echo.proto

service Echo {
  rpc OneToOne(Message) returns (Message) {}
  rpc OneToMany(Message) returns (stream Message) {}
  rpc ManyToOne(stream Message) returns (Message) {}
  rpc ManyToMany(stream Message) returns (stream Message) {}
}

message Message {
  int32 seq = 1;
  string title = 2;
  string content = 3;
}