Copilot commented on code in PR #3862:
URL: https://github.com/apache/avro/pull/3862#discussion_r3565707315
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lang/ruby/lib/avro/io.rb:
##########
@@ -496,6 +541,45 @@ def skip_record(writers_schema, decoder)
end
private
+ # Minimum number of bytes a single value of the given schema can occupy
on
+ # the wire. Used to reject an array/map block count that could not be
+ # backed by the bytes remaining. A type that can encode to zero bytes
+ # (null) returns 0, which disables the check for it (so an array of nulls
+ # is not falsely rejected).
+ def min_bytes_per_element(schema, visited = nil)
+ visited ||= {}.compare_by_identity
+ case schema.type_sym
+ when :null then 0
+ when :float then 4
+ when :double then 8
+ when :fixed then schema.size
+ when :record, :error, :request
+ return 0 if visited[schema]
+ visited[schema] = true
+ total = schema.fields.sum { |field|
min_bytes_per_element(field.type, visited) }
+ visited.delete(schema)
+ total
+ else
+ # boolean, int, long, bytes, string, enum, union, array, map: >= 1
byte
+ # (a union encodes at least a 1-byte branch index).
+ 1
+ end
+ end
+
+ # Reject a collection (array or map) block whose declared element count
+ # could not be backed by the bytes actually remaining, before iterating.
+ # Skipped when the per-element minimum is zero or when the reader cannot
+ # report how many bytes remain.
+ def ensure_collection_available(decoder, count, min_bytes_per_element)
+ return if count <= 0 || min_bytes_per_element <= 0
+ remaining = decoder.bytes_remaining
+ # Compare via integer division rather than multiplying, so a huge count
+ # does not create a large intermediate product.
+ if remaining && count > remaining / min_bytes_per_element
+ raise AvroError, "Collection claims #{count} elements with at least
#{min_bytes_per_element} bytes each, but only #{remaining} bytes are available"
+ end
+ end
Review Comment:
`ensure_collection_available` unconditionally calls
`decoder.bytes_remaining`. Any decoder that implements the read protocol
(`read_long`, `read_string`, etc.) but does not implement `bytes_remaining`
will now raise `NoMethodError`, even though the intended behavior for “cannot
report remaining size” is to skip the check. Guard this call with `respond_to?`
(or rescue `NoMethodError`) and treat the remaining size as unknown (`nil`).
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