serde_ext_duration

Flexible Serde (de)serializers for std::time::Duration.

• Input (any of these accepted on deserialization):
  • integer → seconds
  • float → seconds + fractional·1000ms (rounded to nearest millisecond)
  • string → human tokens with units d, h, m, s, ms (case‑insensitive, order‑free, whitespace optional), e.g. "1h 23m 45s", "30m 1h", "1m250ms", "250ms".
• Output (choose one serialization shape via #[serde(with = ...)]):
  • human → canonical human string, e.g. "1h 2m 3s 250ms"
  • secs → integer seconds (u64)
  • millis → integer milliseconds (u64, ms‑rounded)
  • secs_f64_ms → f64 seconds with millisecond precision (3 decimals)

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Quick start

Human output (default) with flexible input

use serde::{Deserialize, Serialize};
use std::time::Duration;

#[derive(Serialize, Deserialize)]
struct Cfg {
    #[serde(with = "serde_ext_duration")] // human out; flexible in
    timeout: Duration,
}

Pick a specific output shape

use serde::{Deserialize, Serialize};
use std::time::Duration;

#[derive(Serialize, Deserialize)]
struct Cfg {
    #[serde(with = "serde_ext_duration::human")]      a: Duration, // "1h 2m 3s 250ms"
    #[serde(with = "serde_ext_duration::secs")]       b: Duration, // 3723
    #[serde(with = "serde_ext_duration::millis")]     c: Duration, // 3723250
    #[serde(with = "serde_ext_duration::secs_f64_ms")] d: Duration, // 3723.250
}

Optional newtype

use serde::{Deserialize, Serialize};
use serde_ext_duration::ExtDuration; // Serialize → human; Deserialize ← flexible
use std::time::Duration;

#[derive(Serialize, Deserialize)]
struct Cfg { t: ExtDuration }

let cfg = Cfg { t: ExtDuration(Duration::from_millis(65_000)) };
let json = serde_json::to_string(&cfg)?; // {"t":"1m 5s"}
let back: Cfg = serde_json::from_str(&json)?; // round‑trips

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Option<Duration> support (opt module)

Serde does not automatically apply with = "…" to the inner type of an Option<T>. The provided opt modules target the field type Option<Duration> directly.

Important: when using #[serde(with = ...)] on an Option<…> field and you want missing fields to become None, add #[serde(default)].

Human output (root)

#[derive(serde::Serialize, serde::Deserialize)]
struct Cfg {
  // missing or null -> None; otherwise parse int/float/string -> Some(Duration)
  #[serde(default, with = "serde_ext_duration::opt")]
  timeout: Option<std::time::Duration>,
}

Choose specific output shapes for Option<Duration>

#[derive(serde::Serialize, serde::Deserialize)]
struct Cfg {
  #[serde(default, with = "serde_ext_duration::opt::human")]      a: Option<std::time::Duration>,
  #[serde(default, with = "serde_ext_duration::opt::secs")]       b: Option<std::time::Duration>,
  #[serde(default, with = "serde_ext_duration::opt::millis")]     c: Option<std::time::Duration>,
  #[serde(default, with = "serde_ext_duration::opt::secs_f64_ms")] d: Option<std::time::Duration>,
}

Elide None at serialization

#[derive(serde::Serialize, serde::Deserialize)]
struct Cfg {
  #[serde(default, with = "serde_ext_duration::opt")]
  #[serde(skip_serializing_if = "Option::is_none")]
  timeout: Option<std::time::Duration>,
}

Alternative: let Serde handle missing/None with a newtype

If you prefer no with attributes at all:

#[derive(serde::Serialize, serde::Deserialize)]
struct Cfg {
  timeout: Option<serde_ext_duration::ExtDuration>, // ExtDuration implements Serde itself
}

Access the inner duration via timeout.map(|d| d.0).

---

String grammar

• Grammar is a sequence of <unsigned-integer><unit> tokens, separated by optional ASCII whitespace.
• Units (case‑insensitive): d (days), h (hours), m (minutes), s (seconds), ms (milliseconds).
• Order is free: "30m 1h" equals "1h 30m".
• Empty strings, unknown units, and negative numbers are rejected.

Examples:

"1h 23m 45s"
"90m"          # 1h 30m
"1m250ms"
"250ms"

---

Behavior

• Deserialization

  • Integers are seconds.
  • Floats are seconds; the fractional part is interpreted as milliseconds and rounded to the nearest ms. 1.9996 → 2.000s.
  • Strings follow the grammar above. Mixed units accumulate; overflow is detected and reported.
  • Negatives (ints/floats) and non‑finite floats are rejected.

• Serialization

  • human produces a minimal canonical sequence d h m s ms, omitting zero parts; zero duration renders as "0s".
  • secs truncates sub‑second parts (same as Duration::as_secs).
  • millis rounds to nearest millisecond and returns a u64 count.
  • secs_f64_ms rounds to 3 decimals (millisecond precision) to avoid implying higher precision.

---

Examples

JSON (human)

#[derive(serde::Serialize, serde::Deserialize)]
struct Job { #[serde(with = "serde_ext_duration")] timeout: std::time::Duration }

let src = Job { timeout: std::time::Duration::from_millis(3_723_250) };
let json = serde_json::to_string(&src)?;       // {"timeout":"1h 2m 3s 250ms"}
let dst: Job = serde_json::from_str(&json)?;   // round‑trip OK

YAML (mixed inputs)

#[derive(serde::Deserialize, Debug)]
struct Mixed {
    #[serde(with = "serde_ext_duration")] a: std::time::Duration, // string
    #[serde(with = "serde_ext_duration")] b: std::time::Duration, // float
    #[serde(with = "serde_ext_duration")] c: std::time::Duration, // int
}

let doc = r#"
---
a: "1h 2m 3s"
b: 2.5
c: 42
"#;
let val: Mixed = serde_yaml::from_str(doc)?;

---

MSRV & features

• MSRV: aims to work on stable Rust 1.70+ (no special features). If you rely on an older compiler, adjust as needed.
• no_std: not supported (uses std::time::Duration).

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License

Dual‑licensed under either:

• MIT — see LICENSE-MIT
• Apache‑2.0 — see LICENSE-APACHE

at your option.