Add support for custom onProxyReq and onProxyRes

[amaury1093]

I think it would be useful to add onProxyReq and onProxyRes options in the constructor function:

httpProxyMiddleware(req, res, {
      // You can use the `http-proxy` option
      target: 'https://www.example.com',
      // In addition, you can use the `pathRewrite` option provided by `next-http-proxy-middleware`
      pathRewrite: [{
        patternStr: '^/api/new',
        replaceStr: '/v2'
      }, {
        patternStr: '^/api',
        replaceStr: ''
      }],
+     onProxyReq: (proxyReq, req, res) => {...},
+     onProxyRes: (proxyRes, req, res) => {...},
    })

This will allow more fine-grained request and response rewriting.

[stegano]

Hi @AmauryM
Please see #31
Thanks :)

[amaury1093]

#31 seems to solve onProxyReq, thanks.

How about onProxyRes?

If I do:

async function handler(req: NextApiRequest, res: NextApiResponse): Promise<void> {
	return httpProxyMiddleware(req, res, {
		target: TARGET_HOST,
	})
	.then(() => {
		res.setHeader(...);
	})
}

then I get Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

[stegano]

Hi @AmauryM
From v1.2.0 version, you can access the http-proxy instance through an option. Please refer to the document. 😀
https://github.com/stegano/next-http-proxy-middleware#onproxyinit-option

[amaury1093]

Sounds good, thanks