Replace advanced proxy with user provided proxy.js (#3366)

[iansu]

Remove "advanced proxy" object from package.json, replace with user provided proxy.js.

Closes #3366

[iansu]

Work in progress on new proxy.

TODO

1. Figure out what exactly needs to be passed to user function to generate proxy config. Everything being passed now might not be necessary or there might be a better way to pass it (config object?)
2. Possibly reload app when proxy.js changes (this is probably very difficult as the proxy is part of the webpack dev server config
3. Clean up comments and error messages
4. Test various proxy configs

[iansu]

This is the proxy.js I'm using for testing:

module.exports = function(paths, resolveLoopback, mayProxy, onProxyError) {
  let target;
  if (process.platform === 'win32') {
    target = resolveLoopback('http://localhost:8000');
  } else {
    target = 'http://localhost:8000'
  }

  return [
    {
      path: '/api/**/*',
      target,
      logLevel: 'silent',
      context: function(pathname, req) {
        return (
          req.method !== 'GET' ||
          (mayProxy(pathname) &&
            req.headers.accept &&
            req.headers.accept.indexOf('text/html') === -1)
        );
      },
      onProxyReq: proxyReq => {
        // Browers may send Origin headers even with same-origin
        // requests. To prevent CORS issues, we have to change
        // the Origin to match the target URL.
        if (proxyReq.getHeader('origin')) {
          proxyReq.setHeader('origin', target);
        }
      },
      onError: onProxyError(target),
      secure: false,
      changeOrigin: true,
      ws: true,
      xfwd: true
    }
  ];
};

[FezVrasta]

I don't think this allows to proxy the root path, right?

I'd like to proxy the root path and serve the CRA from a sub directory

I have described how to make it work here:
#3366 (comment)

[donverduyn]

Any progress on this?

[yyfearth]

@iansu As I commented on the #3366
I suggest to put the filename proxy.js into the proxy config of the package.json.
So the filename do not have to be hardcoded, and user have the freedom to chose other names.

[ng-parth]

Any updates? Any idea if this PR is going to be accepted?

[iansu]

Closing this as it was superseded by #5073