"Generator raised StopIteration" error when sending static file from filesystem

[ned-pcs]

I really like Microdot (which greatly resembles Sinatra, which I've used a lot in Ruby).

I'm using the latest version of Microdot-asyncio on an ESP32.
I would like to pre-compile my static files into frozen strings (and use pkg_resources.resource_stream('static', 'filename')).
I've tried both that method (which returns an io.BytesIO object), and serving these files from my filesystem.
I've tried returning an opened file handle in the Response, as well as using send_file().
In all of the above cases, what I get is a RuntimeError: generator raised StopIteration exception:

Send file /lib/static/js/toast.js
Response header {'Content-Type': 'application/javascript', 'Cache-Control': 'max-age=86400'}
Traceback (most recent call last):
  File "uasyncio/core.py", line 1, in run_until_complete
  File "microdot/microdot_asyncio.py", line 269, in serve
  File "microdot/microdot_asyncio.py", line 337, in handle_request
  File "microdot/microdot_asyncio.py", line 155, in write
RuntimeError: generator raised StopIteration

Templates (using utemplate) and static strings work fine in the Responses.

Here's how I'm trying to return an opened file:

f = open(filename, 'rb')
return Response(body=f, status_code=status_code, headers=response_header)

Using send_file():

return send_file(filename, status_code=status_code, content_type=content_type)

Sending from compiled resources:

f = pkg_resources.resource_stream('static', fname)
return Response(body=f, status_code=status_code, headers=response_header)

or sending from compiled resources using send_file():

f = pkg_resources.resource_stream('static', fname)
return send_file(filename, status_code=status_code, content_type=content_type, stream=f)

Any suggestions?

[miguelgrinberg]

I believe this is a bug in the async version of Microdot's send_file function. I will look into it and provide a fix soon.

[ned-pcs]

I've also seen this error without using send_file, if that helps.

[miguelgrinberg]

How do you import the send_file function? Could you be importing it from microdot instead of microdot_asyncio? I've found that I've made a mistake in an import on the static_async.py example in this repository, so I'm wondering if maybe you based your code on it.

[ned-pcs]

I was importing it from microdot_asyncio. I've updated my code since then, and am no longer using send_file. It's possible I was running into another problem, though; as I've re-written chunks of the static-file sending code the issue has gone away.
Here's what I came up with for a generic static file serving routine, which so far is working for me (you're welcome to use it):

import pkg_resources, os
from microdot_asyncio import Response

def path_exists(path):
    try:
        _ = os.stat(path)
        return True
    except OSError:
        return False

def response_for_file(filename: str, allow_gz: bool = False) -> Response:
    """
    Return the Response object for a static file.
    Static files are either served from the /lib/static/<filetype> directory,
    or from pre-compiled strings using pkg_resources in the 'static' namespace.
    Assumes static files are separated into directories based on their extension.

    :param      filename:  The filename
    :type       filename:  str

    :param      allow_gz:  Whether to allow gzipped files to be served.
    :type       allow_gz:  bool

    :returns:   The response for the file.
    :rtype:     Response
    """
    if '..' in filename:
        return Response(body='Not found', status_code=404, headers={}, reason='Directory traversal is not allowed')

    # split the filename into parts, and get the extension
    ext = filename.split('.')[-1]
    # get the content-type for the extension
    content_type = Response.types_map.get(ext, 'application/octet-stream')
    headers = {}
    headers['Content-Type'] = content_type
    headers['Cache-Control'] = 'max-age=86400'
    static_path = f"/lib/static/{ext}/{filename}"
    if allow_gz:
        zipped = static_path + '.gz'
        if path_exists(zipped):
            headers['Content-Encoding'] = 'gzip'
            return Response(body = open(zipped, 'rb'), status_code=200, headers=headers)
    elif path_exists(static_path):
        return Response(body = open(static_path, 'rb'), status_code=200, headers=headers)
    try:
        f = pkg_resources.resource_stream('static', f"{ext}/{filename}")
        return Response(body = f, status_code=200, headers=headers)
    except KeyError:
        return Response(body='File not found', status_code=404)

I am trying to freeze everything into flash, using utemplate_util.py for the utemplate templates, and using mpy_bin2res.py for the other static content.