Implement -k option for cfn-get-metadata

The -k argument can be a top-level key or a nested key in which case
the keys are separated by dots (eg "foo.bar"). In case a key contains a
dot character, it needs to be surrounded by single quotes (eg
"foo.'bar.1'.fred).
If the -k option is not provided, the command prints out the full
metadata structure as before.

Change-Id: Ib05d39672086001b83e8d7f56bc42cc4ba75751c
Fixes: bug #1183299

3 files changed, 134 insertions, 8 deletions

diff --git a/bin/cfn-get-metadata b/bin/cfn-get-metadata
index e0fa067..93bd57d 100755
--- a/bin/cfn-get-metadata
+++ b/bin/cfn-get-metadata
@@ -82,4 +82,4 @@ metadata = cfn_helper.Metadata(args.stack_name,
                                credentials_file=args.credential_file)
 metadata.retrieve()
 LOG.debug(str(metadata))
-metadata.display()
+metadata.display(args.key)
diff --git a/heat_cfntools/cfntools/cfn_helper.py b/heat_cfntools/cfntools/cfn_helper.py
index 282a1b0..1d76bf7 100644
--- a/heat_cfntools/cfntools/cfn_helper.py
+++ b/heat_cfntools/cfntools/cfn_helper.py
@@ -1182,9 +1182,47 @@ class Metadata(object):
     def __str__(self):
         return json.dumps(self._metadata)
 
-    def display(self):
-        if self._metadata is not None:
+    def display(self, key=None):
+        """Print the metadata to the standard output stream. By default the
+        full metadata is displayed but the ouptut can be limited to a specific
+        with the <key> argument.
+
+        Arguments:
+            key -- the metadata's key to display, nested keys can be specified
+                   separating them by the dot character.
+                        e.g., "foo.bar"
+                   If the key contains a dot, it should be surrounded by single
+                   quotes
+                        e.g., "foo.'bar.1'"
+        """
+        if self._metadata is None:
+            return
+
+        if key is None:
             print(str(self))
+            return
+
+        value = None
+        md = self._metadata
+        while True:
+            key_match = re.match(r'^(?:(?:\'([^\']+)\')|([^\.]+))(?:\.|$)',
+                                 key)
+            if not key_match:
+                break
+
+            k = key_match.group(1) or key_match.group(2)
+            if isinstance(md, dict) and k in md:
+                key = key.replace(key_match.group(), '')
+                value = md = md[k]
+            else:
+                break
+
+        if key != '':
+            value = None
+
+        if value is not None:
+            print(json.dumps(value))
+
         return
 
     def _is_valid_metadata(self):
diff --git a/heat_cfntools/tests/test_cfn_helper.py b/heat_cfntools/tests/test_cfn_helper.py
index 6aec2b0..aea8765 100644
--- a/heat_cfntools/tests/test_cfn_helper.py
+++ b/heat_cfntools/tests/test_cfn_helper.py
@@ -563,11 +563,6 @@ class TestMetadataRetrieve(testtools.TestCase):
         md_str = json.dumps(md_data)
 
         md = cfn_helper.Metadata('teststack', None)
-        self.assertTrue(md.retrieve(meta_str=md_str,
-                                    last_path=self.last_file))
-        self.assertThat(md_data, ttm.Equals(md._metadata))
-
-        md = cfn_helper.Metadata('teststack', None)
         self.assertTrue(md.retrieve(meta_str=md_data,
                                     last_path=self.last_file))
         self.assertThat(md_data, ttm.Equals(md._metadata))
@@ -583,6 +578,99 @@ class TestMetadataRetrieve(testtools.TestCase):
                          "\"files\": {\"/tmp/foo\": {\"content\": \"bar\"}"
                          "}}}}\n")
 
+    def test_metadata_retrieve_by_key_passed(self):
+
+        md_data = {"foo": {"bar": {"fred.1": "abcd"}}}
+        md_str = json.dumps(md_data)
+
+        md = cfn_helper.Metadata('teststack', None)
+        self.assertTrue(md.retrieve(meta_str=md_data,
+                                    last_path=self.last_file))
+        self.assertThat(md_data, ttm.Equals(md._metadata))
+        self.assertEqual(md_str, str(md))
+
+        displayed = self.useFixture(fixtures.StringStream('stdout'))
+        fake_stdout = displayed.stream
+        self.useFixture(fixtures.MonkeyPatch('sys.stdout', fake_stdout))
+        md.display("foo")
+        fake_stdout.flush()
+        self.assertEqual(displayed.getDetails()['stdout'].as_text(),
+                         "{\"bar\": {\"fred.1\": \"abcd\"}}\n")
+
+    def test_metadata_retrieve_by_nested_key_passed(self):
+
+        md_data = {"foo": {"bar": {"fred.1": "abcd"}}}
+        md_str = json.dumps(md_data)
+
+        md = cfn_helper.Metadata('teststack', None)
+        self.assertTrue(md.retrieve(meta_str=md_data,
+                                    last_path=self.last_file))
+        self.assertThat(md_data, ttm.Equals(md._metadata))
+        self.assertEqual(md_str, str(md))
+
+        displayed = self.useFixture(fixtures.StringStream('stdout'))
+        fake_stdout = displayed.stream
+        self.useFixture(fixtures.MonkeyPatch('sys.stdout', fake_stdout))
+        md.display("foo.bar.'fred.1'")
+        fake_stdout.flush()
+        self.assertEqual(displayed.getDetails()['stdout'].as_text(),
+                         '"abcd"\n')
+
+    def test_metadata_retrieve_key_none(self):
+
+        md_data = {"AWS::CloudFormation::Init": {"config": {"files": {
+            "/tmp/foo": {"content": "bar"}}}}}
+        md_str = json.dumps(md_data)
+
+        md = cfn_helper.Metadata('teststack', None)
+        self.assertTrue(md.retrieve(meta_str=md_data,
+                                    last_path=self.last_file))
+        self.assertThat(md_data, ttm.Equals(md._metadata))
+        self.assertEqual(md_str, str(md))
+
+        displayed = self.useFixture(fixtures.StringStream('stdout'))
+        fake_stdout = displayed.stream
+        self.useFixture(fixtures.MonkeyPatch('sys.stdout', fake_stdout))
+        md.display("no_key")
+        fake_stdout.flush()
+        self.assertEqual(displayed.getDetails()['stdout'].as_text(), "")
+
+    def test_metadata_retrieve_by_nested_key_none(self):
+
+        md_data = {"foo": {"bar": {"fred.1": "abcd"}}}
+        md_str = json.dumps(md_data)
+
+        md = cfn_helper.Metadata('teststack', None)
+        self.assertTrue(md.retrieve(meta_str=md_data,
+                                    last_path=self.last_file))
+        self.assertThat(md_data, ttm.Equals(md._metadata))
+        self.assertEqual(md_str, str(md))
+
+        displayed = self.useFixture(fixtures.StringStream('stdout'))
+        fake_stdout = displayed.stream
+        self.useFixture(fixtures.MonkeyPatch('sys.stdout', fake_stdout))
+        md.display("foo.fred")
+        fake_stdout.flush()
+        self.assertEqual(displayed.getDetails()['stdout'].as_text(), "")
+
+    def test_metadata_retrieve_by_nested_key_none_with_matching_string(self):
+
+        md_data = {"foo": "bar"}
+        md_str = json.dumps(md_data)
+
+        md = cfn_helper.Metadata('teststack', None)
+        self.assertTrue(md.retrieve(meta_str=md_data,
+                                    last_path=self.last_file))
+        self.assertThat(md_data, ttm.Equals(md._metadata))
+        self.assertEqual(md_str, str(md))
+
+        displayed = self.useFixture(fixtures.StringStream('stdout'))
+        fake_stdout = displayed.stream
+        self.useFixture(fixtures.MonkeyPatch('sys.stdout', fake_stdout))
+        md.display("foo.bar")
+        fake_stdout.flush()
+        self.assertEqual(displayed.getDetails()['stdout'].as_text(), "")
+
     def test_metadata_creates_cache(self):
         temp_home = tempfile.mkdtemp()