API issue: API sends back empty data

Hi Jeroen, while we have received reports of issues with add-apt-repository in the past 24 hours or so, the API URL for the team is https://api.launchpad.net/1.0/~strukturag (notice the ~ character before the team name). Can you elaborate where you saw this incorrect URL?

Hi! I did not see the incorrect URL in the logs since it was not there, the error that I did have was:

```
Traceback (most recent call last):
  File "/usr/bin/add-apt-repository", line 137, in <module>
    shortcut = shortcut_handler(line)
  File "/usr/lib/python3/dist-packages/softwareproperties/SoftwareProperties.py", line 885, in shortcut_handler
    ret = factory(shortcut)
  File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 469, in shortcut_handler
    return PPAShortcutHandler(shortcut)
  File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 426, in __init__
    info = get_ppa_info(self.shortcut)
  File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 392, in get_ppa_info
    _get_suggested_ppa_message(user, ppa))
  File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 349, in _get_suggested_ppa_message
    lp_user = get_info_from_lp(LAUNCHPAD_USER_API % user)
  File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 104, in get_info_from_lp
    return get_info_from_https(lp_url, True)
  File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 98, in get_info_from_https
    return json.loads(data)
  File "/usr/lib/python3.8/json/__init__.py", line 357, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python3.8/json/decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.8/json/decoder.py", line 355, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)
```

So I looked up the line, checked what it was doing, reconstructed the URL and then tried to go there with the browser, that's how I ended up with that URL, when I visited the URL I saw a response that would go with the JSON error, so I assumed I had the URL correct.

I will do some more tests to see what the URL is that it actually makes.

Yep, you're right, it looks like this was just a red herring, it does indeed correctly build that URL (https://launchpad.net/api/1.0/~strukturag), it looks like this exception swallows the actual error from "get_ppa_info".

I can only reproduce this in our CI environment, so I'll try to figure out how to debug that.

Ok so sometimes the API just returns an empty body it seems:

URL: https://launchpad.net/api/devel/~strukturag/+archive/ubuntu/libde265
Status Code: 200
Body: b''

Request Headers:
{'Accept': 'application/json'}

Response Headers:
[('Date', 'Fri, 13 Oct 2023 11:39:11 GMT'), ('Server', 'gunicorn'), ('Content-Type', 'application/json'), ('x-powered-by', 'Zope (www.zope.org), Python (www.python.org)'), ('Content-Length', '0'), ('content-security-policy', "frame-ancestors 'self';"), ('ETag', '"8d97a612cce8d1f79bfeb337dcbc9df891a362e9-d436ad11fd487e0f0b3cf2d1063add1f6491f60c"'), ('strict-transport-security', 'max-age=15552000'), ('Vary', 'Accept'), ('x-content-type-options', 'nosniff'), ('x-frame-options', 'SAMEORIGIN'), ('x-launchpad-revision', 'bd6cfd0cfc024dbe1dcd7d5d91165fb4f6a6c596'), ('x-lazr-notifications', '[]'), ('x-xss-protection', '1; mode=block'), ('x-vcs-revision', 'bd6cfd0cfc024dbe1dcd7d5d91165fb4f6a6c596'), ('x-request-id', '8b5e07ab-2f2e-4631-bbd6-4609aa239602'), ('Age', '280'), ('X-Cache', 'HIT from juju-98d295-prod-launchpad-29'), ('X-Cache-Lookup', 'HIT from juju-98d295-prod-launchpad-29:3128'), ('Via', '1.1 juju-98d295-prod-launchpad-29 (squid/4.10)'), ('Connection', 'close')]

I've also seen errors from apt-add-repository, starting about a week ago. It's particularly bad in Github Actions. Last Thursday it was reproducible from my laptop, but I didn't think to collect details. I will try to do so today.

So far, I cannot reproduce this locally - only from Github Actions. Maybe a new source-based rate limit has been deployed?

For the past few hours, my laptop has been running a loop that does `apt-add-repository` in a fresh ubuntu 22.04 container. So far, I've seen zero failures.

But during that same time, team members have seen multiple failures of the exact same thing in Github Actions.

See bug 2039251, where I've been debugging this.

This should be fixed now.