Make maximum size of values be explicit.

5 files changed, 44 insertions, 4 deletions

diff --git a/btree/__init__.py b/btree/__init__.py
index 60f8c46..44f5cd7 100644
--- a/btree/__init__.py
+++ b/btree/__init__.py
@@ -19,7 +19,7 @@ version = '0.16'
 
 from nodes import LeafNode, IndexNode
 from codec import NodeCodec, CodecError
-from tree import BTree, KeySizeMismatch
+from tree import BTree, KeySizeMismatch, ValueTooLarge
 from forest import Forest
 from nodestore import (NodeStore, NodeStoreTests, NodeMissing, NodeTooBig, 
                        NodeExists)
diff --git a/btree/nodestore.py b/btree/nodestore.py
index c356f98..ad67ccf 100644
--- a/btree/nodestore.py
+++ b/btree/nodestore.py
@@ -95,7 +95,8 @@ class NodeStore(object): # pragma: no cover
     def __init__(self, node_size, codec):
         self.node_size = node_size
         self.codec = codec
-      
+        self.max_value_size = (node_size / 2) - codec.leaf_header.size
+
     def max_index_pairs(self):
         return self.codec.max_index_pairs(self.node_size)
         
@@ -191,6 +192,10 @@ class NodeStoreTests(object): # pragma: no cover
     
     def test_sets_node_size(self):
         self.assertEqual(self.ns.node_size, self.node_size)
+        
+    def test_sets_max_value_size(self):
+        self.assert_(self.ns.max_value_size > 1)
+        self.assert_(self.ns.max_value_size < self.node_size / 2)
 
     def test_has_no_metadata_initially(self):
         self.assertEqual(self.ns.get_metadata_keys(), [])
diff --git a/btree/tree.py b/btree/tree.py
index 7138414..e4f8bab 100644
--- a/btree/tree.py
+++ b/btree/tree.py
@@ -32,6 +32,17 @@ class KeySizeMismatch(Exception):
     def __str__(self):
         return 'Key %s is of wrong length (%d, should be %d)' % \
                 (repr(self.key), len(self.key), self.wanted_size)
+
+
+class ValueTooLarge(Exception):
+
+    def __init__(self, value, max_size):
+        self.value = value
+        self.max_size = max_size
+        
+    def __str__(self):
+        return 'Value %s is too long (%d, max %d)' % \
+                (repr(self.value), len(self.value), self.max_size)
        
 
 class BTree(object):
@@ -39,7 +50,9 @@ class BTree(object):
     '''B-tree.
     
     The nodes are stored in an external node store; see the NodeStore
-    class. Key sizes are fixed, and given in bytes.
+    class. Key sizes are fixed, and given in bytes. Values may be of
+    any size up to slightly less than half the maximum size of a node.
+    See NodeStore.max_value_size for the exact value.
     
     '''
 
@@ -59,6 +72,10 @@ class BTree(object):
         if len(key) != self.node_store.codec.key_bytes:
             raise KeySizeMismatch(key, self.node_store.codec.key_bytes)
 
+    def check_value_size(self, value):
+        if len(value) > self.node_store.max_value_size:
+            raise ValueTooLarge(value, self.node_store.max_value_size)
+
     def new_id(self):
         '''Generate a new node identifier.'''
         return self.forest.new_id()
@@ -201,6 +218,7 @@ class BTree(object):
         '''
 
         self.check_key_size(key)
+        self.check_value_size(value)
 
         # Is the tree empty? This needs special casing to keep
         # _insert_into_index simpler.
diff --git a/btree/tree_tests.py b/btree/tree_tests.py
index 24efad8..86b5684 100644
--- a/btree/tree_tests.py
+++ b/btree/tree_tests.py
@@ -35,6 +35,7 @@ class DummyNodeStore(object):
 
     def __init__(self, node_size, codec):
         self.node_size = node_size
+        self.max_value_size = node_size / 2 - 1
         self.codec = codec
         self.nodes = dict()
         self.metadata = dict()
@@ -87,6 +88,18 @@ class KeySizeMismatchTests(unittest.TestCase):
         self.assert_('4' in str(self.err))
 
 
+class ValueTooLargeTests(unittest.TestCase):
+
+    def setUp(self):
+        self.err = btree.ValueTooLarge('foobar', 3)
+        
+    def test_error_message_contains_value(self):
+        self.assert_('foobar' in str(self.err))
+        
+    def test_error_message_contains_max_size(self):
+        self.assert_('3' in str(self.err))
+
+
 class BTreeTests(unittest.TestCase):
 
     def setUp(self):
@@ -190,6 +203,10 @@ class BTreeTests(unittest.TestCase):
     def test_insert_with_wrong_size_key_raises_error(self):
         self.assertRaises(btree.KeySizeMismatch, self.tree.insert, '', '')
 
+    def test_insert_with_too_large_value_raises_error(self):
+        self.assertRaises(btree.ValueTooLarge, self.tree.insert, 'xxx', 
+                          'x' * (self.ns.max_value_size + 1))
+
     def test_remove_from_empty_tree_raises_keyerror(self):
         self.assertRaises(KeyError, self.tree.remove, 'foo')
 
diff --git a/insert-remove-test b/insert-remove-test
index 83ef0c7..c59e9b9 100755
--- a/insert-remove-test
+++ b/insert-remove-test
@@ -83,7 +83,7 @@ def main():
 
     key_size = 19
     value_size = 128
-    node_size = 256
+    node_size = 300
 
     codec = btree.NodeCodec(key_size)