strftime

README

strftime

Fast strftime for Go

SYNOPSIS

f, err := strftime.New(`.... pattern ...`)
if err := f.Format(buf, time.Now()); err != nil {
    log.Println(err.Error())
}

DESCRIPTION

The goals for this library are

• Optimized for the same pattern being called repeatedly
• Be flexible about destination to write the results out
• Be as complete as possible in terms of conversion specifications

API

Format(string, time.Time) (string, error)

Takes the pattern and the time, and formats it. This function is a utility function that recompiles the pattern every time the function is called. If you know beforehand that you will be formatting the same pattern multiple times, consider using New to create a Strftime object and reuse it.

New(string) (*Strftime, error)

Takes the pattern and creates a new Strftime object.

obj.Pattern() string

Returns the pattern string used to create this Strftime object

obj.Format(io.Writer, time.Time) error

Formats the time according to the pre-compiled pattern, and writes the result to the specified io.Writer

obj.FormatString(time.Time) string

Formats the time according to the pre-compiled pattern, and returns the result string.

SUPPORTED CONVERSION SPECIFICATIONS

pattern	description
%A	national representation of the full weekday name
%a	national representation of the abbreviated weekday
%B	national representation of the full month name
%b	national representation of the abbreviated month name
%C	(year / 100) as decimal number; single digits are preceded by a zero
%c	national representation of time and date
%D	equivalent to %m/%d/%y
%d	day of the month as a decimal number (01-31)
%e	the day of the month as a decimal number (1-31); single digits are preceded by a blank
%F	equivalent to %Y-%m-%d
%H	the hour (24-hour clock) as a decimal number (00-23)
%h	same as %b
%I	the hour (12-hour clock) as a decimal number (01-12)
%j	the day of the year as a decimal number (001-366)
%k	the hour (24-hour clock) as a decimal number (0-23); single digits are preceded by a blank
%l	the hour (12-hour clock) as a decimal number (1-12); single digits are preceded by a blank
%M	the minute as a decimal number (00-59)
%m	the month as a decimal number (01-12)
%n	a newline
%p	national representation of either "ante meridiem" (a.m.) or "post meridiem" (p.m.) as appropriate.
%R	equivalent to %H:%M
%r	equivalent to %I:%M:%S %p
%S	the second as a decimal number (00-60)
%T	equivalent to %H:%M:%S
%t	a tab
%U	the week number of the year (Sunday as the first day of the week) as a decimal number (00-53)
%u	the weekday (Monday as the first day of the week) as a decimal number (1-7)
%V	the week number of the year (Monday as the first day of the week) as a decimal number (01-53)
%v	equivalent to %e-%b-%Y
%W	the week number of the year (Monday as the first day of the week) as a decimal number (00-53)
%w	the weekday (Sunday as the first day of the week) as a decimal number (0-6)
%X	national representation of the time
%x	national representation of the date
%Y	the year with century as a decimal number
%y	the year without century as a decimal number (00-99)
%Z	the time zone name
%z	the time zone offset from UTC
%%	a '%'

EXTENSIONS / CUSTOM SPECIFICATIONS

This library in general tries to be POSIX compliant, but sometimes you just need that extra specification or two that is relatively widely used but is not included in the POSIX specification.

For example, POSIX does not specify how to print out milliseconds, but popular implementations allow %f or %L to achieve this.

For those instances, strftime.Strftime can be configured to use a custom set of specifications:

ss := strftime.NewSpecificationSet()
ss.Set('L', ...) // provide implementation for `%L`

// pass this new specification set to the strftime instance
p, err := strftime.New(`%L`, strftime.WithSpecificationSet(ss))
p.Format(..., time.Now())

The implementation must implement the Appender interface, which is

type Appender interface {
  Append([]byte, time.Time) []byte
}

For commonly used extensions such as the millisecond example and Unix timestamp, we provide a default implementation so the user can do one of the following:

// (1) Pass a specification byte and the Appender
//     This allows you to pass arbitrary Appenders
p, err := strftime.New(
  `%L`,
  strftime.WithSpecification('L', strftime.Milliseconds),
)

// (2) Pass an option that knows to use strftime.Milliseconds
p, err := strftime.New(
  `%L`,
  strftime.WithMilliseconds('L'),
)

Similarly for Unix Timestamp:

// (1) Pass a specification byte and the Appender
//     This allows you to pass arbitrary Appenders
p, err := strftime.New(
  `%s`,
  strftime.WithSpecification('s', strftime.UnixSeconds),
)

// (2) Pass an option that knows to use strftime.UnixSeconds
p, err := strftime.New(
  `%s`,
  strftime.WithUnixSeconds('s'),
)

If a common specification is missing, please feel free to submit a PR (but please be sure to be able to defend how "common" it is)

List of available extensions

• Milliseconds (related option: WithMilliseconds);

• Microseconds (related option: WithMicroseconds);

• UnixSeconds (related option: WithUnixSeconds).

PERFORMANCE / OTHER LIBRARIES

The following benchmarks were run separately because some libraries were using cgo on specific platforms (notabley, the fastly version)

// On my OS X 10.14.6, 2.3 GHz Intel Core i5, 16GB memory.
// go version go1.13.4 darwin/amd64
hummingbird% go test -tags bench -benchmem -bench .
<snip>
BenchmarkTebeka-4                 	  297471	      3905 ns/op	     257 B/op	      20 allocs/op
BenchmarkJehiah-4                 	  818444	      1773 ns/op	     256 B/op	      17 allocs/op
BenchmarkFastly-4                 	 2330794	       550 ns/op	      80 B/op	       5 allocs/op
BenchmarkLestrrat-4               	  916365	      1458 ns/op	      80 B/op	       2 allocs/op
BenchmarkLestrratCachedString-4   	 2527428	       546 ns/op	     128 B/op	       2 allocs/op
BenchmarkLestrratCachedWriter-4   	  537422	      2155 ns/op	     192 B/op	       3 allocs/op
PASS
ok  	github.com/lestrrat-go/strftime	25.618s

// On a host on Google Cloud Platform, machine-type: f1-micro (vCPU x 1, memory: 0.6GB)
// (Yes, I was being skimpy)
// Linux <snip> 4.9.0-11-amd64 #1 SMP Debian 4.9.189-3+deb9u1 (2019-09-20) x86_64 GNU/Linux
// go version go1.13.4 linux/amd64
hummingbird% go test -tags bench -benchmem -bench .
<snip>
BenchmarkTebeka                   254997              4726 ns/op             256 B/op         20 allocs/op
BenchmarkJehiah                   659289              1882 ns/op             256 B/op         17 allocs/op
BenchmarkFastly                   389150              3044 ns/op             224 B/op         13 allocs/op
BenchmarkLestrrat                 699069              1780 ns/op              80 B/op          2 allocs/op
BenchmarkLestrratCachedString    2081594               589 ns/op             128 B/op          2 allocs/op
BenchmarkLestrratCachedWriter     825763              1480 ns/op             192 B/op          3 allocs/op
PASS
ok      github.com/lestrrat-go/strftime 11.355s

This library is much faster than other libraries IF you can reuse the format pattern.

Here's the annotated list from the benchmark results. You can clearly see that (re)using a Strftime object and producing a string is the fastest. Writing to an io.Writer seems a bit sluggish, but since the one producing the string is doing almost exactly the same thing, we believe this is purely the overhead of writing to an io.Writer

Import Path	Score	Note
github.com/lestrrat-go/strftime	3000000	Using FormatString() (cached)
github.com/fastly/go-utils/strftime	2000000	Pure go version on OS X
github.com/lestrrat-go/strftime	1000000	Using Format() (NOT cached)
github.com/jehiah/go-strftime	1000000
github.com/fastly/go-utils/strftime	1000000	cgo version on Linux
github.com/lestrrat-go/strftime	500000	Using Format() (cached)
github.com/tebeka/strftime	300000

However, depending on your pattern, this speed may vary. If you find a particular pattern that seems sluggish, please send in patches or tests.

Please also note that this benchmark only uses the subset of conversion specifications that are supported by ALL of the libraries compared.

Somethings to consider when making performance comparisons in the future:

• Can it write to io.Writer?
• Which %specification does it handle?

Documentation

Index

• func Format(p string, t time.Time, options ...Option) (string, error)
• type AppendFunc
  • func (af AppendFunc) Append(b []byte, t time.Time) []byte
• type Appender
  • func Microseconds() Appender
  • func Milliseconds() Appender
  • func StdlibFormat(s string) Appender
  • func UnixSeconds() Appender
  • func Verbatim(s string) Appender
• type Option
  • func WithMicroseconds(b byte) Option
  • func WithMilliseconds(b byte) Option
  • func WithSpecification(b byte, a Appender) Option
  • func WithSpecificationSet(ds SpecificationSet) Option
  • func WithUnixSeconds(b byte) Option
• type SpecificationSet
  • func NewSpecificationSet() SpecificationSet
• type Strftime
  • func New(p string, options ...Option) (*Strftime, error)
  • func (f *Strftime) Dump(out io.Writer)
  • func (f *Strftime) Format(dst io.Writer, t time.Time) error
  • func (f *Strftime) FormatBuffer(dst []byte, t time.Time) []byte
  • func (f *Strftime) FormatString(t time.Time) string
  • func (f *Strftime) Pattern() string

Examples

• SpecificationSet

Functions

func Format

func Format(p string, t time.Time, options ...Option) (string, error)

Format takes the format `s` and the time `t` to produce the format date/time. Note that this function re-compiles the pattern every time it is called.

If you know beforehand that you will be reusing the pattern within your application, consider creating a `Strftime` object and reusing it.

Types

type AppendFunc

type AppendFunc func([]byte, time.Time) []byte

AppendFunc is an utility type to allow users to create a function-only version of an Appender

func (AppendFunc) Append

func (af AppendFunc) Append(b []byte, t time.Time) []byte

type Appender

type Appender interface {
	Append([]byte, time.Time) []byte
}

Appender is the interface that must be fulfilled by components that implement the translation of specifications to actual time value.

The Append method takes the accumulated byte buffer, and the time to use to generate the textual representation. The resulting byte sequence must be returned by this method, normally by using the append() builtin function.

func Microseconds

func Microseconds() Appender

Microsecond returns the Appender suitable for creating a zero-padded, 6-digit microsecond textual representation.

func Milliseconds

func Milliseconds() Appender

Milliseconds returns the Appender suitable for creating a zero-padded, 3-digit millisecond textual representation.

func StdlibFormat

func StdlibFormat(s string) Appender

StdlibFormat returns an Appender that simply goes through `time.Format()` For example, if you know you want to display the abbreviated month name for %b, you can create a StdlibFormat with the pattern `Jan` and register that for specification `b`:

a := StdlibFormat(`Jan`) ss := NewSpecificationSet() ss.Set('b', a) // does %b -> abbreviated month name

func UnixSeconds

func UnixSeconds() Appender

UnixSeconds returns the Appender suitable for creating unix timestamp textual representation.

func Verbatim

func Verbatim(s string) Appender

Verbatim returns an Appender suitable for generating static text. For static text, this method is slightly favorable than creating your own appender, as adjacent verbatim blocks will be combined at compile time to produce more efficient Appenders

type Option

type Option interface {
	Name() string
	Value() interface{}
}

func WithMicroseconds

func WithMicroseconds(b byte) Option

WithMicroseconds is similar to WithSpecification, and specifies that the Strftime object should interpret the pattern `%b` (where b is the byte that you specify as the argument) as the zero-padded, 3 letter microseconds of the time.

func WithMilliseconds

func WithMilliseconds(b byte) Option

WithMilliseconds is similar to WithSpecification, and specifies that the Strftime object should interpret the pattern `%b` (where b is the byte that you specify as the argument) as the zero-padded, 3 letter milliseconds of the time.

func WithSpecification

func WithSpecification(b byte, a Appender) Option

WithSpecification allows you to create a new specification set on the fly, to be used only for that invocation.

func WithSpecificationSet

func WithSpecificationSet(ds SpecificationSet) Option

WithSpecification allows you to specify a custom specification set

func WithUnixSeconds

func WithUnixSeconds(b byte) Option

WithUnixSeconds is similar to WithSpecification, and specifies that the Strftime object should interpret the pattern `%b` (where b is the byte that you specify as the argument) as the unix timestamp in seconds

type SpecificationSet

type SpecificationSet interface {
	Lookup(byte) (Appender, error)
	Delete(byte) error
	Set(byte, Appender) error
}

SpecificationSet is a container for patterns that Strftime uses. If you want a custom strftime, you can copy the default SpecificationSet and tweak it

Example

package main

import (
	"fmt"
	"os"
	"time"

	"github.com/lestrrat-go/strftime"
)

var ref = time.Unix(1136239445, 123456789).UTC()

func main() {
	{
		// I want %L as milliseconds!
		p, err := strftime.New(`%L`, strftime.WithMilliseconds('L'))
		if err != nil {
			fmt.Println(err)
			return
		}
		p.Format(os.Stdout, ref)
		os.Stdout.Write([]byte{'\n'})
	}

	{
		// I want %f as milliseconds!
		p, err := strftime.New(`%f`, strftime.WithMilliseconds('f'))
		if err != nil {
			fmt.Println(err)
			return
		}
		p.Format(os.Stdout, ref)
		os.Stdout.Write([]byte{'\n'})
	}

	{
		// I want %X to print out my name!
		a := strftime.Verbatim(`Daisuke Maki`)
		p, err := strftime.New(`%X`, strftime.WithSpecification('X', a))
		if err != nil {
			fmt.Println(err)
			return
		}
		p.Format(os.Stdout, ref)
		os.Stdout.Write([]byte{'\n'})
	}

	{
		// I want a completely new specification set, and I want %X to print out my name!
		a := strftime.Verbatim(`Daisuke Maki`)

		ds := strftime.NewSpecificationSet()
		ds.Set('X', a)
		p, err := strftime.New(`%X`, strftime.WithSpecificationSet(ds))
		if err != nil {
			fmt.Println(err)
			return
		}
		p.Format(os.Stdout, ref)
		os.Stdout.Write([]byte{'\n'})
	}

	{
		// I want %s as unix timestamp!
		p, err := strftime.New(`%s`, strftime.WithUnixSeconds('s'))
		if err != nil {
			fmt.Println(err)
			return
		}
		p.Format(os.Stdout, ref)
		os.Stdout.Write([]byte{'\n'})
	}

}

Output:

123
123
Daisuke Maki
Daisuke Maki
1136239445

func NewSpecificationSet

func NewSpecificationSet() SpecificationSet

NewSpecificationSet creates a specification set with the default specifications.

type Strftime

type Strftime struct {
	// contains filtered or unexported fields
}

Strftime is the object that represents a compiled strftime pattern

func New

func New(p string, options ...Option) (*Strftime, error)

New creates a new Strftime object. If the compilation fails, then an error is returned in the second argument.

func (*Strftime) Dump

func (f *Strftime) Dump(out io.Writer)

Dump outputs the internal structure of the formatter, for debugging purposes. Please do NOT assume the output format to be fixed: it is expected to change in the future.

func (*Strftime) Format

func (f *Strftime) Format(dst io.Writer, t time.Time) error

Format takes the destination `dst` and time `t`. It formats the date/time using the pre-compiled pattern, and outputs the results to `dst`

func (*Strftime) FormatBuffer

func (f *Strftime) FormatBuffer(dst []byte, t time.Time) []byte

FormatBuffer is equivalent to Format, but appends the result directly to supplied slice dst, returning the updated slice. This avoids any internal memory allocation.

func (*Strftime) FormatString

func (f *Strftime) FormatString(t time.Time) string

FormatString takes the time `t` and formats it, returning the string containing the formated data.

func (*Strftime) Pattern

func (f *Strftime) Pattern() string

Pattern returns the original pattern string