[Tarantool-patches] [PATCH 1.10 07/16] WIP: module api/lua: add luaT_tuple_encode()

[Alexander Turenko <alexander.turenko@tarantool.org>]

It is the same as luaT_tuple_new(), but returns raw MsgPack data (not
<box_tuple_t>) allocated on Lua shared ibuf (<tarantool_lua_ibuf>).

The reason to introduce this function is to provide ability to use
box_tuple_compare_with_key() function from an external module for a key
passed as a Lua table. The compare function has the following signature:

 | API_EXPORT int
 | box_tuple_compare_with_key(box_tuple_t *tuple_a, const char *key_b,
 |                            box_key_def_t *key_def);

The second parameter is a key encoded as an MsgPack array, not a tuple
structure. So luaT_tuple_new() is not applicable here (it is not
worthful to create a tuple structure if we need just MsgPack data).

XXX: Add a module API test.

Part of #5273

(cherry picked from commit 5cbb2e41bb32a3184d2663f678b705aef823dc85)
---
 extra/exports       |  1 +
 src/box/lua/tuple.c | 21 +++++++++++++++++----
 src/box/lua/tuple.h | 29 +++++++++++++++++++++++++++++
 3 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/extra/exports b/extra/exports
index 7f8a27ea2..7feaaa05e 100644
--- a/extra/exports
+++ b/extra/exports
@@ -130,6 +130,7 @@ luaL_touint64
 luaL_toint64
 luaT_pushtuple
 luaT_istuple
+luaT_tuple_encode
 luaT_tuple_new
 luaT_error
 luaT_call
diff --git a/src/box/lua/tuple.c b/src/box/lua/tuple.c
index 6732ac71a..ddc4f6087 100644
--- a/src/box/lua/tuple.c
+++ b/src/box/lua/tuple.c
@@ -97,8 +97,8 @@ luaT_istuple(struct lua_State *L, int narg)
 	return *(struct tuple **) data;
 }
 
-box_tuple_t *
-luaT_tuple_new(struct lua_State *L, int idx, box_tuple_format_t *format)
+char *
+luaT_tuple_encode(struct lua_State *L, int idx, size_t *tuple_len_ptr)
 {
 	if (idx != 0 && !lua_istable(L, idx) && !luaT_istuple(L, idx)) {
 		diag_set(IllegalParams, "A tuple or a table expected, got %s",
@@ -126,8 +126,21 @@ luaT_tuple_new(struct lua_State *L, int idx, box_tuple_format_t *format)
 		luamp_encode_tuple(L, &tuple_serializer, &stream, idx);
 	}
 	mpstream_flush(&stream);
-	box_tuple_t *tuple = box_tuple_new(format, buf->buf,
-					   buf->buf + ibuf_used(buf));
+	if (tuple_len_ptr != NULL)
+		*tuple_len_ptr = ibuf_used(buf);
+	return buf->buf;
+
+}
+
+box_tuple_t *
+luaT_tuple_new(struct lua_State *L, int idx, box_tuple_format_t *format)
+{
+	size_t tuple_len;
+	char *tuple_data = luaT_tuple_encode(L, idx, &tuple_len);
+	if (tuple_data == NULL)
+		return NULL;
+	box_tuple_t *tuple = box_tuple_new(format, tuple_data,
+					   tuple_data + tuple_len);
 	if (tuple == NULL)
 		return NULL;
 	ibuf_reinit(tarantool_lua_ibuf);
diff --git a/src/box/lua/tuple.h b/src/box/lua/tuple.h
index 196a38c2d..fcb7a9d87 100644
--- a/src/box/lua/tuple.h
+++ b/src/box/lua/tuple.h
@@ -67,6 +67,35 @@ luaT_pushtuple(struct lua_State *L, box_tuple_t *tuple);
 box_tuple_t *
 luaT_istuple(struct lua_State *L, int idx);
 
+/**
+ * Encode a Lua table, a tuple or objects on a Lua stack as raw
+ * tuple data (MsgPack).
+ *
+ * @param L             Lua state
+ * @param idx           acceptable index on the Lua stack
+ *                      (or zero, see below)
+ * @param tuple_len_ptr where to store tuple data size in bytes
+ *                      (or NULL)
+ *
+ * Set idx to zero to create the new tuple from objects on the Lua
+ * stack.
+ *
+ * The data is encoded on the shared buffer: so called
+ * <tarantool_lua_ibuf> (it also available as <buffer.SHARED_IBUF>
+ * in Lua). The data is valid until next similar call. It is
+ * generally safe to pass the result to a box function (copy it if
+ * doubt). No need to release this buffer explicitly, it'll be
+ * reused by later calls.
+ *
+ * If encoding fails, raise an error.
+ *
+ * In case of any other error set a diag and return NULL.
+ *
+ * @sa luaT_tuple_new()
+ */
+API_EXPORT char *
+luaT_tuple_encode(struct lua_State *L, int idx, size_t *tuple_len_ptr);
+
 /**
  * Create a new tuple with specific format from a Lua table, a
  * tuple, or objects on the lua stack.
-- 
2.25.0