[英]making http requests in nodejs loop
Finding it almost impossible to capture the response of http requests in a loop as an array. 发现几乎不可能将循环中的http请求的响应捕获为数组。 I can see the array in console.log but when I pass the array to be the response of http server I get a blank array. 我可以在console.log中看到该数组,但是当我将该数组传递为http服务器的响应时,我得到了一个空白数组。 What am I doing wrong , or are there better ways to do this? 我在做什么错,还是有更好的方法来做到这一点?
Code : 代码:
router.route('/uprns').post(function(request, response){
response.setHeader('content-type', 'application/text');
console.log('first element from the array is '+request.body.UPRNS[0]);
console.log('Number of items in array is '+request.body.UPRNS.length);
if (request.body.UPRNS.length == 0) {
response.send( 'no UPRNS in request' );
}
var output = [];
var obj = '';
for( var i = 0; i < request.body.UPRNS.length; i++) {
obj = request.body.UPRNS[i];
//Make HTTP calls to
var options = {
host: 'orbisdigital.azure-api.net',
path: '/nosecurity/addresses?uprn='+obj // full URL as path
};
callback = function(res) {
res.on('data', function (chunk) {
output.push(chunk.toString());
});
//the whole response has been recieved
res.on('end', function () {
console.log(output);
});
}
Https.request(options, callback).end();
}
response.send(output);
});
I know there is a lot of talk about blocking process in a for loop , but there is no definitive recommended way to deal with http calls in a loop. 我知道有很多关于在for循环中阻塞进程的讨论,但是没有确定的推荐方法可以处理循环中的http调用。 Thank you . 谢谢 。
Here is the code. 这是代码。 See the code for the added comments. 请参阅代码以获取添加的注释。 Do some reading on asynchronous programming with node.js, here's a starter . 阅读有关使用node.js进行异步编程的内容, 这是一个入门指南 。
router.route( '/uprns' ).post( function ( request, response ) {
response.setHeader( 'content-type', 'application/text' );
console.log( 'first element from the array is ' + request.body.UPRNS[ 0 ] ); // your 1st element in JSON array.
console.log( 'Number of items in array is ' + request.body.UPRNS.length );
var output = [];
var obj = '';
for ( var i = 0; i < request.body.UPRNS.length; i++ ) {
obj = request.body.UPRNS[ i ];
console.log( obj );
//Make HTTP calls to
var options = {
host: 'orbisdigital.azure-api.net',
path: '/nosecurity/addresses?uprn=' + obj // full URL as path
};
Https.request( options, callback ).end();
}
var countResponses = 0;
// Don't make functions in a loop, so I moved this function down
// here.
function callback( res ) {
res.on( 'data', function ( chunk ) {
output.push( chunk.toString() );
});
// Handles an error
request.on('error', function(err) {
console.error(err.stack);
response.statusCode = 500; // or what ever.
response.send(500, 'there was an error');
});
//the whole response has been recieved
res.on( 'end', function () {
console.log( output );
countResponses++;
if (countResponses === request.body.UPRNS.length) {
// Previously this code was executed directly
// after the loop finished. It did not wait for
// all the responses, so it sent the empty response.
// However, the other console.log(output) statements
// were called after this.
//
// There is a bug here that if request.body.UPRNS.length
// is zero, then the user will never get a response. I
// let you fix this up :).
response.send( output );
}
} );
}
} );
Better way to handle such scenario is to use async.js instead of for loops. 处理这种情况的更好方法是使用async.js而不是for循环。 https://github.com/caolan/async https://github.com/caolan/async
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