iemejia commented on code in PR #3859:
URL: https://github.com/apache/avro/pull/3859#discussion_r3566941778
##########
lang/c++/include/avro/Stream.hh:
##########
@@ -345,6 +356,28 @@ struct StreamReader {
return next_ != end_ || fill();
}
+ /**
+ * Returns the number of bytes still available to be read: those already
+ * buffered in this reader plus whatever the underlying stream reports as
+ * remaining. Returns a negative value when the underlying stream cannot
+ * report its remaining size.
+ */
+ int64_t remainingBytes() const {
+ if (in_ == nullptr) {
+ return -1;
+ }
+ int64_t streamRemaining = in_->remainingBytes();
+ if (streamRemaining < 0) {
+ return -1;
+ }
+ // Bytes already buffered in this reader, added to what the underlying
+ // stream still has. When next_ and end_ are both null (right after
+ // init()/reset(), before any data is buffered), the subtraction is
+ // well-defined and yields 0.
+ int64_t buffered = end_ - next_;
+ return buffered + streamRemaining;
Review Comment:
This was raised earlier by @Gerrit0 and is actually well-defined: per N4950
7.6.6/5.1, when both pointer operands are null the subtraction yields 0. `end_
- next_` right after init()/reset() (both null) is therefore not UB, so I
removed the guard at his request and kept testBytesRemainingRightAfterInit as
coverage. I've left it as the plain subtraction.
##########
lang/c++/impl/BinaryDecoder.cc:
##########
@@ -163,8 +205,14 @@ size_t BinaryDecoder::arrayStart() {
size_t BinaryDecoder::doDecodeItemCount() {
auto result = doDecodeLong();
if (result < 0) {
+ // INT64_MIN cannot be negated in int64_t (it would overflow); reject
it
+ // rather than propagating 2^63 as an item count that inevitably fails
a
+ // huge allocation downstream.
+ if (result == INT64_MIN) {
+ throw Exception("Invalid negative block count: {}", result);
+ }
doDecodeLong();
- return static_cast<size_t>(-(result + 1)) + 1;
+ return static_cast<size_t>(-result);
}
return static_cast<size_t>(result);
Review Comment:
Fixed in 0884d62263: doDecodeItemCount() now rejects a count that doesn't
fit into size_t before the cast (guarded with `if constexpr (sizeof(size_t) <
sizeof(int64_t))` so it only compiles where size_t is narrower, e.g. 32-bit,
avoiding a useless-cast/tautological-compare warning on 64-bit).
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