serde_special_case_field.rs

use serde::{Deserialize, Deserializer, Serialize, Serializer};
use serde_json;

#[derive(Debug, Serialize, Deserialize)]
struct Foo(String);

#[derive(Debug, Serialize, Deserialize)]
struct Bar(String);

fn foo_ser<S>(value: &Foo, serializer: S) -> Result<S::Ok, S::Error>
where
    S: Serializer,
{
    Foo(format!("{}!!!", value.0)).serialize(serializer)
}

fn foo_de<'de, D>(deserializer: D) -> Result<Foo, D::Error>
where
    D: Deserializer<'de>,
{
    let value = Foo::deserialize(deserializer)?;
    Ok(Foo(String::from(
        value.0.strip_suffix("!!!").unwrap_or(&value.0),
    )))
}

#[derive(Debug, Serialize, Deserialize)]
struct Thing {
    #[serde(serialize_with = "foo_ser", deserialize_with = "foo_de")]
    foo: Foo,
    bar: Bar,
}

fn main() {
    let input = Thing {
        foo: Foo(String::from("foo")),
        bar: Bar(String::from("bar")),
    };
    let json = serde_json::to_string(&input).unwrap();
    let output: Thing = serde_json::from_str(&json).unwrap();
    println!("   {input:?}\n-> {json}\n-> {output:?}");
}

//    Thing { foo: Foo("foo"), bar: Bar("bar") }
// -> {"foo":"foo!!!","bar":"bar"}
// -> Thing { foo: Foo("foo"), bar: Bar("bar") }