feat: try to proxy body even after body-parser middleware

[midgleyc]

If a body parser middleware is added before the proxy is configured, proxying POST requests with bodies fails. This fixes that and provides a test, as requested by @chimurai in #460.

Code from #460 by @sarumont and from #320 by @repl-chris used -- thanks to both!

Fixes #90
Fixes #320
Fixes #417

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[coveralls]

Coverage decreased (-0.9%) to 84.516% when pulling 71bef4d on midgleyc:body-parser-test into 1704875 on chimurai:master.

[chimurai]

Thanks @midgleyc for this PR. (Sorry for late reply)

Could you separate this.fixBody function to external handler? Similar to responseInterceptor's implementation. https://github.com/chimurai/http-proxy-middleware/tree/master/src/handlers

And maybe rename fixBody to fixRequestBody, to avoid ambiguity between request body and response body.

This'll make fixRequestBody optional, since not everyone is having this issue. And it'll prevent bloat in the core functionality.

It's usage will be like this:

const { createProxyMiddleware, fixRequestBody } = require('http-proxy-middleware');

const proxy = createProxyMiddleware({
  /**
   * Fix bodyParser
   **/
  onProxyReq: fixRequestBody,
});

Planning to work on a preset-like functionality where something like recommended contains a collection of handlers for the common of use-cases.

[midgleyc]

@chimurai Done, how does it look now?

[chimurai]

That's quick :)

Could you add some documentation before or after:
https://github.com/chimurai/http-proxy-middleware/blob/master/README.md#intercept-and-manipulate-responses

[midgleyc]

Changes made.

You should be able to make changes to my branch directly, if you'd like.

[chimurai]

lgtm

[chimurai]

Thanks @midgleyc !

[midgleyc]

You're welcome, thanks for merging :)

[dhurtrci]

This workaround doesn't seem to work for my case.

In later versions, the proxyReq etc. are set inside the on property:

on: {
                        /**
                        * Fix bodyParser
                        **/
                        proxyReq: fixRequestBody
                    }

In my case I have an https proxy agent as well in the options (without that I don't even need to try the workaround!). Unfortunately I need that as my server runs inside company network and needs to go via proxy to the target.

In such a set-up, I get an error in the fixRequestBody method (where it sets the content type header), and is says (something like) 'cannot change headers after they are sent to the client'.

Specifically the error is:

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at new NodeError (node:internal/errors:406:5)
    at ClientRequest.setHeader (node:_http_outgoing:652:11)
    at writeBody (D:\API_Mapping_Server\api-mapping-express-frontend-server\dist\PathMapping.js:22:18)

Basically, it seems that the proxyReq isn't able to modify the headers, which seems to largely defeat the point of this 'hook' (in my case at least).....

[chimurai]

@dhurtrci Can you please open a new issue and provide a reproduction so it can be investigated?