Copilot commented on code in PR #3861:
URL: https://github.com/apache/avro/pull/3861#discussion_r3567535733
##########
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, TypeError):
+ # Not seekable, or the position could not be determined.
+ return None
+ try:
+ reader.seek(0, os.SEEK_END)
+ end = reader.tell()
+ return end - pos
Review Comment:
`bytes_remaining()` can return a negative value if the underlying stream is
positioned past EOF (e.g., a seekable file-like object allows seeking beyond
the end). This can produce confusing errors like “only -5 remain” and may cause
large reads/collection checks to be rejected incorrectly. Clamp negative
results to 0 so the method’s contract (“bytes still available to read”) stays
non-negative.
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