[PATCH v2 3/6] lua: add luaT_newtuple()

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

The function allows to create a tuple with specific tuple format in C
code using a Lua table, an another tuple or objects on a Lua stack.

Needed for #3276.
---
 src/box/lua/tuple.c | 91 +++++++++++++++++++++++++++++++++------------
 src/box/lua/tuple.h | 15 ++++++++
 2 files changed, 83 insertions(+), 23 deletions(-)

diff --git a/src/box/lua/tuple.c b/src/box/lua/tuple.c
index 1867f810f..7e9ad89fe 100644
--- a/src/box/lua/tuple.c
+++ b/src/box/lua/tuple.c
@@ -92,6 +92,65 @@ luaT_istuple(struct lua_State *L, int narg)
 	return *(struct tuple **) data;
 }
 
+struct tuple *
+luaT_newtuple(struct lua_State *L, int idx, box_tuple_format_t *format)
+{
+	struct tuple *tuple;
+
+	if (idx == 0 || lua_istable(L, idx)) {
+		struct ibuf *buf = tarantool_lua_ibuf;
+		ibuf_reset(buf);
+		struct mpstream stream;
+		mpstream_init(&stream, buf, ibuf_reserve_cb, ibuf_alloc_cb,
+		      luamp_error, L);
+		if (idx == 0) {
+			/*
+			 * Create the tuple from lua stack
+			 * objects.
+			 */
+			int argc = lua_gettop(L);
+			mpstream_encode_array(&stream, argc);
+			for (int k = 1; k <= argc; ++k) {
+				luamp_encode(L, luaL_msgpack_default, &stream,
+					     k);
+			}
+		} else {
+			/* Create the tuple from a Lua table. */
+			luamp_encode_tuple(L, luaL_msgpack_default, &stream,
+					   idx);
+		}
+		mpstream_flush(&stream);
+		tuple = box_tuple_new(format, buf->buf,
+				      buf->buf + ibuf_used(buf));
+		if (tuple == NULL) {
+			luaT_pusherror(L, diag_last_error(diag_get()));
+			return NULL;
+		}
+		ibuf_reinit(tarantool_lua_ibuf);
+		return tuple;
+	}
+
+	tuple = luaT_istuple(L, idx);
+	if (tuple == NULL) {
+		lua_pushfstring(L, "A tuple or a table expected, got %s",
+				lua_typename(L, lua_type(L, -1)));
+		return NULL;
+	}
+
+	/*
+	 * Create the new tuple with the necessary format from
+	 * the another tuple.
+	 */
+	const char *tuple_beg = tuple_data(tuple);
+	const char *tuple_end = tuple_beg + tuple->bsize;
+	tuple = box_tuple_new(format, tuple_beg, tuple_end);
+	if (tuple == NULL) {
+		luaT_pusherror(L, diag_last_error(diag_get()));
+		return NULL;
+	}
+	return tuple;
+}
+
 int
 lbox_tuple_new(lua_State *L)
 {
@@ -100,33 +159,19 @@ lbox_tuple_new(lua_State *L)
 		lua_newtable(L); /* create an empty tuple */
 		++argc;
 	}
-	struct ibuf *buf = tarantool_lua_ibuf;
-
-	ibuf_reset(buf);
-	struct mpstream stream;
-	mpstream_init(&stream, buf, ibuf_reserve_cb, ibuf_alloc_cb,
-		      luamp_error, L);
-
-	if (argc == 1 && (lua_istable(L, 1) || luaT_istuple(L, 1))) {
-		/* New format: box.tuple.new({1, 2, 3}) */
-		luamp_encode_tuple(L, luaL_msgpack_default, &stream, 1);
-	} else {
-		/* Backward-compatible format: box.tuple.new(1, 2, 3). */
-		mpstream_encode_array(&stream, argc);
-		for (int k = 1; k <= argc; ++k) {
-			luamp_encode(L, luaL_msgpack_default, &stream, k);
-		}
-	}
-	mpstream_flush(&stream);
-
+	/*
+	 * Use backward-compatible parameters format:
+	 * box.tuple.new(1, 2, 3) (idx == 0), or the new one:
+	 * box.tuple.new({1, 2, 3}) (idx == 1).
+	 */
+	int idx = argc == 1 && (lua_istable(L, 1) ||
+		luaT_istuple(L, 1));
 	box_tuple_format_t *fmt = box_tuple_format_default();
-	struct tuple *tuple = box_tuple_new(fmt, buf->buf,
-					   buf->buf + ibuf_used(buf));
+	struct tuple *tuple = luaT_newtuple(L, idx, fmt);
 	if (tuple == NULL)
-		return luaT_error(L);
+		return lua_error(L);
 	/* box_tuple_new() doesn't leak on exception, see public API doc */
 	luaT_pushtuple(L, tuple);
-	ibuf_reinit(tarantool_lua_ibuf);
 	return 1;
 }
 
diff --git a/src/box/lua/tuple.h b/src/box/lua/tuple.h
index 5d7062eb8..3319b951e 100644
--- a/src/box/lua/tuple.h
+++ b/src/box/lua/tuple.h
@@ -41,6 +41,8 @@ typedef struct tuple box_tuple_t;
 struct lua_State;
 struct mpstream;
 struct luaL_serializer;
+struct tuple_format;
+typedef struct tuple_format box_tuple_format_t;
 
 /** \cond public */
 
@@ -66,6 +68,19 @@ luaT_istuple(struct lua_State *L, int idx);
 
 /** \endcond public */
 
+/**
+ * Create the new tuple with specific format from a Lua table, a
+ * tuple or objects on the lua stack.
+ *
+ * Set idx to zero to create the new tuple from objects on the lua
+ * stack.
+ *
+ * In case of an error push the error message to the Lua stack and
+ * return NULL.
+ */
+struct tuple *
+luaT_newtuple(struct lua_State *L, int idx, box_tuple_format_t *format);
+
 int
 lbox_tuple_new(struct lua_State *L);
 
-- 
2.20.1