nordisk/graph-ar

src/io/json.rs

// 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.

use std::{
    fs::File,
    io::{BufReader, BufWriter, Seek, SeekFrom, Write},
    path::Path,
    sync::Arc,
};

use arrow::json::{LineDelimitedWriter, ReaderBuilder, reader::infer_json_schema};
use arrow_array::RecordBatch;

use crate::error::Result;

pub fn read(path: impl AsRef<Path>) -> Result<Vec<RecordBatch>> {
    read_typed(path, None)
}

/// Read a JSON-lines chunk, with declared types as in [`super::csv::read_typed`].
pub fn read_typed(
    path: impl AsRef<Path>,
    declared: Option<&arrow_schema::Schema>,
) -> Result<Vec<RecordBatch>> {
    let mut reader = BufReader::new(File::open(path.as_ref())?);
    let (inferred, _) = infer_json_schema(&mut reader, None)?;
    let schema = super::apply_declared_types(&inferred, declared);
    reader.seek(SeekFrom::Start(0))?;

    let reader = ReaderBuilder::new(Arc::new(schema)).build(reader)?;
    let mut batches = Vec::new();
    for batch in reader {
        batches.push(batch?);
    }
    Ok(batches)
}

pub fn write(path: impl AsRef<Path>, batches: &[RecordBatch]) -> Result<()> {
    if batches.is_empty() {
        return Ok(());
    }
    let file = BufWriter::new(File::create(path)?);
    let mut writer = LineDelimitedWriter::new(file);
    writer.write_batches(&batches.iter().collect::<Vec<_>>())?;
    writer.finish()?;
    // Flush the BufWriter explicitly so any error surfaces here rather than
    // being swallowed on drop. `finish()` flushes the Arrow writer's own state;
    // `into_inner().flush()` drains the BufWriter into the file.
    writer.into_inner().flush()?;
    Ok(())
}