Convert bytes to string not working

Question

I receive Array with bytes:

var requestPtr = [3, 64, 0, 73, 0, 110, 0, 116, 0, 101, 0, 114, 0, 110, 0, 97, 0, 108, 0, 32, 0, 70, 0, 108, 0, 97, 0, 115, 0, 104, 0, 32, 0, 32, 0, 47, 0, 48, 0, 120, 0, 48, 0, 56, 0, 48, 0, 48, 0, 48, 0, 48, 0, 48, 0, 48, 0, 47, 0, 48, 0, 52, 0, 42, 0, 48, 0, 49, 0, 54, 0, 75, 0, 103, 0, 44, 0, 48, 0, 49, 0, 42, 0, 48, 0, 54, 0, 52, 0, 75, 0, 103, 0, 44, 0, 48, 0, 55, 0, 42, 0, 49, 0, 50, 0, 56, 0, 75, 0, 103, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

Then remove first byte and convert array to string with this code:

requestPtr.remove(at: 0)

let nsdata = NSData(bytes: requestPtr, length: requestPtr.count)
var str = String(data: nsdata as Data, encoding: String.Encoding.utf8)!

If i do print in console it returns me string: But i get weird encoding, when try to copy message.

And functions like str.hasPrefix("@Internal Flash") not working.

And var tmp1 = description.components(separatedBy: ["/"]) returns:

["\u{03}@\0I\0n\0t\0e\0r\0n\0a\0l\0 \0F\0l\0a\0s\0h\0 \0 \0", "\00\0x\00\08\00\00\00\00\00\00\0", "\00\04\0*\00\01\06\0K\0g\0,\00\01\0*\00\06\04\0K\0g\0,\00\07\0*\01\02\08\0K\0g\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"]

Gurdev Singh · Accepted Answer · 2016-12-16 11:36:42Z

1

There is a need to define the byte array of type [UInt8]. Below mentioned will work and return True

var requestPtr:[UInt8] = [3, 73, 110, 116, 101, 114, 110, 97, 108, 32, 70, 108, 97, 115, 104] requestPtr.remove(at: 0) print(requestPtr.count) print(requestPtr) let nsdata = NSData(bytes: requestPtr as [UInt8], length: requestPtr.count) var str = String(data: nsdata as Data, encoding: String.Encoding.utf8)! str.hasPrefix("Internal Flash")

answered Dec 16, 2016 at 11:36

Gurdev Singh

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1 Comment

Gurdev Singh Over a year ago

@Arti in your original code array is define with implicit type conversion due to which it's being converted differently when byte array is being converted to NSData. In my answer code byte array is explicitly defined as array of UInt8.

OOPer · Accepted Answer · 2016-12-16 15:48:58Z

1

It seems the data is encoded in UTF-16LE (little endian UTF-16), not in UTF-8.

(Code updated to clarify, with what data I have got the result shown.)

var requestPtr = [3, 64, 0, 73, 0, 110, 0, 116, 0, 101, 0, 114, 0, 110, 0, 97, 0, 108, 0, 32, 0, 70, 0, 108, 0, 97, 0, 115, 0, 104, 0, 32, 0, 32, 0, 47, 0, 48, 0, 120, 0, 48, 0, 56, 0, 48, 0, 48, 0, 48, 0, 48, 0, 48, 0, 48, 0, 47, 0, 48, 0, 52, 0, 42, 0, 48, 0, 49, 0, 54, 0, 75, 0, 103, 0, 44, 0, 48, 0, 49, 0, 42, 0, 48, 0, 54, 0, 52, 0, 75, 0, 103, 0, 44, 0, 48, 0, 55, 0, 42, 0, 49, 0, 50, 0, 56, 0, 75, 0, 103, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

requestPtr.remove(at: 0)

let data = Data(bytes: requestPtr.map{UInt8($0)})
var str = String(data: data, encoding: String.Encoding.utf16LittleEndian)!.trimmingCharacters(in: CharacterSet(charactersIn: "\0"))

debugPrint(str) //->"@Internal Flash  /0x08000000/04*016Kg,01*064Kg,07*128Kg"

(The actual data is said to be [UInt8], but .map{UInt8($0)} is making it.)

edited Dec 16, 2016 at 15:48

answered Dec 16, 2016 at 11:32

OOPer

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9 Comments

Arti Over a year ago

how do you detect encoding? this doesn't work

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OOPer Over a year ago

UTF-16LE is one possible candidate to interpret your byte sequence. And please explain how you get that this doesn't work string.

OOPer Over a year ago

@Arti, I have found it. You have tried my code without your requestPtr.remove(at: 0). Please try my code after requestPtr.remove(at: 0).

OOPer Over a year ago

@Arti, and one more thing you should know, USB devices use UTF16LE encoding.

OOPer Over a year ago

@Arti, then you are mistaking something. I'm very sure my code works when put after var requestPtr = [...] and requestPtr.remove(at: 0). The output shown in my answer is taken from the actual output in the Playground.

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Adrian Bobrowski · Accepted Answer · 2016-12-16 10:51:18Z

0

You recevie array with byte, but only every second byte is correct

try this:

let test = String(requestPtr.enumerated().filter{ index, element in
    return index % 2 == 1
}.map { index, element in
    return Character(UnicodeScalar(element)! )
})

They are probably better solutions, but nothing comes to mind

answered Dec 16, 2016 at 10:51

Adrian Bobrowski

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3 Comments

Arti Over a year ago

thank you. Your solution works. Could you explain it please

Adrian Bobrowski Over a year ago

i can try, but i need your function to recived bytes

Arti Over a year ago

i receive bytes from usb device:

var request = IOUSBDevRequest(bmRequestType: 128, bRequest: 6, wValue: 0x300 | UInt16(index), wIndex: 0, wLength: 255, pData: &requestPtr, wLenDone: 255)                  kr = deviceInterface.DeviceRequest(deviceInterfacePtrPtr, &request)

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