From 66d1ae1cde1225b62d821f91482a34581285fcc4 Mon Sep 17 00:00:00 2001
From: dishmaker <141624503+dishmaker@users.noreply.github.com>
Date: Fri, 3 Oct 2025 16:12:00 +0200
Subject: [PATCH] der: wip: Cow<'a, OctetStringRef> traits

---
 der/src/referenced.rs | 96 +++++++++++++++++++++++++++++++++++++++++++
 x509-cert/src/ext.rs  | 14 +++++--
 2 files changed, 106 insertions(+), 4 deletions(-)

diff --git a/der/src/referenced.rs b/der/src/referenced.rs
index 22060b93b..124d93648 100644
--- a/der/src/referenced.rs
+++ b/der/src/referenced.rs
@@ -61,6 +61,12 @@ where
 
 #[cfg(feature = "alloc")]
 mod allocating {
+    use std::borrow::Cow;
+
+    use crate::{
+        DecodeValue, Encode, EncodeValue, FixedTag, Header, Length, Reader, Tag, Tagged, Writer,
+    };
+
     use super::{OwnedToRef, RefToOwned};
     use alloc::boxed::Box;
 
@@ -79,4 +85,94 @@ mod allocating {
             self.as_ref()
         }
     }
+
+    impl<'a, T> FixedTag for Cow<'a, T>
+    where
+        T: Clone,
+        &'a T: FixedTag,
+    {
+        const TAG: Tag = <&'a T as FixedTag>::TAG;
+    }
+
+    // impl<'a, T> Tagged for Cow<'a, T>
+    // where
+    //     T: Clone,
+    //     &'a T: Tagged,
+    // {
+    //     fn tag(&self) -> Tag {
+    //         match self {
+    //             Cow::Borrowed(object) => object.tag(),
+    //             Cow::Owned(object) => object.tag(),
+    //         }
+    //     }
+    // }
+
+    // impl<'a, T> Decode<'a> for Cow<'a, T>
+    // where
+    //     T: Clone,
+    //     &'a T: Decode<'a>,
+    // {
+    //     type Error = <&'a T as Decode<'a>>::Error;
+
+    //     fn decode<R: Reader<'a>>(reader: &mut R) -> Result<Self, Self::Error> {
+    //         let object = <&'a T as Decode<'a>>::decode(reader)?;
+    //         Ok(Self::Borrowed(object))
+    //     }
+    // }
+
+    impl<'a, T> DecodeValue<'a> for Cow<'a, T>
+    where
+        T: Clone,
+        &'a T: DecodeValue<'a>,
+    {
+        type Error = <&'a T as DecodeValue<'a>>::Error;
+
+        fn decode_value<R: Reader<'a>>(
+            reader: &mut R,
+            header: Header,
+        ) -> Result<Self, Self::Error> {
+            let value = <&'a T as DecodeValue<'a>>::decode_value(reader, header)?;
+            Ok(Self::Borrowed(value))
+        }
+    }
+
+    impl<'a, T> Encode for &'a Cow<'a, T>
+    where
+        T: Clone,
+        &'a T: Encode,
+    {
+        fn encoded_len(&self) -> crate::Result<Length> {
+            match self {
+                Cow::Borrowed(object) => object.encoded_len(),
+                Cow::Owned(object) => object.encoded_len(),
+            }
+        }
+
+        fn encode(&self, encoder: &mut impl Writer) -> crate::Result<()> {
+            match self {
+                Cow::Borrowed(object) => object.encode(encoder),
+                Cow::Owned(object) => object.encode(encoder),
+            }
+        }
+    }
+
+    impl<'a, T> EncodeValue for &'a Cow<'a, T>
+    where
+        T: Clone,
+        &'a T: EncodeValue,
+    {
+        fn value_len(&self) -> crate::Result<Length> {
+            match self {
+                Cow::Borrowed(value) => value.value_len(),
+                Cow::Owned(value) => value.value_len(),
+            }
+        }
+
+        fn encode_value(&self, encoder: &mut impl Writer) -> crate::Result<()> {
+            match self {
+                Cow::Borrowed(value) => value.encode_value(encoder),
+                Cow::Owned(value) => value.encode_value(encoder),
+            }
+        }
+    }
 }
diff --git a/x509-cert/src/ext.rs b/x509-cert/src/ext.rs
index 71232fabc..b26184ec3 100644
--- a/x509-cert/src/ext.rs
+++ b/x509-cert/src/ext.rs
@@ -1,7 +1,12 @@
 //! Standardized X.509 Certificate Extensions
 
+use std::borrow::Cow;
+
 use const_oid::AssociatedOid;
-use der::{Sequence, ValueOrd, asn1::OctetString};
+use der::{
+    Sequence, ValueOrd,
+    asn1::{OctetString, OctetStringRef},
+};
 use spki::ObjectIdentifier;
 
 pub mod pkix;
@@ -26,13 +31,14 @@ pub mod pkix;
 #[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 #[derive(Clone, Debug, Eq, PartialEq, Sequence, ValueOrd)]
 #[allow(missing_docs)]
-pub struct Extension {
+pub struct Extension<'a> {
     pub extn_id: ObjectIdentifier,
 
     #[asn1(default = "Default::default")]
     pub critical: bool,
 
-    pub extn_value: OctetString,
+    // maybe #[asn1(type = "OCTET STRING", deref = "true")]
+    pub extn_value: Cow<'a, OctetStringRef>,
 }
 
 /// Extensions as defined in [RFC 5280 Section 4.1.2.9].
@@ -42,7 +48,7 @@ pub struct Extension {
 /// ```
 ///
 /// [RFC 5280 Section 4.1.2.9]: https://datatracker.ietf.org/doc/html/rfc5280#section-4.1.2.9
-pub type Extensions = alloc::vec::Vec<Extension>;
+pub type Extensions = alloc::vec::Vec<Extension<'static>>;
 
 /// Trait to be implemented by extensions to allow them to be formatted as x509 v3 extensions by
 /// builder.