Add a bit of client side constraint validation

Fixes #661

Since the constraints are parsed at the client side, we might as well
validate the constraints before sending, instead of relying on the
provider's capability of handling invalid constraints. In #661 it is
reported that an invalid constraint is not raising an exception on MAAS.

Author: cderici

juju/constraints.py

@@ -32,6 +32,25 @@
     "Y": 1024 ** 6
 }
 
+# List of supported constraint keys, see
+# http://github.com/cderici/juju/blob/2.9/core/constraints/constraints.go#L20-L39
+SUPPORTED_KEYS = [
+    "arch",
+    "container",
+    "cpu_cores",
+    "cores",
+    "cpu_power",
+    "mem",
+    "root_disk",
+    "root_disk_source",
+    "tags",
+    "instance_role",
+    "instance_type",
+    "spaces",
+    "virt_type",
+    "zones",
+    "allocate_public_ip"]
+
 LIST_KEYS = {'tags', 'spaces'}
 
 SNAKE1 = re.compile(r'(.)([A-Z][a-z]+)')
@@ -51,24 +70,29 @@ def parse(constraints):
         # Fowards compatibilty: already parsed
         return constraints
 
-    constraints = {
-        normalize_key(k): (
-            normalize_list_value(v) if k in LIST_KEYS else
-            normalize_value(v)
-        ) for k, v in [s.split("=") for s in constraints.split(" ")]}
+    normalized_constraints = {}
+    for s in constraints.split(" "):
+        if "=" not in s:
+            raise Exception("malformed constraint %s" % s)
+
+        k, v = s.split("=")
+        normalized_constraints[normalize_key(k)] = normalize_list_value(v) if\
+            k in LIST_KEYS else normalize_value(v)
 
-    return constraints
+    return normalized_constraints
 
 
-def normalize_key(key):
-    key = key.strip()
+def normalize_key(orig_key):
+    key = orig_key.strip()
 
     key = key.replace("-", "_")  # Our _client lib wants "_" in place of "-"
 
     # Convert camelCase to snake_case
     key = SNAKE1.sub(r'\1_\2', key)
     key = SNAKE2.sub(r'\1_\2', key).lower()
 
+    if key not in SUPPORTED_KEYS:
+        raise Exception("unknown constraint in %s" % orig_key)
     return key
 
 

tests/unit/test_constraints.py

@@ -20,11 +20,13 @@ def test_mem_regex(self):
     def test_normalize_key(self):
         _ = constraints.normalize_key
 
-        self.assertEqual(_("test-key"), "test_key")
-        self.assertEqual(_("test-key  "), "test_key")
-        self.assertEqual(_("  test-key"), "test_key")
-        self.assertEqual(_("TestKey"), "test_key")
-        self.assertEqual(_("testKey"), "test_key")
+        self.assertEqual(_("root-disk"), "root_disk")
+        self.assertEqual(_("root-disk  "), "root_disk")
+        self.assertEqual(_("  root-disk"), "root_disk")
+        self.assertEqual(_("RootDisk"), "root_disk")
+        self.assertEqual(_("rootDisk"), "root_disk")
+
+        self.assertRaises(Exception, lambda: _("not-one-of-the-supported-keys"))
 
     def test_normalize_val(self):
         _ = constraints.normalize_value
@@ -53,13 +55,16 @@ def test_parse_constraints(self):
         )
 
         self.assertEqual(
-            _("mem=10G foo=bar,baz tags=tag1 spaces=space1,space2"),
+            _("mem=10G zones=bar,baz tags=tag1 spaces=space1,space2"),
             {"mem": 10 * 1024,
-             "foo": "bar,baz",
+             "zones": "bar,baz",
              "tags": ["tag1"],
              "spaces": ["space1", "space2"]}
         )
 
+        self.assertRaises(Exception, lambda: _("root-disk>16G"))
+        self.assertRaises(Exception, lambda: _("root-disk>=16G"))
+
     def test_parse_storage_constraint(self):
         _ = constraints.parse_storage_constraint