BLE: image transfer between 2 ios devices using CoreBluetooth

Question

I have 2 iOS devices: one is Peripheral and the other Central. I want that the data would be image.

I have tried with a string value and it is working fine but with image I get this error:

read_user_chunkIDOT:1221: invalid PNG file: no valid iEnd chunk

Also I can see that the bytes are different (<CBCharacteristic: 0x1c40bde20, UUID = 2A38, properties = 0x2, value = (null), notifying = NO> Optional(526 bytes)), they are larger when I get them.

This is the peripheral:

if let img = UIImage(named: "maiden") {
        let data = UIImagePNGRepresentation(img)
        let base64 = data?.base64EncodedData(options: .lineLength64Characters)
        let char = CBMutableCharacteristic(type: CHAR_UUID, properties: [.read], value: base64!, permissions: [.readable])
        let myRoei = CBMutableService(type: RX_UUID, primary: true)
        
        myRoei.characteristics = [char]
        cameraPeripheralManager.add(myRoei)
        cameraPeripheralManager.startAdvertising([CBAdvertisementDataServiceUUIDsKey:[RX_UUID], CBAdvertisementDataLocalNameKey: advertisementData])
    }

This is the Central inside didUpdateValueFor characteristic:

print(characteristic.value as Any)
    switch characteristic.uuid {
    case CHAR_UUID:
        let image = UIImage(data: Data(base64Encoded: characteristic.value!, options: .ignoreUnknownCharacters)!)

        self.imageView.image = image
        _ = bodyLocation(from: characteristic)
    case RX_UUID: break
       // onHeartRateReceived(bpm)
    default:
        print("Unhandled Characteristic UUID: \(characteristic.uuid)")
    }

I would like to know where I am wrong.

Answer 1

I have managed doing so with this code:

func sendData() {
    if sendingEOM {
        // send it
        let didSend = cameraPeripheralManager?.updateValue(
            "EOM".data(using: String.Encoding.utf8)!,
            for: char!,
            onSubscribedCentrals: nil
        )
        // Did it send?
        if (didSend == true) {
            // It did, so mark it as sent
            sendingEOM = false
            print("Sent: EOM")
        }
        return
    }
    
    // We're not sending an EOM, so we're sending data
    
    // Is there any left to send?
    guard sendDataIndex! < (dataToSend?.count)! else {
        // No data left.  Do nothing
        return
    }
    
    // There's data left, so send until the callback fails, or we're done.
    var didSend = true
    
    while didSend {
        // Make the next chunk
        
        // Work out how big it should be
        var amountToSend = dataToSend!.count - sendDataIndex!;
        
        // Can't be longer than 20 bytes
        if (amountToSend > NOTIFY_MTU) {
            amountToSend = NOTIFY_MTU;
        }
        
        // Copy out the data we want
        let chunk = dataToSend!.withUnsafeBytes{(body: UnsafePointer<UInt8>) in
            return Data(
                bytes: body + sendDataIndex!,
                count: amountToSend
            )
        }
        
        // Send it
        didSend = cameraPeripheralManager!.updateValue(
            chunk as Data,
            for: char!,
            onSubscribedCentrals: nil
        )
        
        // If it didn't work, drop out and wait for the callback
        if (!didSend) {
            return
        }
        
        let stringFromData = NSString(
            data: chunk as Data,
            encoding: String.Encoding.utf8.rawValue
        )
        
        print("Sent: \(String(describing: stringFromData))")
        
        // It did send, so update our index
        sendDataIndex! += amountToSend;
        
        // Was it the last one?
        if (sendDataIndex! >= dataToSend!.count) {
            
            // It was - send an EOM
            
            // Set this so if the send fails, we'll send it next time
            sendingEOM = true
            
            // Send it
            let eomSent = cameraPeripheralManager!.updateValue(
                "EOM".data(using: String.Encoding.utf8)!,
                for: char!,
                onSubscribedCentrals: nil
            )
            
            if (eomSent) {
                // It sent, we're all done
                sendingEOM = false
                print("Sent: EOM")
            }
            
            return
        }
    }
}

The code below is the client side:

func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) {
    print(characteristic.value as Any)
    switch characteristic.uuid {
    case Constants.CHAR_UUID:
        imageView.image = nil
        print("Char value: \(String(describing: characteristic.value))")
        guard error == nil else {
            print("Error discovering services: \(error!.localizedDescription)")
            return
        }
        
        if  let stringFromData = NSString(data: characteristic.value!, encoding: String.Encoding.utf8.rawValue){
            
            if  (stringFromData.isEqual(to:"EOM")){
                countNumberOfImages += 1
                imageView.image = UIImage(data: data as Data)
               // peripheral.setNotifyValue(false, for: characteristic)
                print("Image number: \(countNumberOfImages)")

                let end = NSDate()   // <<<<<<<<<<   end time
                print("Total data: \(data.length)")
                
                let start = NSDate() // <<<<<<<<<< Start time
                
                data.setData(NSData() as Data)
                //totalData.setData(NSData() as Data)
               // centralManager?.cancelPeripheralConnection(peripheral)
                
            } else {
                // Otherwise, just add the data on to what we already have
                data.append(characteristic.value!)
                totalData.append(characteristic.value!)
                count += 1
               // print("Times: +\(count)")
                // Log it
                print("Received: \(data.length)")
            }
        } else {
            data.append(characteristic.value!)
            totalData.append(characteristic.value!)
            count += 1
          //  print("Times: +\(count)")
            // Log it
            print("Received: \(data.length)")
        }
    default:
        print("Unhandled Characteristic UUID: \(characteristic.uuid)")
    }
}

Very useful code that helps you break the data into chunks and deliver the last chunk with a string to notify the central device that the transfer finished.