refactor(assets): modular architecture + async two-phase scanner & background seeder (#12621)

app/assets/services/hashing.py

@@ -0,0 +1,95 @@
+import io
+import os
+from contextlib import contextmanager
+from dataclasses import dataclass
+from typing import IO, Any, Callable, Iterator
+
+from blake3 import blake3
+
+DEFAULT_CHUNK = 8 * 1024 * 1024
+
+InterruptCheck = Callable[[], bool]
+
+
+@dataclass
+class HashCheckpoint:
+    """Saved state for resuming an interrupted hash computation."""
+
+    bytes_processed: int
+    hasher: Any  # blake3 hasher instance
+    mtime_ns: int = 0
+    file_size: int = 0
+
+
+@contextmanager
+def _open_for_hashing(fp: str | IO[bytes]) -> Iterator[tuple[IO[bytes], bool]]:
+    """Yield (file_object, is_path) with appropriate setup/teardown."""
+    if hasattr(fp, "read"):
+        seekable = getattr(fp, "seekable", lambda: False)()
+        orig_pos = None
+        if seekable:
+            try:
+                orig_pos = fp.tell()
+                if orig_pos != 0:
+                    fp.seek(0)
+            except io.UnsupportedOperation:
+                orig_pos = None
+        try:
+            yield fp, False
+        finally:
+            if orig_pos is not None:
+                fp.seek(orig_pos)
+    else:
+        with open(os.fspath(fp), "rb") as f:
+            yield f, True
+
+
+def compute_blake3_hash(
+    fp: str | IO[bytes],
+    chunk_size: int = DEFAULT_CHUNK,
+    interrupt_check: InterruptCheck | None = None,
+    checkpoint: HashCheckpoint | None = None,
+) -> tuple[str | None, HashCheckpoint | None]:
+    """Compute BLAKE3 hash of a file, with optional checkpoint support.
+
+    Args:
+        fp: File path or file-like object
+        chunk_size: Size of chunks to read at a time
+        interrupt_check: Optional callable that returns True if the operation
+            should be interrupted (e.g. paused or cancelled). Must be
+            non-blocking so file handles are released immediately. Checked
+            between chunk reads.
+        checkpoint: Optional checkpoint to resume from (file paths only)
+
+    Returns:
+        Tuple of (hex_digest, None) on completion, or
+        (None, checkpoint) on interruption (file paths only), or
+        (None, None) on interruption of a file object
+    """
+    if chunk_size <= 0:
+        chunk_size = DEFAULT_CHUNK
+
+    with _open_for_hashing(fp) as (f, is_path):
+        if checkpoint is not None and is_path:
+            f.seek(checkpoint.bytes_processed)
+            h = checkpoint.hasher
+            bytes_processed = checkpoint.bytes_processed
+        else:
+            h = blake3()
+            bytes_processed = 0
+
+        while True:
+            if interrupt_check is not None and interrupt_check():
+                if is_path:
+                    return None, HashCheckpoint(
+                        bytes_processed=bytes_processed,
+                        hasher=h,
+                    )
+                return None, None
+            chunk = f.read(chunk_size)
+            if not chunk:
+                break
+            h.update(chunk)
+            bytes_processed += len(chunk)
+
+        return h.hexdigest(), None