Units

timeout = 30 is ambiguous and max_body = 67108864 is unreadable, so both are usually written with a unit — which no stock Deserialize accepts:

#![allow(unused)]
fn main() {
#[derive(Deserialize)]
struct Limits {
    #[serde(with = "dynamic_config::duration")]
    timeout: Duration,      // "30s", "1h30m", "500ms", or a number of seconds
    #[serde(default, with = "dynamic_config::duration::option")]
    grace: Option<Duration>,
    #[serde(with = "dynamic_config::bytes")]
    max_body: u64,          // "64MiB", "1GB", or a number of bytes
}
}

KiB/MiB/GiB are powers of 1024, KB/MB/GB powers of 1000, and a bare K/M/G is read as the binary form. An unknown unit is an error listing the valid ones, never a silent zero.