Add util methods for checking json and yaml formatted file

As part of oslo_policy policy_file JSON to YAML migration BP,
we need to check if oslo policy_file is JSON or YAML formatted
(almost on all projects with policy in code, example Needed-By).
- https://specs.openstack.org/openstack/oslo-specs/specs/victoria/policy-json-to-yaml.html

These util methods try quick checks of file type by loading the file using
json or yaml.

Needed-By: https://review.opendev.org/#/c/748059/

Related Blueprint: policy-json-to-yaml

Change-Id: I0edf030dc5cd6b77e0101089746589332860fa16

oslo_utils/fileutils.py

@@ -22,10 +22,12 @@ File utilities.
 import contextlib
 import errno
 import hashlib
+import json
 import os
 import stat
 import tempfile
 import time
+import yaml
 
 from oslo_utils import excutils
 
@@ -158,3 +160,50 @@ def last_bytes(path, num):
                 raise
         unread_bytes = fp.tell()
         return (fp.read(), unread_bytes)
+
+
+def is_json(file_path):
+    """Check if file is of json type or not.
+
+    This function try to load the input file using json.loads()
+    and return False if ValueError otherwise True.
+
+    :param file_path: The file path to check
+
+    :returns: bool
+
+    """
+    with open(file_path, 'r') as fh:
+        data = fh.read()
+    try:
+        json.loads(data)
+        return True
+    except ValueError:
+        return False
+
+
+def is_yaml(file_path):
+    """Check if file is of yaml type or not.
+
+    This function try to load the input file using yaml.safe_load()
+    and return True if loadable. Because every json file can be loadable
+    in yaml, so this function return False if file is loadable using
+    json.loads() means it is json file.
+
+    :param file_path: The file path to check
+
+    :returns: bool
+
+    """
+    with open(file_path, 'r') as fh:
+        data = fh.read()
+        is_yaml = False
+        try:
+            json.loads(data)
+        except ValueError:
+            try:
+                yaml.safe_load(data)
+                is_yaml = True
+            except yaml.scanner.ScannerError:
+                pass
+        return is_yaml

oslo_utils/tests/test_fileutils.py

@@ -15,6 +15,7 @@
 
 import errno
 import hashlib
+import json
 import os
 import shutil
 import stat
@@ -22,13 +23,13 @@ import tempfile
 import time
 from unittest import mock
 import uuid
+import yaml
 
 from oslotest import base as test_base
 import six
 
 from oslo_utils import fileutils
 
-
 TEST_PERMISSIONS = stat.S_IRWXU
 
 
@@ -289,3 +290,30 @@ class LastBytesTestCase(test_base.BaseTestCase):
     def test_non_exist_file(self):
         self.assertRaises(IOError, fileutils.last_bytes,
                           'non_exist_file', 1000)
+
+
+class FileTypeTestCase(test_base.BaseTestCase):
+    """Test the is_yaml() and is_json() utility methods."""
+
+    def setUp(self):
+        super(FileTypeTestCase, self).setUp()
+        data = {
+            'name': 'test',
+            'website': 'example.com'
+        }
+        temp_dir = tempfile.mkdtemp()
+        self.json_file = tempfile.mktemp(dir=temp_dir)
+        self.yaml_file = tempfile.mktemp(dir=temp_dir)
+
+        with open(self.json_file, 'w') as fh:
+            json.dump(data, fh)
+        with open(self.yaml_file, 'w') as fh:
+            yaml.dump(data, fh)
+
+    def test_is_json(self):
+        self.assertTrue(fileutils.is_json(self.json_file))
+        self.assertFalse(fileutils.is_json(self.yaml_file))
+
+    def test_is_yaml(self):
+        self.assertTrue(fileutils.is_yaml(self.yaml_file))
+        self.assertFalse(fileutils.is_yaml(self.json_file))

releasenotes/notes/add-methods-for-json-yaml-file-check-746dca0a11c2f9c9.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    New method ``is_json`` ``is_yaml`` added in fileutils.
+    These can be used to check if file is JSON or YAML
+    formatted.