62 lines
1.9 KiB
Python
62 lines
1.9 KiB
Python
"""On-demand thumbnail generation with disk caching.
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Thumbnails are stored under UPLOAD_DIR/.thumbs/<size>/<original relative path>.jpg
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and generated lazily the first time they are requested. This keeps the
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documents list fast even with hundreds of full-resolution uploads.
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"""
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from __future__ import annotations
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from pathlib import Path
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from typing import Optional
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from PIL import Image, ImageOps
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from config import UPLOAD_DIR
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THUMB_ROOT = Path(UPLOAD_DIR) / ".thumbs"
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DEFAULT_SIZE = 320 # px on the longest edge
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JPEG_QUALITY = 78
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def _safe_rel(rel_path: str) -> Optional[Path]:
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"""Resolve rel_path against UPLOAD_DIR, rejecting traversal."""
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base = Path(UPLOAD_DIR).resolve()
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target = (base / rel_path).resolve()
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try:
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target.relative_to(base)
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except ValueError:
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return None
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return target
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def get_or_create_thumbnail(rel_path: str, size: int = DEFAULT_SIZE) -> Optional[Path]:
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"""Return a path to a cached JPEG thumbnail for the given upload,
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creating it if needed. Returns None if the source doesn't exist."""
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source = _safe_rel(rel_path)
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if source is None or not source.is_file():
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return None
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thumb_dir = THUMB_ROOT / str(size)
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thumb_path = thumb_dir / (rel_path + ".jpg")
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# Regenerate if missing or source is newer
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if thumb_path.is_file():
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try:
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if thumb_path.stat().st_mtime >= source.stat().st_mtime:
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return thumb_path
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except OSError:
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pass
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thumb_path.parent.mkdir(parents=True, exist_ok=True)
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try:
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with Image.open(source) as im:
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im = ImageOps.exif_transpose(im)
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im.thumbnail((size, size), Image.LANCZOS)
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if im.mode not in ("RGB", "L"):
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im = im.convert("RGB")
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im.save(thumb_path, "JPEG", quality=JPEG_QUALITY, optimize=True)
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except (OSError, Image.UnidentifiedImageError):
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return None
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return thumb_path
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