feat: Added handler option.

[ShogunPanda]

Summary

Adds a new handler option to customize HTTP proxy response handling while preserving the existing default behavior.

Changes

• Added opts.handler support in index.js.
• Defaults to reply.from(dest, options) when no custom handler is provided.
• Validates that handler, when provided, is a function.
• Added runtime tests for:
  • custom response handling
  • delegating back to reply.from(dest, options)
  • invalid handler option validation
• Added TypeScript definitions and type tests for the new option.
• Documented the handler option in README.md.

Checklist

• run npm run test && npm run benchmark --if-present
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[climba03003]

What is it different from using reply.fromParameters in preHandler ?

const { url, options } = reply.fromParameters('/updated', { ...request.params, serverId: 42 })
reply.from(url, options)

or onResponse ?

reply.from(source, {
  onResponse(request, reply, res) => {
    reply.removeHeader('content-length');
    reply.send('New body of different length');
  }
})

[ShogunPanda]

@climba03003 Sometimes I want to totally skip reply.from but take advantage of all other goodies. Do you see a different way to do that?

[climba03003]

@climba03003 Sometimes I want to totally skip reply.from but take advantage of all other goodies. Do you see a different way to do that?

That is exactly why you need to use reply.fromParameters.
I don't see a good use-case to change the handler only, but not using the reply.fromParameters.

Bypassing the handler means you only need to proxy the websocket? or websocket with some route?
If that is the case, reply.wsProxy also did the job for you.

[ShogunPanda]

I use fromParameters.
Then I replace the final .from with the optional custom handler.
That happens AFTER checking web sockets.
In my use case I want to skip reply-from completely.

[mcollina]

lgtm