[#1011] Fix a 500 to a 404

Catch Genshi TemplateNotFound errors when rendering the package read
page. This can happen if an IDatasetForm plugin returns a custom package
read template, e.g. 'read.html', but the user has requested the dataset
in RDF format and the plugin does not provide a corresponding 'read.rdf'
template. (CKAN will take the path to read.html, replace the filename
extension with rdf, try to render this non-existing template file, and
crash.)

Replace this crash with a proper 404.

Add to the IDatasetForm docs, explaining how to provide RDF templates
for datasets.

Fixes #1011.

ckan/controllers/package.py

@@ -5,6 +5,7 @@
 from pylons import config
 from genshi.template import MarkupTemplate
 from genshi.template.text import NewTextTemplate
+import genshi.template.loader
 from paste.deploy.converters import asbool
 
 import ckan.logic as logic
@@ -352,7 +353,15 @@ def read(self, id, format='html'):
         template = self._read_template(package_type)
         template = template[:template.index('.') + 1] + format
 
-        return render(template, loader_class=loader)
+        try:
+            return render(template, loader_class=loader)
+        except genshi.template.loader.TemplateNotFound:
+            msg = _("Viewing {package_type} datasets in {format} format is "
+                    "not supported (template file {file} not found).".format(
+                    package_type=package_type, format=format, file=template))
+            abort(404, msg)
+
+        assert False, "We should never get here"
 
     def history(self, id):
         package_type = self._get_package_type(id.split('@')[0])

ckan/plugins/interfaces.py

@@ -676,6 +676,15 @@ def read_template(self):
         The path should be relative to the plugin's templates dir, e.g.
         ``'package/read.html'``.
 
+        If the user requests the dataset in a format other than HTML
+        (CKAN supports returning datasets in RDF or N3 format by appending .rdf
+        or .n3 to the dataset read URL, see :doc:`linked-data-and-rdf`) then
+        CKAN will try to render
+        a template file with the same path as returned by this function,
+        but a different filename extension, e.g. ``'package/read.rdf'``.
+        If your extension doesn't have this RDF version of the template
+        file, the user will get a 404 error.
+
         :rtype: string
 
         '''