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# Minify Build Status GoDoc Coverage Status Join the chat at https://gitter.im/tdewolff/minify

The preferred stable release is v2. Master has some new changes for SVG that haven't yet endured the test of time, bug reports are appreciated.

Online demo if you need to minify files now.

Command line tool that minifies concurrently and supports watching file changes.

All releases on Equinox for various platforms.

If this software is useful to you, consider making a donation! When a significant amount has been deposited, I will write a much improved JS minifier.

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

The core functionality associates mimetypes with minification functions, allowing embedded resources (like CSS or JS within HTML files) to be minified as well. Users can add new implementations that are triggered based on a mimetype (or pattern), or redirect to an external command (like ClosureCompiler, UglifyCSS, ...).

Table of Contents

Status

  • CSS: fully implemented
  • HTML: fully implemented
  • JS: basic JSmin-like implementation
  • JSON: fully implemented
  • SVG: partially implemented; in development
  • XML: fully implemented

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 and Google Closure Compiler for JS. As most existing implementations either use Java or JavaScript and don't focus on performance, they are pretty slow. And loading the whole file into memory is bad for really large files (or impossible for infinite streams).

This minifier proves to be that fast and extensive minifier that can handle HTML and any other filetype it may contain (CSS, JS, ...). It streams the input and output and can minify files concurrently.

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"
)

API stability

There is no guarantee for absolute stability, but I take issues and bugs seriously and don't take API changes lightly. The library will be maintained in a compatible way unless vital bugs prevent me from doing so. There has been one API change after v1 which added options support and I took the opportunity to push through some more API clean up as well. There are no plans whatsoever for future API changes.

  • minify-v1.0.0 depends on parse-v1.0.0
  • minify-v1.1.0 depends on parse-v1.1.0
  • minify-v2.0.0 depends on parse-v2.0.0
  • minify-tip will always compile with my other packages on tip

The API differences between v1 and v2 are listed below. If m := minify.New() and w and r are your writer and reader respectfully, then v1 → v2:

  • minify.Bytes(m, ...) → m.Bytes(...)
  • minify.String(m, ...) → m.String(...)
  • html.Minify(m, "text/html", w, r) → html.Minify(m, w, r, nil) also for css, js, ...
  • css.Minify(m, "text/css;inline=1", w, r) → css.Minify(m, w, r, map[string]string{"inline":"1"})

Testing

For all subpackages and the imported parse and buffer packages, test coverage of 100% is pursued. Besides full coverage, the minifiers are fuzz tested using github.com/dvyukov/go-fuzz, see the wiki for the most important bugs found by fuzz testing. Furthermore am I working on adding visual testing to ensure that minification doesn't change anything visually. By using the WebKit browser to render the original and minified pages we can check whether any pixel is different.

These tests ensure that everything works as intended, the code does not crash (whatever the input) and that it doesn't change the final result visually. If you still encounter a bug, please report here!

HTML

HTML (with JS and CSS) minification typically runs at about 40MB/s ~= 140GB/h, depending on the composition of the file.

Website Original Minified Ratio Time*
Amazon 463kB 414kB 90% 10ms
BBC 113kB 96kB 85% 3ms
StackOverflow 201kB 182kB 91% 5ms
Wikipedia 435kB 410kB 94%** 11ms

*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.

The HTML5 minifier uses these minifications:

  • strip unnecessary whitespace and otherwise collapse it to one space (or newline if it originally contained a newline)
  • 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

Options:

  • KeepDefaultAttrVals do not remove default attribute value such as <script type="text/javascript">
  • KeepDocumentTags do not remove html, head and body tags
  • KeepWhitespace do not remove whitespace between inline tags but still collapse multiple whitespace characters into one

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!

Whitespace removal

The whitespace removal mechanism collapses all sequences of whitespace (spaces, newlines, tabs) to a single space. If the sequence contained a newline or carriage return it will collapse into a newline character instead. 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 25MB/s ~= 90GB/h.

Library Original Minified Ratio Time*
Bootstrap 134kB 111kB 83% 4ms
Gumby 182kB 167kB 90% 7ms

*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 employs all the rules that JSMin does too, but has additional improvements. For example the prefix-postfix bug is fixed.

Minification typically runs at about 50MB/s ~= 180GB/h. Common speeds of PHP and JS implementations are about 100-300kB/s (see Uglify2, Adventures in PHP web asset minimization).

Library Original Minified Ratio Time*
ACE 630kB 442kB 70% 12ms
jQuery 242kB 130kB 54% 5ms
jQuery UI 459kB 300kB 65% 10ms
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 95MB/s ~= 340GB/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

Minification typically runs at about 15MB/s ~= 55GB/h. Performance improvement are due.

The SVG minifier uses these minifications:

  • trim and collapse whitespace between all tags
  • strip comments, empty 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 path data
  • convert rect, line, polygon, polyline to path
  • use relative or absolute positions in path data whichever is shorter

TODO:

  • convert attributes to style attribute whenever shorter
  • merge path data? (same style and no intersection -- the latter is difficult)
  • truncate decimals

XML

Minification typically runs at about 70MB/s ~= 250GB/h.

The XML minifier uses these minifications:

  • strip unnecessary whitespace and otherwise collapse it to one space (or newline if it originally contained a newline)
  • strip comments
  • collapse tags with no content to a void tag
  • strip CDATA sections wherever possible

Options:

  • KeepWhitespace do not remove whitespace between inline tags but still collapse multiple whitespace characters into one

Usage

Any input stream is being buffered by the minification functions. This is how the underlying buffer package inherently works to ensure high performance. The output stream however is not buffered. It is wise to preallocate a buffer as big as the input to which the output is written, or otherwise use bufio to buffer to a streaming writer.

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)

You can set options to several minifiers.

m.Add("text/html", &html.Minifier{
	KeepDefaultAttrVals: true,
	KeepWhitespace: true,
})

From reader

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

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

From bytes

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

b, err = m.Bytes(mediatype, b)
if err != nil {
	panic(err)
}

From string

Minify from and to a string for a specific mediatype.

s, err = m.String(mediatype, s)
if err != nil {
	panic(err)
}

From reader

Get a minifying reader for a specific mediatype.

mr := m.Reader(mediatype, r)
if _, err := mr.Read(b); err != nil {
	panic(err)
}

From writer

Get a minifying writer for a specific mediatype. Must be explicitly closed because it uses an io.Pipe underneath.

mw := m.Writer(mediatype, w)
if mw.Write([]byte("input")); err != nil {
	panic(err)
}
if err := mw.Close(); err != nil {
	panic(err)
}

Custom minifier

Add a minifier for a specific mimetype.

type CustomMinifier struct {
	KeepLineBreaks bool
}

func (c *CustomMinifier) Minify(m *minify.M, w io.Writer, r io.Reader, params map[string]string) error {
	// ...
	return nil
}

m.Add(mimetype, &CustomMinifier{KeepLineBreaks: true})
// or
m.AddRegexp(regexp.MustCompile("/x-custom$"), &CustomMinifier{KeepLineBreaks: true})

Add a minify function for a specific mimetype.

m.AddFunc(mimetype, func(m *minify.M, w io.Writer, r io.Reader, params map[string]string) error {
	// ...
	return nil
})
m.AddFuncRegexp(regexp.MustCompile("/x-custom$"), func(m *minify.M, w io.Writer, r io.Reader, params map[string]string) error {
	// ...
	return nil
})

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

m.AddCmd(mimetype, exec.Command(cmd, args...))
m.AddCmdRegexp(regexp.MustCompile("/x-custom$"), exec.Command(cmd, args...))

Mediatypes

Using the params map[string]string argument one can pass parameters to the minifier such as seen in mediatypes (type/subtype; key1=val2; key2=val2). Examples are the encoding or charset of the data. Calling Minify will split the mimetype and parameters for the minifiers for you, but MinifyMimetype can be used if you already have them split up.

Minifiers can also be added using a regular expression. For example a minifier with image/.* will match any image mime.

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 {
		panic(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"
)

func main() {
	m := minify.New()
	m.AddFunc("text/plain", func(m *minify.M, w io.Writer, r io.Reader, _ map[string]string) error {
		// remove newlines and spaces
		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
	})

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

ResponseWriter

Middleware

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)

	http.Handle("/", m.Middleware(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		http.ServeFile(w, r, path.Join("www", r.URL.Path))
	})))
}

ResponseWriter

func Serve(w http.ResponseWriter, r *http.Request) {
	mw := m.ResponseWriter(w, r)
	defer mw.Close()
	w = mw

	http.ServeFile(w, r, path.Join("www", r.URL.Path))
}

Custom response writer

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.WriteCloser
}

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

// MinifyResponseWriter must be closed explicitly by calling site.
func MinifyFilter(mediatype string, res http.ResponseWriter) MinifyResponseWriter {
	m := minify.New()
	// add minfiers

	mw := m.Writer(mediatype, res)
	return MinifyResponseWriter{res, mw}
}
// Usage
func(w http.ResponseWriter, req *http.Request) {
	w = MinifyFilter("text/html", w)
	if _, err := io.WriteString(w, "<p class="message"> This HTTP response will be minified. </p>"); err != nil {
		panic(err)
	}
	if err := w.Close(); err != nil {
		panic(err)
	}
	// Output: <p class=message>This HTTP response will be minified.
}

Templates

Here's an example of a replacement for template.ParseFiles from template/html, which automatically minifies each template before parsing it.

Be aware that minifying templates will work in most cases but not all. Because the HTML minifier only works for valid HTML5, your template must be valid HTML5 of itself. Template tags are parsed as regular text by the minifier.

func compileTemplates(filenames ...string) (*template.Template, error) {
	m := minify.New()
	m.AddFunc("text/html", html.Minify)

	var tmpl *template.Template
	for _, filename := range filenames {
		name := filepath.Base(filename)
		if tmpl == nil {
			tmpl = template.New(name)
		} else {
			tmpl = tmpl.New(name)
		}

		b, err := ioutil.ReadFile(filename)
		if err != nil {
			return nil, err
		}

		mb, err := m.Bytes("text/html", b)
		if err != nil {
			return nil, err
		}
		tmpl.Parse(string(mb))
	}
	return tmpl, nil
}

Example usage:

templates := template.MustCompile(compileTemplates("view.html", "home.html"))

License

Released under the MIT license.

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