Add support for S3-backed image storage

scripts/split_nsfw_test_image.py

@@ -0,0 +1,63 @@
+#!/usr/bin/env python3
+"""Split an image into two lossless, random-looking PNG fixture shares."""
+
+from __future__ import annotations
+
+import argparse
+from io import BytesIO
+from pathlib import Path
+import secrets
+
+from PIL import Image
+
+
+def split_image(input_path: Path, output_dir: Path, index: int | None = None) -> tuple[Path, Path]:
+    if index is None:
+        index = 1
+        while any((output_dir / f"image_{index}{part}.png").exists() for part in ("a", "b")):
+            index += 1
+    if index < 1:
+        raise ValueError("Image index must be a positive integer")
+
+    paths = (
+        output_dir / f"image_{index}a.png",
+        output_dir / f"image_{index}b.png",
+    )
+    for path in paths:
+        if path.exists():
+            raise FileExistsError(f"Refusing to overwrite {path}; choose another --index")
+
+    # RGBA shares preserve every decoded pixel, including transparency. For animated
+    # inputs, use the first frame, matching the dashboard's static image upload behavior.
+    with Image.open(input_path) as source:
+        image = source.convert("RGBA")
+    pixels = image.tobytes()
+    first = secrets.token_bytes(len(pixels))
+    second = bytes(pixel ^ mask for pixel, mask in zip(pixels, first))
+
+    output_dir.mkdir(parents=True, exist_ok=True)
+    for path, share in zip(paths, (first, second)):
+        # Exclusive creation also prevents overwriting a file created during splitting.
+        encoded = BytesIO()
+        Image.frombytes("RGBA", image.size, share).save(encoded, format="PNG")
+        with path.open("xb") as output:
+            output.write(encoded.getvalue())
+    return paths
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("input_image", type=Path)
+    parser.add_argument("--output-dir", type=Path, default=Path("."))
+    parser.add_argument("--index", type=int, help="Fixture number (default: first unused positive index)")
+    args = parser.parse_args()
+    try:
+        paths = split_image(args.input_image, args.output_dir, args.index)
+    except (OSError, ValueError) as error:
+        parser.exit(1, f"Could not split image: {error}\n")
+    for path in paths:
+        print(path)
+
+
+if __name__ == "__main__":
+    main()