Reducing a request body stream of Uint8List fails in shelf 1.1.1 or later

[fertrig]

The test below passes in shelf 1.0.0, but fails in shelf 1.1.1 (or later) with this message:

type '(List<int>, List<int>) => List<int>' is not a subtype of type '(Uint8List, Uint8List) => Uint8List' of 'combine'

import 'dart:convert';
import 'dart:typed_data';

import 'package:shelf/shelf.dart';
import 'package:test/test.dart';

void main() {
  group('shelf.Request.read', () {
    test('reduce stream of Uint8List', () async {
      var request = _request(body: genUint8List());
      var bodyBytes = await request.read().reduce((previous, element) {
        return [...previous, ...element];
      });
      expect(bodyBytes, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
    });
  });
}

Request _request({Map<String, String>? headers, body, Encoding? encoding}) {
  return Request('POST', Uri.parse('http://localhost/'),
      headers: headers, body: body, encoding: encoding);
}

Stream<Uint8List> genUint8List() async* {
  for (var i = 0; i <= 9; i++) {
    await Future.microtask(() => null);
    yield Uint8List.fromList([i]);
  }
}

My client application is sending json. The server started failing with that error message when I upgraded shelf. This test reproduces the error I am getting in production.

The same test passes when using a stream of List<int>. Here is a gist showing both scenarios.

[kevmoo]

This is...funky.

We used to wrap (cast) all of the lists going into the Request. This made sure the runtime time was List, but it was horrible for performance.

We fixed that here: 4b9294e

The result: the static return type of read is still Stream<List<int>>, but the runtime type is now Stream<Uint8List>.

So reduce isn't happy.

The fix:

      var bodyBytes = await request.read().fold<List<int>>(
        <int>[],
        (previous, element) => previous..addAll(element),
      );

You also only allocate ONE array, instead of a new one each time around.

[kevmoo]

@natebosch likely has better ideas, too 😄