Fix serde / no_std incompatibility

Co-authored-by: ryan kurte <ryan@kurte.nz>
Co-authored-by: Vlad Semenov <semenov.vlad.by@gmail.com>

.github/workflows/rust.yml

@@ -82,8 +82,7 @@ jobs:
       - uses: taiki-e/install-action@cargo-hack
       # No default features build
       - run: cargo build --target thumbv7em-none-eabi --release --no-default-features
-      # TODO: serde pending PR#288
-      - run: cargo hack build --target thumbv7em-none-eabi --release --each-feature --exclude-features default,std,serde
+      - run: cargo hack build --target thumbv7em-none-eabi --release --each-feature --exclude-features default,std
 
   bench:
     name: Check that benchmarks compile

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"

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"]

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)
     }
 }
 
@@ -644,8 +640,37 @@ 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)
+            }
+
+            fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+            where
+                A: serde::de::SeqAccess<'de>,
+            {
+                let mut bytes = [0u8; 32];
+                for i in 0..32 {
+                    bytes[i] = seq
+                        .next_element()?
+                        .ok_or_else(|| serde::de::Error::invalid_length(i, &"expected 32 bytes"))?;
+                }
+                SigningKey::try_from(bytes).map_err(serde::de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_bytes(SigningKeyVisitor)
     }
 }
 

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 +548,36 @@ 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)
+            }
+
+            fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+            where
+                A: serde::de::SeqAccess<'de>,
+            {
+                let mut bytes = [0u8; 32];
+                for i in 0..32 {
+                    bytes[i] = seq
+                        .next_element()?
+                        .ok_or_else(|| serde::de::Error::invalid_length(i, &"expected 32 bytes"))?;
+                }
+                VerifyingKey::try_from(&bytes[..]).map_err(serde::de::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_bytes(VerifyingKeyVisitor)
     }
 }