[SOLVED] NFC - Android device can't read Type 4 NDEF tag content emulated from ACR122U (PN532)

NFC - Android device can't read Type 4 NDEF tag content emulated from ACR122U (PN532)

I'm writing C# application to emulate NFC tag via ACR122U, which uses PN532 internally. I want Android to read simple URI NDEF Tag.

I'm able to communicate with Android using NFC Forum Type 4 Tag protocol, Android detects the tag, but is not able to read the NDEF file - checked with NFC Tools app.

The communication looks like this:

tgInitAsTarget:
> FF-00-00-00-27-D4-8C-05-04-00-12-34-56-20-01-FE-05-01-86-04-02-02-03-00-4B-02-4F-49-8A-00-FF-FF-01-01-66-6D-01-01-10-02-00-00-00-00
< D5-8D-08-E0-80-90-00

> FF-00-00-00-02-D4-86 // tgGetData
< D5-87-00-00-A4-04-00-07-D2-76-00-00-85-01-01-00-90-00 // NDEF Tag applcation select
> FF-00-00-00-04-D4-8E-90-00 // optional File Control Information not provided
< D5-87-00-00-A4-00-0C-02-E1-03-90-00 // Capability Container select
> FF-00-00-00-04-D4-8E-90-00 // OK
< D5-87-00-00-B0-00-00-0F-90-00 // ReadBinary data from CC file
> FF-00-00-00-13-D4-8E-00-0F-20-00-FF-00-FF-04-06-E1-04-00-14-00-00-90-00 // CC content as per protocol
< D5-87-00-00-A4-00-0C-02-E1-04-90-00 // NDEF Select command
> FF-00-00-00-04-D4-8E-90-00 // OK
< D5-87-00-00-B0-00-00-02-90-00 // ReadBinary NLEN field from NDEF file
> FF-00-00-00-06-D4-8E-00-12-90-00 // NDEF will have 18 (12h) bytes
< D5-87-00-00-B0-00-02-12-90-00 // ReadBinary NDEF file
> FF-00-00-00-16-D4-8E-00-10-D1-01-0C-55-01-67-6F-6F-67-6C-65-2E-63-6F-6D-2F-90-00 // NDEF content - Well known URI type: google.com/

Some helpful tips:

FF-00-00-00 means pseudo APDU sent to NFC device, every APDU needs to start with it if we want to emulate rather than communicate with actual card
D5-87-00 is a prefix of output of tgGetData command, each successful response from PN532 starts with this
D4-8E is PN532 tgSetData command prefix. So each command sent from application in emulation mode should look like: FF-00-00-00-(length)-D4-8E-...-90-00
I excluded tgSetData and tgGetData commands for better readability

It looks like I must be doing something wrong at the very last step of the communication. Is the NDEF file formatted correctly?

Solution

The problem is indeed in the last message. Just before that Android was asking for NDEF content from offset 02: < D5-87-00-00-B0-00-02-12-90-00

Last message included the whole NDEF content including the size on first 2 bytes: 00-10. This must be removed:

FF-00-00-00-14-D4-8E-D1-01-0C-55-01-67-6F-6F-67-6C-65-2E-63-6F-6D-2F-90-00

This worked and Android open google.com.