Optimize hexadecimal conversions in serde_utils to speed up JSON serialization of byte collections

Cargo.toml

@@ -300,6 +300,7 @@ bytesize = { version = '1', features = ['serde'] }
 cached = '0.53'
 chrono = '0.4'
 clap = { version = '4', features = ['derive'] }
+const-hex = '1.14'
 const_format = '0.2'
 constant_time_eq = '0.3'
 conv = '0.3'
@@ -339,7 +340,6 @@ hash_hasher = '2'
 hashlink = '0.9'
 hex = { version = '0.4', features = ['serde'] }
 hex-literal = '0.4'
-hex_fmt = '0.3'
 hmac = '0.12'
 http = '1'
 http-body-util = '0.1'

serde_utils/Cargo.toml

@@ -7,9 +7,9 @@ authors = ["Grandine <[email protected]>"]
 workspace = true
 
 [dependencies]
+const-hex = { workspace = true }
 generic-array = { workspace = true }
 hex = { workspace = true }
-hex_fmt = { workspace = true }
 itertools = { workspace = true }
 num-traits = { workspace = true }
 serde = { workspace = true }

serde_utils/src/prefixed_hex_or_bytes_array.rs

@@ -29,7 +29,7 @@ pub fn deserialize<'de, D: Deserializer<'de>, const N: usize>(
             let digits = shared::strip_hex_prefix(string)?;
 
             let mut bytes = [0; N];
-            hex::decode_to_slice(digits, &mut bytes).map_err(E::custom)?;
+            const_hex::decode_to_slice(digits, &mut bytes).map_err(E::custom)?;
 
             Ok(bytes)
         }

serde_utils/src/prefixed_hex_or_bytes_cow.rs

@@ -34,7 +34,7 @@ pub fn deserialize<'de, D: Deserializer<'de>>(deserializer: D) -> Result<Cow<'de
 
         fn visit_str<E: Error>(self, string: &str) -> Result<Self::Value, E> {
             let digits = shared::strip_hex_prefix(string)?;
-            let bytes = hex::decode(digits).map_err(E::custom)?;
+            let bytes = const_hex::decode(digits).map_err(E::custom)?;
             Ok(Cow::Owned(bytes))
         }
     }

serde_utils/src/prefixed_hex_or_bytes_generic_array.rs

@@ -43,7 +43,7 @@ pub fn deserialize<'de, D: Deserializer<'de>, N: ArrayLength<u8>>(
             let digits = shared::strip_hex_prefix(string)?;
 
             let mut bytes = GenericArray::default();
-            hex::decode_to_slice(digits, &mut bytes).map_err(E::custom)?;
+            const_hex::decode_to_slice(digits, &mut bytes).map_err(E::custom)?;
 
             Ok(bytes)
         }

serde_utils/src/prefixed_hex_or_bytes_slice.rs

@@ -1,9 +1,8 @@
-use hex_fmt::HexFmt;
 use serde::Serializer;
 
 pub fn serialize<S: Serializer>(bytes: impl AsRef<[u8]>, serializer: S) -> Result<S::Ok, S::Error> {
     if serializer.is_human_readable() {
-        serializer.collect_str(&format_args!("0x{}", HexFmt(bytes)))
+        serializer.serialize_str(const_hex::encode_prefixed(bytes).as_str())
     } else {
         serializer.serialize_bytes(bytes.as_ref())
     }