LibSQL: BTree index, Heap, and Meta objects for SQL Storage layer

Unfortunately this patch is quite large.

The main functionality included are a BTree index implementation and
the Heap class which manages persistent storage.

Also included are a Key subclass of the Tuple class, which is a
specialization for index key tuples. This "dragged in" the Meta layer,
which has classes defining SQL objects like tables and indexes.

Userland/Libraries/LibSQL/BTree.cpp

@@ -0,0 +1,113 @@
+/*
+ * Copyright (c) 2021, Jan de Visser <jan@de-visser.net>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Format.h>
+#include <LibSQL/BTree.h>
+#include <LibSQL/Meta.h>
+
+namespace SQL {
+
+BTree::BTree(Heap& heap, TupleDescriptor const& descriptor, bool unique, u32 pointer)
+    : Index(heap, descriptor, unique, pointer)
+    , m_root(nullptr)
+{
+}
+
+BTree::BTree(Heap& heap, TupleDescriptor const& descriptor, u32 pointer)
+    : BTree(heap, descriptor, true, pointer)
+{
+}
+
+BTreeIterator BTree::begin()
+{
+    if (!m_root)
+        initialize_root();
+    VERIFY(m_root);
+    return BTreeIterator(m_root, -1);
+}
+
+BTreeIterator BTree::end()
+{
+    return BTreeIterator(nullptr, -1);
+}
+
+void BTree::initialize_root()
+{
+    if (pointer()) {
+        if (pointer() < heap().size()) {
+            auto buffer = read_block(pointer());
+            size_t offset = 0;
+            m_root = make<TreeNode>(*this, nullptr, pointer(), buffer, offset);
+        } else {
+            m_root = make<TreeNode>(*this, nullptr, pointer());
+        }
+    } else {
+        set_pointer(new_record_pointer());
+        m_root = make<TreeNode>(*this, nullptr, pointer());
+        if (on_new_root)
+            on_new_root();
+    }
+}
+
+TreeNode* BTree::new_root()
+{
+    set_pointer(new_record_pointer());
+    m_root = make<TreeNode>(*this, nullptr, m_root.leak_ptr(), pointer());
+    add_to_write_ahead_log(m_root->as_index_node());
+    if (on_new_root)
+        on_new_root();
+    return m_root;
+}
+
+bool BTree::insert(Key const& key)
+{
+    if (!m_root)
+        initialize_root();
+    VERIFY(m_root);
+    return m_root->insert(key);
+}
+
+bool BTree::update_key_pointer(Key const& key)
+{
+    if (!m_root)
+        initialize_root();
+    VERIFY(m_root);
+    return m_root->update_key_pointer(key);
+}
+
+Optional<u32> BTree::get(Key& key)
+{
+    if (!m_root)
+        initialize_root();
+    VERIFY(m_root);
+    return m_root->get(key);
+}
+
+BTreeIterator BTree::find(Key const& key)
+{
+    if (!m_root)
+        initialize_root();
+    VERIFY(m_root);
+    for (auto node = m_root->node_for(key); node; node = node->up()) {
+        for (auto ix = 0u; ix < node->size(); ix++) {
+            auto match = (*node)[ix].match(key);
+            if (match == 0)
+                return BTreeIterator(node, (int)ix);
+            else if (match > 0)
+                return end();
+        }
+    }
+    return end();
+}
+
+void BTree::list_tree()
+{
+    if (!m_root)
+        initialize_root();
+    m_root->list_node(0);
+}
+
+}