如何向 node-http-proxy 响应添加标头

Question

I need to solve CORS on a third party service, so I want to build a proxy to add the header "Access-Control-Allow-Origin: *".

Why is this code is not adding the header?

httpProxy = require('http-proxy');

var URL = 'https://third_party_server...';

httpProxy.createServer({ secure: false, target: URL }, function (req, res, proxy) {

  res.oldWriteHead = res.writeHead;
  res.writeHead = function(statusCode, headers) {
    /* add logic to change headers here */

    res.setHeader('Access-Control-Allow-Origin', '*');
    res.setHeader('Access-Control-Allow-Methods', 'POST, GET, OPTIONS');

    res.oldWriteHead(statusCode, headers);
  }

  proxy.proxyRequest(req, res, { secure: false, target: URL });

}).listen(8000);

Answer 1

You have the proxyRes event available.

So something like that should work:

proxy.on('proxyRes', function(proxyRes, req, res) {
  res.setHeader('Access-Control-Allow-Origin', '*');
  res.setHeader('Access-Control-Allow-Methods', 'POST, GET, OPTIONS');
});

Full working example (well, when I say full I do not mean this is a secure-failsafe-real proxy, but it does the job for your question):

var http = require('http'),
    httpProxy = require('http-proxy');
var proxy = httpProxy.createProxyServer({});
var server = http.createServer(function(req, res) {
    proxy.web(req, res, {
        target: 'https://third_party_server...',
        secure: false,
        ws: false,
        prependPath: false,
        ignorePath: false,
    });
});
console.log("listening on port 8000")
server.listen(8000);

// Listen for the `error` event on `proxy`.
// as we will generate a big bunch of errors
proxy.on('error', function (err, req, res) {
  console.log(err)
  res.writeHead(500, {
    'Content-Type': 'text/plain'
  });
  res.end("Oops");
});

proxy.on('proxyRes', function(proxyRes, req, res) {
  res.setHeader('Access-Control-Allow-Origin', '*');
  res.setHeader('Access-Control-Allow-Methods', 'POST, GET, OPTIONS');
});

Answer 2

Even though this question is old, it's the first result from Google and the current answer isn't terribly informative.

The first point of note is that proxyRes does not have a setHeader() method. Additionally, if you try to override a proxyRes header with res.setHeader('Header-to-Override', 'new value') , it won't work (I assume due to headers being copied from proxyRes to res after this event is fired.

It appears we're not the only ones with this issue: https://github.com/http-party/node-http-proxy/issues/1401

Here's my solution for adding an additional cache-control header in my situation:

 proxy.on('proxyRes', function(proxyRes, req, res) { if (proxyRes.headers['cache-control']) { proxyRes.headers['cache-control'] += ', proxy-revalidate' } else { proxyRes.headers['cache-control'] = 'proxy-revalidate' } })

Answer 3

For those coming across this in the future, here's an updated answer. Combining Michael Gummelt's comment and Nicholas Mitrousis' answer, any headers set on res will be overridden if the response from upstream in proxyRes has the same header set. So to answer the original question:

proxy.on('proxyRes', function(proxyRes, req, res) {
 proxyRes.headers["access-control-allow-origin"] = "*";
 proxyRes.headers["Access-Control-Allow-Methods"] = "POST, GET, OPTIONS";
}