feature: add conditional support for serde

src/hash/blake/mod.rs

@@ -1,5 +1,8 @@
 use super::{Digest, ElementHasher, Felt, FieldElement, Hasher, StarkField};
-use crate::utils::{ByteReader, ByteWriter, Deserializable, DeserializationError, Serializable};
+use crate::utils::{
+    bytes_to_hex_string, hex_to_bytes, string::String, ByteReader, ByteWriter, Deserializable,
+    DeserializationError, HexParseError, Serializable,
+};
 use core::{
     mem::{size_of, transmute, transmute_copy},
     ops::Deref,
@@ -24,6 +27,8 @@ const DIGEST20_BYTES: usize = 20;
 /// Note: `N` can't be greater than `32` because [`Digest::as_bytes`] currently supports only 32
 /// bytes.
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[cfg_attr(feature = "serde", serde(into = "String", try_from = "&str"))]
 pub struct Blake3Digest<const N: usize>([u8; N]);
 
 impl<const N: usize> Default for Blake3Digest<N> {
@@ -52,6 +57,20 @@ impl<const N: usize> From<[u8; N]> for Blake3Digest<N> {
     }
 }
 
+impl<const N: usize> From<Blake3Digest<N>> for String {
+    fn from(value: Blake3Digest<N>) -> Self {
+        bytes_to_hex_string(value.as_bytes())
+    }
+}
+
+impl<const N: usize> TryFrom<&str> for Blake3Digest<N> {
+    type Error = HexParseError;
+
+    fn try_from(value: &str) -> Result<Self, Self::Error> {
+        hex_to_bytes(value).map(|v| v.into())
+    }
+}
+
 impl<const N: usize> Serializable for Blake3Digest<N> {
     fn write_into<W: ByteWriter>(&self, target: &mut W) {
         target.write_bytes(&self.0);

src/hash/rpo/digest.rs

@@ -1,13 +1,19 @@
 use super::{Digest, Felt, StarkField, DIGEST_SIZE, ZERO};
 use crate::utils::{
-    string::String, ByteReader, ByteWriter, Deserializable, DeserializationError, Serializable,
+    bytes_to_hex_string, hex_to_bytes, string::String, ByteReader, ByteWriter, Deserializable,
+    DeserializationError, HexParseError, Serializable,
 };
 use core::{cmp::Ordering, fmt::Display, ops::Deref};
 
+/// The number of bytes needed to encoded a digest
+pub const DIGEST_BYTES: usize = 32;
+
 // DIGEST TRAIT IMPLEMENTATIONS
 // ================================================================================================
 
 #[derive(Debug, Default, Copy, Clone, Eq, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[cfg_attr(feature = "serde", serde(into = "String", try_from = "&str"))]
 pub struct RpoDigest([Felt; DIGEST_SIZE]);
 
 impl RpoDigest {
@@ -19,7 +25,7 @@ impl RpoDigest {
         self.as_ref()
     }
 
-    pub fn as_bytes(&self) -> [u8; 32] {
+    pub fn as_bytes(&self) -> [u8; DIGEST_BYTES] {
         <Self as Digest>::as_bytes(self)
     }
 
@@ -32,8 +38,8 @@ impl RpoDigest {
 }
 
 impl Digest for RpoDigest {
-    fn as_bytes(&self) -> [u8; 32] {
-        let mut result = [0; 32];
+    fn as_bytes(&self) -> [u8; DIGEST_BYTES] {
+        let mut result = [0; DIGEST_BYTES];
 
         result[..8].copy_from_slice(&self.0[0].as_int().to_le_bytes());
         result[8..16].copy_from_slice(&self.0[1].as_int().to_le_bytes());
@@ -107,18 +113,73 @@ impl From<RpoDigest> for [u64; DIGEST_SIZE] {
     }
 }
 
-impl From<&RpoDigest> for [u8; 32] {
+impl From<&RpoDigest> for [u8; DIGEST_BYTES] {
     fn from(value: &RpoDigest) -> Self {
         value.as_bytes()
     }
 }
 
-impl From<RpoDigest> for [u8; 32] {
+impl From<RpoDigest> for [u8; DIGEST_BYTES] {
     fn from(value: RpoDigest) -> Self {
         value.as_bytes()
     }
 }
 
+impl From<RpoDigest> for String {
+    fn from(value: RpoDigest) -> Self {
+        bytes_to_hex_string(value.as_bytes())
+    }
+}
+
+impl From<&RpoDigest> for String {
+    fn from(value: &RpoDigest) -> Self {
+        (*value).into()
+    }
+}
+
+impl TryFrom<[u8; DIGEST_BYTES]> for RpoDigest {
+    type Error = HexParseError;
+
+    fn try_from(value: [u8; DIGEST_BYTES]) -> Result<Self, Self::Error> {
+        // Note: the input length is known, the conversion from slice to array must succeed so the
+        // `unwrap`s below are safe
+        let a = u64::from_le_bytes(value[0..8].try_into().unwrap());
+        let b = u64::from_le_bytes(value[8..16].try_into().unwrap());
+        let c = u64::from_le_bytes(value[16..24].try_into().unwrap());
+        let d = u64::from_le_bytes(value[24..32].try_into().unwrap());
+
+        if [a, b, c, d].iter().any(|v| *v >= Felt::MODULUS) {
+            return Err(HexParseError::OutOfRange);
+        }
+
+        Ok(RpoDigest([Felt::new(a), Felt::new(b), Felt::new(c), Felt::new(d)]))
+    }
+}
+
+impl TryFrom<&str> for RpoDigest {
+    type Error = HexParseError;
+
+    fn try_from(value: &str) -> Result<Self, Self::Error> {
+        hex_to_bytes(value).and_then(|v| v.try_into())
+    }
+}
+
+impl TryFrom<String> for RpoDigest {
+    type Error = HexParseError;
+
+    fn try_from(value: String) -> Result<Self, Self::Error> {
+        value.as_str().try_into()
+    }
+}
+
+impl TryFrom<&String> for RpoDigest {
+    type Error = HexParseError;
+
+    fn try_from(value: &String) -> Result<Self, Self::Error> {
+        value.as_str().try_into()
+    }
+}
+
 impl Deref for RpoDigest {
     type Target = [Felt; DIGEST_SIZE];
 
@@ -158,9 +219,8 @@ impl PartialOrd for RpoDigest {
 
 impl Display for RpoDigest {
     fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
-        for byte in self.as_bytes() {
-            write!(f, "{byte:02x}")?;
-        }
+        let encoded: String = self.into();
+        write!(f, "{}", encoded)?;
         Ok(())
     }
 }
@@ -170,8 +230,7 @@ impl Display for RpoDigest {
 
 #[cfg(test)]
 mod tests {
-
-    use super::{Deserializable, Felt, RpoDigest, Serializable};
+    use super::{Deserializable, Felt, RpoDigest, Serializable, DIGEST_BYTES};
     use crate::utils::SliceReader;
     use rand_utils::rand_value;
 
@@ -186,11 +245,27 @@ mod tests {
 
         let mut bytes = vec![];
         d1.write_into(&mut bytes);
-        assert_eq!(32, bytes.len());
+        assert_eq!(DIGEST_BYTES, bytes.len());
 
         let mut reader = SliceReader::new(&bytes);
         let d2 = RpoDigest::read_from(&mut reader).unwrap();
 
         assert_eq!(d1, d2);
     }
+
+    #[cfg(feature = "std")]
+    #[test]
+    fn digest_encoding() {
+        let digest = RpoDigest([
+            Felt::new(rand_value()),
+            Felt::new(rand_value()),
+            Felt::new(rand_value()),
+            Felt::new(rand_value()),
+        ]);
+
+        let string: String = digest.into();
+        let round_trip: RpoDigest = string.try_into().expect("decoding failed");
+
+        assert_eq!(digest, round_trip);
+    }
 }