feat(routing): Allow digits and underscore in compile_uri_template

Allow URI template fields to contain numbers so long as the field name
does not start with a numeral. Example: "test123" is valid, while
"123test" is not.

This patch adds support for this in the legacy template helpers, and also
adds an additional test for these chars for the current router spec.

Co-Authored-By: Kurt Griffiths <mail@kgriffs.com>

falcon/routing/util.py

@@ -65,7 +65,9 @@ def compile_uri_template(template):
     if template != '/' and template.endswith('/'):
         template = template[:-1]
 
-    expression_pattern = r'{([a-zA-Z][a-zA-Z_]*)}'
+    # template names should be able to start with A-Za-z
+    # but also contain 0-9_ in the remaining portion
+    expression_pattern = r'{([a-zA-Z]\w*)}'
 
     # Get a list of field names
     fields = set(re.findall(expression_pattern, template))

tests/test_uri_templates.py

@@ -27,6 +27,18 @@ def on_get(self, req, resp, id, name):
         self.called = True
 
 
+class NameAndDigitResource(object):
+    def __init__(self):
+        self.id = None
+        self.name51 = None
+        self.called = False
+
+    def on_get(self, req, resp, id, name51):
+        self.id = id
+        self.name51 = name51
+        self.called = True
+
+
 class TestUriTemplates(testing.TestBase):
 
     def before(self):
@@ -116,6 +128,20 @@ def test_single(self):
         self.assertNotIn(kwargs, 'Id')
         self.assertEqual(req.get_param('id'), None)
 
+    def test_single_with_trailing_digits(self):
+        self.api.add_route('/widgets/{id12}', self.resource)
+
+        self.simulate_request('/widgets/123')
+        self.assertTrue(self.resource.called)
+        self.assertEqual(self.resource.kwargs['id12'], '123')
+
+    def test_single_with_underscore(self):
+        self.api.add_route('/widgets/{widget_id}', self.resource)
+
+        self.simulate_request('/widgets/123')
+        self.assertTrue(self.resource.called)
+        self.assertEqual(self.resource.kwargs['widget_id'], '123')
+
     def test_single_trailing_slash(self):
         resource1 = IDResource()
         self.api.add_route('/1/{id}/', resource1)
@@ -158,6 +184,19 @@ def test_multiple(self):
         self.assertEqual(resource.id, test_id)
         self.assertEqual(resource.name, test_name)
 
+    def test_multiple_with_digits(self):
+        resource = NameAndDigitResource()
+        self.api.add_route('/messages/{id}/names/{name51}', resource)
+
+        test_id = self.getUniqueString()
+        test_name = self.getUniqueString()
+        path = '/messages/' + test_id + '/names/' + test_name
+        self.simulate_request(path)
+        self.assertTrue(resource.called)
+
+        self.assertEqual(resource.id, test_id)
+        self.assertEqual(resource.name51, test_name)
+
     def test_empty_path_component(self):
         self.assertRaises(ValueError, self.api.add_route,
                           '//', self.resource)

tests/test_uri_templates_legacy.py

@@ -69,15 +69,30 @@ def test_one_field(self):
         self.assertTrue(result)
         self.assertEqual(result.groupdict(), {'name': 'Kelsier'})
 
+    def test_one_field_with_digits(self):
+        fields, pattern = routing.compile_uri_template('/{name123}')
+        self.assertEqual(fields, set(['name123']))
+
+        result = pattern.match('/Kelsier')
+        self.assertTrue(result)
+        self.assertEqual(result.groupdict(), {'name123': 'Kelsier'})
+
+    def test_one_field_with_prefixed_digits(self):
+        fields, pattern = routing.compile_uri_template('/{37signals}')
+        self.assertEqual(fields, set())
+
+        result = pattern.match('/s2n')
+        self.assertFalse(result)
+
     @ddt.data('', '/')
     def test_two_fields(self, postfix):
-        path = '/book/{id}/characters/{name}' + postfix
+        path = '/book/{book_id}/characters/{n4m3}' + postfix
         fields, pattern = routing.compile_uri_template(path)
-        self.assertEqual(fields, set(['name', 'id']))
+        self.assertEqual(fields, set(['n4m3', 'book_id']))
 
         result = pattern.match('/book/0765350386/characters/Vin')
         self.assertTrue(result)
-        self.assertEqual(result.groupdict(), {'name': 'Vin', 'id': '0765350386'})
+        self.assertEqual(result.groupdict(), {'n4m3': 'Vin', 'book_id': '0765350386'})
 
     def test_three_fields(self):
         fields, pattern = routing.compile_uri_template('/{a}/{b}/x/{c}')