be/src/storage/segment/stream_reader.h

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

#pragma once

#include <memory>

#include "core/column/column.h"
#include "core/column/subcolumn_tree.h"
#include "core/data_type/data_type.h"

namespace doris::segment_v2 {

// This file Defined ColumnIterator and ColumnReader for reading variant subcolumns. The types from read schema and from storage are
// different, so we need to wrap the ColumnIterator from execution phase and storage column reading phase.And we also
// maintain the tree structure to get the full JSON structure for variants.

// Wrapped ColumnIterator from execution phase, the type is from read schema
class ColumnIterator;
class ColumnReader;

struct SubstreamIterator {
    MutableColumnPtr column;
    std::unique_ptr<ColumnIterator> iterator;
    std::shared_ptr<const IDataType> type;
    std::shared_ptr<DataTypeSerDe> serde;
    bool inited = false;
    size_t rows_read = 0;
    SubstreamIterator() = default;
    SubstreamIterator(MutableColumnPtr&& col, std::unique_ptr<ColumnIterator>&& it,
                      std::shared_ptr<const IDataType> t);
};

// path -> SubstreamIterator
using SubstreamReaderTree = SubcolumnsTree<SubstreamIterator, false>;

// Meta for the storage layer, the file_column_type indicates the read type of the column in segment file
struct SubcolumnMeta {
    std::shared_ptr<const IDataType> file_column_type;
    int32_t footer_ordinal = -1;
};
using SubcolumnColumnMetaInfo = SubcolumnsTree<SubcolumnMeta, true>;

} // namespace doris::segment_v2