wgtmac commented on code in PR #34668:
URL: https://github.com/apache/arrow/pull/34668#discussion_r1144166948
##########
cpp/src/parquet/encoding.cc:
##########
@@ -2708,7 +2708,14 @@ class DeltaLengthByteArrayDecoder : public DecoderImpl,
void SetData(int num_values, const uint8_t* data, int len) override {
num_values_ = num_values;
- if (len == 0) return;
+ if (len == 0) {
+ if (num_values > 0) {
Review Comment:
I did a quick check. `num_values` is the number of values with nulls
considered in a data page.
https://github.com/apache/arrow/blob/main/cpp/src/parquet/column_reader.cc#L922
```cpp
current_decoder_->SetData(static_cast<int>(num_buffered_values_), buffer,
static_cast<int>(data_size));
```
https://github.com/apache/arrow/blob/main/cpp/src/parquet/column_reader.cc#L949
```cpp
// The total number of values stored in the data page. This is the maximum
of
// the number of encoded definition levels or encoded values. For
// non-repeated, required columns, this is equal to the number of encoded
// values. For repeated or optional values, there may be fewer data values
// than levels, and this tells you how many encoded levels there are in
that
// case.
int64_t num_buffered_values_;
```
Therefore, the input `num_values > 0 && len == 0` looks valid to me. Should
we not throw here but decode nothing from the decoder instead?
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