format: "{{%PROTOCOL%}}   %RESP(not exist)%++%RESP(test)% %REQ(FIRST?SECOND)% %RESP(FIRST?SECOND)%\t@%TRAILER(THIRD)%@\t%TRAILER(TEST?TEST-2)%[]"
request_headers {
  headers {
    key: "first"
    value: "GET"
  }
  headers {
    key: ":path"
    value: "/"
  }
}
response_headers {
  headers {
    key: "second"
    value: "PUT"
  }
  headers {
    key: "test"
    value: "test"
  }
}
response_trailers {
  headers {
    key: "third"
    value: "POST"
  }
  headers {
    key: "test-2"
    value: "test-2"
  }
}
