Add informational message for failed loading of nn-ensemble model

annif/backend/nn_ensemble.py

@@ -21,7 +21,11 @@
 import annif.corpus
 import annif.parallel
 import annif.util
-from annif.exception import NotInitializedException, NotSupportedException
+from annif.exception import (
+    NotInitializedException,
+    NotSupportedException,
+    OperationFailedException,
+)
 from annif.suggestion import SuggestionBatch, vector_to_suggestions
 
 from . import backend, ensemble
@@ -129,9 +133,14 @@ def initialize(self, parallel: bool = False) -> None:
                 backend_id=self.backend_id,
             )
         self.debug("loading Keras model from {}".format(model_filename))
-        self._model = load_model(
-            model_filename, custom_objects={"MeanLayer": MeanLayer}
-        )
+        try:
+            self._model = load_model(
+                model_filename, custom_objects={"MeanLayer": MeanLayer}
+            )
+        except ValueError:
+            md = annif.util.get_keras_model_metadata(model_filename)
+            message = f"loading model from {model_filename}; model metadata: {md}"
+            raise OperationFailedException(message, backend_id=self.backend_id)
 
     def _merge_source_batches(
         self,

annif/util.py

@@ -3,10 +3,12 @@
 from __future__ import annotations
 
 import glob
+import json
 import logging
 import os
 import os.path
 import tempfile
+import zipfile
 from typing import Any, Callable
 
 from annif import logger
@@ -50,6 +52,18 @@ def atomic_save(
         os.rename(fn, newname)
 
 
+def get_keras_model_metadata(model_file_path: str) -> dict:
+    """Read metadata from Keras model files."""
+    try:
+        with zipfile.ZipFile(model_file_path, "r") as zip:
+            with zip.open("metadata.json") as metadata_file:
+                metadata_str = metadata_file.read().decode("utf-8")
+                metadata = json.loads(metadata_str)
+                return metadata
+    except Exception:
+        return dict()
+
+
 def cleanup_uri(uri: str) -> str:
     """remove angle brackets from a URI, if any"""
     if uri.startswith("<") and uri.endswith(">"):

tests/test_util.py

@@ -17,3 +17,9 @@ def test_metric_code():
 
     for input, output in zip(inputs, outputs):
         assert annif.util.metric_code(input) == output
+
+
+def test_get_keras_model_metadata():
+    model_file_path = "tests/dummy-nn-model.keras"  # nn-ensemble-model.zip"
+    expected_md = {"keras_version": "xx.yy.zz", "date_saved": "2024-04-11@01:01:01"}
+    assert annif.util.get_keras_model_metadata(model_file_path) == expected_md