feature gate no_std

Cargo.toml

@@ -11,3 +11,7 @@ rust-version = "1.56.1"
 
 [dependencies]
 uncased = "0.9.10"
+
+[features]
+std = []
+default = ["std"]

README.md

@@ -18,4 +18,10 @@ for node_result in parse(header_value) {
 }
 ```
 
+## `no_std`
+
+This crate can be used in a `no_std` environment by disabling the default `std` feature.
+
+The only impact disabling this feature has is using `core::error::Error` and `core::net::IpAddr` instead of the `std` variants and increasing the msrv to 1.81.
+
 [rfc7239]: https://tools.ietf.org/html/rfc7239

src/lib.rs

@@ -1,4 +1,5 @@
-#![no_std]
+#![cfg_attr(not(feature = "std"), no_std)]
+
 //! Parser for [rfc7239] formatted `Forwarded` headers.
 //!
 //! ## Usage
@@ -23,15 +24,25 @@
 //!
 //! [rfc7239]: https://tools.ietf.org/html/rfc7239
 
-#[cfg(test)]
+#[cfg(all(test, not(feature = "std")))]
 extern crate std;
-#[cfg(test)]
+#[cfg(all(test, not(feature = "std")))]
 use std::{format, vec, vec::Vec};
 
-use core::error::Error;
-use core::fmt::{Debug, Display, Formatter};
-use core::net::IpAddr;
-use core::str::FromStr;
+#[cfg(not(feature = "std"))]
+use core::{
+    error::Error,
+    fmt::{Debug, Display, Formatter},
+    net::IpAddr,
+    str::FromStr,
+};
+#[cfg(feature = "std")]
+use std::{
+    error::Error,
+    fmt::{Debug, Display, Formatter},
+    net::IpAddr,
+    str::FromStr,
+};
 use uncased::UncasedStr;
 
 #[derive(Debug)]