Fix external render, make iframe render work (#35727, #35730) (#35731)

Backport #35727 and #35730

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>

modules/markup/render.go

@@ -6,12 +6,14 @@ package markup
 import (
 	"context"
 	"fmt"
+	"html/template"
 	"io"
 	"net/url"
 	"strconv"
 	"strings"
 	"time"
 
+	"code.gitea.io/gitea/modules/htmlutil"
 	"code.gitea.io/gitea/modules/markup/internal"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/util"
@@ -120,31 +122,38 @@ func (ctx *RenderContext) WithHelper(helper RenderHelper) *RenderContext {
 	return ctx
 }
 
-// Render renders markup file to HTML with all specific handling stuff.
-func Render(ctx *RenderContext, input io.Reader, output io.Writer) error {
+// FindRendererByContext finds renderer by RenderContext
+// TODO: it should be merged with other similar functions like GetRendererByFileName, DetectMarkupTypeByFileName, etc
+func FindRendererByContext(ctx *RenderContext) (Renderer, error) {
 	if ctx.RenderOptions.MarkupType == "" && ctx.RenderOptions.RelativePath != "" {
 		ctx.RenderOptions.MarkupType = DetectMarkupTypeByFileName(ctx.RenderOptions.RelativePath)
 		if ctx.RenderOptions.MarkupType == "" {
-			return util.NewInvalidArgumentErrorf("unsupported file to render: %q", ctx.RenderOptions.RelativePath)
+			return nil, util.NewInvalidArgumentErrorf("unsupported file to render: %q", ctx.RenderOptions.RelativePath)
 		}
 	}
 
 	renderer := renderers[ctx.RenderOptions.MarkupType]
 	if renderer == nil {
-		return util.NewInvalidArgumentErrorf("unsupported markup type: %q", ctx.RenderOptions.MarkupType)
+		return nil, util.NewNotExistErrorf("unsupported markup type: %q", ctx.RenderOptions.MarkupType)
 	}
 
-	if ctx.RenderOptions.RelativePath != "" {
-		if externalRender, ok := renderer.(ExternalRenderer); ok && externalRender.DisplayInIFrame() {
-			if !ctx.RenderOptions.InStandalonePage {
-				// for an external "DisplayInIFrame" 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 renderer, nil
+}
 
-	return render(ctx, renderer, input, output)
+func RendererNeedPostProcess(renderer Renderer) bool {
+	if r, ok := renderer.(PostProcessRenderer); ok && r.NeedPostProcess() {
+		return true
+	}
+	return false
+}
+
+// Render renders markup file to HTML with all specific handling stuff.
+func Render(ctx *RenderContext, input io.Reader, output io.Writer) error {
+	renderer, err := FindRendererByContext(ctx)
+	if err != nil {
+		return err
+	}
+	return RenderWithRenderer(ctx, renderer, input, output)
 }
 
 // RenderString renders Markup string to HTML with all specific handling stuff and return string
@@ -156,24 +165,20 @@ func RenderString(ctx *RenderContext, content string) (string, error) {
 	return buf.String(), 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,
+func renderIFrame(ctx *RenderContext, sandbox string, output io.Writer) error {
+	src := fmt.Sprintf("%s/%s/%s/render/%s/%s", setting.AppSubURL,
 		url.PathEscape(ctx.RenderOptions.Metas["user"]),
 		url.PathEscape(ctx.RenderOptions.Metas["repo"]),
-		ctx.RenderOptions.Metas["RefTypeNameSubURL"],
-		url.PathEscape(ctx.RenderOptions.RelativePath),
-	))
+		util.PathEscapeSegments(ctx.RenderOptions.Metas["RefTypeNameSubURL"]),
+		util.PathEscapeSegments(ctx.RenderOptions.RelativePath),
+	)
+
+	var sandboxAttrValue template.HTML
+	if sandbox != "" {
+		sandboxAttrValue = htmlutil.HTMLFormat(`sandbox="%s"`, sandbox)
+	}
+	iframe := htmlutil.HTMLFormat(`<iframe data-src="%s" class="external-render-iframe" %s></iframe>`, src, sandboxAttrValue)
+	_, err := io.WriteString(output, string(iframe))
 	return err
 }
 
@@ -185,13 +190,34 @@ func pipes() (io.ReadCloser, io.WriteCloser, func()) {
 	}
 }
 
-func render(ctx *RenderContext, renderer Renderer, input io.Reader, output io.Writer) error {
+func getExternalRendererOptions(renderer Renderer) (ret ExternalRendererOptions, _ bool) {
+	if externalRender, ok := renderer.(ExternalRenderer); ok {
+		return externalRender.GetExternalRendererOptions(), true
+	}
+	return ret, false
+}
+
+func RenderWithRenderer(ctx *RenderContext, renderer Renderer, input io.Reader, output io.Writer) error {
+	var extraHeadHTML template.HTML
+	if extOpts, ok := getExternalRendererOptions(renderer); ok && extOpts.DisplayInIframe {
+		if !ctx.RenderOptions.InStandalonePage {
+			// for an external "DisplayInIFrame" 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, extOpts.ContentSandbox, output)
+		}
+		// else: this is a standalone page, fallthrough to the real rendering, and add extra JS/CSS
+		extraStyleHref := setting.AppSubURL + "/assets/css/external-render-iframe.css"
+		extraScriptSrc := setting.AppSubURL + "/assets/js/external-render-iframe.js"
+		// "<script>" must go before "<link>", to make Golang's http.DetectContentType() can still recognize the content as "text/html"
+		extraHeadHTML = htmlutil.HTMLFormat(`<script src="%s"></script><link rel="stylesheet" href="%s">`, extraScriptSrc, extraStyleHref)
+	}
+
 	ctx.usedByRender = true
 	if ctx.RenderHelper != nil {
 		defer ctx.RenderHelper.CleanUp()
 	}
 
-	finalProcessor := ctx.RenderInternal.Init(output)
+	finalProcessor := ctx.RenderInternal.Init(output, extraHeadHTML)
 	defer finalProcessor.Close()
 
 	// input -> (pw1=pr1) -> renderer -> (pw2=pr2) -> SanitizeReader -> finalProcessor -> output
@@ -202,7 +228,7 @@ func render(ctx *RenderContext, renderer Renderer, input io.Reader, output io.Wr
 	eg, _ := errgroup.WithContext(ctx)
 	var pw2 io.WriteCloser = util.NopCloser{Writer: finalProcessor}
 
-	if r, ok := renderer.(ExternalRenderer); !ok || !r.SanitizerDisabled() {
+	if r, ok := renderer.(ExternalRenderer); !ok || !r.GetExternalRendererOptions().SanitizerDisabled {
 		var pr2 io.ReadCloser
 		var close2 func()
 		pr2, pw2, close2 = pipes()
@@ -214,7 +240,7 @@ func render(ctx *RenderContext, renderer Renderer, input io.Reader, output io.Wr
 	}
 
 	eg.Go(func() (err error) {
-		if r, ok := renderer.(PostProcessRenderer); ok && r.NeedPostProcess() {
+		if RendererNeedPostProcess(renderer) {
 			err = PostProcessDefault(ctx, pr1, pw2)
 		} else {
 			_, err = io.Copy(pw2, pr1)