json_file_splitter.py

#
# Copyright (c) 2022, Neptune Labs Sp. z o.o.
#
# Licensed 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.
#
import json
from collections import deque
from io import StringIO
from json import JSONDecodeError
from typing import Optional


class JsonFileSplitter:

    BUFFER_SIZE = 64 * 1024
    MAX_PART_READ = 8 * 1024

    def __init__(self, file_path: str):
        self._file = open(file_path, "r")
        self._decoder = json.JSONDecoder(strict=False)
        self._part_buffer = StringIO()
        self._parsed_queue = deque()
        self._start_pos = 0

    def close(self) -> None:
        self._file.close()
        self._part_buffer.close()

    def get(self) -> Optional[dict]:
        if self._parsed_queue:
            return self._parsed_queue.popleft()
        self._read_data()
        if self._parsed_queue:
            return self._parsed_queue.popleft()

    def _read_data(self):
        if self._part_buffer.tell() < self.MAX_PART_READ:
            data = self._file.read(self.BUFFER_SIZE)
            if not data:
                return
            if self._part_buffer.tell() > 0:
                data = self._reset_part_buffer() + data
            self._decode(data)

        if not self._parsed_queue:
            data = self._file.read(self.BUFFER_SIZE)
            while data:
                self._part_buffer.write(data)
                data = self._file.read(self.BUFFER_SIZE)
            data = self._reset_part_buffer()
            self._decode(data)

    def _decode(self, data: str):
        start = self._json_start(data)
        while start is not None:
            try:
                json_data, start = self._decoder.raw_decode(data, start)
            except JSONDecodeError:
                self._part_buffer.write(data[start:])
                break
            else:
                self._parsed_queue.append(json_data)
                start = self._json_start(data, start)

    @staticmethod
    def _json_start(data: str, start: int = 0) -> Optional[int]:
        try:
            return data.index("{", start)
        except ValueError:
            return None

    def _reset_part_buffer(self) -> str:
        data = self._part_buffer.getvalue()
        self._part_buffer.close()
        self._part_buffer = StringIO()
        return data