Fix markdown render (go-gitea#33870)

Fix go-gitea#33869, some code block is moved to make it easier to test.

Added a new test

Author: wxiaoguang

modules/markup/markdown/markdown.go

@@ -159,27 +159,27 @@ func render(ctx *markup.RenderContext, input io.Reader, output io.Writer) error
 		limit: setting.UI.MaxDisplayFileSize * 3,
 	}
 
+	// FIXME: Don't read all to memory, but goldmark doesn't support
+	buf, err := io.ReadAll(input)
+	if err != nil {
+		log.Error("Unable to ReadAll: %v", err)
+		return err
+	}
+	buf = giteautil.NormalizeEOL(buf)
+
 	// FIXME: should we include a timeout to abort the renderer if it takes too long?
 	defer func() {
 		err := recover()
 		if err == nil {
 			return
 		}
 
-		log.Warn("Unable to render markdown due to panic in goldmark: %v", err)
-		if (!setting.IsProd && !setting.IsInTesting) || log.IsDebug() {
-			log.Error("Panic in markdown: %v\n%s", err, log.Stack(2))
-		}
+		log.Error("Panic in markdown: %v\n%s", err, log.Stack(2))
+		escapedHTML := template.HTMLEscapeString(giteautil.UnsafeBytesToString(buf))
+		_, _ = output.Write(giteautil.UnsafeStringToBytes(escapedHTML))
 	}()
 
-	// FIXME: Don't read all to memory, but goldmark doesn't support
 	pc := newParserContext(ctx)
-	buf, err := io.ReadAll(input)
-	if err != nil {
-		log.Error("Unable to ReadAll: %v", err)
-		return err
-	}
-	buf = giteautil.NormalizeEOL(buf)
 
 	// Preserve original length.
 	bufWithMetadataLength := len(buf)

modules/markup/markdown/markdown_attention_test.go

@@ -23,6 +23,11 @@ func TestAttention(t *testing.T) {
 	defer svg.MockIcon("octicon-alert")()
 	defer svg.MockIcon("octicon-stop")()
 
+	test := func(input, expected string) {
+		result, err := markdown.RenderString(markup.NewTestRenderContext(), input)
+		assert.NoError(t, err)
+		assert.Equal(t, strings.TrimSpace(expected), strings.TrimSpace(string(result)))
+	}
 	renderAttention := func(attention, icon string) string {
 		tmpl := `<blockquote class="attention-header attention-{attention}"><p><svg class="attention-icon attention-{attention} svg {icon}" width="16" height="16"></svg><strong class="attention-{attention}">{Attention}</strong></p>`
 		tmpl = strings.ReplaceAll(tmpl, "{attention}", attention)
@@ -31,12 +36,6 @@ func TestAttention(t *testing.T) {
 		return tmpl
 	}
 
-	test := func(input, expected string) {
-		result, err := markdown.RenderString(markup.NewTestRenderContext(), input)
-		assert.NoError(t, err)
-		assert.Equal(t, strings.TrimSpace(expected), strings.TrimSpace(string(result)))
-	}
-
 	test(`
 > [!NOTE]
 > text
@@ -53,4 +52,7 @@ func TestAttention(t *testing.T) {
 
 	// legacy GitHub style
 	test(`> **warning**`, renderAttention("warning", "octicon-alert")+"\n</blockquote>")
+
+	// edge case (it used to cause panic)
+	test(">\ntext", "<blockquote>\n</blockquote>\n<p>text</p>")
 }

modules/markup/markdown/transform_blockquote.go

@@ -115,6 +115,9 @@ func (g *ASTTransformer) transformBlockquote(v *ast.Blockquote, reader text.Read
 
 	// grab these nodes and make sure we adhere to the attention blockquote structure
 	firstParagraph := v.FirstChild()
+	if firstParagraph == nil {
+		return ast.WalkContinue, nil
+	}
 	g.applyElementDir(firstParagraph)
 
 	attentionType, processedNodes := g.extractBlockquoteAttentionEmphasis(firstParagraph, reader)