Error writing short text

[Spooky12]

Hello,

When I write a short text message (<9 characters) to a NFC tag, I get this error when I read the tag and try to parse it:

Uncaught (in promise) NdefExceptionMessages.ExMessageBeginMissing

I think the error come from the method prepareBytesToWrite, because I don't have any problem when I try to parse short messages encoded in a NDEF format by another program.

[somq]

This error comes from ndef-lib and is pretty self explanatory MB flag (message begin) is missing.

Can try to encode the same message using nfccard-tool and compare raw tags byte per byte?

Also, you can try to log or breakpoint directly in the ndef-lib where I set the line stop in the link above.

Pretty hard to tell you more without a repro or any code...

[Spooky12]

I am using an ACR122 reader along with nfc-pcsc to read and write tags. And for the code to encode and write NDEF messages I'm using the same as your example, the only change I made is:

const message = [
  { type: 'text', text: myText, language: 'en' },
]

I tried to encode the text 'test' with both nfccard-tool and another program and this the buffer I get:

• nfccard-tool: Buffer(211) [3, 209, 1, 7, 84, 2, 101, 110, 116, 101, 115, 116, 254, 0, 0, 0, 97, 103, 254, 0, 97, 110, 111, 116, 104, 101, 114, 32, 116, 97, 103, 254, 0, 0, 0, …] (there are 0 until the end)
• Other program: Buffer(13) [3, 11, 209, 1, 7, 84, 2, 101, 110, 116, 101, 115, 116]

I also tried to encode the text 'testtest1' and I get the same buffer from both nfccard-tool and the other program: Buffer(18) [3, 16, 209, 1, 12, 84, 2, 101, 110, 116, 101, 115, 116, 116, 101, 115, 116, 49]

It looks like the message length is not added to the buffer when the text is <9 characters so the whole buffer is shifted by one. I don't know why it happens but I'll look at the code of the prepareBytesToWrite method to try to find out why.

[Spooky12]

I found out why it happens, it's because of this:

let NDEFMessageLength = NDEFMessage.toByteArray().length; // second and final write
let NDEF_MESSAGE_TLV_L_LENGTH = new Buffer(NDEFMessageLength.toString(16), 'hex'); // 0x00 - first write

When I want to encode a short message (<9 characters), NDEFMessageLength < 16 so NDEFMessageLength.toString(16) length is 1 so there is an error when the buffer is created.

But if I add a 0 before then it works fine.

E.g. if I have NDEFMessageLength=15 then NDEFMessageLength.toString(16) is 'f' which will create an error at the creation of the buffer but if I add 0 before to get '0f' then it works fine, the NDEF message is correct and I don't get NdefExceptionMessages.ExMessageBeginMissing when I try to read my tag.

[somq]

Ok, I dug this one a bit and you are right. This error comes from a wrong conversion of decimal to hex. Anyway Buffer constructor usage is deprecated and these tricky converts are not ideal. Si I'm replacing by a standard Buffer.from and everything should be OK.

I will commit a package update as well as a fix asap, afterthen I will publish it to npm but it the meantime you should be able to test and work with master.

Let me know if everything is OK on your side...

[Spooky12]

Great, thank you!

[somq]

Your welcome, published to npm aswell. Let me know if it works properly whenever you can.

[Spooky12]

It works properly now, I can create NFC tags with messages that contain less than 9 characters, thanks.