add endpoint for getting student signature images

zesje/api.py

@@ -6,6 +6,7 @@ from .resources.exams import Exams, ExamConfig
 from .resources.pdfs import Pdfs
 from .resources.students import Students
 from .resources.submissions import Submissions
+from .resources import signature
 
 api_bp = Blueprint(__name__, __name__)
 
@@ -26,3 +27,12 @@ api.add_resource(Students, '/students')
 api.add_resource(Submissions,
                  '/submissions/<int:exam_id>',
                  '/submissions/<int:exam_id>/<int:submission_id>')
+
+# Other resources that don't return JSON
+# It is possible to get flask_restful to work with these, but not
+# very idiomatic.
+api_bp.add_url_rule(
+    '/images/signature/<int:exam_id>/<int:submission_id>',
+    'signature',
+    signature.get,
+)

zesje/resources/signature.py

+from flask import abort, Response
+from pony import orm
+
+from ..helpers import yaml_helper, image_helper
+from ..models import Exam, Submission
+
+
+@orm.db_session
+def get(exam_id, submission_id):
+    """get student signature for the given submission.
+
+    Parameters
+    ----------
+    exam_id : int
+    submission_id : int
+        The copy number of the submission. This uniquely identifies
+        the submission *within a given exam*.
+
+    Returns
+    -------
+    Image (JPEG mimetype)
+    """
+    # We could register an app-global error handler for this,
+    # but it would add more code then it removes.
+    exam = Exam.get(id=exam_id)
+    if not exam:
+        abort(404)
+    sub = Submission.get(exam=exam, copy_number=submission_id)
+    if not sub:
+        abort(404)
+
+    *_, widgets = yaml_helper.parse(yaml_helper.read(sub.exam.yaml_path))
+    first_page = next(p.path for p in sub.pages if 'page1' in p.path)
+    image = image_helper.get_widget_image(first_page,
+                                          widgets.loc['studentnr'])
+
+    return Response(image, 200, mimetype='image/jpeg')

zesje/resources/submissions.py

@@ -13,6 +13,9 @@ class Submissions(Resource):
         Parameters
         ----------
         exam_id : int
+        submission_id : int, optional
+            The copy number of the submission. This uniquely identifies
+            the submission *within a given exam*.
 
         Returns
         -------