When using preHandler in proxy, body is not parsed but instead is overwritten with the request object.

To Reproduce

To reproduce the behavior create a simple reverse proxy and make a POST or PUT request with a body. (JSON)

fastify.register(require("fastify-http-proxy"), {
  upstream: "http://localhost:8080", 
  prefix: "/api/proxy",
  async preHandler(request, reply) {
    console.log(request.body) // This line logs whole fastify request object instead of body
    return
  }
})

Expected behavior

As is preHandler hook on routes, the body should be accessible from proxy's preHandler.

Digging through code I did found a custom body-parser, which I believe disables parsing.

// Code from index.js
fastify.addContentTypeParser('application/json', bodyParser)
fastify.addContentTypeParser('*', bodyParser)

function bodyParser (req, done) {
    done(null, req)
  }

After disabling (commenting out) contentTypeParser the preHandler is working as expected (the body is parsed and accessible).

Is that the expected behavior and if so are there any workarounds?

Your Environment

• node version: 12.16.1
• fastify version: 2.12.1
• os: Linux