From 61e0b5b29048a2efd41a5f49e02e2c85436ab5c4 Mon Sep 17 00:00:00 2001
From: Valery Kotov <kotov.valery@gmail.com>
Date: Thu, 2 Nov 2023 20:45:07 +0100
Subject: [PATCH] Added lower bound functionality (#7)

---
 include/cpp_lmdb/iterators.hpp    |  8 +++++++
 include/cpp_lmdb/transactions.hpp | 13 +++++++++++
 test/unit/test_transaction.cpp    | 38 +++++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+)

diff --git a/include/cpp_lmdb/iterators.hpp b/include/cpp_lmdb/iterators.hpp
index 6256636..baddf82 100644
--- a/include/cpp_lmdb/iterators.hpp
+++ b/include/cpp_lmdb/iterators.hpp
@@ -128,6 +128,14 @@ class ro_iterator
         base::navigate_cursor(MDB_FIRST, nullptr);
     }
 
+    explicit ro_iterator(
+        LmdbApi const &api, MDB_cursor &cursor, byte_span const &key) noexcept
+        : base{api, cursor}
+    {
+        auto db_key = details::to_mdb_val(key);
+        base::navigate_cursor(MDB_SET_RANGE, &db_key);
+    }
+
     ro_iterator(ro_iterator &&) = default;
     auto operator=(ro_iterator &&) -> ro_iterator & = default;
 
diff --git a/include/cpp_lmdb/transactions.hpp b/include/cpp_lmdb/transactions.hpp
index cd8695f..91c761e 100644
--- a/include/cpp_lmdb/transactions.hpp
+++ b/include/cpp_lmdb/transactions.hpp
@@ -38,6 +38,8 @@ class transaction {
 
     using ro_view
         = db_view<ro_iterator<key_trait, value_trait, LmdbApi>, LmdbApi>;
+    using ro_lo_view
+        = db_dup_view<ro_iterator<key_trait, value_trait, LmdbApi>, LmdbApi>;
     using ro_dup_view = db_dup_view<
         ro_dup_iterator<key_trait, value_trait, LmdbApi>,
         LmdbApi>;
@@ -90,6 +92,17 @@ class transaction {
         return {};
     }
 
+    auto lower_bound(key_type const &key) const noexcept
+        -> std::expected<ro_lo_view, error_t>
+    {
+        auto cursor = details::make_cursor(_api, _txn.get(), _db_index);
+        if (!cursor)
+            return std::unexpected{error_t{cursor.error()}};
+
+        auto const key_bytes = key_trait::to_bytes(key);
+        return ro_lo_view{std::move(*cursor), key_bytes};
+    }
+
     auto get(key_type const &key) const noexcept
         -> std::expected<value_type, error_t>
         requires(!details::key_value_trait_helper<
diff --git a/test/unit/test_transaction.cpp b/test/unit/test_transaction.cpp
index 0159bb3..ca93049 100644
--- a/test/unit/test_transaction.cpp
+++ b/test/unit/test_transaction.cpp
@@ -266,4 +266,42 @@ TEST_F(test_transaction, trivial_types_dup_iterate_by_key)
     ASSERT_TRUE(result);
 }
 
+TEST_F(test_transaction, trivial_types_transaction_lower_bound)
+{
+    std::array<uint8_t, 4> test_value{0x30, 0x0, 0x0, 0x20};
+
+    lmdb::
+        transaction<test_trait, lmdb::read_only_t::no, StrictMock<mocks::api>>
+            transaction{test_dbi, std::move(txn)};
+
+    auto *cursor{reinterpret_cast<MDB_cursor *>(0x84)};
+
+    {
+        InSequence const seq;
+
+        EXPECT_CALL(api, mdb_cursor_open(test_txn, test_dbi, _))
+            .WillOnce(DoAll(SetArgPointee<2>(cursor), Return(MDB_SUCCESS)));
+
+        EXPECT_CALL(api, mdb_cursor_get(cursor, Pointee(MdbValBytesAre{0x78, 0x56, 0x34, 0x12}), _, MDB_SET_RANGE))
+            .WillOnce(DoAll(
+                SetArgPointee<2>(
+                    MDB_val{test_value.size(), test_value.data()}),
+                Return(MDB_SUCCESS)));
+
+        EXPECT_CALL(api, mdb_cursor_close(cursor));
+        EXPECT_CALL(api, mdb_txn_abort(test_txn));
+    }
+
+    const auto result = transaction.lower_bound(0x12345678);
+    ASSERT_TRUE(result);
+
+    auto const& db_view = *result;
+    auto const it = db_view.begin();
+    EXPECT_NE(it, db_view.end());
+
+    auto const& key_value = *it;
+    EXPECT_EQ(key_value.key(), 0x12345678);
+    EXPECT_EQ(key_value.value(), 0x20000030);
+}
+
 }  // namespace cpp_lmdb_tests