How to receive cross-origin requests sent via POST method with Node.js

With the rapid development of front-end technology, web development has also become complex and changeable. Especially when we need to request data from different domain names, we will encounter cross-domain problems. This article will introduce how to use Node.js to receive cross-domain requests sent through the POST method.

First of all, cross-domain problems are caused by the browser’s same-origin policy. The same-origin policy means that scripts with different domain names, different protocols, and different ports cannot obtain data from each other. This means that if our page needs to obtain data from other domain names, an error will be reported. In order to solve this problem, we need to use some means to bypass the same origin policy.

One way to solve the cross-domain problem is to use CORS (Cross-Origin Resource Sharing) technology. CORS allows us to explicitly specify in the response which domain names can access our resources through Ajax. However, if our API server does not implement CORS, or we cannot modify the configuration on the server, we need to try other methods to solve the problem.

A common method is to use JSONP technology. JSONP dynamically creates a script tag in the page, and then requests cross-domain data through the tag. The src attribute of this tag points to a JavaScript file on the API server that returns JSON data. JSONP solves the cross-domain problem, but it can only send GET requests, not POST requests.

Therefore, we need another way to implement cross-domain POST requests. The following is an example of using Node.js to implement a cross-domain POST request:

First, we need to use the http module of Node.js to create a web server and listen for POST requests from the client:

const http = require('http');

const server = http.createServer((req, res) => {
  if (req.method === 'POST') {
    let body = '';
    req.on('data', data => {
      body += data;
    });
    req.on('end', () => {
      console.log(body);
      res.end();
    });
  }
});
server.listen(8080);

This simple web server will listen to POST requests from the client on port 8080, and output the request body to the console.

Next, we need to use the XMLHttpRequest object on the client to send the POST request. However, due to cross-domain issues, we cannot directly send the request to the API server. Therefore, we first need to create a proxy server on the client side, and then let the proxy server forward the request.

The code of the proxy server is as follows:

const http = require('http');

const clientReq = http.request({
  method: 'POST',
  hostname: 'yourapi.com',
  path: '/path/to/api',
  headers: {
    'Content-Type': 'application/json'
  }
}, (res) => {
  res.on('data', (data) => { /* do something */ });
});

clientReq.on('error', (error) => { /* handle error */ });

process.stdin.on('data', (chunk) => {
  clientReq.write(chunk);
});

process.stdin.on('end', () => {
  clientReq.end();
});

This proxy server will forward the request read from the standard input to the API server.

Finally, we need to implement cross-domain POST requests by starting the proxy server on the client and then sending the POST request to the proxy server. The sample code is as follows:

const http = require('http');
const querystring = require('querystring');

const postData = querystring.stringify({
  'msg': 'Hello World!'
});

const options = {
  hostname: 'localhost',
  port: 8080,
  path: '/proxy',
  method: 'POST',
  headers: {
    'Content-Type': 'application/x-www-form-urlencoded',
    'Content-Length': Buffer.byteLength(postData)
  }
};

const req = http.request(options, (res) => {
  res.setEncoding('utf8');
  res.on('data', (chunk) => {
    console.log(`BODY: ${chunk}`);
  });
  res.on('end', () => {
    console.log('No more data in response.')
  })
});

req.on('error', (e) => {
  console.error(`problem with request: ${e.message}`);
});

// 请求的数据
req.write(postData);
req.end();

This code snippet will send a POST request to the proxy server, and the proxy server will forward the request to the API server. The response returned by the API server will be forwarded back to the client by the proxy server.

Summary: Cross-domain issues are an important issue in web development and require us to take some technical means to solve them. In this article we introduce how to use Node.js to receive cross-domain POST requests and use a proxy server to bypass the same-origin policy. Hope this article is helpful to you.

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