Add support for minification of final output

Hugo Pipes added minification support for resources fetched via ´resources.Get` and similar.

This also adds support for minification of the final output for supported output formats: HTML, XML, SVG, CSS, JavaScript, JSON.

To enable, run Hugo with the `--minify` flag:

```bash
hugo --minify
```

This commit is also a major spring cleaning of the `transform` package to allow the new minification step fit into that processing chain.

Fixes #1251

2 files changed, 161 insertions, 0 deletions

diff --git a/minifiers/minifiers.go b/minifiers/minifiers.go
new file mode 100644
index 000000000..70d42843f
--- /dev/null
+++ b/minifiers/minifiers.go
@@ -0,0 +1,126 @@
+// Copyright 2018 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package minifiers contains minifiers mapped to MIME types. This package is used
+// in both the resource transformation, i.e. resources.Minify, and in the publishing
+// chain.
+package minifiers
+
+import (
+	"io"
+
+	"github.com/gohugoio/hugo/output"
+	"github.com/gohugoio/hugo/transform"
+
+	"github.com/gohugoio/hugo/media"
+	"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"
+)
+
+// Client wraps a minifier.
+type Client struct {
+	m *minify.M
+}
+
+// Transformer returns a func that can be used in the transformer publishing chain.
+// TODO(bep) minify config etc
+func (m Client) Transformer(mediatype media.Type) transform.Transformer {
+	_, params, min := m.m.Match(mediatype.Type())
+	if min == nil {
+		// No minifier for this MIME type
+		return nil
+	}
+
+	return func(ft transform.FromTo) error {
+		// Note that the source io.Reader will already be buffered, but it implements
+		// the Bytes() method, which is recognized by the Minify library.
+		return min.Minify(m.m, ft.To(), ft.From(), params)
+	}
+}
+
+// Minify tries to minify the src into dst given a MIME type.
+func (m Client) Minify(mediatype media.Type, dst io.Writer, src io.Reader) error {
+	return m.m.Minify(mediatype.Type(), dst, src)
+}
+
+// New creates a new Client with the provided MIME types as the mapping foundation.
+// The HTML minifier is also registered for additional HTML types (AMP etc.) in the
+// provided list of output formats.
+func New(mediaTypes media.Types, outputFormats output.Formats) Client {
+	m := minify.New()
+	htmlMin := &html.Minifier{
+		KeepDocumentTags: true,
+	}
+
+	// We use the Type definition of the media types defined in the site if found.
+	addMinifierFunc(m, mediaTypes, "text/css", "css", css.Minify)
+	addMinifierFunc(m, mediaTypes, "application/javascript", "js", js.Minify)
+	addMinifierFunc(m, mediaTypes, "application/json", "json", json.Minify)
+	addMinifierFunc(m, mediaTypes, "image/svg+xml", "svg", svg.Minify)
+	addMinifierFunc(m, mediaTypes, "application/xml", "xml", xml.Minify)
+	addMinifierFunc(m, mediaTypes, "application/rss", "xml", xml.Minify)
+
+	// HTML
+	addMinifier(m, mediaTypes, "text/html", "html", htmlMin)
+	for _, of := range outputFormats {
+		if of.IsHTML {
+			addMinifier(m, mediaTypes, of.MediaType.Type(), "html", htmlMin)
+		}
+	}
+	return Client{m: m}
+
+}
+
+func addMinifier(m *minify.M, mt media.Types, typeString, suffix string, min minify.Minifier) {
+	resolvedTypeStr := resolveMediaTypeString(mt, typeString, suffix)
+	m.Add(resolvedTypeStr, min)
+	if resolvedTypeStr != typeString {
+		m.Add(typeString, min)
+	}
+}
+
+func addMinifierFunc(m *minify.M, mt media.Types, typeString, suffix string, fn minify.MinifierFunc) {
+	resolvedTypeStr := resolveMediaTypeString(mt, typeString, suffix)
+	m.AddFunc(resolvedTypeStr, fn)
+	if resolvedTypeStr != typeString {
+		m.AddFunc(typeString, fn)
+	}
+}
+
+func resolveMediaTypeString(types media.Types, typeStr, suffix string) string {
+	if m, found := resolveMediaType(types, typeStr, suffix); found {
+		return m.Type()
+	}
+	// Fall back to the default.
+	return typeStr
+}
+
+// Make sure we match the matching pattern with what the user have actually defined
+// in his or hers media types configuration.
+func resolveMediaType(types media.Types, typeStr, suffix string) (media.Type, bool) {
+	if m, found := types.GetByType(typeStr); found {
+		return m, true
+	}
+
+	if m, found := types.GetFirstBySuffix(suffix); found {
+		return m, true
+	}
+
+	return media.Type{}, false
+
+}
diff --git a/minifiers/minifiers_test.go b/minifiers/minifiers_test.go
new file mode 100644
index 000000000..6d72dc44e
--- /dev/null
+++ b/minifiers/minifiers_test.go
@@ -0,0 +1,35 @@
+// Copyright 2018 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package minifiers
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"github.com/gohugoio/hugo/media"
+
+	"github.com/gohugoio/hugo/output"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNew(t *testing.T) {
+	assert := require.New(t)
+	m := New(media.DefaultTypes, output.DefaultFormats)
+
+	var b bytes.Buffer
+
+	assert.NoError(m.Minify(media.CSSType, &b, strings.NewReader("body { color: blue; }")))
+	assert.Equal("body{color:blue}", b.String())
+}