Add Image Diff for SVG files (#14867)

* Added type sniffer.

* Switched content detection from base to typesniffer.

* Added GuessContentType to Blob.

* Moved image info logic to client.
Added support for SVG images in diff.

* Restore old blocked svg behaviour.

* Added missing image formats.

* Execute image diff only when container is visible.

* add margin to spinner

* improve BIN tag on image diffs

* Default to render view.

* Show image diff on incomplete diff.

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Lauris BH <lauris@nix.lv>

2 files changed, 193 insertions, 0 deletions

diff --git a/modules/typesniffer/typesniffer.go b/modules/typesniffer/typesniffer.go
new file mode 100644
index 0000000000..7c89f66699
--- /dev/null
+++ b/modules/typesniffer/typesniffer.go
@@ -0,0 +1,96 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package typesniffer
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"regexp"
+	"strings"
+)
+
+// Use at most this many bytes to determine Content Type.
+const sniffLen = 1024
+
+// SvgMimeType MIME type of SVG images.
+const SvgMimeType = "image/svg+xml"
+
+var svgTagRegex = regexp.MustCompile(`(?si)\A\s*(?:(<!--.*?-->|<!DOCTYPE\s+svg([\s:]+.*?>|>))\s*)*<svg[\s>\/]`)
+var svgTagInXMLRegex = regexp.MustCompile(`(?si)\A<\?xml\b.*?\?>\s*(?:(<!--.*?-->|<!DOCTYPE\s+svg([\s:]+.*?>|>))\s*)*<svg[\s>\/]`)
+
+// SniffedType contains informations about a blobs type.
+type SniffedType struct {
+	contentType string
+}
+
+// IsText etects if content format is plain text.
+func (ct SniffedType) IsText() bool {
+	return strings.Contains(ct.contentType, "text/")
+}
+
+// IsImage detects if data is an image format
+func (ct SniffedType) IsImage() bool {
+	return strings.Contains(ct.contentType, "image/")
+}
+
+// IsSvgImage detects if data is an SVG image format
+func (ct SniffedType) IsSvgImage() bool {
+	return strings.Contains(ct.contentType, SvgMimeType)
+}
+
+// IsPDF detects if data is a PDF format
+func (ct SniffedType) IsPDF() bool {
+	return strings.Contains(ct.contentType, "application/pdf")
+}
+
+// IsVideo detects if data is an video format
+func (ct SniffedType) IsVideo() bool {
+	return strings.Contains(ct.contentType, "video/")
+}
+
+// IsAudio detects if data is an video format
+func (ct SniffedType) IsAudio() bool {
+	return strings.Contains(ct.contentType, "audio/")
+}
+
+// IsRepresentableAsText returns true if file content can be represented as
+// plain text or is empty.
+func (ct SniffedType) IsRepresentableAsText() bool {
+	return ct.IsText() || ct.IsSvgImage()
+}
+
+// DetectContentType extends http.DetectContentType with more content types. Defaults to text/unknown if input is empty.
+func DetectContentType(data []byte) SniffedType {
+	if len(data) == 0 {
+		return SniffedType{"text/unknown"}
+	}
+
+	ct := http.DetectContentType(data)
+
+	if len(data) > sniffLen {
+		data = data[:sniffLen]
+	}
+
+	if (strings.Contains(ct, "text/plain") || strings.Contains(ct, "text/html")) && svgTagRegex.Match(data) ||
+		strings.Contains(ct, "text/xml") && svgTagInXMLRegex.Match(data) {
+		// SVG is unsupported. https://github.com/golang/go/issues/15888
+		ct = SvgMimeType
+	}
+
+	return SniffedType{ct}
+}
+
+// DetectContentTypeFromReader guesses the content type contained in the reader.
+func DetectContentTypeFromReader(r io.Reader) (SniffedType, error) {
+	buf := make([]byte, sniffLen)
+	n, err := r.Read(buf)
+	if err != nil && err != io.EOF {
+		return SniffedType{}, fmt.Errorf("DetectContentTypeFromReader io error: %w", err)
+	}
+	buf = buf[:n]
+
+	return DetectContentType(buf), nil
+}
diff --git a/modules/typesniffer/typesniffer_test.go b/modules/typesniffer/typesniffer_test.go
new file mode 100644
index 0000000000..a3b47c4598
--- /dev/null
+++ b/modules/typesniffer/typesniffer_test.go
@@ -0,0 +1,97 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package typesniffer
+
+import (
+	"bytes"
+	"encoding/base64"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDetectContentTypeLongerThanSniffLen(t *testing.T) {
+	// Pre-condition: Shorter than sniffLen detects SVG.
+	assert.Equal(t, "image/svg+xml", DetectContentType([]byte(`<!-- Comment --><svg></svg>`)).contentType)
+	// Longer than sniffLen detects something else.
+	assert.NotEqual(t, "image/svg+xml", DetectContentType([]byte(`<!-- `+strings.Repeat("x", sniffLen)+` --><svg></svg>`)).contentType)
+}
+
+func TestIsTextFile(t *testing.T) {
+	assert.True(t, DetectContentType([]byte{}).IsText())
+	assert.True(t, DetectContentType([]byte("lorem ipsum")).IsText())
+}
+
+func TestIsSvgImage(t *testing.T) {
+	assert.True(t, DetectContentType([]byte("<svg></svg>")).IsSvgImage())
+	assert.True(t, DetectContentType([]byte("    <svg></svg>")).IsSvgImage())
+	assert.True(t, DetectContentType([]byte(`<svg width="100"></svg>`)).IsSvgImage())
+	assert.True(t, DetectContentType([]byte("<svg/>")).IsSvgImage())
+	assert.True(t, DetectContentType([]byte(`<?xml version="1.0" encoding="UTF-8"?><svg></svg>`)).IsSvgImage())
+	assert.True(t, DetectContentType([]byte(`<!-- Comment -->
+	<svg></svg>`)).IsSvgImage())
+	assert.True(t, DetectContentType([]byte(`<!-- Multiple -->
+	<!-- Comments -->
+	<svg></svg>`)).IsSvgImage())
+	assert.True(t, DetectContentType([]byte(`<!-- Multiline
+	Comment -->
+	<svg></svg>`)).IsSvgImage())
+	assert.True(t, DetectContentType([]byte(`<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1 Basic//EN"
+	"http://www.w3.org/Graphics/SVG/1.1/DTD/svg11-basic.dtd">
+	<svg></svg>`)).IsSvgImage())
+	assert.True(t, DetectContentType([]byte(`<?xml version="1.0" encoding="UTF-8"?>
+	<!-- Comment -->
+	<svg></svg>`)).IsSvgImage())
+	assert.True(t, DetectContentType([]byte(`<?xml version="1.0" encoding="UTF-8"?>
+	<!-- Multiple -->
+	<!-- Comments -->
+	<svg></svg>`)).IsSvgImage())
+	assert.True(t, DetectContentType([]byte(`<?xml version="1.0" encoding="UTF-8"?>
+	<!-- Multline
+	Comment -->
+	<svg></svg>`)).IsSvgImage())
+	assert.True(t, DetectContentType([]byte(`<?xml version="1.0" encoding="UTF-8"?>
+	<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+	<!-- Multline
+	Comment -->
+	<svg></svg>`)).IsSvgImage())
+	assert.False(t, DetectContentType([]byte{}).IsSvgImage())
+	assert.False(t, DetectContentType([]byte("svg")).IsSvgImage())
+	assert.False(t, DetectContentType([]byte("<svgfoo></svgfoo>")).IsSvgImage())
+	assert.False(t, DetectContentType([]byte("text<svg></svg>")).IsSvgImage())
+	assert.False(t, DetectContentType([]byte("<html><body><svg></svg></body></html>")).IsSvgImage())
+	assert.False(t, DetectContentType([]byte(`<script>"<svg></svg>"</script>`)).IsSvgImage())
+	assert.False(t, DetectContentType([]byte(`<!-- <svg></svg> inside comment -->
+	<foo></foo>`)).IsSvgImage())
+	assert.False(t, DetectContentType([]byte(`<?xml version="1.0" encoding="UTF-8"?>
+	<!-- <svg></svg> inside comment -->
+	<foo></foo>`)).IsSvgImage())
+}
+
+func TestIsPDF(t *testing.T) {
+	pdf, _ := base64.StdEncoding.DecodeString("JVBERi0xLjYKJcOkw7zDtsOfCjIgMCBvYmoKPDwvTGVuZ3RoIDMgMCBSL0ZpbHRlci9GbGF0ZURlY29kZT4+CnN0cmVhbQp4nF3NPwsCMQwF8D2f4s2CNYk1baF0EHRwOwg4iJt/NsFb/PpevUE4Mjwe")
+	assert.True(t, DetectContentType(pdf).IsPDF())
+	assert.False(t, DetectContentType([]byte("plain text")).IsPDF())
+}
+
+func TestIsVideo(t *testing.T) {
+	mp4, _ := base64.StdEncoding.DecodeString("AAAAGGZ0eXBtcDQyAAAAAGlzb21tcDQyAAEI721vb3YAAABsbXZoZAAAAADaBlwX2gZcFwAAA+gA")
+	assert.True(t, DetectContentType(mp4).IsVideo())
+	assert.False(t, DetectContentType([]byte("plain text")).IsVideo())
+}
+
+func TestIsAudio(t *testing.T) {
+	mp3, _ := base64.StdEncoding.DecodeString("SUQzBAAAAAABAFRYWFgAAAASAAADbWFqb3JfYnJhbmQAbXA0MgBUWFhYAAAAEQAAA21pbm9yX3Zl")
+	assert.True(t, DetectContentType(mp3).IsAudio())
+	assert.False(t, DetectContentType([]byte("plain text")).IsAudio())
+}
+
+func TestDetectContentTypeFromReader(t *testing.T) {
+	mp3, _ := base64.StdEncoding.DecodeString("SUQzBAAAAAABAFRYWFgAAAASAAADbWFqb3JfYnJhbmQAbXA0MgBUWFhYAAAAEQAAA21pbm9yX3Zl")
+	st, err := DetectContentTypeFromReader(bytes.NewReader(mp3))
+	assert.NoError(t, err)
+	assert.True(t, st.IsAudio())
+}