Allow render HTML with css/js external links (#19017)

* Allow render HTML with css/js external links

* Fix bug because of filename escape chars

* Fix lint

* Update docs about new configuration item

* Fix bug of render HTML in sub directory

* Add CSP head for displaying iframe in rendering file

* Fix test

* Apply suggestions from code review

Co-authored-by: delvh <dev.lh@web.de>

* Some improvements

* some improvement

* revert change in SanitizerDisabled of external renderer

* Add sandbox for iframe and support allow-scripts and allow-same-origin

* refactor

* fix

* fix lint

* fine tune

* use single option RENDER_CONTENT_MODE, use sandbox=allow-scripts

* fine tune CSP

* Apply suggestions from code review

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

7 files changed, 94 insertions, 59 deletions

diff --git a/modules/markup/console/console.go b/modules/markup/console/console.go
index b59594acb7..597593eee1 100644
--- a/modules/markup/console/console.go
+++ b/modules/markup/console/console.go
@@ -33,9 +33,6 @@ func (Renderer) Name() string {
 	return MarkupName
 }
 
-// NeedPostProcess implements markup.Renderer
-func (Renderer) NeedPostProcess() bool { return false }
-
 // Extensions implements markup.Renderer
 func (Renderer) Extensions() []string {
 	return []string{".sh-session"}
@@ -48,11 +45,6 @@ func (Renderer) SanitizerRules() []setting.MarkupSanitizerRule {
 	}
 }
 
-// SanitizerDisabled disabled sanitize if return true
-func (Renderer) SanitizerDisabled() bool {
-	return false
-}
-
 // CanRender implements markup.RendererContentDetector
 func (Renderer) CanRender(filename string, input io.Reader) bool {
 	buf, err := io.ReadAll(input)
diff --git a/modules/markup/csv/csv.go b/modules/markup/csv/csv.go
index 17c3fe6f4f..5095b85465 100644
--- a/modules/markup/csv/csv.go
+++ b/modules/markup/csv/csv.go
@@ -29,9 +29,6 @@ func (Renderer) Name() string {
 	return "csv"
 }
 
-// NeedPostProcess implements markup.Renderer
-func (Renderer) NeedPostProcess() bool { return false }
-
 // Extensions implements markup.Renderer
 func (Renderer) Extensions() []string {
 	return []string{".csv", ".tsv"}
@@ -46,11 +43,6 @@ func (Renderer) SanitizerRules() []setting.MarkupSanitizerRule {
 	}
 }
 
-// SanitizerDisabled disabled sanitize if return true
-func (Renderer) SanitizerDisabled() bool {
-	return false
-}
-
 func writeField(w io.Writer, element, class, field string) error {
 	if _, err := io.WriteString(w, "<"); err != nil {
 		return err
diff --git a/modules/markup/external/external.go b/modules/markup/external/external.go
index a587abcc3b..23dd45ba0a 100644
--- a/modules/markup/external/external.go
+++ b/modules/markup/external/external.go
@@ -34,6 +34,11 @@ type Renderer struct {
 	*setting.MarkupRenderer
 }
 
+var (
+	_ markup.PostProcessRenderer = (*Renderer)(nil)
+	_ markup.ExternalRenderer    = (*Renderer)(nil)
+)
+
 // Name returns the external tool name
 func (p *Renderer) Name() string {
 	return p.MarkupName
@@ -56,7 +61,12 @@ func (p *Renderer) SanitizerRules() []setting.MarkupSanitizerRule {
 
 // SanitizerDisabled disabled sanitize if return true
 func (p *Renderer) SanitizerDisabled() bool {
-	return p.DisableSanitizer
+	return p.RenderContentMode == setting.RenderContentModeNoSanitizer || p.RenderContentMode == setting.RenderContentModeIframe
+}
+
+// DisplayInIFrame represents whether render the content with an iframe
+func (p *Renderer) DisplayInIFrame() bool {
+	return p.RenderContentMode == setting.RenderContentModeIframe
 }
 
 func envMark(envName string) string {
diff --git a/modules/markup/html_test.go b/modules/markup/html_test.go
index f6aabc6272..f494998c59 100644
--- a/modules/markup/html_test.go
+++ b/modules/markup/html_test.go
@@ -29,10 +29,10 @@ func TestRender_Commits(t *testing.T) {
 	setting.AppURL = TestAppURL
 	test := func(input, expected string) {
 		buffer, err := RenderString(&RenderContext{
-			Ctx:       git.DefaultContext,
-			Filename:  ".md",
-			URLPrefix: TestRepoURL,
-			Metas:     localMetas,
+			Ctx:          git.DefaultContext,
+			RelativePath: ".md",
+			URLPrefix:    TestRepoURL,
+			Metas:        localMetas,
 		}, input)
 		assert.NoError(t, err)
 		assert.Equal(t, strings.TrimSpace(expected), strings.TrimSpace(buffer))
@@ -80,9 +80,9 @@ func TestRender_CrossReferences(t *testing.T) {
 
 	test := func(input, expected string) {
 		buffer, err := RenderString(&RenderContext{
-			Filename:  "a.md",
-			URLPrefix: setting.AppSubURL,
-			Metas:     localMetas,
+			RelativePath: "a.md",
+			URLPrefix:    setting.AppSubURL,
+			Metas:        localMetas,
 		}, input)
 		assert.NoError(t, err)
 		assert.Equal(t, strings.TrimSpace(expected), strings.TrimSpace(buffer))
@@ -124,8 +124,8 @@ func TestRender_links(t *testing.T) {
 
 	test := func(input, expected string) {
 		buffer, err := RenderString(&RenderContext{
-			Filename:  "a.md",
-			URLPrefix: TestRepoURL,
+			RelativePath: "a.md",
+			URLPrefix:    TestRepoURL,
 		}, input)
 		assert.NoError(t, err)
 		assert.Equal(t, strings.TrimSpace(expected), strings.TrimSpace(buffer))
@@ -223,8 +223,8 @@ func TestRender_email(t *testing.T) {
 
 	test := func(input, expected string) {
 		res, err := RenderString(&RenderContext{
-			Filename:  "a.md",
-			URLPrefix: TestRepoURL,
+			RelativePath: "a.md",
+			URLPrefix:    TestRepoURL,
 		}, input)
 		assert.NoError(t, err)
 		assert.Equal(t, strings.TrimSpace(expected), strings.TrimSpace(res))
@@ -281,8 +281,8 @@ func TestRender_emoji(t *testing.T) {
 	test := func(input, expected string) {
 		expected = strings.ReplaceAll(expected, "&", "&amp;")
 		buffer, err := RenderString(&RenderContext{
-			Filename:  "a.md",
-			URLPrefix: TestRepoURL,
+			RelativePath: "a.md",
+			URLPrefix:    TestRepoURL,
 		}, input)
 		assert.NoError(t, err)
 		assert.Equal(t, strings.TrimSpace(expected), strings.TrimSpace(buffer))
diff --git a/modules/markup/markdown/markdown.go b/modules/markup/markdown/markdown.go
index 7ebdfea6c4..37e11e606f 100644
--- a/modules/markup/markdown/markdown.go
+++ b/modules/markup/markdown/markdown.go
@@ -205,12 +205,14 @@ func init() {
 // Renderer implements markup.Renderer
 type Renderer struct{}
 
+var _ markup.PostProcessRenderer = (*Renderer)(nil)
+
 // Name implements markup.Renderer
 func (Renderer) Name() string {
 	return MarkupName
 }
 
-// NeedPostProcess implements markup.Renderer
+// NeedPostProcess implements markup.PostProcessRenderer
 func (Renderer) NeedPostProcess() bool { return true }
 
 // Extensions implements markup.Renderer
@@ -223,11 +225,6 @@ func (Renderer) SanitizerRules() []setting.MarkupSanitizerRule {
 	return []setting.MarkupSanitizerRule{}
 }
 
-// SanitizerDisabled disabled sanitize if return true
-func (Renderer) SanitizerDisabled() bool {
-	return false
-}
-
 // Render implements markup.Renderer
 func (Renderer) Render(ctx *markup.RenderContext, input io.Reader, output io.Writer) error {
 	return render(ctx, input, output)
diff --git a/modules/markup/orgmode/orgmode.go b/modules/markup/orgmode/orgmode.go
index 2f394b992b..8c9f3b3da7 100644
--- a/modules/markup/orgmode/orgmode.go
+++ b/modules/markup/orgmode/orgmode.go
@@ -29,12 +29,14 @@ func init() {
 // Renderer implements markup.Renderer for orgmode
 type Renderer struct{}
 
+var _ markup.PostProcessRenderer = (*Renderer)(nil)
+
 // Name implements markup.Renderer
 func (Renderer) Name() string {
 	return "orgmode"
 }
 
-// NeedPostProcess implements markup.Renderer
+// NeedPostProcess implements markup.PostProcessRenderer
 func (Renderer) NeedPostProcess() bool { return true }
 
 // Extensions implements markup.Renderer
@@ -47,11 +49,6 @@ func (Renderer) SanitizerRules() []setting.MarkupSanitizerRule {
 	return []setting.MarkupSanitizerRule{}
 }
 
-// SanitizerDisabled disabled sanitize if return true
-func (Renderer) SanitizerDisabled() bool {
-	return false
-}
-
 // Render renders orgmode rawbytes to HTML
 func Render(ctx *markup.RenderContext, input io.Reader, output io.Writer) error {
 	htmlWriter := org.NewHTMLWriter()
diff --git a/modules/markup/renderer.go b/modules/markup/renderer.go
index 6e4ae4e08c..e88fa31187 100644
--- a/modules/markup/renderer.go
+++ b/modules/markup/renderer.go
@@ -10,6 +10,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"net/url"
 	"path/filepath"
 	"strings"
 	"sync"
@@ -43,17 +44,18 @@ type Header struct {
 
 // RenderContext represents a render context
 type RenderContext struct {
-	Ctx             context.Context
-	Filename        string
-	Type            string
-	IsWiki          bool
-	URLPrefix       string
-	Metas           map[string]string
-	DefaultLink     string
-	GitRepo         *git.Repository
-	ShaExistCache   map[string]bool
-	cancelFn        func()
-	TableOfContents []Header
+	Ctx              context.Context
+	RelativePath     string // relative path from tree root of the branch
+	Type             string
+	IsWiki           bool
+	URLPrefix        string
+	Metas            map[string]string
+	DefaultLink      string
+	GitRepo          *git.Repository
+	ShaExistCache    map[string]bool
+	cancelFn         func()
+	TableOfContents  []Header
+	InStandalonePage bool // used by external render. the router "/org/repo/render/..." will output the rendered content in a standalone page
 }
 
 // Cancel runs any cleanup functions that have been registered for this Ctx
@@ -88,12 +90,24 @@ func (ctx *RenderContext) AddCancel(fn func()) {
 type Renderer interface {
 	Name() string // markup format name
 	Extensions() []string
-	NeedPostProcess() bool
 	SanitizerRules() []setting.MarkupSanitizerRule
-	SanitizerDisabled() bool
 	Render(ctx *RenderContext, input io.Reader, output io.Writer) error
 }
 
+// PostProcessRenderer defines an interface for renderers who need post process
+type PostProcessRenderer interface {
+	NeedPostProcess() bool
+}
+
+// PostProcessRenderer defines an interface for external renderers
+type ExternalRenderer interface {
+	// SanitizerDisabled disabled sanitize if return true
+	SanitizerDisabled() bool
+
+	// DisplayInIFrame represents whether render the content with an iframe
+	DisplayInIFrame() bool
+}
+
 // RendererContentDetector detects if the content can be rendered
 // by specified renderer
 type RendererContentDetector interface {
@@ -142,7 +156,7 @@ func DetectRendererType(filename string, input io.Reader) string {
 func Render(ctx *RenderContext, input io.Reader, output io.Writer) error {
 	if ctx.Type != "" {
 		return renderByType(ctx, input, output)
-	} else if ctx.Filename != "" {
+	} else if ctx.RelativePath != "" {
 		return renderFile(ctx, input, output)
 	}
 	return errors.New("Render options both filename and type missing")
@@ -163,6 +177,27 @@ type nopCloser struct {
 
 func (nopCloser) Close() error { return nil }
 
+func renderIFrame(ctx *RenderContext, output io.Writer) error {
+	// set height="0" ahead, otherwise the scrollHeight would be max(150, realHeight)
+	// at the moment, only "allow-scripts" is allowed for sandbox mode.
+	// "allow-same-origin" should never be used, it leads to XSS attack, and it makes the JS in iframe can access parent window's config and CSRF token
+	// TODO: when using dark theme, if the rendered content doesn't have proper style, the default text color is black, which is not easy to read
+	_, err := io.WriteString(output, fmt.Sprintf(`
+<iframe src="%s/%s/%s/render/%s/%s"
+name="giteaExternalRender"
+onload="this.height=giteaExternalRender.document.documentElement.scrollHeight"
+width="100%%" height="0" scrolling="no" frameborder="0" style="overflow: hidden"
+sandbox="allow-scripts"
+></iframe>`,
+		setting.AppSubURL,
+		url.PathEscape(ctx.Metas["user"]),
+		url.PathEscape(ctx.Metas["repo"]),
+		ctx.Metas["BranchNameSubURL"],
+		url.PathEscape(ctx.RelativePath),
+	))
+	return err
+}
+
 func render(ctx *RenderContext, renderer Renderer, input io.Reader, output io.Writer) error {
 	var wg sync.WaitGroup
 	var err error
@@ -175,7 +210,12 @@ func render(ctx *RenderContext, renderer Renderer, input io.Reader, output io.Wr
 	var pr2 io.ReadCloser
 	var pw2 io.WriteCloser
 
-	if !renderer.SanitizerDisabled() {
+	var sanitizerDisabled bool
+	if r, ok := renderer.(ExternalRenderer); ok {
+		sanitizerDisabled = r.SanitizerDisabled()
+	}
+
+	if !sanitizerDisabled {
 		pr2, pw2 = io.Pipe()
 		defer func() {
 			_ = pr2.Close()
@@ -194,7 +234,7 @@ func render(ctx *RenderContext, renderer Renderer, input io.Reader, output io.Wr
 
 	wg.Add(1)
 	go func() {
-		if renderer.NeedPostProcess() {
+		if r, ok := renderer.(PostProcessRenderer); ok && r.NeedPostProcess() {
 			err = PostProcess(ctx, pr, pw2)
 		} else {
 			_, err = io.Copy(pw2, pr)
@@ -239,8 +279,15 @@ func (err ErrUnsupportedRenderExtension) Error() string {
 }
 
 func renderFile(ctx *RenderContext, input io.Reader, output io.Writer) error {
-	extension := strings.ToLower(filepath.Ext(ctx.Filename))
+	extension := strings.ToLower(filepath.Ext(ctx.RelativePath))
 	if renderer, ok := extRenderers[extension]; ok {
+		if r, ok := renderer.(ExternalRenderer); ok && r.DisplayInIFrame() {
+			if !ctx.InStandalonePage {
+				// for an external render, it could only output its content in a standalone page
+				// otherwise, a <iframe> should be outputted to embed the external rendered page
+				return renderIFrame(ctx, output)
+			}
+		}
 		return render(ctx, renderer, input, output)
 	}
 	return ErrUnsupportedRenderExtension{extension}