iemejia commented on code in PR #3861:
URL: https://github.com/apache/avro/pull/3861#discussion_r3565728596
##########
lang/py/avro/io.py:
##########
@@ -214,11 +222,43 @@ def read(self, n: int) -> bytes:
"""
if n < 0:
raise avro.errors.InvalidAvroBinaryEncoding(f"Requested {n} bytes
to read, expected positive integer.")
+ if n > self._MAX_UNCHECKED_READ:
+ remaining = self.bytes_remaining()
+ if remaining is not None and n > remaining:
+ raise avro.errors.InvalidAvroBinaryEncoding(f"Requested {n}
bytes to read, but only {remaining} remain.")
read_bytes = self.reader.read(n)
if len(read_bytes) != n:
raise avro.errors.InvalidAvroBinaryEncoding(f"Read
{len(read_bytes)} bytes, expected {n} bytes")
return read_bytes
+ def bytes_remaining(self) -> Optional[int]:
+ """
+ Return the number of bytes still available to read, or ``None`` when
+ that count is not known (a non-seekable reader, or one whose position
+ cannot be obtained). Used to reject a declared length or collection
+ block count that exceeds the data actually available before allocating
+ for it.
+ """
+ reader = self.reader
+ try:
+ pos = reader.tell()
+ except (OSError, ValueError, AttributeError):
+ # Not seekable, or the position could not be determined.
+ return None
+ try:
+ reader.seek(0, os.SEEK_END)
+ end = reader.tell()
+ return end - pos
+ except (OSError, ValueError, AttributeError):
+ return None
+ finally:
+ # Always restore the original position, even if seeking to the end
+ # or reading it failed, so the reader is never left at EOF.
+ try:
+ reader.seek(pos)
+ except (OSError, ValueError):
Review Comment:
Fixed in 102061267c: the finally block now also catches AttributeError when
restoring the position, so a reader that implements tell() but not seek()
reliably falls back to None instead of raising.
##########
lang/py/avro/test/test_io.py:
##########
@@ -550,6 +551,136 @@ def test_deserialization_fails(self) -> None:
)
+class TestBinaryDecoderAvailableBytes(unittest.TestCase):
+ """A bytes/string value declares a length prefix; a malicious or truncated
+ input can declare far more bytes than actually exist. On a seekable reader
+ that is rejected before allocating for it."""
+
+ @staticmethod
+ def _encode_length_prefix(length: int) -> bytes:
+ buf = io.BytesIO()
+ avro.io.BinaryEncoder(buf).write_long(length)
+ return buf.getvalue()
+
+ def test_read_rejects_length_beyond_stream(self) -> None:
+ # Declares 100 MiB but provides no data.
+ prefix = self._encode_length_prefix(100 * 1024 * 1024)
+ with io.BytesIO(prefix) as bio:
+ decoder = avro.io.BinaryDecoder(bio)
+ self.assertRaises(avro.errors.InvalidAvroBinaryEncoding,
decoder.read_bytes)
+
+ def test_read_within_stream_still_reads(self) -> None:
+ # A well-formed large value whose data is actually present still reads.
+ payload = b"x" * (2 * 1024 * 1024)
+ buf = io.BytesIO()
+ avro.io.BinaryEncoder(buf).write_bytes(payload)
+ with io.BytesIO(buf.getvalue()) as bio:
+ decoder = avro.io.BinaryDecoder(bio)
+ self.assertEqual(decoder.read_bytes(), payload)
+
+ def test_bytes_remaining_restores_position(self) -> None:
+ # bytes_remaining() must leave the reader position unchanged.
+ with io.BytesIO(b"abcdefghij") as bio:
+ bio.seek(3)
+ decoder = avro.io.BinaryDecoder(bio)
+ self.assertEqual(decoder.bytes_remaining(), 7)
+ self.assertEqual(bio.tell(), 3)
+
+ def test_bytes_remaining_restores_position_on_error(self) -> None:
+ # If reading the end offset fails after seeking, the original position
+ # must still be restored (via the finally block).
+ class FailingEndStream(io.BytesIO):
+ def __init__(self, data: bytes) -> None:
+ super().__init__(data)
+ self._calls = 0
+
Review Comment:
Removed the unused self._calls assignment from the FailingEndStream test
helper in 102061267c.
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