Just imagine that you need to provide a file on a server in response to a client's request. The following code will do this:

import 'dart:io';

main() {
  HttpServer
  .bind(InternetAddress.ANY_IP_V4, 8080)
  .then((server) {
    server.listen((HttpRequest request) {
      new File('data.txt').readAsString()
      .then((String contents) {
        request.response.write(contents);
        request.response.close();
      });
    });
  });
}

In the preceding code, we read the entire file and buffered it into the memory of every request before sending the result to the clients. This code works perfectly for small files, but what will happen if the data.txt file is very large? The program will consume a lot of memory because it serves a lot of users concurrently, especially on slow connections. One big disadvantage of this code is that we have to wait for an entire file to be buffered in memory before the content can be submitted to the clients.

The HttpServer object...