Raise exceptions if key or node size is missing from metadata

3 files changed, 35 insertions, 4 deletions

diff --git a/larch/__init__.py b/larch/__init__.py
index 91fa40f..1c8d274 100644
--- a/larch/__init__.py
+++ b/larch/__init__.py
@@ -20,7 +20,8 @@ __version__ = '0.30'
 from nodes import FrozenNode, Node, LeafNode, IndexNode
 from codec import NodeCodec, CodecError
 from tree import BTree, KeySizeMismatch, ValueTooLarge
-from forest import Forest, open_forest, BadKeySize, BadNodeSize
+from forest import (Forest, open_forest, BadKeySize, BadNodeSize, 
+                    MetadataMissingKey)
 from nodestore import (NodeStore, NodeStoreTests, NodeMissing, NodeTooBig, 
                        NodeExists, NodeCannotBeModified)
 from refcountstore import RefcountStore
diff --git a/larch/forest.py b/larch/forest.py
index 881fb86..2443da1 100644
--- a/larch/forest.py
+++ b/larch/forest.py
@@ -19,6 +19,15 @@ import tracing
 import larch
 
 
+class MetadataMissingKey(Exception):
+
+    def __init__(self, key_name):
+        self.msg = 'larch forest metadata missing "%s"' % key_name
+
+    def __str__(self): # pragma: no cover
+        return self.msg
+
+
 class BadKeySize(Exception):
 
     '''Exception for a bad key size.'''
@@ -179,9 +188,11 @@ def open_forest(allow_writes=None, key_size=None, node_size=None, codec=None,
         # since we won't be accessing nodes or keys.
         c_temp = codec(42)
         ns_temp = node_store(False, 42, c_temp, **kwargs)
-        
-        assert 'key_size' in ns_temp.get_metadata_keys()
-        assert 'node_size' in ns_temp.get_metadata_keys()
+
+        if 'key_size' not in ns_temp.get_metadata_keys():
+            raise MetadataMissingKey('key_size')
+        if 'node_size' not in ns_temp.get_metadata_keys():
+            raise MetadataMissingKey('node_size')
         
         if key_size is None:
             key_size = int(ns_temp.get_metadata('key_size'))
diff --git a/larch/forest_tests.py b/larch/forest_tests.py
index 7603b86..9a786bd 100644
--- a/larch/forest_tests.py
+++ b/larch/forest_tests.py
@@ -14,6 +14,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 
+import os
 import shutil
 import tempfile
 import unittest
@@ -136,6 +137,24 @@ class OpenForestTests(unittest.TestCase):
         self.assertEqual(f.node_store.codec.key_bytes, self.key_size)
         self.assertEqual(f.node_store.node_size, self.node_size)
 
+    def test_fail_if_metadata_missing_key_size(self):
+        with open(os.path.join(self.tempdir, 'metadata'), 'w') as f:
+            f.write('[metadata]\n')
+            f.write('format=1/1\n')
+            f.write('node_size=%s\n' % self.node_size)
+        self.assertRaises(larch.MetadataMissingKey, larch.open_forest,
+                          key_size=self.key_size, node_size=None,
+                          dirname=self.tempdir, allow_writes=False)
+
+    def test_fail_if_metadata_missing_node_size(self):
+        with open(os.path.join(self.tempdir, 'metadata'), 'w') as f:
+            f.write('[metadata]\n')
+            f.write('format=1/1\n')
+            f.write('key_size=%s\n' % self.key_size)
+        self.assertRaises(larch.MetadataMissingKey, larch.open_forest,
+                          key_size=self.key_size, node_size=None,
+                          dirname=self.tempdir, allow_writes=False)
+
     def test_fail_if_existing_tree_has_incompatible_key_size(self):
         f = larch.open_forest(key_size=self.key_size, node_size=self.node_size,
                               dirname=self.tempdir, allow_writes=True)