Transfer files directly from one SFTP server to another?

Question

I have files within directories that needs to be transferred from one SFTP server to another. Common ways I have found are to download the files from server 1 and then transfer them to server 2. My goal is to automate the transfer using serverless GCP cloud functions with Python. Any suggestions will be helpful.

I have tried using the popular Paramiko library, but it fails to authenticate. Python's asyncssh library seems to connect to the servers. But I cannot figure out a way to transfer the files with the same directory format.

Edit: Here is the current implementation. Where we establish a connection with the SFTP server, downloads the files to GCP Cloud storage.

import asyncio
import asyncssh
import stat
from flask import jsonify, make_response
import functions_framework
from google.cloud import storage

async def download_files(server_url, username, private_key_path, remote_path, bucket_name):
    storage_client = storage.Client()
    bucket = storage_client.bucket(bucket_name)
    downloaded_files = []

    async with asyncssh.connect(
        server_url, username=username, client_keys=[private_key_path], known_hosts=None
    ) as conn:
        async with conn.start_sftp_client() as sftp:
            await recursive_download(sftp, remote_path, bucket, downloaded_files)

    return downloaded_files

async def recursive_download(sftp, remote_path, bucket, downloaded_files):
    for filename in await sftp.listdir(remote_path):
        remote_file = remote_path + "/" + filename
        attrs = await sftp.stat(remote_file)
        if stat.S_ISREG(attrs.permissions):  

            async with sftp.open(remote_file) as remote_file_obj:
                file_data = await remote_file_obj.read()


            blob = bucket.blob(remote_file)


            blob.upload_from_string(file_data)

            print(f"Downloaded {remote_file}")
            downloaded_files.append(remote_file)
        elif stat.S_ISDIR(attrs.permissions):  
            await recursive_download(sftp, remote_file, bucket, downloaded_files)
            



@functions_framework.http
def main(request):
    try:
        server_url = "your_server_url"
        username = "your_username"
        private_key_path = "your_private_key_path"
        remote_path = "your_remote_path"
        bucket_name = "your_bucket_name" 

        downloaded_files = asyncio.run(download_files(server_url, username, private_key_path, remote_path, bucket_name))

        return make_response(jsonify({"message": f"Files downloaded successfully. Total files: {len(downloaded_files)}. Files: {downloaded_files}"}), 200)
    except Exception as e:
        return make_response(jsonify({"error": str(e)}), 500)

The code works but feels very complicated for the logic I want to implement next. Such as download the files and sub-directories of the specified remote path.