How do I print a Zoned as an RFC 3339 timestamp with an offset (and no time zone annotation)?

[tisonkun]

Is there a way to convert Zoned to (Timestamp, Offset/TimeZone)?

The original use case is fast/logforth#169 (comment) that I'd like to print a timestamp with offset in RFC3339 format.

Currently, Logforth writes:

let time = match self.tz.clone() {
    Some(tz) => Timestamp::now().to_zoned(tz),
    None => Zoned::now(),
};

format!("{time:.6} ...")

I can foresee a refactor as:

let ts = Timestamp::now();
let tz = self.tz.clone().unwrap_or_else(|| TimeZone::system());
let offset = tz.to_offset(ts);
format!("{:.6} ...", ts.display_with_offset(offset));

And I'd expect a possible tighter form:

let time = match self.tz.clone() {
    Some(tz) => Timestamp::now().to_zoned(tz),
    None => Zoned::now(),
};

let (ts, tz) = time.to_timestamp_with_timezone();
let offset = tz.to_offset(ts);

format!("{:.6} ...", ts.display_with_offset(offset))

Given that it's a reasonable self-reflection over Zoned, I open this issue for feedback.

[tisonkun]

Just noticed that Zoned has a offset() method. Resolved at fast/logforth#172.

[BurntSushi]

Yeah, the Zoned::offset() method is the key. Bringing it all together:

use jiff::Zoned;

fn main() -> anyhow::Result<()> {
    let zdt = Zoned::now();
    println!("{zdt}");
    println!("{}", zdt.timestamp().display_with_offset(zdt.offset()));

    Ok(())
}

Has this output:

$ cargo r -q
2025-09-26T08:16:24.791183579-04:00[America/New_York]
2025-09-26T08:16:24.791183579-04:00

[tisonkun]

I may further create the timestamp from SystemTime, is there a way to get Offset like TimeZone::system()? Or I'd like to know the reason why getting the offset should involve a timestamp (tz.to_offset(ts)).

[BurntSushi]

It isn't possible to know the offset without knowing the time (or a range of time) because the offset can change. When it changes is based on rules parameterized by a range of time.

You can access the underlying data with: https://docs.rs/jiff/latest/jiff/tz/struct.TimeZone.html#method.preceding

[BurntSushi]

And for time zonew whose offset never varies, you can use: https://docs.rs/jiff/latest/jiff/tz/struct.TimeZone.html#method.to_fixed_offset