fix(preprod): Use odiff CLI mode to work around server-mode false match bug

src/sentry/preprod/snapshots/image_diff/compare.py

@@ -8,7 +8,7 @@
 
 from PIL import Image
 
-from .odiff import OdiffServer
+from .odiff import OdiffServer, compare_cli
 from .types import DiffResult
 
 logger = logging.getLogger(__name__)
@@ -79,13 +79,17 @@ def compare_images_batch(
         tmpdir_path = Path(tmpdir)
         if server is not None:
             return _compare_pairs(pairs, server, tmpdir_path)
-        with OdiffServer() as new_server:
-            return _compare_pairs(pairs, new_server, tmpdir_path)
+        # Temporarily skip creating OdiffServer due to server-mode stdin
+        # buffer reuse bug (https://github.com/dmtrKovalenko/odiff/pull/170).
+        # Revert once the fix is released in odiff-bin.
+        # with OdiffServer() as new_server:
+        #     return _compare_pairs(pairs, new_server, tmpdir_path)
+        return _compare_pairs(pairs, None, tmpdir_path)
 
 
 def _compare_pairs(
     pairs: Sequence[tuple[bytes | Image.Image, bytes | Image.Image]],
-    server: OdiffServer,
+    server: OdiffServer | None,
     tmpdir_path: Path,
 ) -> list[DiffResult | None]:
     return [
@@ -98,7 +102,7 @@ def _compare_single_pair(
     idx: int,
     before: bytes | Image.Image,
     after: bytes | Image.Image,
-    server: OdiffServer,
+    server: OdiffServer | None,
     tmpdir_path: Path,
 ) -> DiffResult | None:
     before_img: Image.Image | None = None
@@ -123,23 +127,35 @@ def _compare_single_pair(
         after_padded.save(after_path, "PNG")
 
         output_path = tmpdir_path / f"diff_{idx}.png"
-        resp = server.compare(
+        # Use CLI mode instead of server mode to work around stdin buffer
+        # reuse bug (https://github.com/dmtrKovalenko/odiff/pull/170).
+        # Revert to server.compare() once the fix is released in odiff-bin.
+        # resp = server.compare(
+        #     before_path,
+        #     after_path,
+        #     output_path,
+        #     threshold=ODIFF_SENSITIVITY_DIFF_THRESHOLD,
+        #     antialiasing=True,
+        #     outputDiffMask=True,
+        # )
+        resp = compare_cli(
             before_path,
             after_path,
             output_path,
             threshold=ODIFF_SENSITIVITY_DIFF_THRESHOLD,
             antialiasing=True,
             outputDiffMask=True,
         )
-        changed_pixels = resp.diffCount or 0
         total_pixels = max_w * max_h
 
-        if changed_pixels == 0:
+        if resp.match:
+            changed_pixels = 0
             diff_mask = Image.new("L", (max_w, max_h), 0)
         elif not output_path.exists():
             raise RuntimeError(f"odiff did not produce output file: {output_path}")
         else:
             diff_mask = _mask_from_diff_output(output_path)
+            changed_pixels = sum(diff_mask.histogram()[1:])
 
         diff_mask_png = _encode_mask_png(diff_mask)
 

src/sentry/preprod/snapshots/image_diff/odiff.py

@@ -10,6 +10,10 @@
 from sentry.preprod.snapshots.image_diff.types import OdiffResponse
 from sentry.utils import json
 
+_CLI_FLAG_MAP = {
+    "outputDiffMask": "diff-mask",
+}
+
 ODIFF_PLATFORM_SUFFIXES = {
     ("arm64", "Darwin"): "macos-arm64",
     ("aarch64", "Darwin"): "macos-arm64",
@@ -38,6 +42,42 @@ def _find_odiff_binary() -> str:
     raise FileNotFoundError("odiff binary not found. Run 'pnpm install' to install odiff-bin.")
 
 
+def compare_cli(
+    base_path: str | Path,
+    compare_path: str | Path,
+    output_path: str | Path,
+    **options: object,
+) -> OdiffResponse:
+    """Run a single odiff comparison via CLI (no server mode).
+
+    Workaround for server-mode stdin buffer reuse bug
+    (https://github.com/dmtrKovalenko/odiff/pull/170).
+    Remove once the fix is released in odiff-bin.
+    """
+    binary = _find_odiff_binary()
+    cmd = [binary, str(base_path), str(compare_path), str(output_path)]
+
+    for key, value in options.items():
+        flag = _CLI_FLAG_MAP.get(key, key)
+        if isinstance(value, bool):
+            if value:
+                cmd.append(f"--{flag}")
+        else:
+            cmd.extend([f"--{flag}", str(value)])
+
+    result = subprocess.run(cmd, capture_output=True, timeout=30)
+
+    # Exit codes: 0=match, 21=layout diff, 22=pixel diff
+    if result.returncode not in (0, 21, 22):
+        stderr = result.stderr.decode(errors="replace").strip()
+        raise RuntimeError(f"odiff CLI error (exit {result.returncode}): {stderr}")
+
+    return OdiffResponse(
+        requestId=0,
+        match=(result.returncode == 0),
+    )
+
+
 class OdiffServer:
     def __init__(self) -> None:
         self._process: subprocess.Popen[bytes] | None = None