Decoding JSON in an Isolate

[techouse]

Since the JSON payloads can be quite large, using json.decode() on the main thread could cause janking in Flutter.

One solution would be to expose a method that does the decoding which defaults to json.decode but allow it to be overridden in order to use compute() or any other Isolate method.

I have swapped out all internal package references to

json.decode(response.body)

with

await algolia.decodeJson(response.body)

Here's an example of an override using compute():

import 'dart:async';
import 'dart:convert';
import 'package:algolia/algolia.dart';

class IsolateDecodingAlgolia extends Algolia {
  IsolateDecodingAlgolia.init({
    super.applicationId,
    super.apiKey,
    super.extraHeaders,
    super.extraUserAgents,
  });

  /// Override the default JSON decoder with an Isolated one using compute
  @override
  Future<dynamic> decodeJson(
    String source, {
    Object? Function(Object? key, Object? value)? reviver,
  }) => 
      compute(json.decode, source);
}

In pure Dart < 2.19 you have to either get creative with the low-level Isolate API or simply import the compute package.

Thankfully, Dart 2.19 will soon come with Isolate.run()

@override
Future<dynamic> decodeJson(
  String source, {
  Object? Function(Object? key, Object? value)? reviver,
}) => 
    Isolate.run(() => json.decode(source));

Another option would also be using a worker pool. The squadron package provides an excellent API and builder just for that purpose.

This addresses #103