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

9 files changed, 352 insertions, 293 deletions

diff --git a/transform/chain.go b/transform/chain.go
index f71de94c8..74217dc72 100644
--- a/transform/chain.go
+++ b/transform/chain.go
@@ -1,4 +1,4 @@
-// Copyright 2015 The Hugo Authors. All rights reserved.
+// 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.
@@ -20,67 +20,74 @@ import (
 	bp "github.com/gohugoio/hugo/bufferpool"
 )
 
-type trans func(rw contentTransformer)
+// Transformer is the func that needs to be implemented by a transformation step.
+type Transformer func(ft FromTo) error
 
-type link trans
+// BytesReader wraps the Bytes method, usually implemented by bytes.Buffer, and an
+// io.Reader.
+type BytesReader interface {
+	// The slice given by Bytes is valid for use only until the next buffer modification.
+	// That is, if you want to use this value outside of the current transformer step,
+	// you need to take a copy.
+	Bytes() []byte
 
-type chain []link
+	io.Reader
+}
 
-// NewChain creates a chained content transformer given the provided transforms.
-func NewChain(trs ...link) chain {
-	return trs
+// FromTo is sent to each transformation step in the chain.
+type FromTo interface {
+	From() BytesReader
+	To() io.Writer
 }
 
-// NewEmptyTransforms creates a new slice of transforms with a capacity of 20.
-func NewEmptyTransforms() []link {
-	return make([]link, 0, 20)
+// Chain is an ordered processing chain. The next transform operation will
+// receive the output from the previous.
+type Chain []Transformer
+
+// New creates a content transformer chain given the provided transform funcs.
+func New(trs ...Transformer) Chain {
+	return trs
 }
 
-// contentTransformer is an interface that enables rotation  of pooled buffers
-// in the transformer chain.
-type contentTransformer interface {
-	Path() []byte
-	Content() []byte
-	io.Writer
+// NewEmpty creates a new slice of transformers with a capacity of 20.
+func NewEmpty() Chain {
+	return make(Chain, 0, 20)
 }
 
 // Implements contentTransformer
 // Content is read from the from-buffer and rewritten to to the to-buffer.
 type fromToBuffer struct {
-	path []byte
 	from *bytes.Buffer
 	to   *bytes.Buffer
 }
 
-func (ft fromToBuffer) Path() []byte {
-	return ft.path
+func (ft fromToBuffer) From() BytesReader {
+	return ft.from
 }
 
-func (ft fromToBuffer) Write(p []byte) (n int, err error) {
-	return ft.to.Write(p)
+func (ft fromToBuffer) To() io.Writer {
+	return ft.to
 }
 
-func (ft fromToBuffer) Content() []byte {
-	return ft.from.Bytes()
-}
-
-func (c *chain) Apply(w io.Writer, r io.Reader, p []byte) error {
+// Apply passes the given from io.Reader through the transformation chain.
+// The result is written to to.
+func (c *Chain) Apply(to io.Writer, from io.Reader) error {
 	if len(*c) == 0 {
-		_, err := io.Copy(w, r)
+		_, err := io.Copy(to, from)
 		return err
 	}
 
 	b1 := bp.GetBuffer()
 	defer bp.PutBuffer(b1)
 
-	if _, err := b1.ReadFrom(r); err != nil {
+	if _, err := b1.ReadFrom(from); err != nil {
 		return err
 	}
 
 	b2 := bp.GetBuffer()
 	defer bp.PutBuffer(b2)
 
-	fb := &fromToBuffer{path: p, from: b1, to: b2}
+	fb := &fromToBuffer{from: b1, to: b2}
 
 	for i, tr := range *c {
 		if i > 0 {
@@ -95,9 +102,11 @@ func (c *chain) Apply(w io.Writer, r io.Reader, p []byte) error {
 			}
 		}
 
-		tr(fb)
+		if err := tr(fb); err != nil {
+			return err
+		}
 	}
 
-	_, err := fb.to.WriteTo(w)
+	_, err := fb.to.WriteTo(to)
 	return err
 }
diff --git a/transform/chain_test.go b/transform/chain_test.go
index ae5f06a2d..e34024296 100644
--- a/transform/chain_test.go
+++ b/transform/chain_test.go
@@ -1,4 +1,4 @@
-// Copyright 2015 The Hugo Authors. All rights reserved.
+// 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.
@@ -15,142 +15,44 @@ package transform
 
 import (
 	"bytes"
-	"path/filepath"
 	"strings"
 	"testing"
 
-	bp "github.com/gohugoio/hugo/bufferpool"
-	"github.com/gohugoio/hugo/helpers"
 	"github.com/stretchr/testify/assert"
 )
 
-const (
-	h5JsContentDoubleQuote      = "<!DOCTYPE html><html><head><script src=\"foobar.js\"></script><script src=\"/barfoo.js\"></script></head><body><nav><h1>title</h1></nav><article>content <a href=\"foobar\">foobar</a>. <a href=\"/foobar\">Follow up</a></article></body></html>"
-	h5JsContentSingleQuote      = "<!DOCTYPE html><html><head><script src='foobar.js'></script><script src='/barfoo.js'></script></head><body><nav><h1>title</h1></nav><article>content <a href='foobar'>foobar</a>. <a href='/foobar'>Follow up</a></article></body></html>"
-	h5JsContentAbsURL           = "<!DOCTYPE html><html><head><script src=\"http://user@host:10234/foobar.js\"></script></head><body><nav><h1>title</h1></nav><article>content <a href=\"https://host/foobar\">foobar</a>. Follow up</article></body></html>"
-	h5JsContentAbsURLSchemaless = "<!DOCTYPE html><html><head><script src=\"//host/foobar.js\"></script><script src='//host2/barfoo.js'></head><body><nav><h1>title</h1></nav><article>content <a href=\"//host/foobar\">foobar</a>. <a href='//host2/foobar'>Follow up</a></article></body></html>"
-	corectOutputSrcHrefDq       = "<!DOCTYPE html><html><head><script src=\"foobar.js\"></script><script src=\"http://base/barfoo.js\"></script></head><body><nav><h1>title</h1></nav><article>content <a href=\"foobar\">foobar</a>. <a href=\"http://base/foobar\">Follow up</a></article></body></html>"
-	corectOutputSrcHrefSq       = "<!DOCTYPE html><html><head><script src='foobar.js'></script><script src='http://base/barfoo.js'></script></head><body><nav><h1>title</h1></nav><article>content <a href='foobar'>foobar</a>. <a href='http://base/foobar'>Follow up</a></article></body></html>"
-
-	h5XMLXontentAbsURL        = "<?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"yes\" ?><feed xmlns=\"http://www.w3.org/2005/Atom\"><entry><content type=\"html\">&lt;p&gt;&lt;a href=&#34;/foobar&#34;&gt;foobar&lt;/a&gt;&lt;/p&gt; &lt;p&gt;A video: &lt;iframe src=&#39;/foo&#39;&gt;&lt;/iframe&gt;&lt;/p&gt;</content></entry></feed>"
-	correctOutputSrcHrefInXML = "<?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"yes\" ?><feed xmlns=\"http://www.w3.org/2005/Atom\"><entry><content type=\"html\">&lt;p&gt;&lt;a href=&#34;http://base/foobar&#34;&gt;foobar&lt;/a&gt;&lt;/p&gt; &lt;p&gt;A video: &lt;iframe src=&#39;http://base/foo&#39;&gt;&lt;/iframe&gt;&lt;/p&gt;</content></entry></feed>"
-	h5XMLContentGuarded       = "<?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"yes\" ?><feed xmlns=\"http://www.w3.org/2005/Atom\"><entry><content type=\"html\">&lt;p&gt;&lt;a href=&#34;//foobar&#34;&gt;foobar&lt;/a&gt;&lt;/p&gt; &lt;p&gt;A video: &lt;iframe src=&#39;//foo&#39;&gt;&lt;/iframe&gt;&lt;/p&gt;</content></entry></feed>"
-)
-
-const (
-	// additional sanity tests for replacements testing
-	replace1 = "No replacements."
-	replace2 = "ᚠᛇᚻ ᛒᛦᚦ ᚠᚱᚩᚠᚢᚱ\nᚠᛁᚱᚪ ᚷᛖᚻᚹᛦᛚᚳᚢᛗ"
-	replace3 = `End of file: src="/`
-	replace4 = `End of file: srcset="/`
-	replace5 = `Srcsett with no closing quote: srcset="/img/small.jpg do be do be do.`
-
-	// Issue: 816, schemaless links combined with others
-	replaceSchemalessHTML        = `Pre. src='//schemaless' src='/normal'  <a href="//schemaless">Schemaless</a>. <a href="/normal">normal</a>. Post.`
-	replaceSchemalessHTMLCorrect = `Pre. src='//schemaless' src='http://base/normal'  <a href="//schemaless">Schemaless</a>. <a href="http://base/normal">normal</a>. Post.`
-	replaceSchemalessXML         = `Pre. src=&#39;//schemaless&#39; src=&#39;/normal&#39;  <a href=&#39;//schemaless&#39;>Schemaless</a>. <a href=&#39;/normal&#39;>normal</a>. Post.`
-	replaceSchemalessXMLCorrect  = `Pre. src=&#39;//schemaless&#39; src=&#39;http://base/normal&#39;  <a href=&#39;//schemaless&#39;>Schemaless</a>. <a href=&#39;http://base/normal&#39;>normal</a>. Post.`
-)
-
-const (
-	// srcset=
-	srcsetBasic                 = `Pre. <img srcset="/img/small.jpg 200w, /img/medium.jpg 300w, /img/big.jpg 700w" alt="text" src="/img/foo.jpg">`
-	srcsetBasicCorrect          = `Pre. <img srcset="http://base/img/small.jpg 200w, http://base/img/medium.jpg 300w, http://base/img/big.jpg 700w" alt="text" src="http://base/img/foo.jpg">`
-	srcsetSingleQuote           = `Pre. <img srcset='/img/small.jpg 200w, /img/big.jpg 700w' alt="text" src="/img/foo.jpg"> POST.`
-	srcsetSingleQuoteCorrect    = `Pre. <img srcset='http://base/img/small.jpg 200w, http://base/img/big.jpg 700w' alt="text" src="http://base/img/foo.jpg"> POST.`
-	srcsetXMLBasic              = `Pre. <img srcset=&#34;/img/small.jpg 200w, /img/big.jpg 700w&#34; alt=&#34;text&#34; src=&#34;/img/foo.jpg&#34;>`
-	srcsetXMLBasicCorrect       = `Pre. <img srcset=&#34;http://base/img/small.jpg 200w, http://base/img/big.jpg 700w&#34; alt=&#34;text&#34; src=&#34;http://base/img/foo.jpg&#34;>`
-	srcsetXMLSingleQuote        = `Pre. <img srcset=&#34;/img/small.jpg 200w, /img/big.jpg 700w&#34; alt=&#34;text&#34; src=&#34;/img/foo.jpg&#34;>`
-	srcsetXMLSingleQuoteCorrect = `Pre. <img srcset=&#34;http://base/img/small.jpg 200w, http://base/img/big.jpg 700w&#34; alt=&#34;text&#34; src=&#34;http://base/img/foo.jpg&#34;>`
-	srcsetVariations            = `Pre. 
-Missing start quote: <img srcset=/img/small.jpg 200w, /img/big.jpg 700w" alt="text"> src='/img/foo.jpg'> FOO. 
-<img srcset='/img.jpg'> 
-schemaless: <img srcset='//img.jpg' src='//basic.jpg'>
-schemaless2: <img srcset="//img.jpg" src="//basic.jpg2> POST
-`
-)
-
-const (
-	srcsetVariationsCorrect = `Pre. 
-Missing start quote: <img srcset=/img/small.jpg 200w, /img/big.jpg 700w" alt="text"> src='http://base/img/foo.jpg'> FOO. 
-<img srcset='http://base/img.jpg'> 
-schemaless: <img srcset='//img.jpg' src='//basic.jpg'>
-schemaless2: <img srcset="//img.jpg" src="//basic.jpg2> POST
-`
-	srcsetXMLVariations = `Pre. 
-Missing start quote: &lt;img srcset=/img/small.jpg 200w /img/big.jpg 700w&quot; alt=&quot;text&quot;&gt; src=&#39;/img/foo.jpg&#39;&gt; FOO. 
-&lt;img srcset=&#39;/img.jpg&#39;&gt; 
-schemaless: &lt;img srcset=&#39;//img.jpg&#39; src=&#39;//basic.jpg&#39;&gt;
-schemaless2: &lt;img srcset=&quot;//img.jpg&quot; src=&quot;//basic.jpg2&gt; POST
-`
-	srcsetXMLVariationsCorrect = `Pre. 
-Missing start quote: &lt;img srcset=/img/small.jpg 200w /img/big.jpg 700w&quot; alt=&quot;text&quot;&gt; src=&#39;http://base/img/foo.jpg&#39;&gt; FOO. 
-&lt;img srcset=&#39;http://base/img.jpg&#39;&gt; 
-schemaless: &lt;img srcset=&#39;//img.jpg&#39; src=&#39;//basic.jpg&#39;&gt;
-schemaless2: &lt;img srcset=&quot;//img.jpg&quot; src=&quot;//basic.jpg2&gt; POST
-`
-
-	relPathVariations        = `PRE. a href="/img/small.jpg" POST.`
-	relPathVariationsCorrect = `PRE. a href="../../img/small.jpg" POST.`
-
-	testBaseURL = "http://base/"
-)
-
-var (
-	absURLlBenchTests = []test{
-		{h5JsContentDoubleQuote, corectOutputSrcHrefDq},
-		{h5JsContentSingleQuote, corectOutputSrcHrefSq},
-		{h5JsContentAbsURL, h5JsContentAbsURL},
-		{h5JsContentAbsURLSchemaless, h5JsContentAbsURLSchemaless},
-	}
-
-	xmlAbsURLBenchTests = []test{
-		{h5XMLXontentAbsURL, correctOutputSrcHrefInXML},
-		{h5XMLContentGuarded, h5XMLContentGuarded},
-	}
-
-	sanityTests    = []test{{replace1, replace1}, {replace2, replace2}, {replace3, replace3}, {replace3, replace3}, {replace5, replace5}}
-	extraTestsHTML = []test{{replaceSchemalessHTML, replaceSchemalessHTMLCorrect}}
-	absURLTests    = append(absURLlBenchTests, append(sanityTests, extraTestsHTML...)...)
-	extraTestsXML  = []test{{replaceSchemalessXML, replaceSchemalessXMLCorrect}}
-	xmlAbsURLTests = append(xmlAbsURLBenchTests, append(sanityTests, extraTestsXML...)...)
-	srcsetTests    = []test{{srcsetBasic, srcsetBasicCorrect}, {srcsetSingleQuote, srcsetSingleQuoteCorrect}, {srcsetVariations, srcsetVariationsCorrect}}
-	srcsetXMLTests = []test{
-		{srcsetXMLBasic, srcsetXMLBasicCorrect},
-		{srcsetXMLSingleQuote, srcsetXMLSingleQuoteCorrect},
-		{srcsetXMLVariations, srcsetXMLVariationsCorrect}}
-
-	relurlTests = []test{{relPathVariations, relPathVariationsCorrect}}
-)
-
 func TestChainZeroTransformers(t *testing.T) {
-	tr := NewChain()
+	tr := New()
 	in := new(bytes.Buffer)
 	out := new(bytes.Buffer)
-	if err := tr.Apply(in, out, []byte("")); err != nil {
+	if err := tr.Apply(in, out); err != nil {
 		t.Errorf("A zero transformer chain returned an error.")
 	}
 }
 
 func TestChaingMultipleTransformers(t *testing.T) {
-	f1 := func(ct contentTransformer) {
-		ct.Write(bytes.Replace(ct.Content(), []byte("f1"), []byte("f1r"), -1))
+	f1 := func(ct FromTo) error {
+		_, err := ct.To().Write(bytes.Replace(ct.From().Bytes(), []byte("f1"), []byte("f1r"), -1))
+		return err
 	}
-	f2 := func(ct contentTransformer) {
-		ct.Write(bytes.Replace(ct.Content(), []byte("f2"), []byte("f2r"), -1))
+	f2 := func(ct FromTo) error {
+		_, err := ct.To().Write(bytes.Replace(ct.From().Bytes(), []byte("f2"), []byte("f2r"), -1))
+		return err
 	}
-	f3 := func(ct contentTransformer) {
-		ct.Write(bytes.Replace(ct.Content(), []byte("f3"), []byte("f3r"), -1))
+	f3 := func(ct FromTo) error {
+		_, err := ct.To().Write(bytes.Replace(ct.From().Bytes(), []byte("f3"), []byte("f3r"), -1))
+		return err
 	}
 
-	f4 := func(ct contentTransformer) {
-		ct.Write(bytes.Replace(ct.Content(), []byte("f4"), []byte("f4r"), -1))
+	f4 := func(ct FromTo) error {
+		_, err := ct.To().Write(bytes.Replace(ct.From().Bytes(), []byte("f4"), []byte("f4r"), -1))
+		return err
 	}
 
-	tr := NewChain(f1, f2, f3, f4)
+	tr := New(f1, f2, f3, f4)
 
 	out := new(bytes.Buffer)
-	if err := tr.Apply(out, strings.NewReader("Test: f4 f3 f1 f2 f1 The End."), []byte("")); err != nil {
+	if err := tr.Apply(out, strings.NewReader("Test: f4 f3 f1 f2 f1 The End.")); err != nil {
 		t.Errorf("Multi transformer chain returned an error: %s", err)
 	}
 
@@ -161,107 +63,7 @@ func TestChaingMultipleTransformers(t *testing.T) {
 	}
 }
 
-func BenchmarkAbsURL(b *testing.B) {
-	tr := NewChain(AbsURL)
-
-	b.ResetTimer()
-	for i := 0; i < b.N; i++ {
-		apply(b.Errorf, tr, absURLlBenchTests)
-	}
-}
-
-func BenchmarkAbsURLSrcset(b *testing.B) {
-	tr := NewChain(AbsURL)
-
-	b.ResetTimer()
-	for i := 0; i < b.N; i++ {
-		apply(b.Errorf, tr, srcsetTests)
-	}
-}
-
-func BenchmarkXMLAbsURLSrcset(b *testing.B) {
-	tr := NewChain(AbsURLInXML)
-
-	b.ResetTimer()
-	for i := 0; i < b.N; i++ {
-		apply(b.Errorf, tr, srcsetXMLTests)
-	}
-}
-
-func TestAbsURL(t *testing.T) {
-	tr := NewChain(AbsURL)
-
-	apply(t.Errorf, tr, absURLTests)
-
-}
-
-func TestRelativeURL(t *testing.T) {
-	tr := NewChain(AbsURL)
-
-	applyWithPath(t.Errorf, tr, relurlTests, helpers.GetDottedRelativePath(filepath.FromSlash("/post/sub/")))
-
-}
-
-func TestAbsURLSrcSet(t *testing.T) {
-	tr := NewChain(AbsURL)
-
-	apply(t.Errorf, tr, srcsetTests)
-}
-
-func TestAbsXMLURLSrcSet(t *testing.T) {
-	tr := NewChain(AbsURLInXML)
-
-	apply(t.Errorf, tr, srcsetXMLTests)
-}
-
-func BenchmarkXMLAbsURL(b *testing.B) {
-	tr := NewChain(AbsURLInXML)
-
-	b.ResetTimer()
-	for i := 0; i < b.N; i++ {
-		apply(b.Errorf, tr, xmlAbsURLBenchTests)
-	}
-}
-
-func TestXMLAbsURL(t *testing.T) {
-	tr := NewChain(AbsURLInXML)
-	apply(t.Errorf, tr, xmlAbsURLTests)
-}
-
 func TestNewEmptyTransforms(t *testing.T) {
-	transforms := NewEmptyTransforms()
+	transforms := NewEmpty()
 	assert.Equal(t, 20, cap(transforms))
 }
-
-type errorf func(string, ...interface{})
-
-func applyWithPath(ef errorf, tr chain, tests []test, path string) {
-	out := bp.GetBuffer()
-	defer bp.PutBuffer(out)
-
-	in := bp.GetBuffer()
-	defer bp.PutBuffer(in)
-
-	for _, test := range tests {
-		var err error
-		in.WriteString(test.content)
-		err = tr.Apply(out, in, []byte(path))
-		if err != nil {
-			ef("Unexpected error: %s", err)
-		}
-		if test.expected != out.String() {
-			ef("Expected:\n%s\nGot:\n%s", test.expected, out.String())
-		}
-		out.Reset()
-		in.Reset()
-	}
-}
-
-func apply(ef errorf, tr chain, tests []test) {
-	applyWithPath(ef, tr, tests, testBaseURL)
-}
-
-type test struct {
-	content  string
-	expected string
-}
diff --git a/transform/livereloadinject.go b/transform/livereloadinject/livereloadinject.go
index 4efd0151d..e04b977f7 100644
--- a/transform/livereloadinject.go
+++ b/transform/livereloadinject/livereloadinject.go
@@ -1,4 +1,4 @@
-// Copyright 2015 The Hugo Authors. All rights reserved.
+// 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.
@@ -11,30 +11,37 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package transform
+package livereloadinject
 
 import (
 	"bytes"
 	"fmt"
+
+	"github.com/gohugoio/hugo/helpers"
+	"github.com/gohugoio/hugo/transform"
 )
 
-// LiveReloadInject returns a function that can be used
+// New creates a function that can be used
 // to inject a script tag for the livereload JavaScript in a HTML document.
-func LiveReloadInject(port int) func(ct contentTransformer) {
-	return func(ct contentTransformer) {
+func New(port int) transform.Transformer {
+	return func(ft transform.FromTo) error {
+		b := ft.From().Bytes()
 		endBodyTag := "</body>"
 		match := []byte(endBodyTag)
 		replaceTemplate := `<script data-no-instant>document.write('<script src="/livereload.js?port=%d&mindelay=10"></' + 'script>')</script>%s`
 		replace := []byte(fmt.Sprintf(replaceTemplate, port, endBodyTag))
 
-		newcontent := bytes.Replace(ct.Content(), match, replace, 1)
-		if len(newcontent) == len(ct.Content()) {
+		newcontent := bytes.Replace(b, match, replace, 1)
+		if len(newcontent) == len(b) {
 			endBodyTag = "</BODY>"
 			replace := []byte(fmt.Sprintf(replaceTemplate, port, endBodyTag))
 			match := []byte(endBodyTag)
-			newcontent = bytes.Replace(ct.Content(), match, replace, 1)
+			newcontent = bytes.Replace(b, match, replace, 1)
 		}
 
-		ct.Write(newcontent)
+		if _, err := ft.To().Write(newcontent); err != nil {
+			helpers.DistinctWarnLog.Println("Failed to inject LiveReload script:", err)
+		}
+		return nil
 	}
 }
diff --git a/transform/livereloadinject_test.go b/transform/livereloadinject/livereloadinject_test.go
index 3337243bd..0e0f708d3 100644
--- a/transform/livereloadinject_test.go
+++ b/transform/livereloadinject/livereloadinject_test.go
@@ -1,4 +1,4 @@
-// Copyright 2015 The Hugo Authors. All rights reserved.
+// 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.
@@ -11,13 +11,15 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package transform
+package livereloadinject
 
 import (
 	"bytes"
 	"fmt"
 	"strings"
 	"testing"
+
+	"github.com/gohugoio/hugo/transform"
 )
 
 func TestLiveReloadInject(t *testing.T) {
@@ -29,8 +31,8 @@ func doTestLiveReloadInject(t *testing.T, bodyEndTag string) {
 	out := new(bytes.Buffer)
 	in := strings.NewReader(bodyEndTag)
 
-	tr := NewChain(LiveReloadInject(1313))
-	tr.Apply(out, in, []byte("path"))
+	tr := transform.New(New(1313))
+	tr.Apply(out, in)
 
 	expected := fmt.Sprintf(`<script data-no-instant>document.write('<script src="/livereload.js?port=1313&mindelay=10"></' + 'script>')</script>%s`, bodyEndTag)
 	if string(out.Bytes()) != expected {
diff --git a/transform/hugogeneratorinject.go b/transform/metainject/hugogenerator.go
index 874053087..513b21228 100644
--- a/transform/hugogeneratorinject.go
+++ b/transform/metainject/hugogenerator.go
@@ -1,4 +1,4 @@
-// Copyright 2016 The Hugo Authors. All rights reserved.
+// 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.
@@ -11,7 +11,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package transform
+package metainject
 
 import (
 	"bytes"
@@ -19,32 +19,36 @@ import (
 	"regexp"
 
 	"github.com/gohugoio/hugo/helpers"
+	"github.com/gohugoio/hugo/transform"
 )
 
 var metaTagsCheck = regexp.MustCompile(`(?i)<meta\s+name=['|"]?generator['|"]?`)
 var hugoGeneratorTag = fmt.Sprintf(`<meta name="generator" content="Hugo %s" />`, helpers.CurrentHugoVersion)
 
-// HugoGeneratorInject injects a meta generator tag for Hugo if none present.
-func HugoGeneratorInject(ct contentTransformer) {
-	if metaTagsCheck.Match(ct.Content()) {
-		if _, err := ct.Write(ct.Content()); err != nil {
+// HugoGenerator injects a meta generator tag for Hugo if none present.
+func HugoGenerator(ft transform.FromTo) error {
+	b := ft.From().Bytes()
+	if metaTagsCheck.Match(b) {
+		if _, err := ft.To().Write(b); err != nil {
 			helpers.DistinctWarnLog.Println("Failed to inject Hugo generator tag:", err)
 		}
-		return
+		return nil
 	}
 
 	head := "<head>"
 	replace := []byte(fmt.Sprintf("%s\n\t%s", head, hugoGeneratorTag))
-	newcontent := bytes.Replace(ct.Content(), []byte(head), replace, 1)
+	newcontent := bytes.Replace(b, []byte(head), replace, 1)
 
-	if len(newcontent) == len(ct.Content()) {
+	if len(newcontent) == len(b) {
 		head := "<HEAD>"
 		replace := []byte(fmt.Sprintf("%s\n\t%s", head, hugoGeneratorTag))
-		newcontent = bytes.Replace(ct.Content(), []byte(head), replace, 1)
+		newcontent = bytes.Replace(b, []byte(head), replace, 1)
 	}
 
-	if _, err := ct.Write(newcontent); err != nil {
+	if _, err := ft.To().Write(newcontent); err != nil {
 		helpers.DistinctWarnLog.Println("Failed to inject Hugo generator tag:", err)
 	}
 
+	return nil
+
 }
diff --git a/transform/hugogeneratorinject_test.go b/transform/metainject/hugogenerator_test.go
index d37fea24e..ffb4c1425 100644
--- a/transform/hugogeneratorinject_test.go
+++ b/transform/metainject/hugogenerator_test.go
@@ -1,4 +1,4 @@
-// Copyright 2016 The Hugo Authors. All rights reserved.
+// 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.
@@ -11,12 +11,14 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package transform
+package metainject
 
 import (
 	"bytes"
 	"strings"
 	"testing"
+
+	"github.com/gohugoio/hugo/transform"
 )
 
 func TestHugoGeneratorInject(t *testing.T) {
@@ -48,8 +50,8 @@ func TestHugoGeneratorInject(t *testing.T) {
 		in := strings.NewReader(this.in)
 		out := new(bytes.Buffer)
 
-		tr := NewChain(HugoGeneratorInject)
-		tr.Apply(out, in, []byte(""))
+		tr := transform.New(HugoGenerator)
+		tr.Apply(out, in)
 
 		if out.String() != this.expect {
 			t.Errorf("[%d] Expected \n%q got \n%q", i, this.expect, out.String())
diff --git a/transform/absurl.go b/transform/urlreplacers/absurl.go
index 255ac33b6..029d94da2 100644
--- a/transform/absurl.go
+++ b/transform/urlreplacers/absurl.go
@@ -1,4 +1,4 @@
-// Copyright 2015 The Hugo Authors. All rights reserved.
+// 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.
@@ -11,18 +11,26 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package transform
+package urlreplacers
+
+import "github.com/gohugoio/hugo/transform"
 
 var ar = newAbsURLReplacer()
 
-// AbsURL replaces relative URLs with absolute ones
+// NewAbsURLTransformer replaces relative URLs with absolute ones
 // in HTML files, using the baseURL setting.
-var AbsURL = func(ct contentTransformer) {
-	ar.replaceInHTML(ct)
+func NewAbsURLTransformer(path string) transform.Transformer {
+	return func(ft transform.FromTo) error {
+		ar.replaceInHTML(path, ft)
+		return nil
+	}
 }
 
-// AbsURLInXML replaces relative URLs with absolute ones
+// NewAbsURLInXMLTransformer replaces relative URLs with absolute ones
 // in XML files, using the baseURL setting.
-var AbsURLInXML = func(ct contentTransformer) {
-	ar.replaceInXML(ct)
+func NewAbsURLInXMLTransformer(path string) transform.Transformer {
+	return func(ft transform.FromTo) error {
+		ar.replaceInXML(path, ft)
+		return nil
+	}
 }
diff --git a/transform/absurlreplacer.go b/transform/urlreplacers/absurlreplacer.go
index c659a94e8..1de6b0ca7 100644
--- a/transform/absurlreplacer.go
+++ b/transform/urlreplacers/absurlreplacer.go
@@ -1,4 +1,4 @@
-// Copyright 2015 The Hugo Authors. All rights reserved.
+// 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.
@@ -11,12 +11,14 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package transform
+package urlreplacers
 
 import (
 	"bytes"
 	"io"
 	"unicode/utf8"
+
+	"github.com/gohugoio/hugo/transform"
 )
 
 type matchState int
@@ -260,12 +262,12 @@ func (l *absurllexer) replace() {
 	}
 }
 
-func doReplace(ct contentTransformer, matchers []absURLMatcher) {
+func doReplace(path string, ct transform.FromTo, matchers []absURLMatcher) {
 
 	lexer := &absurllexer{
-		content:  ct.Content(),
-		w:        ct,
-		path:     ct.Path(),
+		content:  ct.From().Bytes(),
+		w:        ct.To(),
+		path:     []byte(path),
 		matchers: matchers}
 
 	lexer.replace()
@@ -303,10 +305,10 @@ func newAbsURLReplacer() *absURLReplacer {
 		}}
 }
 
-func (au *absURLReplacer) replaceInHTML(ct contentTransformer) {
-	doReplace(ct, au.htmlMatchers)
+func (au *absURLReplacer) replaceInHTML(path string, ct transform.FromTo) {
+	doReplace(path, ct, au.htmlMatchers)
 }
 
-func (au *absURLReplacer) replaceInXML(ct contentTransformer) {
-	doReplace(ct, au.xmlMatchers)
+func (au *absURLReplacer) replaceInXML(path string, ct transform.FromTo) {
+	doReplace(path, ct, au.xmlMatchers)
 }
diff --git a/transform/urlreplacers/absurlreplacer_test.go b/transform/urlreplacers/absurlreplacer_test.go
new file mode 100644
index 000000000..7a530862b
--- /dev/null
+++ b/transform/urlreplacers/absurlreplacer_test.go
@@ -0,0 +1,223 @@
+// 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 urlreplacers
+
+import (
+	"path/filepath"
+	"testing"
+
+	bp "github.com/gohugoio/hugo/bufferpool"
+
+	"github.com/gohugoio/hugo/helpers"
+	"github.com/gohugoio/hugo/transform"
+)
+
+const (
+	h5JsContentDoubleQuote      = "<!DOCTYPE html><html><head><script src=\"foobar.js\"></script><script src=\"/barfoo.js\"></script></head><body><nav><h1>title</h1></nav><article>content <a href=\"foobar\">foobar</a>. <a href=\"/foobar\">Follow up</a></article></body></html>"
+	h5JsContentSingleQuote      = "<!DOCTYPE html><html><head><script src='foobar.js'></script><script src='/barfoo.js'></script></head><body><nav><h1>title</h1></nav><article>content <a href='foobar'>foobar</a>. <a href='/foobar'>Follow up</a></article></body></html>"
+	h5JsContentAbsURL           = "<!DOCTYPE html><html><head><script src=\"http://user@host:10234/foobar.js\"></script></head><body><nav><h1>title</h1></nav><article>content <a href=\"https://host/foobar\">foobar</a>. Follow up</article></body></html>"
+	h5JsContentAbsURLSchemaless = "<!DOCTYPE html><html><head><script src=\"//host/foobar.js\"></script><script src='//host2/barfoo.js'></head><body><nav><h1>title</h1></nav><article>content <a href=\"//host/foobar\">foobar</a>. <a href='//host2/foobar'>Follow up</a></article></body></html>"
+	corectOutputSrcHrefDq       = "<!DOCTYPE html><html><head><script src=\"foobar.js\"></script><script src=\"http://base/barfoo.js\"></script></head><body><nav><h1>title</h1></nav><article>content <a href=\"foobar\">foobar</a>. <a href=\"http://base/foobar\">Follow up</a></article></body></html>"
+	corectOutputSrcHrefSq       = "<!DOCTYPE html><html><head><script src='foobar.js'></script><script src='http://base/barfoo.js'></script></head><body><nav><h1>title</h1></nav><article>content <a href='foobar'>foobar</a>. <a href='http://base/foobar'>Follow up</a></article></body></html>"
+
+	h5XMLXontentAbsURL        = "<?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"yes\" ?><feed xmlns=\"http://www.w3.org/2005/Atom\"><entry><content type=\"html\">&lt;p&gt;&lt;a href=&#34;/foobar&#34;&gt;foobar&lt;/a&gt;&lt;/p&gt; &lt;p&gt;A video: &lt;iframe src=&#39;/foo&#39;&gt;&lt;/iframe&gt;&lt;/p&gt;</content></entry></feed>"
+	correctOutputSrcHrefInXML = "<?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"yes\" ?><feed xmlns=\"http://www.w3.org/2005/Atom\"><entry><content type=\"html\">&lt;p&gt;&lt;a href=&#34;http://base/foobar&#34;&gt;foobar&lt;/a&gt;&lt;/p&gt; &lt;p&gt;A video: &lt;iframe src=&#39;http://base/foo&#39;&gt;&lt;/iframe&gt;&lt;/p&gt;</content></entry></feed>"
+	h5XMLContentGuarded       = "<?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"yes\" ?><feed xmlns=\"http://www.w3.org/2005/Atom\"><entry><content type=\"html\">&lt;p&gt;&lt;a href=&#34;//foobar&#34;&gt;foobar&lt;/a&gt;&lt;/p&gt; &lt;p&gt;A video: &lt;iframe src=&#39;//foo&#39;&gt;&lt;/iframe&gt;&lt;/p&gt;</content></entry></feed>"
+)
+
+const (
+	// additional sanity tests for replacements testing
+	replace1 = "No replacements."
+	replace2 = "ᚠᛇᚻ ᛒᛦᚦ ᚠᚱᚩᚠᚢᚱ\nᚠᛁᚱᚪ ᚷᛖᚻᚹᛦᛚᚳᚢᛗ"
+	replace3 = `End of file: src="/`
+	replace4 = `End of file: srcset="/`
+	replace5 = `Srcsett with no closing quote: srcset="/img/small.jpg do be do be do.`
+
+	// Issue: 816, schemaless links combined with others
+	replaceSchemalessHTML        = `Pre. src='//schemaless' src='/normal'  <a href="//schemaless">Schemaless</a>. <a href="/normal">normal</a>. Post.`
+	replaceSchemalessHTMLCorrect = `Pre. src='//schemaless' src='http://base/normal'  <a href="//schemaless">Schemaless</a>. <a href="http://base/normal">normal</a>. Post.`
+	replaceSchemalessXML         = `Pre. src=&#39;//schemaless&#39; src=&#39;/normal&#39;  <a href=&#39;//schemaless&#39;>Schemaless</a>. <a href=&#39;/normal&#39;>normal</a>. Post.`
+	replaceSchemalessXMLCorrect  = `Pre. src=&#39;//schemaless&#39; src=&#39;http://base/normal&#39;  <a href=&#39;//schemaless&#39;>Schemaless</a>. <a href=&#39;http://base/normal&#39;>normal</a>. Post.`
+)
+
+const (
+	// srcset=
+	srcsetBasic                 = `Pre. <img srcset="/img/small.jpg 200w, /img/medium.jpg 300w, /img/big.jpg 700w" alt="text" src="/img/foo.jpg">`
+	srcsetBasicCorrect          = `Pre. <img srcset="http://base/img/small.jpg 200w, http://base/img/medium.jpg 300w, http://base/img/big.jpg 700w" alt="text" src="http://base/img/foo.jpg">`
+	srcsetSingleQuote           = `Pre. <img srcset='/img/small.jpg 200w, /img/big.jpg 700w' alt="text" src="/img/foo.jpg"> POST.`
+	srcsetSingleQuoteCorrect    = `Pre. <img srcset='http://base/img/small.jpg 200w, http://base/img/big.jpg 700w' alt="text" src="http://base/img/foo.jpg"> POST.`
+	srcsetXMLBasic              = `Pre. <img srcset=&#34;/img/small.jpg 200w, /img/big.jpg 700w&#34; alt=&#34;text&#34; src=&#34;/img/foo.jpg&#34;>`
+	srcsetXMLBasicCorrect       = `Pre. <img srcset=&#34;http://base/img/small.jpg 200w, http://base/img/big.jpg 700w&#34; alt=&#34;text&#34; src=&#34;http://base/img/foo.jpg&#34;>`
+	srcsetXMLSingleQuote        = `Pre. <img srcset=&#34;/img/small.jpg 200w, /img/big.jpg 700w&#34; alt=&#34;text&#34; src=&#34;/img/foo.jpg&#34;>`
+	srcsetXMLSingleQuoteCorrect = `Pre. <img srcset=&#34;http://base/img/small.jpg 200w, http://base/img/big.jpg 700w&#34; alt=&#34;text&#34; src=&#34;http://base/img/foo.jpg&#34;>`
+	srcsetVariations            = `Pre. 
+Missing start quote: <img srcset=/img/small.jpg 200w, /img/big.jpg 700w" alt="text"> src='/img/foo.jpg'> FOO. 
+<img srcset='/img.jpg'> 
+schemaless: <img srcset='//img.jpg' src='//basic.jpg'>
+schemaless2: <img srcset="//img.jpg" src="//basic.jpg2> POST
+`
+)
+
+const (
+	srcsetVariationsCorrect = `Pre. 
+Missing start quote: <img srcset=/img/small.jpg 200w, /img/big.jpg 700w" alt="text"> src='http://base/img/foo.jpg'> FOO. 
+<img srcset='http://base/img.jpg'> 
+schemaless: <img srcset='//img.jpg' src='//basic.jpg'>
+schemaless2: <img srcset="//img.jpg" src="//basic.jpg2> POST
+`
+	srcsetXMLVariations = `Pre. 
+Missing start quote: &lt;img srcset=/img/small.jpg 200w /img/big.jpg 700w&quot; alt=&quot;text&quot;&gt; src=&#39;/img/foo.jpg&#39;&gt; FOO. 
+&lt;img srcset=&#39;/img.jpg&#39;&gt; 
+schemaless: &lt;img srcset=&#39;//img.jpg&#39; src=&#39;//basic.jpg&#39;&gt;
+schemaless2: &lt;img srcset=&quot;//img.jpg&quot; src=&quot;//basic.jpg2&gt; POST
+`
+	srcsetXMLVariationsCorrect = `Pre. 
+Missing start quote: &lt;img srcset=/img/small.jpg 200w /img/big.jpg 700w&quot; alt=&quot;text&quot;&gt; src=&#39;http://base/img/foo.jpg&#39;&gt; FOO. 
+&lt;img srcset=&#39;http://base/img.jpg&#39;&gt; 
+schemaless: &lt;img srcset=&#39;//img.jpg&#39; src=&#39;//basic.jpg&#39;&gt;
+schemaless2: &lt;img srcset=&quot;//img.jpg&quot; src=&quot;//basic.jpg2&gt; POST
+`
+
+	relPathVariations        = `PRE. a href="/img/small.jpg" POST.`
+	relPathVariationsCorrect = `PRE. a href="../../img/small.jpg" POST.`
+
+	testBaseURL = "http://base/"
+)
+
+var (
+	absURLlBenchTests = []test{
+		{h5JsContentDoubleQuote, corectOutputSrcHrefDq},
+		{h5JsContentSingleQuote, corectOutputSrcHrefSq},
+		{h5JsContentAbsURL, h5JsContentAbsURL},
+		{h5JsContentAbsURLSchemaless, h5JsContentAbsURLSchemaless},
+	}
+
+	xmlAbsURLBenchTests = []test{
+		{h5XMLXontentAbsURL, correctOutputSrcHrefInXML},
+		{h5XMLContentGuarded, h5XMLContentGuarded},
+	}
+
+	sanityTests    = []test{{replace1, replace1}, {replace2, replace2}, {replace3, replace3}, {replace3, replace3}, {replace5, replace5}}
+	extraTestsHTML = []test{{replaceSchemalessHTML, replaceSchemalessHTMLCorrect}}
+	absURLTests    = append(absURLlBenchTests, append(sanityTests, extraTestsHTML...)...)
+	extraTestsXML  = []test{{replaceSchemalessXML, replaceSchemalessXMLCorrect}}
+	xmlAbsURLTests = append(xmlAbsURLBenchTests, append(sanityTests, extraTestsXML...)...)
+	srcsetTests    = []test{{srcsetBasic, srcsetBasicCorrect}, {srcsetSingleQuote, srcsetSingleQuoteCorrect}, {srcsetVariations, srcsetVariationsCorrect}}
+	srcsetXMLTests = []test{
+		{srcsetXMLBasic, srcsetXMLBasicCorrect},
+		{srcsetXMLSingleQuote, srcsetXMLSingleQuoteCorrect},
+		{srcsetXMLVariations, srcsetXMLVariationsCorrect}}
+
+	relurlTests = []test{{relPathVariations, relPathVariationsCorrect}}
+)
+
+func BenchmarkAbsURL(b *testing.B) {
+	tr := transform.New(NewAbsURLTransformer(testBaseURL))
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		apply(b.Errorf, tr, absURLlBenchTests)
+	}
+}
+
+func BenchmarkAbsURLSrcset(b *testing.B) {
+	tr := transform.New(NewAbsURLTransformer(testBaseURL))
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		apply(b.Errorf, tr, srcsetTests)
+	}
+}
+
+func BenchmarkXMLAbsURLSrcset(b *testing.B) {
+	tr := transform.New(NewAbsURLInXMLTransformer(testBaseURL))
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		apply(b.Errorf, tr, srcsetXMLTests)
+	}
+}
+
+func TestAbsURL(t *testing.T) {
+	tr := transform.New(NewAbsURLTransformer(testBaseURL))
+
+	apply(t.Errorf, tr, absURLTests)
+
+}
+
+func TestRelativeURL(t *testing.T) {
+	tr := transform.New(NewAbsURLTransformer(helpers.GetDottedRelativePath(filepath.FromSlash("/post/sub/"))))
+
+	applyWithPath(t.Errorf, tr, relurlTests)
+
+}
+
+func TestAbsURLSrcSet(t *testing.T) {
+	tr := transform.New(NewAbsURLTransformer(testBaseURL))
+
+	apply(t.Errorf, tr, srcsetTests)
+}
+
+func TestAbsXMLURLSrcSet(t *testing.T) {
+	tr := transform.New(NewAbsURLInXMLTransformer(testBaseURL))
+
+	apply(t.Errorf, tr, srcsetXMLTests)
+}
+
+func BenchmarkXMLAbsURL(b *testing.B) {
+	tr := transform.New(NewAbsURLInXMLTransformer(""))
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		apply(b.Errorf, tr, xmlAbsURLBenchTests)
+	}
+}
+
+func TestXMLAbsURL(t *testing.T) {
+	tr := transform.New(NewAbsURLInXMLTransformer(testBaseURL))
+	apply(t.Errorf, tr, xmlAbsURLTests)
+}
+
+func apply(ef errorf, tr transform.Chain, tests []test) {
+	applyWithPath(ef, tr, tests)
+}
+
+func applyWithPath(ef errorf, tr transform.Chain, tests []test) {
+	out := bp.GetBuffer()
+	defer bp.PutBuffer(out)
+
+	in := bp.GetBuffer()
+	defer bp.PutBuffer(in)
+
+	for _, test := range tests {
+		var err error
+		in.WriteString(test.content)
+		err = tr.Apply(out, in)
+		if err != nil {
+			ef("Unexpected error: %s", err)
+		}
+		if test.expected != out.String() {
+			ef("Expected:\n%s\nGot:\n%s", test.expected, out.String())
+		}
+		out.Reset()
+		in.Reset()
+	}
+}
+
+type test struct {
+	content  string
+	expected string
+}
+
+type errorf func(string, ...interface{})