handle graphviz parsing errors more cleanly

incorporealcms/mdx/pydot.py

@@ -1,10 +1,13 @@
 """Serve dot diagrams inline."""
 import base64
+import logging
 import re
 
 import markdown
 import pydot
 
+logger = logging.getLogger(__name__)
+
 
 class InlinePydot(markdown.Extension):
     """Wrap the markdown prepcoressor."""
@@ -29,6 +32,9 @@ class InlinePydotPreprocessor(markdown.preprocessors.Preprocessor):
 
             # use pydot to turn the text into pydot
             graphs = pydot.graph_from_dot_data(dot_string)
+            if not graphs:
+                logger.debug("some kind of issue with parsed 'dot' %s", dot_string)
+                raise ValueError("error parsing dot text!")
 
             # encode the image and provide as an inline image in markdown
             encoded_image = base64.b64encode(graphs[0].create_png()).decode('ascii')

incorporealcms/pages.py

@@ -61,6 +61,9 @@ def handle_markdown_file_path(resolved_path):
         try:
             md = init_md()
             content = Markup(md.convert(entry))
+        except ValueError:
+            logger.exception("error parsing/rendering markdown!")
+            abort(500)
         except TypeError:
             logger.exception("error loading/rendering markdown!")
             abort(500)

tests/functional_markdown_tests.py

@@ -27,3 +27,13 @@ def test_graphviz_is_rendered():
     assert response.status_code == 200
     assert b'~~~pydot' not in response.data
     assert b'data:image/png;base64' in response.data
+
+
+def test_invalid_graphviz_is_not_rendered():
+    """Check that invalid graphviz doesn't blow things up."""
+    app = app_with_pydot()
+    client = app.test_client()
+
+    response = client.get('/test-invalid-graphviz')
+    assert response.status_code == 500
+    assert b'INTERNAL SERVER ERROR' in response.data

tests/instance/pages/test-invalid-graphviz.md

@@ -0,0 +1,11 @@
+# test
+
+test
+~~~pydot:attack-plan
+    rankdir=LR
+    Earth
+    Mars
+    Earth -> Mars
+}
+~~~
+more test