Parsing datetimes like: 2022-10-25 02:53:28 +0100 BST

[xd009642]

I have this date time 2022-10-25 02:53:28 +0100 BST from a docker image ls --format json which I'm attempting to parse into a rust struct via serde. Unfortunately, both Zoned and Timestamp fail as there's the +0100 BST left unparsed at the end. Just wondering if there's a type that'll parse out into this (hopefully without much effort my side)

[BurntSushi]

Here's a concrete answer to your question:

use jiff::fmt::strtime::BrokenDownTime;

fn main() -> anyhow::Result<()> {
    let input = "2022-10-25 02:53:28 +0100 BST";
    let (tm, _) = BrokenDownTime::parse_prefix("%Y-%m-%d %H:%M:%S %z", input)?;
    let ts = tm.to_timestamp()?;
    println!("{ts}");

    Ok(())
}

And its output:

$ cargo r -q
2022-10-25T01:53:28Z

Or, if you want to parse into a Zoned:

use jiff::fmt::strtime::BrokenDownTime;

fn main() -> anyhow::Result<()> {
    let input = "2022-10-25 02:53:28 +0100 BST";
    let (tm, _) = BrokenDownTime::parse_prefix("%Y-%m-%d %H:%M:%S %z", input)?;
    let zdt = tm.to_zoned()?;
    println!("{zdt}");

    Ok(())
}

And its output:

$ cargo r -q
2022-10-25T02:53:28+01:00[+01:00]

There are two problems with strings like 2022-10-25 02:53:28 +0100 BST.

The first is that it's a completely non-standard format. That makes it an exceptionally poor choice for structured data meant to be parsed by machines, as suggested by the --json flag. Bad Docker, no biscuit for them. That should be a bug filed for Docker.

The second is that BST is a time zone abbreviation and they are fundamentally not parseable because they are ambiguous. For example:

$ biff tz list | xargs -n1 biff time in now | biff time fmt -f '%Q %Z %:z' | rg BST
Europe/Belfast BST +01:00
Europe/Guernsey BST +01:00
Europe/Isle_of_Man BST +01:00
Europe/Jersey BST +01:00
Europe/London BST +01:00
GB BST +01:00
GB-Eire BST +01:00

This means that it's not possible to take BST and turn it into a time zone suitable for a Zoned. That's why the Zoned that was parsed above has a fixed offset time zone. These are generally not what you want because it's impossible to do DST safe arithmetic with them.

The code sample shown above works by completely ignoring the BST time zone abbreviation.

[xd009642]

Wow thanks for the fast response, loving using jiff so far 👍

[BurntSushi]

Also, thank you for asking this question. It's a perfect example of why a datetime library benefits from ad hoc parsing routines like what Jiff's jiff::fmt::strtime module provides.