Dart/Flutter HTTP response is incomplete when downloading large files

I have a Dart/Flutter mobile app that configures itself by downloading files from a server. The files are ZLib compressed, headlessly, and this process has always worked very well - up until now. Here is the relevant code

static Future<String> fileFetch(String url) async
{
 final HttpClientRequest request = await HttpClient().getUrl(Uri.parse(url));
 final HttpClientResponse response = await request.close();
 return await response.pipe(Accumulator());
}

where the Acccumulator class handles the actual file download + ZLib decoding

import 'dart:io';
import 'dart:async';


class Accumulator extends StreamConsumer<List<int>>
{
 List<int> accu = List.empty(growable:true);

 String originalText()
 {
  ZLibCodec zlc = ZLibCodec(raw:true);
  print('Accu ${accu.length}');
  List<int> uncompd = zlc.decode(accu);
  String text = String.fromCharCodes(uncompd); 
  return text;
 }

 void whenData(List<int> data){accu.addAll(data);}

 void whenErr(e){XLog.e('Accu',e.toString());}

 @override
 Future<void> addStream(Stream<List<int>> s) async
 {
  s.listen(whenData);
  return; 
 }

 @override 
 Future<dynamic> close() async
 {
  return Future.value(originalText());
 }
}

For the most part the orignalText being returned is JSON. The offending file that has now started causing an incomplete file download is 132Kb in length and I find that only 42894 bytes of the original (compressed) file are being downloaded.

Why is this happening - intrinsic limits on how much can be handled by the Accumulator?

from Dart/Flutter HTTP response is incomplete when downloading large files