Copilot commented on code in PR #3859:
URL: https://github.com/apache/avro/pull/3859#discussion_r3568127303
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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:
`StreamReader::remainingBytes()` computes `end_ - next_` even when both
pointers are null right after `reset()/init()`. Pointer subtraction on null
pointers is undefined behavior in C++, so this can crash or produce arbitrary
values (and it contradicts the comment claiming it is well-defined).
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