[jira] [Created] (ARROW-15971) Error when reading inner lists within a struct in empty outer lists from C++/Python in Java

["Arrow User (Jira)" <ji...@apache.org>]

Arrow User created ARROW-15971:
----------------------------------

             Summary: Error when reading inner lists within a struct in empty outer lists from C++/Python in Java
                 Key: ARROW-15971
                 URL: https://issues.apache.org/jira/browse/ARROW-15971
             Project: Apache Arrow
          Issue Type: Bug
          Components: C++, Java, Python
    Affects Versions: 7.0.0
            Reporter: Arrow User


### Description

When using C++ (or Python) to construct a null or empty outer array of type `array_1: list<item: struct<array_sub_col: list<item: string>>>`, either:
- `array_1:null` or
- `array_1:[]`

an out of bounds exceptions (see stack trace below) follows when later retrieving the field reader for the inner list (`array_sub_col`) in Java.

### Reproduction

Java: `7.0.0`
C++: `4.0.0`
Python: `7.0.0`

Creating a stream on C++ of type `array_1: list<item: struct<array_sub_col: list<item: string>>> ` with an empty (or null) outer list:
```
arrow::MemoryPool* pool = arrow::default_memory_pool();
arrow::Result<std::shared_ptr<arrow::io::BufferOutputStream>> stream_buffer =
    arrow::io::BufferOutputStream::Create(1, pool);

std::vector<std::shared_ptr<arrow::Field>> inner_list_field{std::make_shared<arrow::Field>(
                                                            "array_sub_col",
                                                            arrow::list(arrow::utf8()))};

// Datatype for the builder: list<struct<list<string>>>
std::shared_ptr<DataType> data_type = list(struct_(inner_list_field));

std::unique_ptr<arrow::ArrayBuilder> builder;
arrow::MakeBuilder(pool, data_type, &builder);
auto* list_builder = dynamic_cast<arrow::ListBuilder*>(builder.get());

// Append a null or an empty list to the outer list
list_builder->AppendNull(); // or list_builder->AppendEmptyValue()

std::vector<std::shared_ptr<arrow::Array>> value_batch;
value_batch.resize(1);
list_builder->Finish(&value_batch[0]);

std::vector<std::shared_ptr<arrow::Field>> outer_list_field{std::make_shared<arrow::Field>("array_1",
                                                            data_type)};
auto schema = std::make_shared<arrow::Schema>(outer_list_field);

// Build a single row record batch
std::shared_ptr<arrow::RecordBatch> batch = RecordBatch::Make(schema, 1, value_batch);
ASSERT_OK(batch->Validate());


// Stream the batch to a file
arrow::Result<std::shared_ptr<ipc::RecordBatchWriter>> stream_writer = 
    arrow::ipc::MakeStreamWriter(stream_buffer.ValueOrDie().get(), schema, arrow::ipc::IpcWriteOptions::Defaults());
stream_writer.ValueOrDie()->WriteRecordBatch(*batch);

arrow::Result<std::shared_ptr<arrow::Buffer>> buffer_result = stream_buffer.ValueOrDie()->Finish();
std::shared_ptr<arrow::Buffer> buffer = buffer_result.ValueOrDie();
auto file_output = arrow::io::FileOutputStream::Open("/tmp/batch_stream.out").ValueOrDie();
file_output->Write(buffer->data(), buffer->size());
file_output->Close();
```

As expected, Python holds the same memory layout for the field vectors as the code above:
```
# Empty or null outer list
array = pa.array([None], type=pa.list_(pa.struct([pa.field("array_sub_col", pa.list_(pa.utf8()))])))
batch = pa.record_batch([struct_array], names=["array_1"])

// Stream the batch to a file
sink = pa.BufferOutputStream()
with pa.ipc.new_stream(sink, batch.schema) as writer:
    writer.write_batch(batch)
buf = sink.getvalue()

with open('/tmp/batch_stream.out', 'wb') as f:
    f.write(buf)
```

**Java fails when then trying to access the inner list's field reader:**
```
File file = new File("/tmp/batch_stream.out");
byte[] bytes = FileUtils.readFileToByteArray(file);
try (ArrowStreamReader reader = new ArrowStreamReader(new ByteArrayInputStream(bytes), allocator)) {
     Schema schema = reader.getVectorSchemaRoot().getSchema();
     reader.loadNextBatch();
     readBatch.getVector("array_1").getReader().reader().reader("array_sub_col");                     // <- fails: reader("array_sub_col") fails with OOB

     // Concrete readers:
     // FieldVector array_1 = readBatch.getVector("array_1");
     // UnionListReader array_1_reader = (UnionListReader) array_1.getReader();
     // NullableStructReaderImpl struct_reader = (NullableStructReaderImpl) array_1_reader.reader();
     // FieldReader union_list_reader = struct_reader.reader("array_sub_col");                        // <- fails: OOB
```

#### Stack trace:
```
java.lang.reflect.InvocationTargetException
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)
    at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke (Method.java:566)
    at org.codehaus.mojo.exec.ExecJavaMojo$1.run (ExecJavaMojo.java:297)
    at java.lang.Thread.run (Thread.java:829)
Caused by: java.lang.IndexOutOfBoundsException: index: 4, length: 4 (expected: range(0, 4))
    at org.apache.arrow.memory.ArrowBuf.checkIndexD (ArrowBuf.java:318)
    at org.apache.arrow.memory.ArrowBuf.chk (ArrowBuf.java:305)
    at org.apache.arrow.memory.ArrowBuf.getInt (ArrowBuf.java:424)
    at com.test.arrow.ValidateArrow.testArrow (ValidateArrow.java:433)
    at com.test.arrow.ValidateArrow.main (ValidateArrow.java:440)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)
    at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke (Method.java:566)
    at org.codehaus.mojo.exec.ExecJavaMojo$1.run (ExecJavaMojo.java:297)
    at java.lang.Thread.run (Thread.java:829)
```



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