fix(workspace): fall back for large markdown previews

static/workspace.js

@@ -175,6 +175,8 @@ const HTML_EXTS   = new Set(['.html','.htm']);
 const PDF_EXTS    = new Set(['.pdf']);
 const AUDIO_EXTS  = new Set(['.mp3','.wav','.m4a','.aac','.ogg','.oga','.opus','.flac']);
 const VIDEO_EXTS  = new Set(['.mp4','.mov','.m4v','.webm','.ogv','.avi','.mkv']);
+const MD_PREVIEW_RICH_RENDER_MAX_BYTES = 64 * 1024;
+const MD_PREVIEW_RICH_RENDER_MAX_LINES = 1500;
 // Binary formats that should download rather than preview
 const DOWNLOAD_EXTS = new Set([
   '.docx','.doc','.xlsx','.xls','.pptx','.ppt','.odt','.ods','.odp',
@@ -186,6 +188,31 @@ const DOWNLOAD_EXTS = new Set([
 
 function fileExt(p){ const i=p.lastIndexOf('.'); return i>=0?p.slice(i).toLowerCase():''; }
 
+function markdownPreviewByteLength(content){
+  const text=String(content||'');
+  if(typeof Blob==='function') return new Blob([text]).size;
+  if(typeof TextEncoder==='function') return new TextEncoder().encode(text).length;
+  return unescape(encodeURIComponent(text)).length;
+}
+
+function markdownPreviewLineCount(content){
+  const text=String(content||'');
+  if(!text) return 1;
+  return text.split('\n').length;
+}
+
+function shouldRenderMarkdownPreviewAsPlainText(content){
+  return markdownPreviewByteLength(content)>MD_PREVIEW_RICH_RENDER_MAX_BYTES
+    || markdownPreviewLineCount(content)>MD_PREVIEW_RICH_RENDER_MAX_LINES;
+}
+
+function largeMarkdownPlainTextStatus(content){
+  const bytes=markdownPreviewByteLength(content);
+  const lines=markdownPreviewLineCount(content);
+  const sizeLabel=bytes>=1024?`${Math.round(bytes/1024)} KB`:`${bytes} B`;
+  return `Large markdown file (${sizeLabel}, ${lines} lines) shown as plain text. Click Edit to view raw.`;
+}
+
 let _previewCurrentPath = '';  // relative path of currently previewed file
 let _previewCurrentMode = '';  // 'code' | 'md' | 'image' | 'html' | 'pdf' | 'audio' | 'video'
 let _previewDirty = false;     // true when edits are unsaved
@@ -317,8 +344,14 @@ async function openFile(path){
     // Markdown: fetch text, render with renderMd, display as formatted HTML
     try{
       const data=await api(`/api/file?session_id=${encodeURIComponent(S.session.session_id)}&path=${encodeURIComponent(path)}`);
-      showPreview('md');
       _previewRawContent = data.content;
+      if(shouldRenderMarkdownPreviewAsPlainText(data.content)){
+        showPreview('code');
+        $('previewCode').textContent=data.content;
+        setStatus(largeMarkdownPlainTextStatus(data.content));
+        return;
+      }
+      showPreview('md');
       $('previewMd').innerHTML=renderMd(data.content);
       requestAnimationFrame(()=>{if(typeof renderKatexBlocks==='function')renderKatexBlocks();});
     }catch(e){setStatus(t('file_open_failed'));}

tests/test_issue2823_large_markdown_preview.py

@@ -0,0 +1,71 @@
+"""Regression coverage for #2823 large Markdown workspace previews."""
+
+from pathlib import Path
+
+
+WORKSPACE_JS = Path("static/workspace.js").read_text(encoding="utf-8")
+
+
+def _open_file_block() -> str:
+    marker = "async function openFile(path){"
+    start = WORKSPACE_JS.find(marker)
+    assert start != -1, "openFile() not found in workspace.js"
+    end = WORKSPACE_JS.find("\nfunction downloadFile", start)
+    assert end != -1, "downloadFile() marker not found after openFile()"
+    return WORKSPACE_JS[start:end]
+
+
+def _markdown_branch() -> str:
+    block = _open_file_block()
+    start = block.find("} else if(MD_EXTS.has(ext)){")
+    assert start != -1, "Markdown preview branch not found in openFile()"
+    end = block.find("} else if(HTML_EXTS.has(ext)){", start)
+    assert end != -1, "HTML preview branch marker not found after Markdown branch"
+    return block[start:end]
+
+
+def test_large_markdown_preview_limits_are_source_controlled():
+    assert "MD_PREVIEW_RICH_RENDER_MAX_BYTES = 64 * 1024" in WORKSPACE_JS
+    assert "MD_PREVIEW_RICH_RENDER_MAX_LINES = 1500" in WORKSPACE_JS
+    assert "function shouldRenderMarkdownPreviewAsPlainText(content)" in WORKSPACE_JS
+
+
+def test_large_markdown_fallback_sets_raw_content_before_size_gate():
+    branch = _markdown_branch()
+    raw_pos = branch.find("_previewRawContent = data.content")
+    gate_pos = branch.find("shouldRenderMarkdownPreviewAsPlainText(data.content)")
+    fallback_pos = branch.find("showPreview('code')")
+    rich_pos = branch.find("showPreview('md')")
+
+    assert raw_pos != -1, "Markdown preview must retain raw text for Edit mode"
+    assert gate_pos != -1, "Markdown preview must guard rich rendering by size/line count"
+    assert fallback_pos != -1, "Large Markdown preview must fall back to plain text"
+    assert rich_pos != -1, "Small Markdown preview must still use rich Markdown mode"
+    assert raw_pos < gate_pos < fallback_pos < rich_pos
+
+
+def test_large_markdown_fallback_uses_code_view_without_rich_render_or_katex():
+    branch = _markdown_branch()
+    gate_pos = branch.find("if(shouldRenderMarkdownPreviewAsPlainText(data.content)){")
+    fallback_end = branch.find("return;", gate_pos)
+    assert gate_pos != -1 and fallback_end != -1, "Large Markdown fallback block not found"
+
+    fallback = branch[gate_pos:fallback_end]
+    compact = fallback.replace(" ", "")
+    assert "$('previewCode').textContent=data.content" in compact
+    assert "setStatus(" in fallback
+    assert "renderMd(" not in fallback
+    assert "renderKatexBlocks" not in fallback
+
+
+def test_small_markdown_still_renders_and_runs_katex_after_render():
+    branch = _markdown_branch()
+    fallback_end = branch.find("return;")
+    assert fallback_end != -1, "Large Markdown fallback must return before rich rendering"
+
+    rich = branch[fallback_end:]
+    render_pos = rich.find("$('previewMd').innerHTML=renderMd(data.content)")
+    katex_pos = rich.rfind("renderKatexBlocks")
+    assert render_pos != -1, "Small Markdown files must still rich-render with renderMd()"
+    assert katex_pos != -1, "Small Markdown file previews must still trigger KaTeX rendering"
+    assert katex_pos > render_pos