Question

我正在尝试将以下Node.js代码段转换为Dart。在我的转换中，一旦有响应就打印出'data returned ...'消息，这与Node.js版本不同，后者等待页面完成请求的2秒延迟。

Node.js的

var http = require('http')    
function fetchPage() {
  console.log('fetching page');
  http.get({ host: 'trafficjamapp.herokuapp.com', path: '/?delay=2000' }, function(res) {
    console.log('data returned from requesting page');
  }).on('error', function(e) {
    console.log("There was an error" + e);
  });
}

达特

import 'dart:io';
import 'dart:uri';

fetchPage() {
  print('fetching page');
  var client = new HttpClient();
  var uri = new Uri.fromComponents(scheme:'http', domain: 'trafficjamapp.herokuapp.com', path: '?delay=2000');
  var connection = client.getUrl(uri);

  connection.onRequest = (HttpClientRequest req) {
    req.outputStream.close();
  };

  connection.onResponse = (HttpClientResponse res){
    print('data returned from requesting page');
  };

  connection.onError = (e) => print('There was an error' ' $e');
}

如何在Dart中实现与节点相同的延迟打印？提前谢谢。

Answer 1

您可以在onResponse回调的文档中找到：

当收到响应的所有标头并准备好接收数据时，将调用回调。

所以它的工作原理如下：

connection.onResponse = (res) {
  print('Headers received, can read the body now');
  var in = res.inputStream;

  in.onData = () {
    // this can be called multiple times
    print('Received data');
    var data = in.read();
    // do something with data, probably?
  };
  in.onClosed = () {
    // this is probably the event you are interested in
    print('No more data available');
  };
  in.onError = (e) {
    print('Error reading data: $e');
  };
};

Answer 2

您的Dart代码几乎是正确的，但有一个错误。您应该使用query命名参数而不是path。我不知道哪个Url会使用您的代码调用，但响应的状态代码为400。为了更具可读性，您还可以使用Uri.fromString构造函数。

此外，您可以省略onRequest设置，因为在未定义onRequest时会执行相同的代码。

以下是代码：

import 'dart:io';
import 'dart:uri';

main() {
  print('fetching page');
  //var uri = new Uri.fromString('http://trafficjamapp.herokuapp.com/?delay=2000');
  var uri = new Uri.fromComponents(scheme:'http',
      domain: 'trafficjamapp.herokuapp.com', query: 'delay=2000');
  var client = new HttpClient();
  var connection = client.getUrl(uri);
  connection.onResponse = (HttpClientResponse res){
    print('data returned from requesting page with status ${res.statusCode}');
  };
  connection.onError = (e) => print('There was an error' ' $e');
}

NodeJs在Dart中请求回调

2 个答案: