GH-47981: [C++][Parquet] Add compatibility with non-compliant RLE stream

Author: pitrou

cpp/src/arrow/util/rle_encoding_internal.h

@@ -679,12 +679,22 @@ auto RleBitPackedParser::PeekImpl(Handler&& handler) const
     ARROW_DCHECK_LT(static_cast<uint64_t>(count) * 8,
                     internal::max_size_for_v<rle_size_t>);
     // Count Already divided by 8 for byte size calculations
-    const auto bytes_read = header_bytes + static_cast<int64_t>(count) * value_bit_width_;
+    auto bytes_read = header_bytes + static_cast<int64_t>(count) * value_bit_width_;
+    auto values_count = static_cast<rle_size_t>(count * 8);
     if (ARROW_PREDICT_FALSE(bytes_read > data_size_)) {
-      // Bit-packed run would overflow data buffer
-      return {0, ControlFlow::Break};
+      // Bit-packed run would overflow data buffer, but we might still be able
+      // to return a truncated bit-packed such as generated by some non-compliant
+      // encoders.
+      // Example in GH-47981: column contains 25 5-bit values, has a single
+      // bit-packed run with count=4 (theoretically 32 values), but only 17
+      // bytes of RLE-bit-packed data (including the one-byte header).
+      bytes_read = data_size_;
+      values_count =
+          static_cast<rle_size_t>((bytes_read - header_bytes) * 8 / value_bit_width_);
+      if (values_count < 1) {
+        return {0, ControlFlow::Break};
+      }
     }
-    const auto values_count = static_cast<rle_size_t>(count * 8);
 
     auto control = handler.OnBitPackedRun(
         BitPackedRun(data_ + header_bytes, values_count, value_bit_width_));
@@ -1215,7 +1225,8 @@ auto RleBitPackedDecoder<T>::GetBatchWithDict(const V* dictionary,
                                               rle_size_t batch_size) -> rle_size_t {
   using ControlFlow = RleBitPackedParser::ControlFlow;
 
-  if (ARROW_PREDICT_FALSE(batch_size <= 0)) {
+  if (ARROW_PREDICT_FALSE(batch_size <= 0 || dictionary_length == 0)) {
+    // Either empty batch or invalid dictionary
     return 0;
   }
 
@@ -1284,6 +1295,17 @@ auto RleBitPackedDecoder<T>::GetBatchWithDictSpaced(
   if (null_count == 0) {
     return GetBatchWithDict<V>(dictionary, dictionary_length, out, batch_size);
   }
+  if (null_count == batch_size) {
+    // All nulls, avoid instantiating DictionaryConverter as dictionary_length
+    // could be 0.
+    std::fill(out, out + batch_size, V{});
+    return batch_size;
+  }
+  if (ARROW_PREDICT_FALSE(batch_size <= 0 || dictionary_length == 0)) {
+    // Either empty batch or invalid dictionary
+    return 0;
+  }
+
   internal::DictionaryConverter<V, value_type> converter{dictionary, dictionary_length};
 
   return GetSpaced(converter, out, batch_size, valid_bits, valid_bits_offset, null_count);