fix: use context manager for file read in pdf_renderer.py

backend/app/services/pdf_renderer.py

@@ -52,7 +52,8 @@ def compile_latex_project(project_dir: str, main_tex: str = "main.tex", engine:
 
 def _requires_xelatex(main_tex_path: str) -> bool:
     try:
-        content = open(main_tex_path, "r", encoding="utf-8", errors="ignore").read(4096)
+        with open(main_tex_path, "r", encoding="utf-8", errors="ignore") as f:
+            content = f.read(4096)
     except OSError:
         return False
     return any(marker in content for marker in ("ctexart", "ctexbook", "ctexrep", "xeCJK", "fontspec"))

backend/tests/test_pr_07_pdf_renderer_file.py

@@ -0,0 +1,75 @@
+"""Test that pdf_renderer.py uses context managers for file reads.
+
+Verifies that _requires_xelatex correctly detects XeTeX markers and that
+no unclosed file reads remain in the module.
+"""
+import os
+import re
+import tempfile
+
+
+def test_requires_xelatex_with_ctexart():
+    """_requires_xelatex should return True for files using ctexart."""
+    from app.services.pdf_renderer import _requires_xelatex
+
+    with tempfile.NamedTemporaryFile(mode="w", suffix=".tex", delete=False, encoding="utf-8") as f:
+        f.write("\\documentclass{ctexart}\n\\begin{document}\nHello\n\\end{document}\n")
+        path = f.name
+
+    try:
+        assert _requires_xelatex(path) is True
+    finally:
+        os.unlink(path)
+
+
+def test_requires_xelatex_with_standard_latex():
+    """_requires_xelatex should return False for standard LaTeX without CJK markers."""
+    from app.services.pdf_renderer import _requires_xelatex
+
+    with tempfile.NamedTemporaryFile(mode="w", suffix=".tex", delete=False, encoding="utf-8") as f:
+        f.write("\\documentclass{article}\n\\begin{document}\nHello world\n\\end{document}\n")
+        path = f.name
+
+    try:
+        assert _requires_xelatex(path) is False
+    finally:
+        os.unlink(path)
+
+
+def test_requires_xelatex_with_fontspec():
+    """_requires_xelatex should return True for files using fontspec."""
+    from app.services.pdf_renderer import _requires_xelatex
+
+    with tempfile.NamedTemporaryFile(mode="w", suffix=".tex", delete=False, encoding="utf-8") as f:
+        f.write("\\documentclass{article}\n\\usepackage{fontspec}\n\\begin{document}\nTest\n\\end{document}\n")
+        path = f.name
+
+    try:
+        assert _requires_xelatex(path) is True
+    finally:
+        os.unlink(path)
+
+
+def test_requires_xelatex_missing_file():
+    """_requires_xelatex should return False for nonexistent files."""
+    from app.services.pdf_renderer import _requires_xelatex
+
+    assert _requires_xelatex("/nonexistent/path/to/file.tex") is False
+
+
+def test_no_unclosed_file_reads():
+    """Verify no open(...).read() patterns remain in pdf_renderer.py."""
+    module_path = os.path.join(
+        os.path.dirname(__file__),
+        "..",
+        "app",
+        "services",
+        "pdf_renderer.py",
+    )
+    with open(module_path, "r", encoding="utf-8") as f:
+        source = f.read()
+
+    unclosed = re.findall(r"open\([^)]+\)\.read\([^)]*\)", source)
+    assert len(unclosed) == 0, (
+        f"Found {len(unclosed)} unclosed file read(s) in pdf_renderer.py: {unclosed}"
+    )