Simple HTTP downloader script in Dart

downloader.dart

// Copyright 2017 Matt Sullivan
// Governed by the 2-Clause BSD license: https://opensource.org/licenses/BSD-2-Clause

import 'dart:io';

import 'package:http/http.dart' as http;
import 'package:args/args.dart';

void main(List<String> args) {
  var parsedArgs = parseArgs(args);
  // download(parsedArgs[0], parsedArgs[1]);
  progressiveDownload(parsedArgs[0], parsedArgs[1]);
}

/// Parse the command line args
List<String> parseArgs(List<String> args) {
  var parser = new ArgParser()
    ..addOption('url', abbr: 'u', help: 'The url to download', valueHelp: 'url')
    ..addOption('filename',
        abbr: 'f', help: 'save filename', valueHelp: 'filename')
    ..addFlag('help', abbr: 'h', help: 'help info');

  var parsedArgs = parser.parse(args);

  if (parsedArgs['help']) {
    print(parser.usage);
    exit(0);
  }

  String url;
  if (parsedArgs['url'] == null) {
    stderr.writeln('A url must be provided');
    exit(1);
  } else {
    url = parsedArgs['url'];
  }

  var filename = parsedArgs['filename'];
  if (filename == null) {
    var uri = Uri.parse(url);
    filename =
        uri.pathSegments.isNotEmpty ? uri.pathSegments.last : 'output.html';
  }

  return [url, filename];
}

/// Downloads and saves the specified URI
void download(String url, String filename) {
  http.get(Uri.parse(url)).then((res) {
    switch (res.statusCode) {
      case 200:
        print('Downloading content of length: ${res.contentLength}');
        new File(filename).writeAsBytes(res.bodyBytes);
        break;
      default:
        stderr.writeln('Unexpected response code : ${res.statusCode}');
    }
  });
}

/// Progressively downloads and saves the specified URI
void progressiveDownload(String url, String filename) {
  var req = new http.Request('GET', Uri.parse(url));
  req.send().then((res) {
    if (res.statusCode == 200) {
      print('Downloading content of length: ${res.contentLength}');
      res.stream.map((chunk) {
        print('Chunk size: ${chunk.length}');
        return chunk;
      }).pipe(new File(filename).openWrite());
    } else {
      stderr.writeln('Unexpected response code : ${res.statusCode}');
      res.stream.drain();
    }
  });
}

pubspec.yaml

name: downloader
version: 0.0.1
description: >
    Simple command line download script

dependencies:
    http: ^0.11.3
    args: ^1.0.2