diff --git a/lualib-src/sproto/lsproto.c b/lualib-src/sproto/lsproto.c
index c33118d4..99448487 100644
--- a/lualib-src/sproto/lsproto.c
+++ b/lualib-src/sproto/lsproto.c
@@ -573,6 +573,55 @@ lloadproto(lua_State *L) {
 	return 1;
 }
 
+static int
+encode_default(const struct sproto_arg *args) {
+	lua_State *L = args->ud;
+	lua_pushstring(L, args->tagname);
+	if (args->index > 0) {
+		lua_newtable(L);
+	} else {
+		switch(args->type) {
+		case SPROTO_TINTEGER:
+			lua_pushinteger(L, 0);
+			break;
+		case SPROTO_TBOOLEAN:
+			lua_pushboolean(L, 0);
+			break;
+		case SPROTO_TSTRING:
+			lua_pushliteral(L, "");
+			break;
+		case SPROTO_TSTRUCT:
+			lua_createtable(L, 0, 1);
+			lua_pushstring(L, sproto_name(args->subtype));
+			lua_setfield(L, -2, "__type");
+			break;
+		}
+	}
+	lua_rawset(L, -3);
+	return 0;
+}
+
+/*
+	lightuserdata sproto_type
+	return default table
+ */
+static int
+ldefault(lua_State *L) {
+	int ret;
+	// 32 is enough for dummy buffer, because ldefault encode nothing but the header.
+	char dummy[32];
+	struct sproto_type * st = lua_touserdata(L, 1);
+	if (st == NULL) {
+		return luaL_argerror(L, 1, "Need a sproto_type object");
+	}
+	lua_newtable(L);
+	ret = sproto_encode(st, dummy, sizeof(dummy), encode_default, L);
+	if (ret<0) {
+		return luaL_error(L, "dummy buffer (%d) is too small", (int)sizeof(dummy));
+	}
+	return 1;
+}
+
 int
 luaopen_sproto_core(lua_State *L) {
 #ifdef luaL_checkversion
@@ -587,6 +636,7 @@ luaopen_sproto_core(lua_State *L) {
 		{ "protocol", lprotocol },
 		{ "loadproto", lloadproto },
 		{ "saveproto", lsaveproto },
+		{ "default", ldefault },
 		{ NULL, NULL },
 	};
 	luaL_newlib(L,l);
diff --git a/lualib-src/sproto/sproto.c b/lualib-src/sproto/sproto.c
index c37fdc1b..11756796 100644
--- a/lualib-src/sproto/sproto.c
+++ b/lualib-src/sproto/sproto.c
@@ -500,7 +500,11 @@ sproto_dump(struct sproto *s) {
 	printf("=== %d protocol ===\n", s->protocol_n);
 	for (i=0;i<s->protocol_n;i++) {
 		struct protocol *p = &s->proto[i];
-		printf("\t%s (%d) request:%s", p->name, p->tag, p->p[SPROTO_REQUEST]->name);
+		if (p->p[SPROTO_REQUEST]) {
+			printf("\t%s (%d) request:%s", p->name, p->tag, p->p[SPROTO_REQUEST]->name);
+		} else {
+			printf("\t%s (%d) request:(null)", p->name, p->tag);
+		}
 		if (p->p[SPROTO_RESPONSE]) {
 			printf(" response:%s", p->p[SPROTO_RESPONSE]->name);
 		}
diff --git a/lualib/sproto.lua b/lualib/sproto.lua
index a9466f9c..911dc877 100644
--- a/lualib/sproto.lua
+++ b/lualib/sproto.lua
@@ -101,27 +101,64 @@ end
 
 function sproto:request_encode(protoname, tbl)
 	local p = queryproto(self, protoname)
-	return core.encode(p.request,tbl) , p.tag
+	local request = p.request
+	if request then
+		return core.encode(request,tbl) , p.tag
+	else
+		return "" , p.tag
+	end
 end
 
 function sproto:response_encode(protoname, tbl)
 	local p = queryproto(self, protoname)
-	return core.encode(p.response,tbl)
+	local response = p.response
+	if response then
+		return core.encode(response,tbl)
+	else
+		return ""
+	end
 end
 
 function sproto:request_decode(protoname, ...)
 	local p = queryproto(self, protoname)
-	return core.decode(p.request,...) , p.name
+	local request = p.request
+	if request then
+		return core.decode(request,...) , p.name
+	else
+		return nil, p.name
+	end
 end
 
 function sproto:response_decode(protoname, ...)
 	local p = queryproto(self, protoname)
-	return core.decode(p.response,...)
+	local response = p.response
+	if response then
+		return core.decode(response,...)
+	end
 end
 
 sproto.pack = core.pack
 sproto.unpack = core.unpack
 
+function sproto:default(typename, type)
+	if type == nil then
+		return core.default(querytype(self, typename))
+	else
+		local p = queryproto(self, typename)
+		if type == "REQUEST" then
+			if p.request then
+				return core.default(p.request)
+			end
+		elseif type == "RESPONSE" then
+			if p.response then
+				return core.default(p.response)
+			end
+		else
+			error "Invalid type"
+		end
+	end
+end
+
 local header_tmp = {}
 
 local function gen_response(self, response, session)
diff --git a/lualib/sprotoparser.lua b/lualib/sprotoparser.lua
index e7da7fa0..7b0b04e2 100644
--- a/lualib/sprotoparser.lua
+++ b/lualib/sprotoparser.lua
@@ -194,7 +194,7 @@ local function check_protocol(r)
 		local request = v.request
 		local response = v.response
 		local p = map[tag]
-		
+
 		if p then
 			error(string.format("redefined protocol tag %d at %s", tag, name))
 		end
@@ -340,9 +340,6 @@ local function packtype(name, t, alltypes)
 end
 
 local function packproto(name, p, alltypes)
---	if p.request == nil then
---		error(string.format("Protocol %s need request", name))
---	end
 	if p.request then
 		local request = alltypes[p.request]
 		if request == nil then