add a (failing) test reproducing #8963

src/borg/testsuite/chunkers/interaction_test.py

@@ -0,0 +1,70 @@
+import os
+import pytest
+from io import BytesIO
+
+from ...chunkers import get_chunker
+from ...constants import *  # NOQA
+
+
+@pytest.mark.parametrize(
+    "chunker_params",
+    [
+        (CH_FIXED, 1048576, 0),  # == reader_block_size
+        (CH_FIXED, 1048576 // 2, 0),  # reader_block_size / N
+        (CH_FIXED, 1048576 * 2, 0),  # N * reader_block_size
+        (CH_FIXED, 1234567, 0),  # does not fit well, larger than reader_block_size
+        (CH_FIXED, 123456, 0),  # does not fit well, smaller than reader_block_size
+        (CH_BUZHASH, CHUNK_MIN_EXP, CHUNK_MAX_EXP, HASH_MASK_BITS, HASH_WINDOW_SIZE),
+        (CH_BUZHASH64, CHUNK_MIN_EXP, CHUNK_MAX_EXP, HASH_MASK_BITS, HASH_WINDOW_SIZE),
+    ],
+)
+def test_reader_chunker_interaction(chunker_params):
+    """
+    Test that chunking random/zero data produces chunks that can be reassembled to match the original data.
+
+    If one of these fails, there is likely a problem with buffer management.
+    """
+    # Generate some data
+    data_size = 6 * 12341234
+    random_data = os.urandom(data_size // 3) + b"\0" * (data_size // 3) + os.urandom(data_size // 3)
+
+    # Chunk the data
+    chunker = get_chunker(*chunker_params)
+    data_file = BytesIO(random_data)
+    chunks = list(chunker.chunkify(data_file))
+
+    data_chunks = 0
+    hole_chunks = 0
+    alloc_chunks = 0
+    for chunk in chunks:
+        if chunk.meta["allocation"] == CH_DATA:
+            data_chunks += 1
+        elif chunk.meta["allocation"] == CH_HOLE:
+            hole_chunks += 1
+        elif chunk.meta["allocation"] == CH_ALLOC:
+            alloc_chunks += 1
+
+    assert data_chunks > 0, "No data chunks found"
+    assert alloc_chunks > 0, "No alloc chunks found"
+    assert hole_chunks == 0, "Hole chunks found, this is not expected!"
+
+    # Reassemble the chunks
+    reassembled = BytesIO()
+    for i, chunk in enumerate(chunks):
+        if chunk.meta["allocation"] == CH_DATA:
+            # For data chunks, write the actual data
+            reassembled.write(bytes(chunk.data))
+        elif chunk.meta["allocation"] in (CH_HOLE, CH_ALLOC):
+            # For hole or alloc chunks, write zeros
+            reassembled.write(b"\0" * chunk.meta["size"])
+
+    # Check that the reassembled data has the correct size
+    reassembled_size = reassembled.tell()
+    assert (
+        reassembled_size == data_size
+    ), f"Reassembled data size ({reassembled_size}) does not equal original data size ({data_size})"
+
+    # Verify that the reassembled data matches the original data
+    reassembled.seek(0)
+    reassembled_data = reassembled.read()
+    assert reassembled_data == random_data, "Reassembled data does not match original data"