Force strings starting with a zero to be quoted.

cfn_flip/yaml_dumper.py

@@ -15,7 +15,9 @@
 from cfn_clean.yaml_dumper import CleanCfnYamlDumper
 from cfn_tools.odict import ODict
 from cfn_tools.yaml_dumper import CfnYamlDumper
+import six
 
+TAG_STR = "tag:yaml.org,2002:str"
 TAG_MAP = "tag:yaml.org,2002:map"
 CONVERTED_SUFFIXES = ["Ref", "Condition"]
 
@@ -46,6 +48,13 @@ class LongCleanDumper(CleanCfnYamlDumper):
     """
 
 
+def string_representer(dumper, value):
+    if value.startswith("0"):
+        return dumper.represent_scalar(TAG_STR, value, style="'")
+
+    return dumper.represent_scalar(TAG_STR, value)
+
+
 def fn_representer(dumper, fn_name, value):
     tag = "!{}".format(fn_name)
 
@@ -82,6 +91,7 @@ def map_representer(dumper, value):
 
 # Customise our dumpers
 Dumper.add_representer(ODict, map_representer)
+Dumper.add_representer(six.text_type, string_representer)
 CleanDumper.add_representer(ODict, map_representer)
 
 

tests/test_flip.py

@@ -502,5 +502,39 @@ def test_get_dumper():
     When invoking get_dumper use clean_up & long_form
     :return: LongCleanDumper
     """
+
     resp = cfn_flip.get_dumper(clean_up=True, long_form=True)
     assert resp == cfn_flip.yaml_dumper.LongCleanDumper
+
+
+def test_quoted_digits():
+    """
+    Any value that is composed entirely of digits
+    should be quoted for safety.
+    CloudFormation is happy for numbers to appear as strings.
+    But the opposite (e.g. account numbers as numbers) can cause issues
+    See https://github.com/awslabs/aws-cfn-template-flip/issues/41
+    """
+
+    value = dump_json(ODict((
+        ("int", 123456),
+        ("float", 123.456),
+        ("oct", "0123456"),
+        ("bad-oct", "012345678"),
+        ("safe-oct", "0o123456"),
+        ("string", "abcdef"),
+    )))
+
+    expected = "\n".join((
+        "int: 123456",
+        "float: 123.456",
+        "oct: '0123456'",
+        "bad-oct: '012345678'",
+        "safe-oct: '0o123456'",
+        "string: abcdef",
+        ""
+    ))
+
+    actual = cfn_flip.to_yaml(value)
+
+    assert actual == expected