Add support for S3-backed image storage

scripts/test_split_nsfw_test_image.py

@@ -0,0 +1,55 @@
+import tempfile
+import unittest
+from pathlib import Path
+
+from PIL import Image
+
+from split_nsfw_test_image import split_image
+
+
+class SplitImageTests(unittest.TestCase):
+    def setUp(self):
+        self.temporary = tempfile.TemporaryDirectory()
+        self.addCleanup(self.temporary.cleanup)
+        self.root = Path(self.temporary.name)
+        self.source = self.root / "source.png"
+        self.image = Image.new("RGBA", (4, 3))
+        self.image.putdata([(i * 21, 255 - i * 21, i * 7, i * 23) for i in range(12)])
+        self.image.save(self.source)
+
+    def test_random_shares_losslessly_reconstruct_pixels_and_alpha(self):
+        first, second = split_image(self.source, self.root / "one")
+        self.assertEqual((first.name, second.name), ("image_1a.png", "image_1b.png"))
+        with Image.open(first) as a, Image.open(second) as b:
+            self.assertEqual(a.mode, "RGBA")
+            self.assertEqual(a.size, self.image.size)
+            self.assertEqual(b.size, self.image.size)
+            reconstructed = bytes(x ^ y for x, y in zip(a.tobytes(), b.tobytes()))
+            self.assertEqual(reconstructed, self.image.tobytes())
+        other_first, _ = split_image(self.source, self.root / "two")
+        self.assertNotEqual(first.read_bytes(), other_first.read_bytes())
+
+    def test_refuses_to_overwrite_and_supports_numbered_pairs(self):
+        directory = self.root / "fixtures"
+        first, second = split_image(self.source, directory)
+        original = (first.read_bytes(), second.read_bytes())
+        with self.assertRaises(FileExistsError):
+            split_image(self.source, directory)
+        self.assertEqual((first.read_bytes(), second.read_bytes()), original)
+        next_pair = split_image(self.source, directory, index=2)
+        self.assertEqual(tuple(path.name for path in next_pair), ("image_2a.png", "image_2b.png"))
+
+    def test_rejects_nonpositive_indices_and_nonimages_without_writing_parts(self):
+        directory = self.root / "fixtures"
+        for index in (0, -1):
+            with self.assertRaises(ValueError):
+                split_image(self.source, directory, index)
+        invalid = self.root / "invalid.txt"
+        invalid.write_text("not an image")
+        with self.assertRaises(OSError):
+            split_image(invalid, directory)
+        self.assertFalse(directory.exists())
+
+
+if __name__ == "__main__":
+    unittest.main()