no_std Compatibility

.cargo/config.toml

@@ -0,0 +1,2 @@
+[unstable]
+features = ["host_dep"]

.github/workflows/build.yml

@@ -40,6 +40,21 @@ jobs:
         with:
           command: test
 
+  ensure_no_std:
+    name: Ensure no_std
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: nightly
+          override: true
+      - name: Install thumbv6m-none-eabi
+        run: rustup target add thumbv6m-none-eabi
+      - name: Build thumbv6m-none-eabi
+        run: cargo build --target thumbv6m-none-eabi --no-default-features
+
   coverage:
     name: Code Coverage
     runs-on: ubuntu-latest

Cargo.toml

@@ -8,12 +8,16 @@ readme = "README.md"
 description = "multibase in rust"
 homepage = "https://github.com/multiformats/rust-multibase"
 repository = "https://github.com/multiformats/rust-multibase"
-keywords = ["ipld", "ipfs", "multihash", "multibase", "cid"]
+keywords = ["ipld", "ipfs", "multihash", "multibase", "cid", "no_std"]
+
+[features]
+default = ["std"]
+std = ["data-encoding/std"]
 
 [dependencies]
-base-x = "0.2"
-data-encoding = "2.2"
-data-encoding-macro = "0.1.8"
+base-x = { version = "0.2.7", default-features = false }
+data-encoding = { version = "2.3.1", default-features = false, features = ["alloc"] }
+data-encoding-macro = "0.1.9"
 
 [dev-dependencies]
 criterion = "0.3"

README.md

@@ -28,9 +28,17 @@ First add this to your `Cargo.toml`
 
 ```toml
 [dependencies]
-multibase = "0.8"
+multibase = "0.9"
 ```
 
+For `no_std`
+```
+[dependencies]
+multibase = { version ="0.9", default-features = false }
+```
+
+**note**: This crate relies on the [currently unstable](https://github.com/rust-lang/cargo/issues/7915) `host_dep` feature to [compile proc macros with the proper dependencies](https://docs.rs/data-encoding-macro/0.1.10/data_encoding_macro/), thus **requiring nightly rustc** to use.
+
 Then run `cargo build`.
 
 ## Usage

src/base.rs

@@ -1,6 +1,9 @@
 use crate::error::{Error, Result};
 use crate::impls::*;
 
+#[cfg(not(feature = "std"))]
+use alloc::{string::String, vec::Vec};
+
 macro_rules! build_base_enum {
     ( $(#[$attr:meta] $code:expr => $base:ident,)* ) => {
         /// List of types currently supported in the multibase spec.

src/error.rs

@@ -1,7 +1,7 @@
-use std::{error, fmt};
+use core::fmt;
 
 /// Type alias to use this library's [`Error`] type in a `Result`.
-pub type Result<T> = std::result::Result<T, Error>;
+pub type Result<T> = core::result::Result<T, Error>;
 
 /// Error types
 #[derive(PartialEq, Eq, Clone, Debug)]
@@ -21,7 +21,8 @@ impl fmt::Display for Error {
     }
 }
 
-impl error::Error for Error {}
+#[cfg(feature = "std")]
+impl std::error::Error for Error {}
 
 impl From<base_x::DecodeError> for Error {
     fn from(_: base_x::DecodeError) -> Self {

src/impls.rs

@@ -1,6 +1,9 @@
 use crate::encoding;
 use crate::error::Result;
 
+#[cfg(not(feature = "std"))]
+use alloc::{string::String, vec::Vec};
+
 macro_rules! derive_base_encoding {
     ( $(#[$doc:meta] $type:ident, $encoding:expr;)* ) => {
         $(

src/lib.rs

@@ -3,6 +3,13 @@
 //! Implementation of [multibase](https://github.com/multiformats/multibase) in Rust.
 
 #![deny(missing_docs)]
+#![cfg_attr(not(feature = "std"), no_std)]
+
+#[cfg(not(feature = "std"))]
+extern crate alloc;
+
+#[cfg(not(feature = "std"))]
+use alloc::{string::String, vec::Vec};
 
 mod base;
 mod encoding;