[Tarantool-patches] [PATCH 2/2] box: introduce "current" for sequence

[olegrok@tarantool.org]

From: Oleg Babin <babinoleg@mail.ru>

This patch introduces "current" function for
sequences. It returns current value of
specified sequence or throws an error
if sequence is not initialized ("next" called
at least once).

Closes #4752

@TarantoolBot document
Title: sequence:current()

New function returns current value of sequence
of throws an error if used before sequence
initialization.

Example

```lua
sq = box.schema.sequence.create('test')
---
...
sq:current()
---
- error: Sequence is not initialized yet
...
sq:next()
---
- 1
...
sq:current()
---
- 1
...
sq:set(42)
---
...
sq:current()
---
- 42
...
```
---
Issue: https://github.com/tarantool/tarantool/issues/4752
Branch: https://github.com/tarantool/tarantool/tree/olegrok/4752-sequence-current
 src/box/box.cc             | 14 ++++++++++++++
 src/box/box.h              | 12 ++++++++++++
 src/box/lua/schema.lua     |  4 ++++
 src/box/lua/sequence.c     | 12 ++++++++++++
 test/box/sequence.result   | 32 ++++++++++++++++++++++++++++++++
 test/box/sequence.test.lua | 12 ++++++++++++
 6 files changed, 86 insertions(+)

diff --git a/src/box/box.cc b/src/box/box.cc
index 09dd67ab4..a5052dba4 100644
--- a/src/box/box.cc
+++ b/src/box/box.cc
@@ -1414,6 +1414,20 @@ box_sequence_next(uint32_t seq_id, int64_t *result)
 	*result = value;
 	return 0;
 }
+
+int
+box_sequence_current(uint32_t seq_id, int64_t *result)
+{
+	struct sequence *seq = sequence_cache_find(seq_id);
+	if (seq == NULL)
+		return -1;
+	if (access_check_sequence(seq) != 0)
+		return -1;
+	if (sequence_get_value(seq, result) != 0)
+		return -1;
+	return 0;
+}
+
 int
 box_sequence_set(uint32_t seq_id, int64_t value)
 {
diff --git a/src/box/box.h b/src/box/box.h
index f37a945eb..8fb723630 100644
--- a/src/box/box.h
+++ b/src/box/box.h
@@ -423,6 +423,18 @@ box_truncate(uint32_t space_id);
 API_EXPORT int
 box_sequence_next(uint32_t seq_id, int64_t *result);
 
+/**
+ * Returns current value of sequence.
+ *
+ * \param seq_id sequence identifier
+ * \param[out] result pointer to a variable where the current sequence
+ * value will be stored on success
+ * \retval -1 on error (check box_error_last())
+ * \retval 0 on success
+ */
+API_EXPORT int
+box_sequence_current(uint32_t seq_id, int64_t *result);
+
 /**
  * Set a sequence value.
  *
diff --git a/src/box/lua/schema.lua b/src/box/lua/schema.lua
index f537c3cec..0cd747350 100644
--- a/src/box/lua/schema.lua
+++ b/src/box/lua/schema.lua
@@ -1812,6 +1812,10 @@ sequence_mt.next = function(self)
     return internal.sequence.next(self.id)
 end
 
+sequence_mt.current = function(self)
+    return internal.sequence.current(self.id)
+end
+
 sequence_mt.set = function(self, value)
     return internal.sequence.set(self.id, value)
 end
diff --git a/src/box/lua/sequence.c b/src/box/lua/sequence.c
index bf0714c1a..ae4b5d3ce 100644
--- a/src/box/lua/sequence.c
+++ b/src/box/lua/sequence.c
@@ -49,6 +49,17 @@ lbox_sequence_next(struct lua_State *L)
 	return 1;
 }
 
+static int
+lbox_sequence_current(struct lua_State *L)
+{
+	uint32_t seq_id = luaL_checkinteger(L, 1);
+	int64_t result;
+	if (box_sequence_current(seq_id, &result) != 0)
+		luaT_error(L);
+	luaL_pushint64(L, result);
+	return 1;
+}
+
 static int
 lbox_sequence_set(struct lua_State *L)
 {
@@ -174,6 +185,7 @@ box_lua_sequence_init(struct lua_State *L)
 {
 	static const struct luaL_Reg sequence_internal_lib[] = {
 		{"next", lbox_sequence_next},
+		{"current", lbox_sequence_current},
 		{"set", lbox_sequence_set},
 		{"reset", lbox_sequence_reset},
 		{NULL, NULL}
diff --git a/test/box/sequence.result b/test/box/sequence.result
index 0a6cfee2c..5a4cc8153 100644
--- a/test/box/sequence.result
+++ b/test/box/sequence.result
@@ -2289,3 +2289,35 @@ box.space._space_sequence:update({s.id}, {{'=', 2, t[2]}})
 s:drop()
 ---
 ...
+--
+-- gh-4752 current value of sequence
+--
+sq = box.schema.sequence.create('test')
+---
+...
+sq:current()
+---
+- error: Sequence is not initialized yet
+...
+sq:next()
+---
+- 1
+...
+sq:current()
+---
+- 1
+...
+sq:set(42)
+---
+...
+sq:current()
+---
+- 42
+...
+sq:current()
+---
+- 42
+...
+sq:drop()
+---
+...
diff --git a/test/box/sequence.test.lua b/test/box/sequence.test.lua
index 8e00571e5..54011225e 100644
--- a/test/box/sequence.test.lua
+++ b/test/box/sequence.test.lua
@@ -780,3 +780,15 @@ pk = s:create_index('pk', {sequence = true})
 t = box.space._space_sequence:get({s.id})
 box.space._space_sequence:update({s.id}, {{'=', 2, t[2]}})
 s:drop()
+
+--
+-- gh-4752 current value of sequence
+--
+sq = box.schema.sequence.create('test')
+sq:current()
+sq:next()
+sq:current()
+sq:set(42)
+sq:current()
+sq:current()
+sq:drop()
-- 
2.23.0