API returns 500 error when combining title and author parameters

[mtibke]

The audiobooks API endpoint returns a 500 Internal Server Error when both title and author parameters are provided together.

Steps to Reproduce

Works (title only):
curl "https://librivox.org/api/feed/audiobooks?format=json&title=Adventskalender+2023"

Returns 200 with correct data

Fails (title + author):
curl "https://librivox.org/api/feed/audiobooks?format=json&title=Adventskalender+2023&author=Various"

Returns 500 Internal Server Error

Suspected Cause

In application/libraries/Librivox_API.php, the function _build_author_project_id_list() returns 0 (integer) when no matching author is found:

return (empty($project_ids)) ? 0 : $project_ids;

This value is then passed to where_in():
$this->db->where_in('p.id', $project_id_list);

CodeIgniter's where_in() expects an array, not an integer, which may cause the error.

Suggested Fix

return (empty($project_ids)) ? [] : $project_ids;
And add a check in _build_data_set() to skip the where_in clause if the array is empty.

[redrun45]

Thank you for digging into this! We'll need to check that it really does work as expected after that code change - for example, I'm not sure why there wouldn't be an author found - but this is a solid lead, and I for one appreciate the detail. 👍

[notartom]

This looks like a good candidate for a reproducer test patch. I strongly suspect we can demonstrate the bug in a test, assert we get the 500, and then follow that up with a patch that both fixes the bug, and adjusts the test to assert the correct behaviour. It might be possible to avoid "manual" work and do this entirely in CI :)