feat: Support no_std environment

apdu-core/Cargo.toml

@@ -14,3 +14,7 @@ authors = [
 ]
 
 [dependencies]
+
+[features]
+std = []
+default = ["std"]

apdu-core/src/command.rs

@@ -1,3 +1,6 @@
+use alloc::vec;
+use alloc::vec::Vec;
+
 /// An APDU command to be transmitted
 pub struct Command {
     pub cla: u8,

apdu-core/src/error.rs

@@ -1,4 +1,4 @@
-use std::fmt::{Display, Formatter};
+use core::fmt::{Display, Formatter};
 
 use crate::Response;
 
@@ -9,7 +9,7 @@ pub struct Error {
 }
 
 impl Display for Error {
-    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
         let (sw1, sw2) = self.response.trailer;
 
         write!(
@@ -20,4 +20,5 @@ impl Display for Error {
     }
 }
 
+#[cfg(feature = "std")]
 impl std::error::Error for Error {}

apdu-core/src/lib.rs

@@ -1,5 +1,9 @@
 //! Core library for composing APDU commands and parsing their responses.
 
+#![cfg_attr(not(feature = "std"), no_std)]
+
+extern crate alloc;
+
 mod command;
 mod error;
 mod response;