click on album in local library results in request for core.library.lookup with "uris": ["undefined"]

[mfremont]

Steps:

1. Browse the local library, navigate to a folder for a specific album
2. Click the table row with the album title and image

Result:

1. The web client displays the notice, "Loading data from Mopidy on hostname. Please wait..."
2. The web client makes a request for core.library.lookup with the "uris" param value["undefined]
3. Mopidy responds with "Application error" and the detail message, "Expected a list of URIs not u'undefined'"

Request:

{"method":"core.library.lookup","params":{"uris":["undefined"]},"jsonrpc":"2.0","id":32}

Response:

{
   "error": {
     "code": 0,
     "data": {
       "message": "Expected a list of URIs, not u'undefined'",
       "traceback": "Traceback (most recent call last):\n  File \"/home/mrf/.local/lib/python2.7/site-packages/mopidy/internal/jsonrpc.py\", line 133, in _handle_single_request\n    result = self._unwrap_result(result)\n  File \"/home/mrf/.local/lib/python2.7/site-packages/mopidy/internal/jsonrpc.py\", line 222, in _unwrap_result\n    result = result.get()\n  File \"/home/mrf/.local/lib/python2.7/site-packages/pykka/threading.py\", line 52, in get\n    compat.reraise(*self._data['exc_info'])\n  File \"/home/mrf/.local/lib/python2.7/site-packages/pykka/compat.py\", line 12, in reraise\n    exec('raise tp, value, tb')\n  File \"/home/mrf/.local/lib/python2.7/site-packages/pykka/actor.py\", line 201, in _actor_loop\n    response = self._handle_receive(message)\n  File \"/home/mrf/.local/lib/python2.7/site-packages/pykka/actor.py\", line 295, in _handle_receive\n    return callee(*message['args'], **message['kwargs'])\n  File \"/home/mrf/.local/lib/python2.7/site-packages/mopidy/core/library.py\", line 217, in lookup\n    uris is None or validation.check_uris(uris)\n  File \"/home/mrf/.local/lib/python2.7/site-packages/mopidy/internal/validation.py\", line 105, in check_uris\n    [check_uri(a, msg) for a in arg]\n  File \"/home/mrf/.local/lib/python2.7/site-packages/mopidy/internal/validation.py\", line 100, in check_uri\n    raise exceptions.ValidationError(msg.format(arg=arg))\nValidationError: Expected a list of URIs, not u'undefined'\n",
       "type": "ValidationError"
     },
     "message": "Application error"
   },
   "id": 32,
   "jsonrpc": "2.0"
 }

Additional details and software versions:

BeetsLocal plugin is being used to access the local library.

Mopidy (2.1.0)
Mopidy-BeetsLocal (0.0.9)
Mopidy-MusicBox-Webclient (2.4.0)
Python 2.7.13
Lubuntu 16.04

[jcass77]

Does this error also occur when browsing using the standard Mopidy ‘File’ or ‘Local Media’ backend extensions?

I don’t have the BeetsLocal extension installed but suspect that might be where the issue is originating from.

[mfremont]

I re-enabled File, Local, and Local SQLite, and then performed a fresh local scan.

With Local SQLite, I can click through the row with the album title in this view:

then the web UI successfully displays an album view:

However, with the File backend, this same sequence instead leaves me with a view like this:

With the File backend, the UI makes a JSON RPC request like the example above, with "params": {"uris": ["undefined"]}.

The backend responds with an application error:

{
  "jsonrpc": "2.0",
  "id": 25,
  "error": {
    "message": "Application error",
    "code": 0,
    "data": {
      "message": "Expected a list of URIs, not u'undefined'",
      "traceback": "Traceback (most recent call last):\n  File \"/usr/lib/python2.7/dist-packages/mopidy/internal/jsonrpc.py\", line 133, in _handle_single_request\n    result = self._unwrap_result(result)\n  File \"/usr/lib/python2.7/dist-packages/mopidy/internal/jsonrpc.py\", line 222, in _unwrap_result\n    result = result.get()\n  File \"/usr/lib/python2.7/dist-packages/pykka/threading.py\", line 52, in get\n    compat.reraise(*self._data['exc_info'])\n  File \"/usr/lib/python2.7/dist-packages/pykka/compat.py\", line 12, in reraise\n    exec('raise tp, value, tb')\n  File \"/usr/lib/python2.7/dist-packages/pykka/actor.py\", line 201, in _actor_loop\n    response = self._handle_receive(message)\n  File \"/usr/lib/python2.7/dist-packages/pykka/actor.py\", line 295, in _handle_receive\n    return callee(*message['args'], **message['kwargs'])\n  File \"/usr/lib/python2.7/dist-packages/mopidy/core/library.py\", line 217, in lookup\n    uris is None or validation.check_uris(uris)\n  File \"/usr/lib/python2.7/dist-packages/mopidy/internal/validation.py\", line 105, in check_uris\n    [check_uri(a, msg) for a in arg]\n  File \"/usr/lib/python2.7/dist-packages/mopidy/internal/validation.py\", line 100, in check_uri\n    raise exceptions.ValidationError(msg.format(arg=arg))\nValidationError: Expected a list of URIs, not u'undefined'\n",
      "type": "ValidationError"
    }
  }
}

undefined does not appear in the previous request/response pairs, so it's not simply a matter of the backend returning a URI of "undefined".

When I take a closer look at the JSON RPC request/response pairs that precede the error, what jumps out is that the Local SQLite backend responds to a lookup request for a track with a album object that contains a uri property for the album:

{
  "method": "core.library.lookup",
  "params": {
    "uris": [
      "local:track:Black%20Star/Mos%20Def%20%26%20Talib%20Kweli%20Are%20Black%20Star/01%20Intro.flac"
    ]
  },
  "jsonrpc": "2.0",
  "id": 24
}

{
  "jsonrpc": "2.0",
  "id": 24,
  "result": {
    "local:track:Black%20Star/Mos%20Def%20%26%20Talib%20Kweli%20Are%20Black%20Star/01%20Intro.flac": [
      {
        "album": {
          "__model__": "Album",
          "name": "Mos Def & Talib Kweli Are Black Star",
          "num_tracks": 13,
          "uri": "local:album:mbid:66df81d2-9787-3838-85fa-fa0de57990f3",
          "artists": [
            {
              "__model__": "Artist",
              "musicbrainz_id": "02708fd6-0fe6-4738-a27d-0561ace8b4c6",
              "name": "Black Star",
              "uri": "local:artist:md5:99d00d9ec7ef29ad8994a8a89468357d"
            }
          ],
          "date": "2002-06-04",
          "musicbrainz_id": "66df81d2-9787-3838-85fa-fa0de57990f3",
          "num_discs": 1
        },
        "composers": [
          {
            "__model__": "Artist",
            "name": "Mos Def",
            "uri": "local:artist:md5:de41d6c37ecd7fdbb01cdcafeb0dbc16"
          }
        ],
        "__model__": "Track",
        "name": "Intro",
        "disc_no": 1,
        "uri": "local:track:Black%20Star/Mos%20Def%20%26%20Talib%20Kweli%20Are%20Black%20Star/01%20Intro.flac",
        "date": "2002-06-04",
        "length": 71880,
        "last_modified": 1509589770651,
        "track_no": 1,
        "artists": [
          {
            "__model__": "Artist",
            "musicbrainz_id": "02708fd6-0fe6-4738-a27d-0561ace8b4c6",
            "name": "Black Star",
            "uri": "local:artist:md5:99d00d9ec7ef29ad8994a8a89468357d"
          }
        ],
        "genre": "Rap",
        "musicbrainz_id": "d342f41f-d995-4185-92bc-4c2db314e5c5"
      }
    ]
  }
}

whereas the album URI is not present in the File backend response:

{
  "method": "core.library.lookup",
  "params": {
    "uris": [
      "file:///media/Music/Library/Black%20Star/Mos%20Def%20%26%20Talib%20Kweli%20Are%20Black%20Star/01%20Intro.flac"
    ]
  },
  "jsonrpc": "2.0",
  "id": 36
}

{
  "jsonrpc": "2.0",
  "id": 36,
  "result": {
    "file:///media/Music/Library/Black%20Star/Mos%20Def%20%26%20Talib%20Kweli%20Are%20Black%20Star/01%20Intro.flac": [
      {
        "album": {
          "__model__": "Album",
          "name": "Mos Def & Talib Kweli Are Black Star",
          "num_tracks": 13,
          "artists": [
            {
              "__model__": "Artist",
              "musicbrainz_id": "02708fd6-0fe6-4738-a27d-0561ace8b4c6",
              "name": "Black Star"
            }
          ],
          "date": "2002-06-04",
          "musicbrainz_id": "66df81d2-9787-3838-85fa-fa0de57990f3",
          "num_discs": 1
        },
        "composers": [
          {
            "__model__": "Artist",
            "name": "Mos Def"
          }
        ],
        "__model__": "Track",
        "name": "Intro",
        "disc_no": 1,
        "uri": "file:///media/Music/Library/Black%20Star/Mos%20Def%20%26%20Talib%20Kweli%20Are%20Black%20Star/01%20Intro.flac",
        "date": "2002-06-04",
        "length": 71880,
        "track_no": 1,
        "artists": [
          {
            "__model__": "Artist",
            "musicbrainz_id": "02708fd6-0fe6-4738-a27d-0561ace8b4c6",
            "name": "Black Star"
          }
        ],
        "genre": "Rap",
        "musicbrainz_id": "d342f41f-d995-4185-92bc-4c2db314e5c5"
      }
    ]
  }
}

It appears that the issue is triggered when the backend responds to a track lookup with an embedded album object that does not include a uri property. It's not clear to me from the Mopidy API documentation whether uri can be expected to be present and non-empty. But even if the backend is returning an incomplete object, i.e. a backend bug, should it also be the responsibility of the UI to not make a malformed request such as "params": ["undefined"] if the uri property is missing?