how to send bytes from bloomrpc?

Question

I defined .proto file like, test.proto

syntax = "proto3";

package unary;

service Greeter {
   rpc greet (Request) returns (Response) {}
}
message Request {
   bytes username = 1;
}
message Response {
   string message = 1;
}

and When i import this test.proto file in bloomrpc it genrate json like,

{
  "username": {
    "type": "Buffer",
    "data": [
      72,
      101,
      108,
      108,
      111
    ]
  }
}

So,can any one explain what is this format of json. what this type as buffer? and data[] list?