feat(recipes): add get_image_dimensions helper with LRU cache

py/utils/exif_utils.py

@@ -1,9 +1,10 @@
+import functools
 import json
 import logging
 import os
 import struct
 from io import BytesIO
-from typing import Any, Optional
+from typing import Any, Optional, Tuple
 
 import piexif
 from PIL import Image, PngImagePlugin
@@ -17,6 +18,22 @@ except ImportError:
 
 logger = logging.getLogger(__name__)
 
+
+@functools.lru_cache(maxsize=2048)
+def _get_image_dimensions_cached(path: str, _mtime_ns: int, _size: int) -> Optional[Tuple[int, int]]:
+    """Return ``(width, height)`` for ``path``, or ``None`` on any failure.
+
+    The ``_mtime_ns`` and ``_size`` arguments are part of the cache key only;
+    they invalidate the entry when the file is replaced with a new image, so a
+    stale preview never serves outdated dimensions.
+    """
+    try:
+        with Image.open(path) as img:
+            return img.size
+    except Exception:
+        return None
+
+
 class ExifUtils:
     """Utility functions for working with EXIF data in images"""
 
@@ -422,6 +439,25 @@ class ExifUtils:
             # Metadata is in the middle of the string
             return user_comment[:recipe_marker_index] + user_comment[next_line_index:]
             
+    @staticmethod
+    def get_image_dimensions(image_path: str) -> Optional[Tuple[int, int]]:
+        """Return ``(width, height)`` for an image, or ``None`` if unavailable.
+
+        Video containers (``.mp4``/``.webm``/``.avi``) and formats PIL cannot
+        read (``.avif``/``.jxl``) return ``None`` before PIL is invoked.
+        Missing or corrupt files return ``None``. Never raises.
+        """
+        try:
+            ext = os.path.splitext(image_path)[1].lower()
+            if ext in ('.mp4', '.webm', '.avi', '.avif', '.jxl'):
+                return None
+            stat = os.stat(image_path)
+            return _get_image_dimensions_cached(
+                image_path, stat.st_mtime_ns, stat.st_size
+            )
+        except Exception:
+            return None
+
     @staticmethod
     def optimize_image(image_data, target_width=250, format='webp', quality=85, preserve_metadata=False):
         """

tests/utils/test_exif_utils.py

@@ -288,3 +288,58 @@ class TestIsobmffBrotliExtraction:
         # Direct extraction should return None because decompressed size exceeds limit
         result = ExifUtils._extract_isobmff_brotli(str(path))
         assert result is None
+
+
+# --- get_image_dimensions tests ---
+
+
+def test_get_image_dimensions_returns_actual_size(tmp_path):
+    """(a) A valid image returns its real (width, height)."""
+    image_path = tmp_path / "preview.png"
+    Image.new("RGB", (64, 32), color="red").save(image_path)
+
+    assert ExifUtils.get_image_dimensions(str(image_path)) == (64, 32)
+
+
+def test_get_image_dimensions_missing_path_returns_none(tmp_path):
+    """(b) A nonexistent path returns None without raising."""
+    assert ExifUtils.get_image_dimensions(str(tmp_path / "missing.png")) is None
+
+
+def test_get_image_dimensions_skips_video_extension_without_pil(tmp_path, monkeypatch):
+    """(c) A .mp4 path returns None and never invokes PIL."""
+    video_path = tmp_path / "preview.mp4"
+    video_path.write_bytes(b"not really a video")
+
+    def fail_if_called(*args, **kwargs):
+        raise AssertionError("PIL Image.open must not be called for video paths")
+
+    monkeypatch.setattr("py.utils.exif_utils.Image.open", fail_if_called)
+
+    assert ExifUtils.get_image_dimensions(str(video_path)) is None
+
+
+def test_get_image_dimensions_corrupt_file_returns_none(tmp_path):
+    """(d) A corrupt file returns None without raising."""
+    image_path = tmp_path / "corrupt.png"
+    image_path.write_bytes(b"\x00\x01\x02\x03 not a real image")
+
+    assert ExifUtils.get_image_dimensions(str(image_path)) is None
+
+
+def test_get_image_dimensions_cache_key_includes_mtime(tmp_path):
+    """(e) Replacing a path with a different-size image returns the new size."""
+    image_path = tmp_path / "replaced.png"
+    Image.new("RGB", (64, 32), color="red").save(image_path)
+    assert ExifUtils.get_image_dimensions(str(image_path)) == (64, 32)
+
+    Image.new("RGB", (100, 50), color="blue").save(image_path)
+    assert ExifUtils.get_image_dimensions(str(image_path)) == (100, 50)
+
+
+def test_get_image_dimensions_skips_unreadable_formats(tmp_path):
+    """(f) .avif/.jxl paths return None without raising."""
+    for ext in (".avif", ".jxl"):
+        image_path = tmp_path / f"preview{ext}"
+        image_path.write_bytes(b"fake container data")
+        assert ExifUtils.get_image_dimensions(str(image_path)) is None