flutter_vid/lib/us/vid_us_data_http_reader.dart

import 'dart:typed_data';

import 'package:dio/dio.dart';
import 'package:flutter/foundation.dart';

//Raised when data is not ready.
class NotReadyException implements Exception {}

//Raised when errro happened during the downloading.
class DownloadErrorException implements Exception {
  String _msg;

  DownloadErrorException(this._msg);

  @override
  String toString() {
    return _msg;
  }
}

typedef DownloadCallback = void Function(double progress);

class VidUsDataHttpReader {
  late final List<int> _data = [];
  late int _index;
  late ByteBuffer _buffer;
  late bool _error;
  late String _errorMsg;
  late String _url;
  late int _chunkSize;
  late Dio _dio;

  DownloadCallback? downloadCallback;

  VidUsDataHttpReader(String url, {this.downloadCallback, int chunkSize = 32768}) {
    _chunkSize = chunkSize;
    _url = url;
    _error = false;
    _errorMsg = '';
    _buffer = Uint8List.fromList(_data).buffer;
    _index = 0;
    _dio = Dio();
    //TODO let the user set the timeout.
    _dio.options.connectTimeout = 5000; //5S
    _dio.options.receiveTimeout = 3000;
    _startDownload();
  }

  void _startDownload() async {
    //get file info
    var fileSize = await _getFileSize();
    if (!_error) {
      var last = fileSize % _chunkSize;
      var chunkCount = fileSize ~/ _chunkSize;
      for (var i = 0; i < chunkCount; i++) {
        var start = i * _chunkSize;
        var end = start + _chunkSize;
        await _downloadChunk(start, end);
        if (_error) {
          break;
        }
        if (downloadCallback != null) {
          var progress = _data.length / fileSize;
          downloadCallback!(progress);
        }
      }
      if (!_error && last > 0) {
        var start = chunkCount * _chunkSize;
        var end = start + last;
        await _downloadChunk(start, end);
        if (!_error && downloadCallback != null) {
          var progress = _data.length / fileSize;
          downloadCallback!(progress);
        }
      }
    }
  }

  Future<int> _getFileSize() async {
    var response = await _dio.head(_url);
    if (response.statusCode != 200) {
      _error = true;
      _errorMsg = 'Get file info error.';
      return 0;
    } else {
      var contentLength = response.headers.value(Headers.contentLengthHeader);
      if (contentLength == null) {
        _error = true;
        _errorMsg = 'No Content-Length from headers.';
        return 0;
      } else {
        var fileSize = int.parse(contentLength);
        return fileSize;
      }
    }
  }

  Future _downloadChunk(int chunkStart, int chunkEnd) async {
    var response = await _dio.get<List<int>>(_url, options: Options(responseType: ResponseType.bytes, headers: {"range": "bytes=$chunkStart-$chunkEnd"}));
    if (response.statusCode == 206) {
      var downloadedData = response.data;
      if (downloadedData == null) {
        _error = true;
        _errorMsg = 'Download chunk error.';
      } else {
        //Update the buffer.
        _data.addAll(downloadedData);
        _buffer = Uint8List.fromList(_data).buffer;
      }
    } else {
      _error = true;
      _errorMsg = 'Target url does not support download with chunks.';
    }
  }

  //Close the reader and its http connection.
  void close(){
    _dio.close(force: true);
  }

  ///Read int value from binary data(little endian),
  int readInt([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_buffer.lengthInBytes - _index) < 4) {
        throw NotReadyException();
      }
      var intData = _buffer.asByteData(_index, 4);
      _index += 4;
      return intData.getInt32(0, Endian.little);
    } else {
      if ((_buffer.lengthInBytes - index) < 4) {
        throw NotReadyException();
      }
      var intData = _buffer.asByteData(index, 4);
      _index = index + 4;
      return intData.getInt32(0, Endian.little);
    }
  }

  ///Read string from the binary data, the string format is utf-16, which is unicode in C#
  String readString([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    int dataLength;
    if (index == -1) {
      dataLength = readInt();
      if ((_buffer.lengthInBytes - _index) < dataLength) {
        throw NotReadyException();
      }
    } else {
      dataLength = readInt(index);
      if ((_buffer.lengthInBytes - index) < dataLength) {
        throw NotReadyException();
      }
    }
    var stringData = _buffer.asUint8List(_index, dataLength);
    _index += dataLength;
    var unicodeStringData = Uint8List.fromList(stringData.toList()).buffer.asUint16List();
    return String.fromCharCodes(unicodeStringData);
  }

  ///Read int16 value from binary data(little endian)
  int readInt16([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_buffer.lengthInBytes - _index) < 2) {
        throw NotReadyException();
      }
      var intData = _buffer.asByteData(_index, 2);
      _index += 2;
      return intData.getInt16(0, Endian.little);
    } else {
      if ((_buffer.lengthInBytes - index) < 2) {
        throw NotReadyException();
      }
      var intData = _buffer.asByteData(index, 2);
      _index = index + 2;
      return intData.getInt16(0, Endian.little);
    }
  }

  ///Read int64 value from binary data(little endian)
  ///this method is not support in web platform use readInt64V2 instead.
  int readInt64([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_buffer.lengthInBytes - _index) < 8) {
        throw NotReadyException();
      }
      var intData = _buffer.asByteData(_index, 8);
      _index += 8;
      return intData.getInt64(0, Endian.little);
    } else {
      if ((_buffer.lengthInBytes - index) < 8) {
        throw NotReadyException();
      }
      var intData = _buffer.asByteData(index, 8);
      _index = index + 8;
      return intData.getInt64(0, Endian.little);
    }
  }

  ///Read int64 value from binary data(little endian)
  ///this method use two int32 to support read int64 on web platform
  int readInt64V2([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_buffer.lengthInBytes - _index) < 8) {
        throw NotReadyException();
      }
      int low = readInt();
      int high = readInt();
      int value = high >> 32;
      value |= low;
      return value;
    } else {
      if ((_buffer.lengthInBytes - index) < 8) {
        throw NotReadyException();
      }
      int low = readInt(index);
      //Read the next int.
      int high = readInt();
      int value = high >> 32;
      value |= low;
      return value;
    }
  }

  ///Read float value from binary data(little endian)
  double readFloat([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_buffer.lengthInBytes - _index) < 4) {
        throw NotReadyException();
      }
      var floatData = _buffer.asByteData(_index, 4);
      _index += 4;
      return floatData.getFloat32(0, Endian.little);
    } else {
      if ((_buffer.lengthInBytes - index) < 4) {
        throw NotReadyException();
      }
      var floatData = _buffer.asByteData(index, 4);
      _index = index + 4;
      return floatData.getFloat32(0, Endian.little);
    }
  }

  ///Read double value from binary data(little endian)
  double readDouble([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_buffer.lengthInBytes - _index) < 8) {
        throw NotReadyException();
      }
      var floatData = _buffer.asByteData(_index, 8);
      _index += 8;
      return floatData.getFloat64(0, Endian.little);
    } else {
      if ((_buffer.lengthInBytes - index) < 8) {
        throw NotReadyException();
      }
      var floatData = _buffer.asByteData(index, 8);
      _index = index + 8;
      return floatData.getFloat64(0, Endian.little);
    }
  }

  ///Read bool value from binary data
  bool readBool([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_buffer.lengthInBytes - _index) < 1) {
        throw NotReadyException();
      }
      var boolData = _buffer.asByteData(_index, 1);
      _index++;
      return boolData.getInt8(0) == 1;
    } else {
      if ((_buffer.lengthInBytes - index) < 1) {
        throw NotReadyException();
      }
      var boolData = _buffer.asByteData(index, 1);
      _index = index + 1;
      return boolData.getInt8(0) == 1;
    }
  }

  ///Read byte value from binary data
  int readByte([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    if (index == -1) {
      if ((_buffer.lengthInBytes - _index) < 1) {
        throw NotReadyException();
      }
      var byteData = _buffer.asByteData(_index, 1);
      _index++;
      return byteData.getInt8(0);
    } else {
      if ((_buffer.lengthInBytes - index) < 1) {
        throw NotReadyException();
      }
      var byteData = _buffer.asByteData(index, 1);
      _index = index + 1;
      return byteData.getInt8(0);
    }
  }

  ///Read bytes from the binary data.
  Uint8List readBytes([int index = -1]) {
    if (_error) {
      throw DownloadErrorException(_errorMsg);
    }
    var dataLength = readInt(index);
    if ((_buffer.lengthInBytes - _index) < dataLength) {
      throw NotReadyException();
    }
    var bytes = _buffer.asUint8List(_index, dataLength);
    _index += dataLength;
    return bytes;
  }
}