Super simple URL unshortener in Dart

unshortener.dart

import 'dart:io' show HttpRequest, HttpClient, HttpServer, ContentType;
import 'dart:convert' show JSON;

void handleRequest(HttpRequest request) {
  // For convenience.
  var response = request.response;

  // No path is expected. Return with 404 for anything else.
  if (request.uri.path != '' && request.uri.path != '/') {
    response.statusCode = 404;
    response.close();
    return;
  }

  var query = request.uri.queryParameters;

  // If there was no url query parameter, return with 400.
  if (query['url'] == null) {
    response.statusCode = 400;
    response.close();
    return;
  }

  var url = Uri.parse(query['url']);

  // We have the information needed to make a request to a remote server. Create a client.
  var client = new HttpClient();

  // Make a HEAD request to resolve redirects, but avoid unnecessary data.
  client.openUrl('HEAD', url)
    .then((req) => req.close())
    .then((res) {
      // The response will be JSON.
      response.headers.contentType = ContentType.parse('application/json; charset=utf-8');

      // Encode a JSON object with the original and resolved URLs and write it to the response.
      response.write(JSON.encode({
        'original': query['url'],
        'resolved': res.redirects.last.location.toString()
      }));

      response.close();
    });
}

void main() {
  HttpServer.bind('127.0.0.1', 8080)
    .then((server) {
      print('Server listening...');
      server.listen(handleRequest);
    });
}

Updated to use show. Definitely much nicer.