Regex: Only returns message string - That's starts with messages and string between parent message curly brace

I want to get all the message data only. Such that it should look for message and all the data between curly braces of the parent message. With the below code, I am getting service details too along with message which I don't want. Any suggestion on this experts thanks in advance.

String data = "/**\r\n" + 
        " * file\r\n" + 
        " */\r\n" + 
        "syntax = \"proto3\";\r\n" + 
        "package demo;\r\n" + 
        "\r\n" + 
        "import \"envoyproxy/protoc-gen-validate/validate/validate.proto\";\r\n" + 
        "import \"google/api/annotations.proto\";\r\n" + 
        "import \"google/protobuf/wrappers.proto\";\r\n" + 
        "import \"protoc-gen-swagger/options/annotations.proto\";\r\n" + 
        "\r\n" + 
        "option go_package = \"bitbucket.com;\r\n" + 
        "option java_multiple_files = true;\r\n" + 
        "\r\n" + 
        "schemes: HTTPS;\r\n" + 
        "consumes: \"application/json\";\r\n" + 
        "produces: \"application/json\";\r\n" + 
        "responses: {\r\n" + 
        "key:\r\n" + 
        "    \"404\";\r\n" + 
        "value: {\r\n" + 
        "description:\r\n" + 
        "    \"not exist.\";\r\n" + 
        "schema: {\r\n" + 
        "json_schema: {\r\n" + 
        "type:\r\n" + 
        "    STRING;\r\n" + 
        "}\r\n" + 
        "}\r\n" + 
        "}\r\n" + 
        "}\r\n" + 
        "responses: {\r\n" + 
        "key:\r\n" + 
        "    \"401\";\r\n" + 
        "value: {\r\n" + 
        "description:\r\n" + 
        "    \"Wrong user.\";\r\n" + 
        "schema: {\r\n" + 
        "json_schema: {\r\n" + 
        "type:\r\n" + 
        "    STRING;\r\n" + 
        "};\r\n" + 
        "example: {\r\n" + 
        "value:\r\n" + 
        "    '{ \"message\": \"wrong user.\" }'\r\n" + 
        "}\r\n" + 
        "}\r\n" + 
        "}\r\n" + 
        "}\r\n" + 
        "\r\n" + 
        "message message1 {\r\n" + 
        "    message message2 {\r\n" + 
        "        enum Enum {\r\n" + 
        "            UNKNOWN = 0;    \r\n" + 
        "        }\r\n" + 
        "    }\r\n" + 
        "    string id = 1;\r\n" + 
        "    string name = 3;\r\n" + 
        "    string account = 4;\r\n" + 
        "}\r\n" + 
        "\r\n" + 
        "message User{\r\n" + 
        "   string firstName = 1 ;\r\n" + 
        "   string lastName  = 2 ;\r\n" + 
        "   string middleName  = 3 [(validate.rules).repeated = { min_items: 0 }];\r\n" + 
        "}\r\n" + 
        "\r\n" + 
        "service Userlogin{\r\n" + 
        "   rpc Login(User) returns (APIResponse);\r\n" + 
        "}";
List<String> allmsg = Arrays.asList(data.replaceAll("(?sm)\\A.*?(?=message)", "").split("\\R+(?=message)"));

I am expecting response like below in my array list of string with size 2.

allMsg.get(0) should be

message message1 {
    message message2 {
        enum Enum {
            UNKNOWN = 0;    
        }
    }
    string id = 1;
    string name = 3;
    string account = 4;
}

allMsg.get(1) should be

message User{
    string firstName = 1 ;
    string lastName  = 2 ;
    string middleName  = 3 [(validate.rules).repeated = { min_items: 0 }];
}