Using https://github.com/tdewolff/minify to minify html response in golang Revel.

revel-minify-js-css-html.go

//
// The MIT License (MIT)
//
// Copyright (c) 2016 Jeevanandam M. (jeeva@myjeeva.com)
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//
// Article: http://myjeeva.com/minify-filter-revel-framework-go-lang.html

package filter

import (
	"io"
	"net/http"
	"regexp"
	"github.com/revel/revel"
	"github.com/tdewolff/minify"
	"github.com/tdewolff/minify/html"
	"github.com/tdewolff/minify/css"
	"github.com/tdewolff/minify/js"
)

var (
	htmlMimeType *regexp.Regexp
	m *minify.M
)

type MinifyWriter struct {
	http.ResponseWriter
	minifyWriter   io.WriteCloser
	shouldMinify   bool
	headersWritten bool
	closeNotify    chan bool
	parentNotify   <-chan bool
	closed         bool
}

func init()  {
	
	m = minify.New()

	m.AddFunc("text/css", css.Minify)
	m.AddFunc("text/javascript", js.Minify)
	m.Add("text/html", &html.Minifier{
		KeepDefaultAttrVals: true,
		KeepWhitespace: false,
	})
	htmlMimeType = regexp.MustCompile("[text|application]/html")
}

func Minify(c *revel.Controller, fc []revel.Filter) {
	fc[0](c, fc[1:])

	if revel.Config.BoolDefault("results.minify", false) {
		if c.Response.Status != http.StatusNoContent && c.Response.Status != http.StatusNotModified {


			// add with options

			mw := m.Writer("text/html; charset=utf-8", c.Response.Out)

			writer := MinifyWriter{c.Response.Out, mw, false, false, make(chan bool, 1), nil, false}
			w, ok := c.Response.Out.(http.CloseNotifier)


			if ok {
				writer.parentNotify = w.CloseNotify()
			}


			c.Response.Out = &writer
		} else {
			revel.TRACE.Printf("Minify disabled for response status (%d)", c.Response.Status)
		}
	}
}

func (c MinifyWriter) CloseNotify() <-chan bool {

	if c.parentNotify != nil {
		return c.parentNotify
	}
	return c.closeNotify
}

func (c *MinifyWriter) WriteHeader(status int) {
	c.headersWritten = true
	c.prepareHeader()
	c.ResponseWriter.WriteHeader(status)


}

func (c *MinifyWriter) prepareHeader() {
	// minify is only applied to HTML content
	if htmlMimeType.MatchString(c.Header().Get("Content-Type")) {
		c.shouldMinify = true
		c.Header().Del("Content-Length")
	}
}

func (c *MinifyWriter) Close() error {
	if c.shouldMinify {
		c.minifyWriter.Close()
	}

	if w, ok := c.ResponseWriter.(io.Closer); ok {
		w.Close()
	}

	// Non-blocking write to the closenotifier, if we for some reason should
	// get called multiple times
	select {
	case c.closeNotify <- true:
	default:
	}
	c.closed = true
	return nil
}

func (c *MinifyWriter) Write(b []byte) (int, error) {
	// Abort if parent has been closed
	if c.parentNotify != nil {
		select {
		case <-c.parentNotify:
			return 0, io.ErrClosedPipe
		default:
		}
	}

	// Abort if we ourselves have been closed
	if c.closed {
		return 0, io.ErrClosedPipe
	}

	if !c.headersWritten {
		c.prepareHeader()
		c.headersWritten = true
	}

	if c.shouldMinify {
		return c.minifyWriter.Write(b)
	} else {
		return c.ResponseWriter.Write(b)
	}
}