Allow overriding or modifying the queryString when proxying websockets

[ttshivers]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the feature has not already been requested

🚀 Feature Proposal

It would be great to have the ability to overwrite or modify the queryString when proxying websockets. Possibly adding a queryString property to the wsClientOptions, in the same way that there is already a rewriteRequestHeaders in the wsClientOptions

Motivation

When proxying regular http connections, the queryString in replyOptions can be used to rewrite or modify the query string. https://github.com/fastify/fastify-reply-from?tab=readme-ov-file#querystring-or-querystringsearch-requrl

A websocket API I want to proxy requires passing an auth token as query parameter and I want to make a proxy with this library to inject it.

Example

fastify.register(require('@fastify/http-proxy'), {
   websocket: true,
   wsUpstream: 'wss://some-domain.com',
   wsClientOptions: {
      queryString(search, reqUrl, req) {
          return {
            authToken: req.authToken
          };
      }
   }
})

[mcollina]

Thanks for reporting! Would you like to send a Pull Request to address this issue? Remember to add unit tests.

[ttshivers]

Sure I can open a PR.