from flask import Response


def (file_path):
    def generate():
        if not os.path.exists(file_path):
            raise "File not found."
        with open(file_path, "rb") as f:
            while True:
                chunk = f.read(chunk_size=10 * 1024 * 1024)
                if not chunk:
                    break
                yield chunk

    return Response(generate(), content_type="application/octet-stream")
```   

執行 Flask app，可以正確下載檔案，但是下載只有實時速度，沒有檔案總大小，導致無法知道下載進度，也沒有檔案型別，這些我們都可以通過增加 header 欄位實現：
```python
response = Response(generate(), mimetype='application/gzip')
response.headers['Content-Disposition'] = 'attachment; filename={}.tar.gz'.format("download_file")
response.headers['content-length'] = os.stat(str(file_path)).st_size
return response
 

from flask import (
    Flask,
    Response,
    stream_with_context
    )
import requests

app = Flask(__name__)

@app.route("/download/<file_path>", method=["GET"])
def (file_path):
    url_prefix = "http://1.1.1.1/"
    remote_url = url_prefix + file_path
    req = requests.get(remote_url, stream = True)
    return Response(stream_with_context(req.iter_content()), 
                    content_type = req.headers['content-type'])

if __name__ == "__main__":
    app.run(host="0.0.0.0", debug=True)
 

def iterable():
    for _ in xrange(10):
        yield b'this is a byte stringx01n'

z = zipstream.ZipFile()
z.write_iter('my_archive_iter', iterable())

with open('zipfile.zip', 'wb') as f:
    for data in z:
        f.write(data)

@app.route("/cluster_download/<file_path>", method=["GET"])
def cluster_download(reqs):
    def generate(req):
        z = zipstream.ZipFile(mode="w", compression=zipstream.ZIP_DEFLATED)
        for req in reqs:
            host = req.raw._fp.fp._sock.getpeername()[0]
            z.write_iter("%s.tar.gz" % host, req.iter_content(chunk_size=10 * 1024 * 1024)
        for chunk in z:
            yield chunk

    def get_file_size(reqs):
        size = 0
        for req in reqs:
            size += int(req.headers.get("content-length"))
        return size

    remote_hosts = ["1.1.1.1", "2.2.2.2"]
    reqs = []
    for host in remote_hosts:
        req = requests.get("http://%s/%s" % (host, file_path), timeout=5, stream=True)
        if req.status_code == 200:
            reqs.append(req)
    response = Response(generate(reqs))
    response.headers['mimetype'] = 'application/zip'
    response.headers['Content-Disposition'] = 'attachment; filename=cluster_logs.zip)
    response.hreads['content-length'] = get_file_size(reqs)

def generate_file(content):
    yield content

z.write_iter("running_status", generate_file)