[PATCH v2 1/9] box: refactor box_lua_find helper

[Kirill Shcherbatov <kshcherbatov@tarantool.org>]

The box_lua_find routine used to work with an empty stack only.
It is unacceptable in following patches because this helper
need to be reused in following patches for environment table
construction.
The definition also is moved to lua/utils.h.

Needed for #4182, #1260
---
 src/box/lua/call.c | 85 ++++++++--------------------------------------
 src/lua/utils.c    | 59 ++++++++++++++++++++++++++++++++
 src/lua/utils.h    | 11 ++++++
 3 files changed, 85 insertions(+), 70 deletions(-)

diff --git a/src/box/lua/call.c b/src/box/lua/call.c
index 04020ef6f..c729778c4 100644
--- a/src/box/lua/call.c
+++ b/src/box/lua/call.c
@@ -44,73 +44,6 @@
 #include "trivia/util.h"
 #include "mpstream.h"
 
-/**
- * A helper to find a Lua function by name and put it
- * on top of the stack.
- */
-static int
-box_lua_find(lua_State *L, const char *name, const char *name_end)
-{
-	int index = LUA_GLOBALSINDEX;
-	int objstack = 0;
-	const char *start = name, *end;
-
-	while ((end = (const char *) memchr(start, '.', name_end - start))) {
-		lua_checkstack(L, 3);
-		lua_pushlstring(L, start, end - start);
-		lua_gettable(L, index);
-		if (! lua_istable(L, -1)) {
-			diag_set(ClientError, ER_NO_SUCH_PROC,
-				 name_end - name, name);
-			luaT_error(L);
-		}
-		start = end + 1; /* next piece of a.b.c */
-		index = lua_gettop(L); /* top of the stack */
-	}
-
-	/* box.something:method */
-	if ((end = (const char *) memchr(start, ':', name_end - start))) {
-		lua_checkstack(L, 3);
-		lua_pushlstring(L, start, end - start);
-		lua_gettable(L, index);
-		if (! (lua_istable(L, -1) ||
-			lua_islightuserdata(L, -1) || lua_isuserdata(L, -1) )) {
-				diag_set(ClientError, ER_NO_SUCH_PROC,
-					  name_end - name, name);
-				luaT_error(L);
-		}
-		start = end + 1; /* next piece of a.b.c */
-		index = lua_gettop(L); /* top of the stack */
-		objstack = index;
-	}
-
-
-	lua_pushlstring(L, start, name_end - start);
-	lua_gettable(L, index);
-	if (!lua_isfunction(L, -1) && !lua_istable(L, -1)) {
-		/* lua_call or lua_gettable would raise a type error
-		 * for us, but our own message is more verbose. */
-		diag_set(ClientError, ER_NO_SUCH_PROC,
-			  name_end - name, name);
-		luaT_error(L);
-	}
-	/* setting stack that it would contain only
-	 * the function pointer. */
-	if (index != LUA_GLOBALSINDEX) {
-		if (objstack == 0) {        /* no object, only a function */
-			lua_replace(L, 1);
-		} else if (objstack == 1) { /* just two values, swap them */
-			lua_insert(L, -2);
-		} else {		    /* long path */
-			lua_insert(L, 1);
-			lua_insert(L, 2);
-			objstack = 1;
-		}
-		lua_settop(L, 1 + objstack);
-	}
-	return 1 + objstack;
-}
-
 /**
  * A helper to find lua stored procedures for box.call.
  * box.call iteslf is pure Lua, to avoid issues
@@ -124,7 +57,12 @@ lbox_call_loadproc(struct lua_State *L)
 	const char *name;
 	size_t name_len;
 	name = lua_tolstring(L, 1, &name_len);
-	return box_lua_find(L, name, name + name_len);
+	int count;
+	if (luaT_func_find(L, name, name + name_len, &count) != 0) {
+		diag_set(ClientError, ER_NO_SUCH_PROC, name_len, name);
+		return luaT_error(L);
+	}
+	return count;
 }
 
 /*
@@ -292,9 +230,16 @@ execute_lua_call(lua_State *L)
 	const char *name = request->name;
 	uint32_t name_len = mp_decode_strl(&name);
 
-	int oc = 0; /* how many objects are on stack after box_lua_find */
+	/*
+	 * How many objects are on stack after
+	 * luaT_func_find call.
+	 */
+	int oc = 0;
 	/* Try to find a function by name in Lua */
-	oc = box_lua_find(L, name, name + name_len);
+	if (luaT_func_find(L, name, name + name_len, &oc) != 0) {
+		diag_set(ClientError, ER_NO_SUCH_PROC, name_len, name);
+		return luaT_error(L);
+	}
 
 	/* Push the rest of args (a tuple). */
 	const char *args = request->args;
diff --git a/src/lua/utils.c b/src/lua/utils.c
index 01a0cd894..27ff6b396 100644
--- a/src/lua/utils.c
+++ b/src/lua/utils.c
@@ -1189,6 +1189,65 @@ void luaL_iterator_delete(struct luaL_iterator *it)
 
 /* }}} */
 
+int
+luaT_func_find(struct lua_State *L, const char *name, const char *name_end,
+	       int *count)
+{
+	int index = LUA_GLOBALSINDEX;
+	int objstack = 0, top = lua_gettop(L);
+	const char *start = name, *end;
+
+	while ((end = (const char *) memchr(start, '.', name_end - start))) {
+		lua_checkstack(L, 3);
+		lua_pushlstring(L, start, end - start);
+		lua_gettable(L, index);
+		if (! lua_istable(L, -1))
+			return -1;
+		start = end + 1; /* next piece of a.b.c */
+		index = lua_gettop(L); /* top of the stack */
+	}
+
+	/* box.something:method */
+	if ((end = (const char *) memchr(start, ':', name_end - start))) {
+		lua_checkstack(L, 3);
+		lua_pushlstring(L, start, end - start);
+		lua_gettable(L, index);
+		if (! (lua_istable(L, -1) ||
+			lua_islightuserdata(L, -1) || lua_isuserdata(L, -1) ))
+				return -1;
+		start = end + 1; /* next piece of a.b.c */
+		index = lua_gettop(L); /* top of the stack */
+		objstack = index - top;
+	}
+
+	lua_pushlstring(L, start, name_end - start);
+	lua_gettable(L, index);
+	if (!lua_isfunction(L, -1) && !lua_istable(L, -1)) {
+		/* lua_call or lua_gettable would raise a type error
+		 * for us, but our own message is more verbose. */
+		return -1;
+	}
+
+	/* setting stack that it would contain only
+	 * the function pointer. */
+	if (index != LUA_GLOBALSINDEX) {
+		if (objstack == 0) {        /* no object, only a function */
+			lua_replace(L, top + 1);
+			lua_pop(L, lua_gettop(L) - top - 1);
+		} else if (objstack == 1) { /* just two values, swap them */
+			lua_insert(L, -2);
+			lua_pop(L, lua_gettop(L) - top - 2);
+		} else {                    /* long path */
+			lua_insert(L, top + 1);
+			lua_insert(L, top + 2);
+			lua_pop(L, objstack - 1);
+			objstack = 1;
+		}
+	}
+	*count = 1 + objstack;
+	return 0;
+}
+
 int
 tarantool_lua_utils_init(struct lua_State *L)
 {
diff --git a/src/lua/utils.h b/src/lua/utils.h
index 943840ec0..81e936bee 100644
--- a/src/lua/utils.h
+++ b/src/lua/utils.h
@@ -592,6 +592,17 @@ void luaL_iterator_delete(struct luaL_iterator *it);
 
 /* }}} */
 
+/**
+ * A helper to find a Lua function by name and put it
+ * on top of the stack.
+ * Returns 0 in case of succsess and -1 otherwise; in case of
+ * success also uses count[out] argument to return the how many
+ * objects are pushed on to stack.
+ */
+int
+luaT_func_find(struct lua_State *L, const char *name, const char *name_end,
+	       int *count);
+
 int
 tarantool_lua_utils_init(struct lua_State *L);
 
-- 
2.21.0