使用 nodeJS 进行异步 http 调用
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Asynchronous http calls with nodeJS
提问by Ludo
I would like to launch asynchronous http calls on my server node, i saw the asyncnode module and i guess the async.parallelenables us to do that.
我想在我的服务器节点上启动异步 http 调用，我看到了async节点模块，我想这async.parallel使我们能够做到这一点。
The documented example is pretty clear, but i don't know how i could manage multiple http calls.
记录的示例非常清楚，但我不知道如何管理多个 http 调用。
I tried the example bellow but it doesn't even launch the http calls:
我尝试了下面的示例，但它甚至没有启动 http 调用：
var http = require('http');
var Calls = [];
Calls.push(function(callback) {
// First call
http.get('http://127.0.0.1:3002/first' callback);
});
Calls.push(function(callback) {
// Second call
http.get('http://127.0.0.1:3002/second' callback);
});
var async = require('async');
async.parallel(Calls, function(err, results) {
console.log('async callback: '+JSON.stringify(results));
res.render('view', results);
});
If i launch the http requests separately, i do have a result, but but calling the async callback i get async callback: [null,null]
如果我单独启动 http 请求，我确实有结果，但是调用异步回调我得到 async callback: [null,null]
回答by freakish
Have a look at the documentation:
看看文档：
With http.request() one must always call req.end() to signify that you're done with the request - even if there is no data being written to the request body.
使用 http.request() 必须始终调用 req.end() 以表示您已完成请求 - 即使没有数据写入请求正文。
You are creating a request, but you are not finalizing it. In your calls you should do:
您正在创建一个请求，但尚未完成它。在您的通话中，您应该执行以下操作：
var req = http.request(options, function(page) {
// some code
});
req.end();
This is assuming you are doing a normal GET request without body.
这是假设您正在执行没有正文的正常 GET 请求。
You should also consider using http.getwhich is a nice shortcut:
您还应该考虑使用http.get，这是一个不错的快捷方式：
http.get("http://127.0.0.1:3002/first", function(res) {
// do something with result
});
UpdateThe other thing is that callbacks in async have to be of the form
更新另一件事是异步中的回调必须采用以下形式
function(err, res) { ... }
The way you are doing it now won't work, because callback to http.get accepts only one argument res. What you need to do is the following:
您现在的做法行不通，因为对 http.get 的回调只接受一个参数res。您需要做的是：
http.get('http://127.0.0.1:3002/second', function(res) {
callback(null, res);
});
回答by Jacek Pietal
dont use capital names for other purpouses than types/classes
不要将大写名称用于类型/类以外的其他目的
below is your code with corrected obvious mistakes
下面是你的代码，更正了明显的错误
var http = require('http');
var calls = [];
calls.push(function(callback) {
// First call
http.get('http://127.0.0.1:3002/first', function (resource) {
resource.setEncoding('utf8');
resource.on('data', function (data) {
console.log('first received', data);
callback();
});
});
});
calls.push(function(callback) {
// Second call
http.get('http://127.0.0.1:3002/second', function (resource) {
resource.setEncoding('utf8');
resource.on('data', function (data) {
console.log('second received', data);
callback();
});
});
});
var async = require('async');
async.parallel(calls, function(err, results) {
console.log('async callback ', results);
res.render('view', results);
});
回答by Ludo
Ok the thing is to call the callback this way callback(null, res);instead callback(res);, i think the first parameter is interpreted as an error and the second one is the real result.
好东西是调用回调函数这种方式callback(null, res);来代替callback(res);，我想到的第一个参数被解释为错误，第二个才是真正的结果。
