Hey Scott,

Removing the prefix bytes worked for all the tags except for the one that was too long. I can work with this solution for the near term events. Thank you so much!!! I’m still very curious what those prefix bytes are for, and like I said, CoreNFC has no problems reading them. If you want the Flomio SDK to be as similar to CoreNFC as possible to get the most adoption in the iOS community, you’ll want to figure out why those bytes are there and how CoreNFC has no problems ignoring them. I’d be happy to test your updated SDK when you figure this stuff out.

– Steven

Thanks Scott! With this info I’m able to read the memory just enough to read the first NDEF encoded message. This’ll be enough for what I need in the near future. Here’s the code for reference:

    func didFind(_ tag: FmTag!, fromDevice deviceUuid: String!) {
        DispatchQueue.main.async {
            if let thisUuid = tag.uuid, let thisDeviceId = deviceUuid {
                print("Did find UUID: \(thisUuid) from Device: \(thisDeviceId)")

                self.getFirstNDEFMessage() { response in

                    print("Response: \(response)")
                    self.printBits(hexString: response)

                    guard let prefix = response.uppercased().components(separatedBy: "D1").first else {
                        print("No prefix")
                        return
                    }

                    let range = NSString(string: response).range(of: prefix)
                    var message = NSString(string: response).replacingCharacters(in: range, with: "")

                    guard let withoutSuffix = message.uppercased().components(separatedBy: "FE").first else {
                        print("Could not remove suffix")
                        return
                    }

                    message = withoutSuffix + "FE"

                    print("ndef message: \(message)")

                    let bytes = Utilities.byteArray(fromHexString: message)
                    let ndefMessage = NdefMessage.init(byteBuffer: bytes)

                    print("ndef: \(ndefMessage)")

                    guard let ndef = ndefMessage else {
                        print("ndef was nil!")
                        return
                    }

                    print("ndef error: \(ndef.error)")

                    guard let ndefRecords = ndef.ndefRecords else {
                        print("ndefRecords was nil!")
                        return
                    }

                    for record in ndefRecords {
                        let ndefRecord = record as! NdefRecord
                        print("Payload: " + ndefRecord.payloadString)

                        let status = ndefRecord.payload[0]
                        let encodingBit = Int(status & 0x80)

                        var encoding: String.Encoding

                        if encodingBit == 0 {
                            encoding = .utf8
                        } else {
                            encoding = .utf16
                        }

                        let length = Int(status & 0x3F)

                        let tagId = String.init(data: ndefRecord.payload[length + 1 ... ndefRecord.payload.count - length + 1], encoding: encoding) ?? "<Unknown>"

                        print("TagId: \(tagId)")

                        DispatchQueue.main.async {
                            self.tagLabel.text = tagId
                        }
                    }
                }
            }
        }
    }

    func getFirstNDEFMessage(completionHandler: @escaping (String) -> Void) {
        readBlockAt(page: 4, fullResponse: "") { (fullResponse) in
            print("FullResponse: \(fullResponse)")

            completionHandler(fullResponse)
        }
    }

    func readBlockAt(page: Int, fullResponse: String, completionHandler: @escaping (String) -> Void) {
        let st = String(format:"%02X", page)
        let apdu: String = "FF B0 00 \(st) 10"

        print("CURRENTPAGE: \(page)")
        print("APDUSTRING: \(apdu)")

        flomioMW.sendApdu(apdu, toDevice: self.deviceUuid) { (response) in

            let response = response?.replacingOccurrences(of: "90 00", with: "")

            let fullResponse = fullResponse + " " + (response ?? "")

            guard response != "63 00" else {
                completionHandler(fullResponse)
                return
            }

            guard !(fullResponse.contains("D1") && fullResponse.contains("FE")) else {
                completionHandler(fullResponse)
                return
            }

            self.readBlockAt(page: page + 4, fullResponse: fullResponse, completionHandler: completionHandler)
        }
    }

Hopefully that helps if not you, someone else.

I have a few more questions I’ve asked the forum if you get the time. Thanks so much for your help!

– Steven