How to pipe Writable Buffer to a ReadStream?

How can I take a writable stream and return a readable stream from a buffer?

I have the following to write the data that comes from an ftp server to an array of chunks:

let chunks = []let writable = new Writablewritable._write = (chunk, encoding, callback) => {  chunks.push(chunk)  callback()}

I am then creating a new readstream:

let readable = new ReadStream()

I then tried to pipe the writable to the readable but that doesn't seem to work:

Argument of type 'ReadStream' is not assignable to parameter of type 'WritableStream'.

writable.pipe(readable)

Here is the entire method:

export class FTP {  readStream(filePath, options = {}) {    let conn = this.getConnection(this.name)    if (!conn) return Buffer.from('')    filePath = this.forceRoot(filePath)     let chunks = []    let writable = new Writable    writable._write = (chunk, encoding, callback) => {      chunks.push(chunk)      callback()    }    let readable = new ReadStream()    conn.client.download(writable, filePath, options.start || undefined)    writable.pipe(readable)    return readable  }}

I then read from the stream and pipe the output to the response object created from http.createServer() like this:

      let stream = store.readStream(file, { start, end })        .on('open', () => stream.pipe(res))        .on('close', () => res.end())        .on('error', err => res.end(err))