Pipe data from Writable to Readable

I am working on getting files from an SFTP server and piping the data to Box.com using their sdk. The Box sdk takes a readable stream as as parameter for uploading a file. The code that I have written to fetch the files from the sftp server uses the npm module ssh2-sftp-client.

The issue I am having is that a writable stream is "the end of the line" with streams unless you are using something like a Transform which is a Duplex and implements both read and write. Below is the code that I am using. Because I am working on this for a client I am intentionally leaving out some stuff that is not necessary.

Below is the method on the sftp class

async getFile(filepath: string): Promise<Readable> {
  logger.info(`Fetching file: ${filepath}`);
  const writable = new Writable();
  const stream = new PassThrough();
  await this.client.get(filepath, writable);
  return writable.pipe(stream);
}

The implementation of getting a file and attempting to pipe to box which is an instance of an authorized BoxSDK client.

try {
  for (const filename of filenames) {
    const stream: Readable = await tmsClient.getFile(
      'redacted' + filename,
    );

    logger.info(`Piping ${filename} to Box...`);
    await box.createFile(filename, 'redacted', stream);
    logger.info(`${filename} successfully downloaded`);
  }
} catch (error) {
  logger.error(`Failed to move files: ${error}`);
}

I am not super well versed in streams but based on my research I think this should work in theory.

I have also tried this implementation where the ssh client returns a buffer and then I try and pipe that buffer as a readable stream. With this implementation though I keep getting errors from the Box sdk that the stream ended unexpectedly.

async getFile(filepath: string): Promise<Readable> {
  logger.info(`Fetching file: ${filepath}`);
  const stream = new Readable();
  const buffer = (await this.client.get(filepath)) as Buffer;
  stream._read = (): void => {
    stream.push(buffer);
    stream.push(null);
  };
  return stream;
}

And the error message: 2020-02-06 15:24:57 error: Failed to move files: Error: Unexpected API Response [400 Bad Request] bad_request - Stream ended unexpectedly.

Any insight is greatly appreciated!