nightly without limitations by adding the relevant feature flag.

This crate is no_std by default — you must opt into enabling std if required.


bare-io = "0.2"

Add the crate, use the things you would usually want from std::io, but instead from bare_io.


  • std: enables std pass-throughs for the polyfilled types, but allows accessing the new types
  • alloc: enable aspects of the Read and Write traits that require alloc support (WIP)
  • nightly: enables nightly-only features, such as BufReader and BufWriter with const generic buffers.
  • nightly-std: enables std with nightly-only features

Differences to std::io

  • No std::io::Error, so we have our own copy without any Os error functions
  • IoSlice and the *_vectored family of functions are not implemented.
  • BufReader and BufWriter have a different signature, as they now use a const generic bounded array for the internal buffer. (Requires nightly feature)

Other than items perhaps being entirely missing or certain functions unavailable on some traits, no function signatures have been changed.


  • Using the buffer types currently requires nightly due to the use of const generics.
  • Using copy or the buffer types with std support currently requires nightly due to the initializer API.

Where is it used?

All of the below are works in progress, but should help with demonstrating how to use this crate.

  • fastvlq: variable-length u64 type with no-std reader support with bare-io
  • byteorder_bare-io: personal fork of byteorder crate
  • zstd-rs: personal fork of zstd crate to demonstrate bare-io in a more complex setting
  • comde: do compression/decompression similarly to how one might use serde


Licensed under either of

at your option.

Almost all of the code in this repository is a copy of the Rust language codebase with minor modifications.

For attributions, see https://thanks.rust-lang.org/.