Minify

Update: online live demo running on a Raspberry Pi 2.

Update: command-line-interface executable minify provided for tooling.

Minify is a minifier package written in Go. It has build-in HTML5, CSS3, JS, JSON, SVG and XML minifiers and provides an interface to implement any minifier. Minification is the process of removing bytes from a file (such as whitespace) without changing its output and therefore speeding up transmission over the internet. The implemented minifiers are high performance and streaming (which implies O(n)).

It associates minification functions with mime types, allowing embedded resources (like CSS or JS in HTML files) to be minified too. The user can add any mime-based implementation. Users can also implement a mime type using an external command (like the ClosureCompiler, UglifyCSS, ...). It is possible to pass parameters through the mimetype to specify the charset for example.

Bottleneck for minification is mainly io and can be significantly sped up by having the file loaded into memory and providing a Bytes() []byte function like bytes.Buffer does.

See the Wiki for a roadmap of what is planned for the future.

Table of Contents

Minify
- Prologue
- Comparison
  - Alternatives
- HTML
  - Beware
- CSS
- JS
- JSON
- SVG
- XML
- Installation
- Usage
- Examples
- License

Prologue

Minifiers or bindings to minifiers exist in almost all programming languages. Some implementations are merely using several regular-expressions to trim whitespace and comments (even though regex for parsing HTML/XML is ill-advised, for a good read see Regular Expressions: Now You Have Two Problems). Some implementations are much more profound, such as the YUI Compressor, Google Closure Compiler for JS and the HTML Compressor.

These industry-grade minifiers are written in Java and are generally relatively slow. Futhermore, these tools provide a large number of configurations which is often confusing or not required. Regular-expression based minifiers are slow anyways because they use multiple regular-expressions, each of which parses the complete document. While regular-expressions are overkill (or ill-advised) for parsing HTML/CSS/JS documents, parsing it a number of times is certainly not speeding things up. Other implementations are mostly written in uncompiled languages such as JS, which is great for bindings with Grunt for example, but catastrophic for the minification speed of large files or projects with many files.

Additionally, many of these minifier either do not follow the specifications or drag a lot of legacy code around. When you are still trying to support IE6 I don't suppose you are squeezing out every bit of performance from your web applications. Supporting old mistakes or work-arounds is not a fairly long-term vision and seldomly justified.

However, implementing an HTML minifier is the bare minimum. HTML documents can contain embedded resources such as CSS, JS and SVG file formats. Thus for increased minification of HTML, other file format minifiers must be present too. A minifier should really handle a number of mediatypes to be successful.

This minifier proves to be that fast and encompassing minifier which stream-minifies files and can minify them concurrently.

Comparison

HTML (with JS and CSS) minification typically runs at about 30MB/s ~= 100GB/h, depending on the composition of the file.

Website	Original	Minified	Ratio	Time^*
Amazon	463kB	414kB	89%	13ms
BBC	113kB	96kB	85%	4ms
StackOverflow	201kB	182kB	91%	7ms
Wikipedia	435kB	410kB	94%^**	14ms

^*These times are measured on my home computer which is an average development computer. The duration varies a lot but it's important to see it's in the 10ms range! The benchmark uses all the minifiers and excludes reading from and writing to the file from the measurement.

^**Is already somewhat minified, so this doesn't reflect the full potential of this minifier.

HTML Compressor performs worse in output size (for HTML and CSS) and speed; it is a magnitude slower. Its whitespace removal is not precise or the user must provide the tags around which can be trimmed. According to HTML Compressor, it produces smaller files than a couple of other libraries. With HTML and CSS minification this package is better, but JS minification it is still too basic.

Alternatives

An alternative library written in Go is https://github.com/dchest/htmlmin. It is simpler (less bugs but not handling edge-cases) but slower. Also https://github.com/omeid/jsmin contains a port of JSMin, just like this JS minifier, but is slower.

Other alternatives are bindings for existing minifiers written in other languages. These are inevitably more robust and tested but will often be slower. For example, Java-based minifiers incur overhead of starting up the JVM.

HTML

The HTML5 minifier uses these minifications:

strip unnecessary whitespace and otherwise collapse it to one space
strip superfluous quotes, or uses single/double quotes whichever requires fewer escapes
strip default attribute values and attribute boolean values
strip some empty attributes
strip unrequired tags (html, head, body, ...)
strip unrequired end tags (tr, td, li, ... and often p)
strip default protocols (http:, https: and javascript:)
strip comments (except conditional comments)
shorten doctype and meta charset
lowercase tags, attributes and some values to enhance gzip compression

After recent benchmarking and profiling it became really fast and minifies pages in the 10ms range, making it viable for on-the-fly minification.

However, be careful when doing on-the-fly minification. Minification typically trims off 10% and does this at worst around about 20MB/s. This means users have to download slower than 2MB/s to make on-the-fly minification worthwhile. This may or may not apply in your situation. Rather use caching!

Beware

Whitespace removal

The whitespace removal mechanism collapses all sequences of whitespace (spaces, newlines, tabs, ...) to a single space. It trims all text parts (in between tags) depending on whether it was preceded by a space from a previous piece of text and whether it is followed up by a block element or an inline element. In the former case we can omit spaces while for inline elements whitespace has significance.

Make sure your HTML doesn't depend on whitespace between block elements that have been changed to inline or inline-block elements using CSS. Your layout should not depend on those whitespaces as the minifier will remove them. An example is a menu consisting of multiple <li> that have display:inline-block applied and have whitespace in between them. It is bad practise to rely on whitespace for element positioning anyways!

CSS

Minification typically runs at about 20MB/s ~= 70GB/h.

Library	Original	Minified	Ratio	Time^*
Bootstrap	134kB	111kB	83%	6ms
Gumby	182kB	167kB	91%	9ms

^*The benchmark excludes the time reading from and writing to a file from the measurement.

The CSS minifier will only use safe minifications:

remove comments and unnecessary whitespace
remove trailing semicolons
optimize margin, padding and border-width number of sides
shorten numbers by removing unnecessary + and zeros and rewriting with/without exponent
remove dimension and percentage for zero values
remove quotes for URLs
remove quotes for font families and make lowercase
rewrite hex colors to/from color names, or to 3 digit hex
rewrite rgb(, rgba(, hsl( and hsla( colors to hex or name
replace normal and bold by numbers for font-weight and font
replace none → 0 for border, background and outline
lowercase all identifiers except classes, IDs and URLs to enhance gzip compression
shorten MS alpha function
rewrite data URIs with base64 or ASCII whichever is shorter
calls minifier for data URI mediatypes, thus you can compress embedded SVG files if you have that minifier attached

It does purposely not use the following techniques:

(partially) merge rulesets
(partially) split rulesets
collapse multiple declarations when main declaration is defined within a ruleset (don't put font-weight within an already existing font, too complex)
remove overwritten properties in ruleset (this not always overwrites it, for example with !important)
rewrite properties into one ruleset if possible (like margin-top, margin-right, margin-bottom and margin-left → margin)
put nested ID selector at the front (body > div#elem p → #elem p)
rewrite attribute selectors for IDs and classes (div[id=a] → div#a)
put space after pseudo-selectors (IE6 is old, move on!)

It's great that so many other tools make comparison tables: CSS Minifier Comparison, CSS minifiers comparison and CleanCSS tests. From the last link, this CSS minifier is almost without doubt the fastest and has near-perfect minification rates. It falls short with the purposely not implemented and often unsafe techniques, so that's fine.

JS

The JS minifier is pretty basic. It removes comments, whitespace and line breaks whenever it can. It follows the rules by JSMin but additionally fixes the error in the 'caution' section.

Minification typically runs at about 45MB/s ~= 160GB/h.

Library	Original	Minified	Ratio	Time^*
ACE	616kB	433kB	70%	13ms
jQuery	242kB	130kB	54%	5ms
jQuery UI	459kB	300kB	65%	11ms
Moment	97kB	51kB	52%	2ms

^*The benchmark excludes the time reading from and writing to a file from the measurement.

TODO:

shorten local variables / function parameters names
precise semicolon and newline omission

JSON

Minification typically runs at about 75MB/s ~= 270GB/h. It shaves off about 15% of filesize for common indented JSON such as generated by JSON Generator.

The JSON minifier only removes whitespace, which is the only thing that can be left out.

SVG

The SVG minifier uses these minifications:

trim and collapse whitespace between all tags
strip comments, doctype, XML prelude, metadata
strip SVG version
strip CDATA sections wherever possible
collapse tags with no content to a void tag
collapse empty container tags (g, svg, ...)
minify style tag and attributes with the CSS minifier
minify colors
shorten lengths and numbers and remove default px unit
shorten the path data m attribute

TODO:

convert rect, line, polygon, polyline to path
convert attributes to style attribute whenever shorter
use relative instead of absolute positions for path data (need bytes2float)
merge path data? (same style and no intersection -- the latter is difficult)

XML

Minification typically runs at about 50MB/s ~= 180GB/h.

The XML minifier uses these minifications:

strip unnecessary whitespace and otherwise collapse it to one space
strip comments
collapse tags with no content to a void tag
strip CDATA sections wherever possible

Installation

Run the following command

go get github.com/tdewolff/minify

or add the following imports and run the project with go get

import (
	"github.com/tdewolff/minify"
	"github.com/tdewolff/minify/css"
	"github.com/tdewolff/minify/html"
	"github.com/tdewolff/minify/js"
	"github.com/tdewolff/minify/json"
	"github.com/tdewolff/minify/svg"
	"github.com/tdewolff/minify/xml"
)

Usage

New

Retrieve a minifier struct which holds a map of mediatype → minifier functions.

m := minify.New()

The following loads all provided minifiers.

m := minify.New()
m.AddFunc("text/css", css.Minify)
m.AddFunc("text/html", html.Minify)
m.AddFunc("text/javascript", js.Minify)
m.AddFunc("image/svg+xml", svg.Minify)
m.AddFuncRegexp(regexp.MustCompile("[/+]json$"), json.Minify)
m.AddFuncRegexp(regexp.MustCompile("[/+]xml$"), xml.Minify)

From reader

Minify from an io.Reader to an io.Writer for a specific mediatype.

if err := m.Minify(mediatype, w, r); err != nil {
	log.Fatal("Minify:", err)
}

Minify HTML, CSS or JS directly from an io.Reader to an io.Writer. The passed mediatype is not required for these functions, but are filled out for clarity.

if err := css.Minify(m, "text/css", w, r); err != nil {
	log.Fatal("css.Minify:", err)
}

if err := html.Minify(m, "text/html", w, r); err != nil {
	log.Fatal("html.Minify:", err)
}

if err := js.Minify(m, "text/javascript", w, r); err != nil {
	log.Fatal("js.Minify:", err)
}

if err := json.Minify(m, "application/json", w, r); err != nil {
	log.Fatal("json.Minify:", err)
}

if err := svg.Minify(m, "image/svg+xml", w, r); err != nil {
	log.Fatal("svg.Minify:", err)
}

if err := xml.Minify(m, "text/xml", w, r); err != nil {
	log.Fatal("xml.Minify:", err)
}

From bytes

Minify from and to a []byte for a specific mediatype.

b, err = minify.Bytes(m, mediatype, b)
if err != nil {
	log.Fatal("minify.Bytes:", err)
}

From string

Minify from and to a string for a specific mediatype.

s, err = minify.String(m, mediatype, s)
if err != nil {
	log.Fatal("minify.String:", err)
}

Custom minifier

Add a function for a specific mediatype.

m.AddFunc(mediatype, func(m minify.Minifier, mediatype string, w io.Writer, r io.Reader) error {
	// ...
	return nil
})

Add a command cmd with arguments args for a specific mediatype.

m.AddCmd(mediatype, exec.Command(cmd, args...))

Mediatypes

Mediatypes can contain parameters (type/subtype; key1=val2; key2=val2). Minifiers can also be added using a regular expression. For example a minifier with image/.* will match any image mime.

Mediatypes such as text/plain; charset=UTF-8 will be processed by text/plain or any regexp it matches. The mediatype string is passed to the minifier function which can retrieve the parameters using the standard library mime.ParseMediaType.

Examples

Common minifiers

Basic example that minifies from stdin to stdout and loads the default HTML, CSS and JS minifiers. Optionally, one can enable java -jar build/compiler.jar to run for JS (for example the ClosureCompiler). Note that reading the file into a buffer first and writing to a pre-allocated buffer would be faster (but would disable streaming).

package main

import (
	"log"
	"os"
	"os/exec"

	"github.com/tdewolff/minify"
	"github.com/tdewolff/minify/css"
	"github.com/tdewolff/minify/html"
	"github.com/tdewolff/minify/js"
	"github.com/tdewolff/minify/json"
	"github.com/tdewolff/minify/svg"
	"github.com/tdewolff/minify/xml"
)

func main() {
	m := minify.New()
	m.AddFunc("text/css", css.Minify)
	m.AddFunc("text/html", html.Minify)
	m.AddFunc("text/javascript", js.Minify)
	m.AddFunc("image/svg+xml", svg.Minify)
	m.AddFuncRegexp(regexp.MustCompile("[/+]json$"), json.Minify)
	m.AddFuncRegexp(regexp.MustCompile("[/+]xml$"), xml.Minify)

	// Or use the following for better minification of JS but lower speed:
	// m.AddCmd("text/javascript", exec.Command("java", "-jar", "build/compiler.jar"))

	if err := m.Minify("text/html", os.Stdout, os.Stdin); err != nil {
		log.Fatal("Minify:", err)
	}
}

Custom minifier

Custom minifier showing an example that implements the minifier function interface. Within a custom minifier, it is possible to call any minifier function (through m minify.Minifier) recursively when dealing with embedded resources.

package main

import (
	"bufio"
	"fmt"
	"io"
	"log"
	"strings"

	"github.com/tdewolff/minify"
)

// Outputs "Becausemycoffeewastoocold,Iheateditinthemicrowave."
func main() {
	m := minify.New()

	// remove newline and space bytes
	m.AddFunc("text/plain", func(m minify.Minifier, mediatype string, w io.Writer, r io.Reader) error {
		rb := bufio.NewReader(r)
		for {
			line, err := rb.ReadString('\n')
			if err != nil && err != io.EOF {
				return err
			}
			if _, errws := io.WriteString(w, strings.Replace(line, " ", "", -1)); errws != nil {
				return errws
			}
			if err == io.EOF {
				break
			}
		}
		return nil
	})

	out, err := minify.String(m, "text/plain", "Because my coffee was too cold, I heated it in the microwave.")
	if err != nil {
		log.Fatal("Minify:", err)
	}
	fmt.Println(out)
}

ResponseWriter

ResponseWriter example which returns a ResponseWriter that minifies the content and then writes to the original ResponseWriter. Any write after applying this filter will be minified.

type MinifyResponseWriter struct {
	http.ResponseWriter
	io.Writer
}

func (m MinifyResponseWriter) Write(b []byte) (int, error) {
	return m.Writer.Write(b)
}

func MinifyFilter(res http.ResponseWriter, mimetype string) http.ResponseWriter {
	m := minify.New()
	// add other minfiers

	pr, pw := io.Pipe()
	go func(w io.Writer) {
		if err := m.Minify(mimetype, w, pr); err != nil {
			panic(err)
		}
	}(res)
	return MinifyResponseWriter{res, pw}
}

License

Released under the MIT license.

Name		Name	Last commit message	Last commit date
Latest commit History 467 Commits
cmd/minify		cmd/minify
css		css
html		html
js		js
json		json
svg		svg
xml		xml
.travis.yml		.travis.yml
LICENSE.md		LICENSE.md
README.md		README.md
common.go		common.go
common_test.go		common_test.go
minify.go		minify.go
minify_test.go		minify_test.go

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Minify

Prologue

Comparison

Alternatives

HTML

Beware

Whitespace removal

CSS

JS

JSON

SVG

XML

Installation

Usage

New

From reader

From bytes

From string

Custom minifier

Mediatypes

Examples

Common minifiers

Custom minifier

ResponseWriter

License

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Minify

Prologue

Comparison

Alternatives

HTML

Beware

Whitespace removal

CSS

JS

JSON

SVG

XML

Installation

Usage

New

From reader

From bytes

From string

Custom minifier

Mediatypes

Examples

Common minifiers

Custom minifier

ResponseWriter

License

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