Fix the deserialization from JSON for I256 and U256 types with custom…

… endianness (#28)

Cargo.toml

@@ -31,3 +31,8 @@ macros = ["ethnum-macros"]
 ethnum-intrinsics = { version = "=1.1.0", path = "intrinsics", optional = true }
 ethnum-macros = { version = "=1.1.0", path = "macros", optional = true }
 serde = { version = "1", default-features = false, optional = true }
+
+[dev-dependencies]
+serde  = { version = "1", features = ["derive"] }
+serde_json = "1"
+bincode = "1"

src/serde.rs

@@ -392,6 +392,19 @@ pub mod bytes {
 
                     Ok(T::from_bytes(bytes))
                 }
+
+                fn visit_seq<S>(self, mut seq: S) -> Result<Self::Value, S::Error>
+                where
+                    S: de::SeqAccess<'de>,
+                {
+                    let mut bytes: [u8; 32] = [0; 32];
+                    for i in 0..32 {
+                        bytes[i] = seq
+                            .next_element()?
+                            .ok_or(de::Error::invalid_length(i, &self))?;
+                    }
+                    Ok(T::from_bytes(bytes))
+                }
             }
 
             #[doc(hidden)]

tests/serialize_deserialize.rs

@@ -0,0 +1,34 @@
+#[cfg(feature = "serde")]
+#[test]
+fn roundtrip() {
+    use ethnum::{I256, U256};
+    use serde::{Deserialize, Serialize};
+
+    #[derive(Debug, Serialize, Deserialize, PartialEq, Eq)]
+    struct Test {
+        #[serde(with = "ethnum::serde::bytes::le")]
+        a: U256,
+        #[serde(with = "ethnum::serde::bytes::be")]
+        b: U256,
+        #[serde(with = "ethnum::serde::bytes::ne")]
+        c: U256,
+        #[serde(with = "ethnum::serde::bytes::le")]
+        d: I256,
+        #[serde(with = "ethnum::serde::bytes::be")]
+        e: I256,
+        #[serde(with = "ethnum::serde::bytes::ne")]
+        f: I256,
+    }
+
+    let original = Test {
+        a: U256::new(1),
+        b: U256::new(2),
+        c: U256::new(3),
+        d: I256::new(4),
+        e: I256::new(5),
+        f: I256::new(6),
+    };
+    let serialized = serde_json::to_string(&original).unwrap();
+    let deserialized: Test = serde_json::from_str(&serialized).unwrap();
+    assert_eq!(original, deserialized);
+}