File: Should Ghostscript go astray, our fallback saves the day.

TYPE: Bugfix
LINK: OGC-1911

src/onegov/file/filters.py

@@ -1,9 +1,13 @@
+import os
 import shlex
+import logging
 import subprocess
 
 from depot.fields.interfaces import FileFilter
 from depot.io.utils import file_from_content
 from io import BytesIO
+
+from onegov.core.utils import module_path
 from onegov.file.utils import IMAGE_MIME_TYPES, get_image_size
 from pathlib import Path
 from PIL import Image
@@ -16,6 +20,9 @@
     from depot.fields.upload import UploadedFile
 
 
+log = logging.getLogger('onegov.file')
+
+
 class ConditionalFilter(FileFilter):
     """ A depot filter that's only run if a condition is met. The condition
     is defined by overriding the :meth:``meets_condition`` returns True.
@@ -192,4 +199,17 @@ def generate_thumbnail(
         # FIXME: This is kinda slow. We should be able to render the
         #        PDF directly at the thumbnail size. Maybe we should
         #        use pdf2image rather than roll our own?
-        return super().generate_thumbnail(self.generate_preview(fp))
+        try:
+            return super().generate_thumbnail(self.generate_preview(fp))
+        except Exception as e:
+            log.warning(f'Thumbnail generation failed: {e!s}')
+            fallback = BytesIO()
+            icon_path = (
+                    module_path('onegov.org', 'static/pdf_preview')
+                    + os.sep
+                    + 'thumbnail_medium_pdf_preview_fallback.png'
+            )
+            with open(icon_path, 'rb') as f:
+                fallback.write(f.read())
+            fallback.seek(0)
+            return super().generate_thumbnail(fallback)

tests/onegov/file/conftest.py

@@ -1,5 +1,4 @@
 import pytest
-
 from depot.manager import DepotManager
 
 

tests/onegov/file/test_models.py

@@ -1,3 +1,5 @@
+import os
+
 import sedate
 import transaction
 import pytest
@@ -8,6 +10,7 @@
 from onegov.core.orm.abstract import associated
 from onegov.core.utils import module_path
 from onegov.file import File, FileSet, AssociatedFiles, NamedFile
+from onegov.file.filters import WithPDFThumbnailFilter
 from onegov.file.models.fileset import file_to_set_associations
 from tests.shared.utils import create_image
 from pathlib import Path
@@ -193,7 +196,7 @@ def test_pdf_preview_creation(session):
     transaction.commit()
 
     pdf = session.query(File).one()
-    pdf.reference['thumbnail_medium']
+    assert pdf.reference.get('thumbnail_medium', None) is not None
 
     # our example file contains a blue backgorund so we can verify that
     # the thumbnail for the pdf is generated correctly
@@ -212,6 +215,41 @@ def test_pdf_preview_creation(session):
     assert w in (362, 396)
 
 
+def test_pdf_preview_creation_with_erroneous_pdf(session, monkeypatch):
+    # There was a pdf which made ghostscript fail with stderr: "circular
+    # reference to indirect object".
+    # However, we can't upload the original pdf due to sensitive information.
+    # So we have to kind of mock the error here.
+    mock = Mock(side_effect=ValueError)
+    monkeypatch.setattr(
+        WithPDFThumbnailFilter,
+        'generate_preview',
+       mock
+    )
+
+    filname = 'example.pdf'
+    path = module_path('tests.onegov.file', f'fixtures/{filname}')
+
+    with open(path, 'rb') as f:
+        session.add(File(name=f'{filname}', reference=f))
+    transaction.commit()
+    pdf = session.query(File).one()
+    assert pdf.reference.get('thumbnail_medium', None) is not None
+    thumb = DepotManager.get().get(pdf.reference['thumbnail_medium']['id'])
+
+    # expect to be the default one
+
+    thumbnail_medium_pdf_preview_fallback = BytesIO(
+        Path(
+            module_path('onegov.org', 'static/pdf_preview')
+            + os.sep
+            + 'thumbnail_medium_pdf_preview_fallback.png'
+        ).read_bytes()
+    )
+
+    assert thumb.read() == thumbnail_medium_pdf_preview_fallback.read()
+
+
 def test_max_image_size(session):
     session.add(File(name='unchanged.png', reference=create_image(2048, 2048)))
     session.add(File(name='limited.png', reference=create_image(2049, 2048)))