From b40661eec3bd27bf8ff6e15b2010b4363ee449da Mon Sep 17 00:00:00 2001
From: ryan kurte <ryan@kurte.nz>
Date: Tue, 21 Mar 2023 10:36:17 +1300
Subject: [PATCH] fix serde / no_std incompatibility

as an alternative to #288 this updates serde `Serialize` and `Deserialize` implementations to use a
custom visitor, removing the need for `alloc` or `std` for embedded use, and making this
consistent with implementations in
[curve25519-dalek](https://github.com/dalek-cryptography/curve25519-dalek/blob/a63e14f4ded078d6bf262ba0b3f47026bdd7f7c0/src/edwards.rs#L269).

@pinkforest seems like it'd be good to have some serde tests / this should go over #289?

Co-Authored-By: Vlad Semenov <semenov.vlad.by@gmail.com>
---
 Cargo.lock       | 10 ----------
 Cargo.toml       |  3 +--
 src/signing.rs   | 27 ++++++++++++++++++++-------
 src/verifying.rs | 26 +++++++++++++++++++-------
 4 files changed, 40 insertions(+), 26 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index e80fe13..6c11e18 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -299,7 +299,6 @@ dependencies = [
  "rand",
  "rand_core",
  "serde",
- "serde_bytes",
  "serde_json",
  "sha2",
  "signature",
@@ -694,15 +693,6 @@ dependencies = [
  "serde_derive",
 ]
 
-[[package]]
-name = "serde_bytes"
-version = "0.11.8"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "718dc5fff5b36f99093fc49b280cfc96ce6fc824317783bff5a1fed0c7a64819"
-dependencies = [
- "serde",
-]
-
 [[package]]
 name = "serde_derive"
 version = "1.0.152"
diff --git a/Cargo.toml b/Cargo.toml
index 57bc2da..3e8a439 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -34,7 +34,6 @@ sha2 = { version = "0.10", default-features = false }
 merlin = { version = "3", default-features = false, optional = true }
 rand_core = { version = "0.6.4", default-features = false, optional = true }
 serde = { version = "1.0", default-features = false, optional = true }
-serde_bytes = { version = "0.11", optional = true }
 zeroize = { version = "1.5", default-features = false, optional = true }
 
 [dev-dependencies]
@@ -68,5 +67,5 @@ legacy_compatibility = []
 pkcs8 = ["ed25519/pkcs8"]
 pem = ["alloc", "ed25519/pem", "pkcs8"]
 rand_core = ["dep:rand_core"]
-serde = ["dep:serde", "serde_bytes", "ed25519/serde"]
+serde = ["dep:serde", "ed25519/serde"]
 zeroize = ["dep:zeroize", "curve25519-dalek/zeroize"]
diff --git a/src/signing.rs b/src/signing.rs
index 28f7346..19e1da2 100644
--- a/src/signing.rs
+++ b/src/signing.rs
@@ -15,12 +15,8 @@ use ed25519::pkcs8;
 #[cfg(any(test, feature = "rand_core"))]
 use rand_core::CryptoRngCore;
 
-#[cfg(feature = "serde")]
-use serde::de::Error as SerdeError;
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
-#[cfg(feature = "serde")]
-use serde_bytes::{ByteBuf as SerdeByteBuf, Bytes as SerdeBytes};
 
 use sha2::Sha512;
 
@@ -634,7 +630,7 @@ impl Serialize for SigningKey {
     where
         S: Serializer,
     {
-        SerdeBytes::new(&self.secret_key).serialize(serializer)
+        serializer.serialize_bytes(&self.secret_key)
     }
 }
 
@@ -644,11 +640,28 @@ impl<'d> Deserialize<'d> for SigningKey {
     where
         D: Deserializer<'d>,
     {
-        let bytes = <SerdeByteBuf>::deserialize(deserializer)?;
-        Self::try_from(bytes.as_ref()).map_err(SerdeError::custom)
+        struct SigningKeyVisitor;
+
+        impl <'de> serde::de::Visitor<'de> for SigningKeyVisitor {
+            type Value = SigningKey;
+
+            fn expecting(&self, formatter: &mut ::core::fmt::Formatter<'_>) -> ::core::fmt::Result {
+                write!(
+                    formatter,
+                    concat!("An ed25519 signing (private) key")
+                )
+            }
+
+            fn visit_borrowed_bytes<E: serde::de::Error>(self, bytes: &'de [u8]) -> Result<Self::Value, E> {
+                SigningKey::try_from(bytes.as_ref()).map_err(E::custom)
+            }
+        }
+
+        deserializer.deserialize_bytes(SigningKeyVisitor)
     }
 }
 
+
 /// An "expanded" secret key.
 ///
 /// This is produced by using an hash function with 512-bits output to digest a
diff --git a/src/verifying.rs b/src/verifying.rs
index 1ea9332..7868b5d 100644
--- a/src/verifying.rs
+++ b/src/verifying.rs
@@ -27,12 +27,8 @@ use sha2::Sha512;
 #[cfg(feature = "pkcs8")]
 use ed25519::pkcs8;
 
-#[cfg(feature = "serde")]
-use serde::de::Error as SerdeError;
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
-#[cfg(feature = "serde")]
-use serde_bytes::{ByteBuf as SerdeByteBuf, Bytes as SerdeBytes};
 
 #[cfg(feature = "digest")]
 use crate::context::Context;
@@ -542,7 +538,7 @@ impl Serialize for VerifyingKey {
     where
         S: Serializer,
     {
-        SerdeBytes::new(self.as_bytes()).serialize(serializer)
+        serializer.serialize_bytes(&self.as_bytes()[..])
     }
 }
 
@@ -552,7 +548,23 @@ impl<'d> Deserialize<'d> for VerifyingKey {
     where
         D: Deserializer<'d>,
     {
-        let bytes = <SerdeByteBuf>::deserialize(deserializer)?;
-        VerifyingKey::try_from(bytes.as_ref()).map_err(SerdeError::custom)
+        struct VerifyingKeyVisitor;
+
+        impl <'de> serde::de::Visitor<'de> for VerifyingKeyVisitor {
+            type Value = VerifyingKey;
+
+            fn expecting(&self, formatter: &mut ::core::fmt::Formatter<'_>) -> ::core::fmt::Result {
+                write!(
+                    formatter,
+                    concat!("An ed25519 verifying (public) key")
+                )
+            }
+
+            fn visit_borrowed_bytes<E: serde::de::Error>(self, bytes: &'de [u8]) -> Result<Self::Value, E> {
+                VerifyingKey::try_from(bytes.as_ref()).map_err(E::custom)
+            }
+        }
+
+        deserializer.deserialize_bytes(VerifyingKeyVisitor)
     }
 }