Created
April 4, 2023 13:37
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DNS resolver - test implemention - not prod ready
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| func handlePacket(packetData: Data,syntheticIp: String) { | |
| if(syntheticIp == "" || syntheticIp.isEmpty){ | |
| os_log(.default, log: self.log, "*****No synthetic ip found") | |
| return | |
| } | |
| let udpPayload : Data = packetData[28..<packetData.count] | |
| do { | |
| //to deserialize we used https://github.com/Bouke/DNS | |
| let dnsQuery = try Message(deserialize: udpPayload) | |
| os_log(.default, log: self.log, "________inside dnsQuery:===>>responseData=>> %{public}@",dnsQuery.debugDescription) | |
| var dnsResponse = Message(id: dnsQuery.id, type: .response) | |
| // Add the questions from the query to the response | |
| dnsResponse.questions = dnsQuery.questions | |
| // Add the answers to the response | |
| let answer = HostRecord<IPv4>(name: dnsQuery.questions.first?.name ?? "", ttl: 3600, ip: IPv4(syntheticIp)!) | |
| dnsResponse.answers.append(answer) | |
| let responseData = try dnsResponse.serialize() | |
| updateDnsDataPacket(packetData: packetData, syntheticIp: syntheticIp, queryResponseData: responseData) | |
| } catch { | |
| os_log(.default, log: self.log, "inside handlePacket:dnsQuery=error %{public}@",error as CVarArg) | |
| } | |
| } | |
| func updateDnsDataPacket(packetData: Data,syntheticIp: String, queryResponseData: Data){ | |
| // Get a mutable copy of the packet | |
| let mutablePacket = NSMutableData(data: packetData) | |
| //convert ipv4 ip address to UInt32 | |
| let newDestinationIP = ipv4StringToUInt32(syntheticIp) | |
| if(newDestinationIP == nil){ | |
| os_log(.default, log: self.log, "syntheticIp to UInt32 failed") | |
| return; | |
| } | |
| // Update the destination IP address | |
| let newDestinationIPBytes = withUnsafeBytes(of: newDestinationIP!.bigEndian) { Data($0) } | |
| newDestinationIPBytes.withUnsafeBytes { (pointer: UnsafeRawBufferPointer) -> Void in | |
| mutablePacket.replaceBytes(in: NSRange(location: 16, length: 4), withBytes: pointer.baseAddress!) | |
| } | |
| let udpLength = queryResponseData.count + 8 //update the udp length [constructed response data length + 8(udp header default length)] | |
| let udpLengthHexString = String(format: "%04X", udpLength) | |
| let ipV4Length = udpLength+20 //update the ipv4 length [udp data length + 20(ipv4 header default length)] | |
| let ipV4LengthHexString = String(format: "%04X", ipV4Length) | |
| var updatedDataPacket = mutablePacket as Data | |
| var updatedHexString = updatedDataPacket.hexEncodedString() | |
| //update ipv4 length | |
| let ipv4StartIndex = updatedHexString.index(updatedHexString.startIndex, offsetBy: 4) //byte offset 2-3 is for ipv4 length | |
| let ipv4EndIndex = updatedHexString.index(updatedHexString.startIndex, offsetBy: 8) | |
| updatedHexString.replaceSubrange(ipv4StartIndex..<ipv4EndIndex, with: ipV4LengthHexString) | |
| //update udp length | |
| let udpStartIndex = updatedHexString.index(updatedHexString.startIndex, offsetBy: 48) //byte offset 24-25 is for udp length | |
| let udpEndIndex = updatedHexString.index(updatedHexString.startIndex, offsetBy: 52) | |
| updatedHexString.replaceSubrange(udpStartIndex..<udpEndIndex, with: udpLengthHexString) | |
| //update udp response | |
| let udpResponseStartIndex = updatedHexString.index(updatedHexString.startIndex, offsetBy: 56) //byte offset 28-END is for udp query data | |
| let udpResponseEndIndex = updatedHexString.index(updatedHexString.startIndex, offsetBy: updatedHexString.count) | |
| updatedHexString.replaceSubrange(udpResponseStartIndex..<udpResponseEndIndex, with: queryResponseData.hexEncodedString()) | |
| os_log(.default, log: self.log, "updatedHexString: %{public}@",updatedHexString) | |
| let rawDataPacket = Data(fromHexEncodedString: updatedHexString)! | |
| let udpPacket : Data = rawDataPacket[20..<rawDataPacket.count]// your UDP packet as Data | |
| os_log(.default, log: self.log, "updatedHexString: udpPacket : %{public}@",udpPacket.hexEncodedString()) | |
| // let byteArray = [UInt8](udpPacket) | |
| // let checksum = checksum(bytes: byteArray) | |
| // os_log(.default, log: self.log, "updatedHexString checksum: %{public}@",checksum.description) | |
| let ipv4CheckSum = calculateIPv4HeaderChecksum(packetData: rawDataPacket) | |
| let ipV4CheckSumString = String(format: "%04X", ipv4CheckSum) | |
| //update ipv4 checksum | |
| let ipv4CheckSumStartIndex = updatedHexString.index(updatedHexString.startIndex, offsetBy: 20) //byte offset 10-11 is for ipv4 checksum | |
| let ipv4CheckSumEndIndex = updatedHexString.index(updatedHexString.startIndex, offsetBy: 24) | |
| updatedHexString.replaceSubrange(ipv4CheckSumStartIndex..<ipv4CheckSumEndIndex, with: ipV4CheckSumString) | |
| //update udp checksum | |
| let udpCheckSumStartIndex = updatedHexString.index(updatedHexString.startIndex, offsetBy: 52) //byte offset 26-27 is for udp checksum | |
| let udpCheckSumEndIndex = updatedHexString.index(updatedHexString.startIndex, offsetBy: 56) | |
| updatedHexString.replaceSubrange(udpCheckSumStartIndex..<udpCheckSumEndIndex, with: "0000") | |
| // let checksum = calculateUDPChecksum(packetData: rawDataPacket) | |
| // os_log(.default, log: self.log, "updatedHexString checksum: %{public}@",checksum) | |
| //finally update the mutable packet with the update hex string | |
| updatedDataPacket = Data(fromHexEncodedString: updatedHexString)! | |
| os_log(.default, log: self.log, "updatedHexString: befire sending %{public}@",updatedDataPacket.hexEncodedString()) | |
| //write packet to server | |
| let proto = protocolNumber(for: updatedDataPacket) | |
| let success = self.packetFlow.writePackets([updatedDataPacket], withProtocols: [proto]) | |
| os_log(.default, log: self.log, "packetFlow.writePackets: %{public}@",success.description) | |
| } | |
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Does it work? where is the method calculateIPv4HeaderChecksum