Adding classes, functions, and utilities for common LMDB operations.

1 files changed, 120 insertions, 0 deletions

diff --git a/src/lmdb/table.h b/src/lmdb/table.h
new file mode 100644
index 000000000..41a3de296
--- /dev/null
+++ b/src/lmdb/table.h
@@ -0,0 +1,120 @@
+#pragma once
+
+#include <utility>
+
+#include "common/expect.h"
+#include "lmdb/error.h"
+#include "lmdb/key_stream.h"
+#include "lmdb/util.h"
+#include "lmdb/value_stream.h"
+
+namespace lmdb
+{
+    //! Helper for grouping typical LMDB DBI options.
+    struct table
+    {
+        char const* const name;
+        const unsigned flags;
+        MDB_cmp_func const* const key_cmp;
+        MDB_cmp_func const* const value_cmp;
+
+        //! \pre `name != nullptr` \return Open table.
+        expect<MDB_dbi> open(MDB_txn& write_txn) const noexcept;
+    };
+
+    //! Helper for grouping typical LMDB DBI options when key and value are fixed types.
+    template<typename K, typename V>
+    struct basic_table : table
+    {
+        using key_type = K;
+        using value_type = V;
+
+        //! \return Additional LMDB flags based on `flags` value.
+        static constexpr unsigned compute_flags(const unsigned flags) noexcept
+        {
+            return flags | ((flags & MDB_DUPSORT) ? MDB_DUPFIXED : 0);
+        }
+
+        constexpr explicit basic_table(const char* name, unsigned flags = 0, MDB_cmp_func value_cmp = nullptr) noexcept
+          : table{name, compute_flags(flags), &lmdb::less<lmdb::native_type<K>>, value_cmp}
+        {}
+
+        /*!
+            \tparam U must be same as `V`; used for sanity checking.
+            \tparam F is the type within `U` that is being extracted.
+            \tparam offset to `F` within `U`.
+
+            \note If using `F` and `offset` to retrieve a specific field, use
+                `MONERO_FIELD` macro in `src/lmdb/util.h` which calculates the
+                offset automatically.
+
+            \return Value of type `F` at `offset` within `value` which has
+                type `U`.
+        */
+        template<typename U, typename F = U, std::size_t offset = 0>
+        static expect<F> get_value(MDB_val value) noexcept
+        {
+            static_assert(std::is_same<U, V>(), "bad MONERO_FIELD?");
+            static_assert(std::is_pod<F>(), "F must be POD");
+            static_assert(sizeof(F) + offset <= sizeof(U), "bad field type and/or offset");
+
+            if (value.mv_size != sizeof(U))
+                return {lmdb::error(MDB_BAD_VALSIZE)};
+
+            F out;
+            std::memcpy(std::addressof(out), static_cast<char*>(value.mv_data) + offset, sizeof(out));
+            return out;
+        }
+
+        /*!
+            \pre `cur != nullptr`.
+            \param cur Active cursor on table. Returned in object on success,
+                otherwise destroyed.
+            \return A handle to the first key/value in the table linked
+                to `cur` or an empty `key_stream`.
+        */
+        template<typename D>
+        expect<key_stream<K, V, D>>
+        static get_key_stream(std::unique_ptr<MDB_cursor, D> cur) noexcept
+        {
+            MONERO_PRECOND(cur != nullptr);
+
+            MDB_val key;
+            MDB_val value;
+            const int err = mdb_cursor_get(cur.get(), &key, &value, MDB_FIRST);
+            if (err)
+            {
+                if (err != MDB_NOTFOUND)
+                    return {lmdb::error(err)};
+                cur.reset(); // return empty set
+            }
+            return key_stream<K, V, D>{std::move(cur)};
+        }
+
+        /*!
+            \pre `cur != nullptr`.
+            \param cur Active cursor on table. Returned in object on success,
+                otherwise destroyed.
+            \return A handle to the first value at `key` in the table linked
+                to `cur` or an empty `value_stream`.
+        */
+        template<typename D>
+        expect<value_stream<V, D>>
+        static get_value_stream(K const& key, std::unique_ptr<MDB_cursor, D> cur) noexcept
+        {
+            MONERO_PRECOND(cur != nullptr);
+
+            MDB_val key_bytes = lmdb::to_val(key);
+            MDB_val value;
+            const int err = mdb_cursor_get(cur.get(), &key_bytes, &value, MDB_SET);
+            if (err)
+            {
+                if (err != MDB_NOTFOUND)
+                    return {lmdb::error(err)};
+                cur.reset(); // return empty set
+            }
+            return value_stream<V, D>{std::move(cur)};
+        }
+    };
+} // lmdb
+