feat: use cryptographically secure random for new document ids (#1162)

Author: probicheaux

packages/google-cloud-firestore/google/cloud/firestore_v1/base_collection.py

@@ -60,6 +60,7 @@
     import datetime
 
 _AUTO_ID_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
+system_random = random.SystemRandom()
 
 
 class BaseCollectionReference(Generic[QueryType]):
@@ -623,8 +624,11 @@ def _auto_id() -> str:
         str: A 20 character string composed of digits, uppercase and
         lowercase and letters.
     """
-
-    return "".join(random.choice(_AUTO_ID_CHARS) for _ in range(20))
+    try:
+        return "".join(system_random.choice(_AUTO_ID_CHARS) for _ in range(20))
+    # Very old Unix systems don't have os.urandom (/dev/urandom), in which case use random.choice
+    except NotImplementedError:
+        return "".join(random.choice(_AUTO_ID_CHARS) for _ in range(20))
 
 
 def _item_to_document_ref(collection_reference, item):

packages/google-cloud-firestore/tests/unit/v1/test_base_collection.py

@@ -437,7 +437,7 @@ def test_basecollectionreference_pipeline(mock_query):
         assert pipeline == mock_query._build_pipeline.return_value
 
 
-@mock.patch("random.choice")
+@mock.patch("random.SystemRandom.choice")
 def test__auto_id(mock_rand_choice):
     from google.cloud.firestore_v1.base_collection import _AUTO_ID_CHARS, _auto_id
 
@@ -450,6 +450,21 @@ def test__auto_id(mock_rand_choice):
     assert mock_rand_choice.mock_calls == mock_calls
 
 
+@mock.patch("random.choice")
+@mock.patch("random.SystemRandom.choice")
+def test__auto_id_fallback_to_random(mock_system_rand_choice, mock_rand_choice):
+    from google.cloud.firestore_v1.base_collection import _AUTO_ID_CHARS, _auto_id
+
+    mock_system_rand_choice.side_effect = NotImplementedError
+    mock_result = "0123456789abcdefghij"
+    mock_rand_choice.side_effect = list(mock_result)
+    result = _auto_id()
+    assert result == mock_result
+
+    mock_calls = [mock.call(_AUTO_ID_CHARS)] * 20
+    assert mock_rand_choice.mock_calls == mock_calls
+
+
 def _make_credentials():
     import google.auth.credentials