id,node_id,number,title,user,user_label,state,locked,assignee,assignee_label,milestone,milestone_label,comments,created_at,updated_at,closed_at,author_association,pull_request,body,repo,repo_label,type,active_lock_reason,performed_via_github_app,reactions,draft,state_reason
870125126,MDU6SXNzdWU4NzAxMjUxMjY=,1310,I'm creating a plugin to export a spreadsheet file (.ods or .xlsx),3747136,ColinMaudry,closed,0,,,,,2,2021-04-28T16:20:11Z,2021-04-30T07:26:11Z,2021-04-30T06:58:46Z,NONE,,"Hi,

I have started developing a plugin to export records as a spreadsheet file. It could be ods or xlsx, whatever is easier.

I have spotted the following packages:

- ods files: https://pypi.org/project/odswriter/
- xlsx files: https://openpyxl.readthedocs.io/en/stable/index.html (quite powerful) or https://xlsxwriter.readthedocs.io/ (faster)

This is the code I have so far, I test it with the `--plugins-dir` option:

```python
from datasette import hookimpl
from datasette.utils.asgi import Response
import odswriter as ods

def render_spreadsheet(rows):
    with ods.writer(open(""test.ods"",""wb"")) as odsfile:
        for row in rows:
            odsfile.writerow([""String"", ""ABCDEF123456"", ""123456""])
        return Response(odsfile, content_type=""application/vnd.oasis.opendocument.spreadsheet"", status=200)


@hookimpl
def register_output_renderer():
    return {""extension"": ""ods"", ""render"": render_spreadsheet}

``` 

I get the following error:

```
Traceback (most recent call last):
  File ""/home/colin/.local/lib/python3.8/site-packages/datasette/app.py"", line 1128, in route_path
    await response.asgi_send(send)
  File ""/home/colin/.local/lib/python3.8/site-packages/datasette/utils/asgi.py"", line 339, in asgi_send
    body = body.encode(""utf-8"")
AttributeError: 'ODSWriter' object has no attribute 'encode'
ERROR:    Exception in ASGI application
Traceback (most recent call last):
  File ""/home/colin/.local/lib/python3.8/site-packages/datasette/app.py"", line 1128, in route_path
    await response.asgi_send(send)
  File ""/home/colin/.local/lib/python3.8/site-packages/datasette/utils/asgi.py"", line 339, in asgi_send
    body = body.encode(""utf-8"")
AttributeError: 'ODSWriter' object has no attribute 'encode'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File ""/home/colin/.local/lib/python3.8/site-packages/uvicorn/protocols/http/h11_impl.py"", line 396, in run_asgi
    result = await app(self.scope, self.receive, self.send)
  File ""/home/colin/.local/lib/python3.8/site-packages/uvicorn/middleware/proxy_headers.py"", line 45, in __call__
    return await self.app(scope, receive, send)
  File ""/home/colin/.local/lib/python3.8/site-packages/datasette/utils/asgi.py"", line 161, in __call__
    await self.app(scope, receive, send)
  File ""/home/colin/.local/lib/python3.8/site-packages/datasette/tracer.py"", line 75, in __call__
    await self.app(scope, receive, send)
  File ""/home/colin/.local/lib/python3.8/site-packages/asgi_csrf.py"", line 107, in app_wrapped_with_csrf
    await app(scope, receive, wrapped_send)
  File ""/home/colin/.local/lib/python3.8/site-packages/datasette/app.py"", line 1086, in __call__
    return await self.route_path(scope, receive, send, path)
  File ""/home/colin/.local/lib/python3.8/site-packages/datasette/app.py"", line 1133, in route_path
    return await self.handle_500(request, send, exception)
  File ""/home/colin/.local/lib/python3.8/site-packages/datasette/app.py"", line 1267, in handle_500
    await asgi_send_html(
  File ""/home/colin/.local/lib/python3.8/site-packages/datasette/utils/asgi.py"", line 217, in asgi_send_html
    await asgi_send(
  File ""/home/colin/.local/lib/python3.8/site-packages/datasette/utils/asgi.py"", line 237, in asgi_send
    await asgi_start(send, status, headers, content_type)
  File ""/home/colin/.local/lib/python3.8/site-packages/datasette/utils/asgi.py"", line 246, in asgi_start
    await send(
  File ""/home/colin/.local/lib/python3.8/site-packages/asgi_csrf.py"", line 103, in wrapped_send
    await send(event)
  File ""/home/colin/.local/lib/python3.8/site-packages/uvicorn/protocols/http/h11_impl.py"", line 482, in send
    raise RuntimeError(msg % message_type)
RuntimeError: Expected ASGI message 'http.response.body', but got 'http.response.start'.
```

I tried with `AsgiFileDownload` like in [DatabaseDownload](https://github.com/simonw/datasette/blob/main/datasette/views/database.py#L150) to deal with the binary nature of the ods file, but the renderer expects a Response:

> <datasette.utils.asgi.AsgiFileDownload object at 0x7f5b9bd503d0> should be dict or Response

However, the `Response` class only supports the following methods, not binary:

- html
- text
- json
- redirect

How would you suggest me to proceed to have my ods file downloaded?

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