Fast and precise systemd time span parser of rust strings to a Duration

Table of Contents

• Table of Contents
  • Overview
  • Audience
  • Installation
  • Format description
  • Benchmarks
  • License

Overview

This crate provides a simple to use and fast parser based on fundu aiming for full compatibility with the systemd time span format as specified in their documentation.

fundu-systemd can parse rust strings like

Note that fundu parses into its own Duration which is a superset of other Durations like std::time::Duration, chrono::Duration and time::Duration. See the documentation how to easily handle the conversion between these durations.

Audience

This crate is for you if you

• seek a fast and reliable systemd compatible duration parser
• want it to simply just work without diving into many customizations
• just like the systemd format
• ...

This crate might not be for you if you want to customize the parser to a format which would not be compatible with systemd. See the main fundu project, if you want to use a parser tailored to your needs.

Installation

Add this to Cargo.toml

[dependencies]
fundu-systemd = "0.3.1"

or install with cargo add fundu-systemd.

Activating the chrono or time feature provides a TryFrom implementation for chrono::Duration or time::Duration. Converting from/to std::time::Duration does not require an additional feature. Activating the serde feature allows some structs and enums to be serialized or deserialized with serde

Description of the Format

Supported time units:

• nsec, ns (can be switched on, per default these are not included)
• usec, us, µs
• msec, ms
• seconds, second, sec, s
• minutes, minute, min, m
• hours, hour, hr, h
• days, day, d
• weeks, week, w
• months, month, M (defined as 30.44 days or a 1/12 year)
• years, year, y (defined as 365.25 days)

Summary of the rest of the format:

• Only numbers like "123 days" or with fraction "1.2 days" but without exponent (like "3e9 days") are allowed
• For numbers without a time unit (like "1234") the default time unit is usually second but can be changed since in some case systemd uses a different granularity.
• Time units without a number (like in "second") are allowed and a value of 1 is assumed.
• The parsed duration represents the value exactly (without rounding errors as would occur in floating point calculations) as it is specified in the source string (just like systemd).
• The maximum supported duration (Duration::MAX) has u64::MAX seconds (18_446_744_073_709_551_615) and 999_999_999 nano seconds. However, systemd uses u64::MAX micro seconds as maximum duration when parsing without nanos and u64::MAX nano seconds when parsing with nanos. fundu-systemd provides the parse and parse_nanos functions to reflect that. If you don't like the maximum duration of systemd it's still possible via parse_with_max and parse_nanos_with_max to adjust this limit to a duration ranging from Duration::ZERO to Duration::MAX.
• The special value "infinity" evaluates to the maximum duration. Note the maximum duration depends on whether parsing with nano seconds or without. If the maximum duration is manually set to a different value then it evaluates to that maximum duration.
• parsed durations larger than the maximum duration (like "100000000000000years") saturate at the maximum duration
• Negative durations are not allowed, also no intermediate negative durations like in "5day -1ms" although the final duration would not be negative.
• Any leading, trailing whitespace or whitespace between the number and the time unit (like in "1 \n sec") and multiple durations (like in "1week \n 2minutes") is ignored and follows the posix definition of whitespace which is:
  • Space (' ')
  • Horizontal Tab ('\x09')
  • Line Feed ('\x0A')
  • Vertical Tab ('\x0B')
  • Form Feed ('\x0C')
  • Carriage Return ('\x0D')

Please see also the systemd documentation for a description of their format.

Benchmarks

To run the benchmarks on your machine, clone the repository

git clone https://github.com/fundu-rs/fundu.git
cd fundu

and then run the fundu-systemd benchmarks with

cargo bench --package fundu-systemd

The above won't run the flamegraph and iai-callgrind benchmarks.

The iai-callgrind (feature = with-iai) and flamegraph (feature = with-flamegraph) benchmarks can only be run on unix. Use the --features option of cargo to run the benchmarks with these features.

To get a rough idea about the parsing times, here the average parsing speed of some inputs (Quad core 3000Mhz, 8GB DDR3, Linux):

1 | 55.572 ns 123456789.123456789 | 88.750 ns format!("{}.{}", "1".repeat(1022), "1".repeat(1022)) | 475.07 ns s | 83.724 ns minutes | 133.26 ns 1ns 1us | 200.59 ns 1ns 1us 1ms 1s | 379.75 ns 1ns 1us 1ns 1us | 391.54 ns "1ns 1us".repeat(100) | 18.644 µs

License

MIT license (LICENSE or http://opensource.org/licenses/MIT)