writing .proto file for nested structure

[Jay Timbadia]

syntax = "proto3";

message request {

    object message = {"source": [1,2,3,4,5], "target": [1,2,3,4,5]}

message response {

    object message = {"source": [1,2,3,4,5], "target": [1,2,3,4,5]}

}

service fetch {

    rpc calculate (request) returns (response) {}

}

I have data input format mentioned up there. 

Can anyone write me a .proto file which will accept such data json from client, process it and send it back in the same format?