}"#;
let got: Record = serde_json::from_str(&json)?;
assert_eq!(got.timestamp, Timestamp::from_second(1517644800)?);
assert_eq!(serde_json::to_string(&got)?, json);

# Ok::<(), Box<dyn std::error::Error>>(())
```

# Example: optional timestamp support

And this example shows how to use an `Option<Timestamp>` instead of a
`Timestamp`. Note that in this case, we show how to roundtrip the number of
**milliseconds** since the Unix epoch:

```
use jiff::Timestamp;

#[derive(Debug, serde::Deserialize, serde::Serialize)]
struct Record {
    #[serde(with = "jiff::fmt::serde::timestamp::millisecond::optional")]
    timestamp: Option<Timestamp>,
}

let json = r#"{"timestamp":1517644800123}"#;
let got: Record = serde_json::from_str(&json)?;
assert_eq!(got.timestamp, Some(Timestamp::from_millisecond(1517644800_123)?));
assert_eq!(serde_json::to_string(&got)?, json);

# Ok::<(), Box<dyn std::error::Error>>(())
```

# Example: the "friendly" duration format

The [`Span`](crate::Span) and [`SignedDuration`](crate::SignedDuration) types
in this crate both implement Serde's `Serialize` and `Deserialize` traits. For
`Serialize`, they both use the [ISO 8601 Temporal duration format], but for
`Deserialize`, they both support the ISO 8601 Temporal duration format and
the ["friendly" duration format] simultaneously. In order to serialize either
type in the "friendly" format, you can either define your own serialization
functions or use one of the convenience routines provided by this module. For
example:

```
use jiff::{ToSpan, Span};

#[derive(Debug, serde::Deserialize, serde::Serialize)]
struct Record {
    #[serde(
        serialize_with = "jiff::fmt::serde::span::friendly::compact::required"
    )]
    span: Span,
}

let json = r#"{"span":"1 year 2 months 36 hours 1100ms"}"#;
let got: Record = serde_json::from_str(&json)?;
assert_eq!(
    got.span,
    1.year().months(2).hours(36).milliseconds(1100).fieldwise(),
);

let expected = r#"{"span":"1y 2mo 36h 1100ms"}"#;
assert_eq!(serde_json::to_string(&got).unwrap(), expected);

# Ok::<(), Box<dyn std::error::Error>>(())
```

[Serde]: https://serde.rs/
[`with` attribute]: https://serde.rs/field-attrs.html#with
[`serialize_with` attribute]: https://serde.rs/field-attrs.html#serialize_with
[ISO 8601 Temporal duration format]: crate::fmt::temporal
["friendly" duration format]: crate::fmt::friendly