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Vesuvius Challenge 25

"""Correct SampleFormat in the exact public eta TIFF, preserving all other bytes.

This source-specific recipe uses an existing TIFF tag correction. It requires
a filesystem supporting hard links so publication cannot replace another file.
"""

import argparse
import hashlib
import json
import os
from pathlib import Path
import sys
import tempfile

SOURCE_SHA256 = "6f3b05d2e6ab8ea1e8055d35dc5b8fa7e0c7385dffc010b4d3df319548622247"
OUTPUT_SHA256 = "5c6b9d2b4ac69b812e53f2220da4e6f8cd123ec0432c98f161fb04e285ad3d90"
SOURCE_BYTES = 58_260_398
OFFSETS = (58_260_392, 58_260_394, 58_260_396)


def _publish_copy(data, output):
    """Make the complete file visible at output, without replacing a destination."""
    temporary = None
    try:
        with tempfile.NamedTemporaryFile(
            mode="wb", prefix=".eta-repair-", suffix=".tmp",
            dir=output.parent, delete=False,
        ) as stream:
            temporary = Path(stream.name)
            if stream.write(data) != len(data):
                raise OSError("Incomplete write; corrected output was not published")
            stream.flush()
            os.fsync(stream.fileno())

        # Unlike replace/rename on some platforms, link refuses a racing destination.
        # The temporary file is already closed and complete before it becomes visible.
        os.link(temporary, output)
    finally:
        if temporary is not None:
            try:
                temporary.unlink(missing_ok=True)
            except OSError as error:
                # Preserve the original error or completed output if cleanup is denied.
                try:
                    print(f"Could not remove temporary file {temporary}: {error}", file=sys.stderr)
                except (OSError, ValueError):
                    # A broken/closed stderr must not mask the result of publication.
                    pass


def repair(source, output):
    """Write a corrected copy; reject a changed source or an existing output."""
    source, output = Path(source), Path(output)
    if source.resolve() == output.resolve():
        raise ValueError("Source and output must differ; original is never overwritten")
    if output.exists() or output.is_symlink():
        raise FileExistsError("Output already exists; refusing to replace it")
    if source.stat().st_size != SOURCE_BYTES:
        raise ValueError("Not the exact supported source size")

    data = bytearray(source.read_bytes())
    if hashlib.sha256(data).hexdigest() != SOURCE_SHA256:
        raise ValueError("Not the exact supported source hash")

    # Each little-endian SHORT changes from floating point (3) to unsigned (1).
    for offset in OFFSETS:
        if data[offset:offset + 2] != b"\x03\x00":
            raise ValueError("Unexpected SampleFormat bytes")
        data[offset] = 1
    if hashlib.sha256(data).hexdigest() != OUTPUT_SHA256:
        raise ValueError("Correction does not match the independently checked artifact")

    _publish_copy(data, output)
    return {
        "source_sha256": SOURCE_SHA256,
        "output_sha256": OUTPUT_SHA256,
        "bytes": SOURCE_BYTES,
        "changed_byte_offsets": list(OFFSETS),
        "source_overwritten": False,
    }


def main():
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("source", type=Path)
    parser.add_argument("output", type=Path)
    args = parser.parse_args()
    print(json.dumps(repair(args.source, args.output), indent=2))


if __name__ == "__main__":
    main()

{
  "checked_utc": "2026-09-30T12:22:54.144011+00:00",
  "status": "PASS",
  "python": "3.12.14 (main, Aug 25 2026, 14:01:42) [MSC v.1944 64 bit (AMD64)]",
  "pillow": "12.3.0",
  "tifffile": "2026.9.9",
  "numpy": "2.3.5",
  "candidate_sha256": "50246d166372036a1000de00b7bc4158d99fd675515e16ac8d106bb4231ef37d",
  "historical_candidate_sha256": "e04df008d2d95b7919a2408b78c1704d0c06a2968bb26b38852847c803bf6299",
  "source_sha256": "6f3b05d2e6ab8ea1e8055d35dc5b8fa7e0c7385dffc010b4d3df319548622247",
  "output_sha256": "5c6b9d2b4ac69b812e53f2220da4e6f8cd123ec0432c98f161fb04e285ad3d90",
  "raw_rgb_sha256": "8b8f724b080256e956aa69576ae2c1d3b3194f79347bbe901f1cfcba55741db3",
  "source_bytes": 58260398,
  "original_pillow_result": "UnidentifiedImageError",
  "original_tifffile_result": {
    "shape": [
      0,
      3617,
      5369,
      3
    ],
    "dtype": "bool",
    "elements": 0
  },
  "changed_offsets": [
    58260392,
    58260394,
    58260396
  ],
  "other_tags_unchanged": true,
  "corrected_pillow_path_and_file_like_match_raw_strips": true,
  "corrected_tifffile_matches_raw_strips": true,
  "existing_tifffile_tag_overwrite_identical_output": true,
  "historical_and_atomic_candidate_identical_output": true,
  "source_preserved": true,
  "refusal_controls": [
    {
      "case": "same size wrong hash",
      "refused": true,
      "destination_preserved": true
    },
    {
      "case": "truncated input",
      "refused": true,
      "destination_preserved": true
    },
    {
      "case": "already corrected input",
      "refused": true,
      "destination_preserved": true
    },
    {
      "case": "existing output",
      "refused": true,
      "destination_preserved": true
    },
    {
      "case": "same source and output",
      "refused": true,
      "destination_preserved": true
    },
    {
      "case": "hard-linked output",
      "refused": true,
      "destination_preserved": true
    },
    {
      "case": "missing source",
      "refused": true,
      "destination_preserved": true
    }
  ],
  "limitations": "Fresh local Pillow, tifffile and byte/structure tests on NTFS. ImageJ result remains historical September 10 evidence. No remote viewer update or end-to-end refresh performed. Directory durability after power loss and forced-termination temporary cleanup are not promised."
}