p.view_node(): check node_id for validity, before sending it to the API

This prevents a pillarsdk.exceptions.MethodNotAllowed exception, which
would result in a 500 Internal Server Error on the frontend.

tests/test_web/test_utils.py

@@ -0,0 +1,37 @@
+# -*- encoding: utf-8 -*-
+
+import unittest
+
+from pillar.web import utils
+
+
+class IsValidIdTest(unittest.TestCase):
+    def test_valid(self):
+        # 24-byte hex strings
+        self.assertTrue(utils.is_valid_id(24 * 'a'))
+        self.assertTrue(utils.is_valid_id(24 * u'a'))
+        self.assertTrue(utils.is_valid_id('deadbeefbeefcacedeadcace'))
+        self.assertTrue(utils.is_valid_id(u'deadbeefbeefcacedeadcace'))
+
+        # 12-byte arbitrary ASCII strings
+        self.assertTrue(utils.is_valid_id('DeadBeefCake'))
+        self.assertTrue(utils.is_valid_id(u'DeadBeefCake'))
+
+        # 12-byte str object
+        self.assertTrue(utils.is_valid_id('beef€67890'))
+
+    def test_bad_length(self):
+        self.assertFalse(utils.is_valid_id(23 * 'a'))
+        self.assertFalse(utils.is_valid_id(25 * u'a'))
+
+    def test_non_string(self):
+        self.assertFalse(utils.is_valid_id(None))
+        self.assertFalse(utils.is_valid_id(1234))
+        self.assertFalse(utils.is_valid_id([24 * 'a']))
+
+    def test_bad_content(self):
+        # 24-character non-hexadecimal string
+        self.assertFalse(utils.is_valid_id('deadbeefbeefcakedeadcake'))
+
+        # unicode variant of valid 12-byte str object
+        self.assertFalse(utils.is_valid_id(u'beef€67890'))