core3-0.1.1 has been yanked.

oxidex core3

~ Made this for my own needs but anyone who wants it can use it.

A no_std replacement for core2. Provides the essential std::io traits (Read, Write, Seek, BufRead, Cursor) for no_std environments.

If you're here because core2 was yanked and you need a drop-in alternative, this is it.

Forked from core2 v0.4.0. Modernized for current Rust:

Removed the error::Error trait polyfill — core::error::Error has been stable since Rust 1.81
Removed nightly-only items (BufReader, BufWriter, LineWriter)
MSRV: 1.81
Single dependency: memchr

Usage

[dependencies]
core3 = { version = "0.1", default-features = false }

use core3::io::{Read, Write, Cursor};

Features

Feature	Default	Description
`std`	✅	Re-exports `std::io` directly
`alloc`	via std	Enables `Vec<u8>` Write impl and allocating Read methods

For no_std without alloc:

core3 = { version = "0.1", default-features = false }

For no_std with alloc:

core3 = { version = "0.1", default-features = false, features = ["alloc"] }

API

Traits: Read, Write, Seek, BufRead

Structs: Cursor, Bytes, Chain, Take, Empty, Repeat, Sink

Enums: SeekFrom, ErrorKind

Types: Error, Result

Free functions: copy, empty, repeat, sink

Utilities

These mirror their std::io equivalents and work in no_std:

Function	Needs `alloc`	Description
`copy(reader, writer)`	no	Stream all bytes from a reader into a writer
`empty()`	no	Returns a reader that is always at EOF
`sink()`	no	Returns a writer that discards all data
`repeat(byte)`	no	Returns a reader that endlessly yields one byte

Additional trait methods (beyond core2)

Method	Needs `alloc`	Description
`Read::read_to_string()`	yes	Read all bytes into a `String`, errors on invalid UTF-8
`BufRead::read_until(byte, buf)`	yes	Read until a delimiter byte or EOF
`BufRead::read_line(buf)`	yes	Read until newline into a `String`

Migrating from core2

`Initializer` is deprecated

The Initializer type and Read::initializer() method from core2 are preserved but deprecated. These mirrored an unstable std API (#![feature(read_initializer)]) that was never stabilized. Zero-initialize buffers before calling read() instead.

Replace the dependency:

# Before
core2 = { version = "0.4", default-features = false }
# After
core3 = { version = "0.1", default-features = false }

Then update imports:

// Before
use core2::io::{Read, Write};

// After
use core3::io::{Read, Write};

Why does this exist?

In April 2026, the all versions of core2 were yanked. Since core::error::Error was stabilized in Rust 1.81 (September 2024), the error polyfill is no longer needed — but the I/O traits (Read, Write, Seek, BufRead, Cursor) still have no equivalent in core.

This crate extracts just the I/O components that the ecosystem still needs.

Alternatives

If core3 isn't the right fit, consider no-std-io2, a maintained fork of core2.

License

Apache-2.0 OR MIT (same as the original core2)

core3 0.1.1