Copilot commented on code in PR #3859:
URL: https://github.com/apache/avro/pull/3859#discussion_r3565744004
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lang/c++/impl/Generic.cc:
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@@ -25,6 +26,88 @@ using std::ostringstream;
using std::string;
using std::vector;
+// Minimum number of bytes a single value of the given schema node 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 collection check for it (so an array of nulls is not
+// falsely rejected). A depth limit breaks self-referencing (symbolic) schemas.
+static int64_t minBytesPerElement(const NodePtr &node, int depth) {
+ if (!node) {
+ return 0;
+ }
+ switch (node->type()) {
+ case AVRO_NULL:
+ return 0;
+ case AVRO_FLOAT:
+ return 4;
+ case AVRO_DOUBLE:
+ return 8;
+ case AVRO_FIXED: {
+ // fixedSize() is a size_t; clamp to int64_t so a huge fixed size
+ // cannot wrap negative.
+ size_t sz = node->fixedSize();
+ return sz >
static_cast<size_t>(std::numeric_limits<int64_t>::max())
+ ? std::numeric_limits<int64_t>::max()
+ : static_cast<int64_t>(sz);
+ }
+ case AVRO_RECORD: {
+ if (depth > 64) {
+ // A cyclic or pathologically deep record. Return 1 (not 0) so
the
+ // collection check stays enabled rather than being silently
+ // bypassed; a valid recursive value always encodes to >= 1
byte.
+ // (The depth guard is applied only here, so zero-byte leaf
types
Review Comment:
minBytesPerElement() uses a hard depth cutoff (depth > 64) for records and
returns 1 byte as the minimum. That breaks the function’s “true lower bound”
contract for deeply nested but valid (acyclic) schemas whose on-wire minimum
can still be 0 (e.g., a chain of records where all leaf fields are null). In
those cases, ensureCollectionAvailable() can incorrectly reject valid
arrays/maps when bytesRemaining() is small even though elements require 0 bytes
on the wire.
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