Swift JSON-RPC 2.0

JSONRPC.swift

import Foundation

class RPCMessage: Codable {
    var container: KeyedDecodingContainer<CodingKeys>
    var timestamp = NSDate.now.timeIntervalSince1970
    
    var jsonrpc = "2.0"
    var method: String?
    var id: Int?
    
    var params: [RPCParameter]?
    var error: RPCError?
    var result: RPCResult?
    
    enum CodingKeys: CodingKey {
        case jsonrpc, method, id, params, error, result
    }
    
    required init(from decoder: Decoder) throws {
        self.container = try decoder.container(keyedBy: CodingKeys.self)
        self.jsonrpc = try container.decode(String.self, forKey: .jsonrpc)
        self.method = try container.decodeIfPresent(String.self, forKey: .method)
        self.id = try container.decodeIfPresent(Int.self, forKey: .id)
        self.error = try container.decodeIfPresent(RPCError.self, forKey: .error)
    }
}

struct RPCError: Codable {
    var code: Code?
    var message: String?
    
    enum Code: Int, Codable {
        case parseError = -32700
        case invalidRequest = -32600
        case methodNotFound = -32601
        case invalidParams = -32602
        case internalError = -32603
    }
}

// inherit for method params
class RPCParameter: Codable {}

// inherit for method results
class RPCResult: Codable {}

// usage
let decoder = JSONDecoder()
let message = try decoder.decode(RPCMessage.self, from: data)

// decode params from request
if message.method != nil {
  let params = try message.container.decode([MyParameter].self, forKey: .params)
}
  
// decode result from response
if message.method == nil {
  let result = try message.container.decode(MyResult.self, forKey: .result)
}