struct JSON: Decodable {
  let block1: Format
  let block2: Format
  let block3: Format
}

struct Format: Decodable {
  let metadata: MetaData //[String: Any]
  let columns: [String] // columns names
  let data: [[Any]] // data of type in metadata
}

struct MetaData: Decodable {

    enum CodingKeys: String, CodingKey {
        case type, bytes
        case maxSize = "max_size"
    }

    let type: String
    let bytes: Int?
    let maxSize: Int?

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)

        self.type = try container.decode(String.self, forKey: .type)
        self.bytes = try container.decode(Int.self, forKey: .bytes)
        self.maxSize = try container.decode(Int.self, forKey: .maxSize)
    }
}