如何使请求等待上一个请求完成？

Question

我正在尝试将API调用发送到NodeJS服务器。 不幸的是，服务器（不是我做的）不允许我进行异步调用。

我试图找出一种方法，使每个请求在发送之前都等待上一个请求完成。

这是我的代码：

var http = require('http');
var fs = require('fs');

// An object of options to indicate where to post to
var post_options = {
    host: 'localhost',
    port: '8080',
    path: '/api/scan',
    method: 'POST',
    headers: {
        'Content-Type': 'application/json'
    }
};
var array = ["ssl.com", "google.com", "hamzakhan.org"];
for (var i=0; i<array.length;i++) {
    //console.log(array[i]);
    var post_req = http.request(post_options, function(res) {
        res.setEncoding('utf8');
        var body = '';
        res.on('data', function(chunk) {
            body += chunk;
        });
        res.on('end', function() {
            body = JSON.parse(body);
            // Make sure it's working
            console.log(body.response.subject);
        });
    });

    var url = array[i];
    var catURL = { "url": url, "path": "/", "port": "443", "live_scan": "false", "advanced": "true" };
    post_req.write(JSON.stringify(catURL), function(err) {
        //console.log(err);
        post_req.end();
    });

}

我当时想我可以将一个while循环嵌套在for循环中，而while循环将具有一个标志，该标志指示for循环何时可以继续进行。

现在，当我将url的值硬编码为单个url时，此代码有效，因此我知道我可以成功发送和接收。

感谢所有/任何帮助！

Answer 1

/**
 * Disclaimer: I did not test your code. I simply added a few
 * lines to illustrate my suggestion.
 */

var http = require('http');
var fs = require('fs');
var EventEmitter = require('events').EventEmitter;

// An object of options to indicate where to post to

var post_options = {
    host: 'localhost',
    port: '8080',
    path: '/api/scan',
    method: 'POST',
    headers: {
        'Content-Type': 'application/json'
    }
};

var array = ["ssl.com", "google.com", "hamzakhan.org"];
var emitter = new EventEmitter();
var counter = 0, n = array.length;

function PostRequest() {
    var post_req = http.request(post_options, function(res) {
        res.setEncoding('utf8');
        var body = '';
        res.on('data', function(chunk) {
            body += chunk;
        });
        res.on('end', function() {
            body = JSON.parse(body);
            // Make sure it's working
            console.log(body.response.subject);

            // ADD THE CALLBACK 
            // OR 
            // TRIGGER EVENT
            return emitter.emit('ResponseEnded');

        });
    });

    var url = array[counter];
    var catURL = { "url": url, "path": "/", "port": "443", "live_scan": "false", "advanced": "true" };
    post_req.write(JSON.stringify(catURL), function(err) {
        //console.log(err);
        post_req.end();
    });
}

emitter.on('ResponseEnded',function() {
    ++counter;
    if (counter < n) {
        PostRequest();
    }
    else {
        console.log('Nothing more request');
    }
});

// Start with the first request
PostRequest();

更新：这是做同一件事的另一种方式。

/**
 * Disclaimer: I did not test your code. I simply added a few
 * lines to illustrate my suggestion.
 */

var http = require('http');
var fs = require('fs');


// An object of options to indicate where to post to

var post_options = {
    host: 'localhost',
    port: '8080',
    path: '/api/scan',
    method: 'POST',
    headers: {
        'Content-Type': 'application/json'
    }
};

var array = ["ssl.com", "google.com", "hamzakhan.org"];
var counter = 0, n = array.length;

function PostRequest() {
    var post_req = http.request(post_options, function(res) {
        res.setEncoding('utf8');
        var body = '';
        res.on('data', function(chunk) {
            body += chunk;
        });
        res.on('end', function() {
            body = JSON.parse(body);
            // Make sure it's working
            console.log(body.response.subject);

            // THIS IS ANOTHER WAY OF DOING IT
            ++counter;
            if (counter < n) {
                /**
                 * This is were your start new 
                 * requests
                 */
                PostRequest();
            }
            else {
                console.log('Nothing more request');
            }            

        });
    });

    var url = array[counter];
    var catURL = { "url": url, "path": "/", "port": "443", "live_scan": "false", "advanced": "true" };
    post_req.write(JSON.stringify(catURL), function(err) {
        //console.log(err);
        post_req.end();
    });
}

// Start with the first request
PostRequest();