在flutter中一次处理大量http请求

Question

Requirement:

I've 1000 URLs of PDF, from which I want to create the zip.

Function:

static Future<bool> downloadZip(List<String> urls) {
    int counter = 0
    for(String url in urls) {
        bytesForFileAtUrl(url).then((bytes){
            counter++;
            if(bytes != null) {
               //Add bytes to the zip encoder
            }
            if(counter == urls.length) {
               //close the zip encoder
               //download the zip file
            }
        }
      }
  }

  static Future<Uint8List> bytesForFileAtUrl(String url) async {
      try {
          http.Response response = await http.get(url);
          return response?.bodyBytes;
      } catch (e) {
          print('Error getting bytes: ${e.toString()}');
          return null;
      }
  }

Problem:

When there is small number of requests its working fine. But in case large number of requests I'm getting the exception: SocketException: Connection failed (OS Error: Too many open files, errno = 24) as reported here . This might because of memory issue on my mobile device, as its working fine on the web platform.

I've tried other solutions like the one using Future.wait() suggested here , but its not working and device is hanged.

Whats the best solution for this scenario ?

Worst Solution:

Using await keyword. No exception at all, but then its taking too long for the overall process to complete.

for(String url in urls) {
    final bytes = await bytesForFileAtUrl(url);
    ...
    ...
}

Answer 1

static Future < bool > downloadZip(List < String > urls) {
  int counter = 0;
  urls.forEach(async() {
    await bytesForFileAtUrl(url).then((bytes){
      counter++;
      if (bytes != null) {
        //Add bytes to the zip encoder
      }
      if (counter == urls.length) {
        //close the zip encoder
        //download the zip file
      }
    });
  });
}

  static Future < Uint8List > bytesForFileAtUrl(String url) async {
  try {
    http.Response response = await http.get(url);
    return response?.bodyBytes;
  } catch (e) {
    print('Error getting bytes: ${e.toString()}');
    return null;
  }
}

maybe try this ?