LibSQL: Database layer

This patch implements the beginnings of a database API allowing for the
creation of tables, inserting rows in those tables, and retrieving those
rows.

Userland/Libraries/LibSQL/Row.h

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2021, Jan de Visser <jan@de-visser.net>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/ByteBuffer.h>
+#include <AK/RefPtr.h>
+#include <LibSQL/Forward.h>
+#include <LibSQL/Value.h>
+
+namespace SQL {
+
+/**
+ * A Tuple is an element of a sequential-access persistence data structure
+ * like a flat table. Like a key it has a definition for all its parts,
+ * but unlike a key this definition is not optional.
+ *
+ * FIXME Tuples should logically belong to a TupleStore object, but right now
+ * they stand by themselves; they contain a row's worth of data and a pointer
+ * to the next Tuple.
+ */
+class Row : public Tuple {
+public:
+    Row();
+    explicit Row(TupleDescriptor const&);
+    explicit Row(RefPtr<TableDef>);
+    Row(RefPtr<TableDef>, u32, ByteBuffer&);
+    Row(Row const&) = default;
+    virtual ~Row() override = default;
+
+    [[nodiscard]] u32 next_pointer() const { return m_next_pointer; }
+    void next_pointer(u32 ptr) { m_next_pointer = ptr; }
+    RefPtr<TableDef> table() const { return m_table; }
+    virtual void serialize(ByteBuffer&) const override;
+    [[nodiscard]] virtual size_t data_length() const override { return Tuple::data_length() + sizeof(u32); }
+
+protected:
+    void copy_from(Row const&);
+
+private:
+    RefPtr<TableDef> m_table;
+    u32 m_next_pointer { 0 };
+};
+
+}