Fixed the NFC COVID certificate scanner (#237)

* Fixed the NFC COVID certificate scanner

* Onboarded Darko Jelen's fix of try/catching the code in onNdefMessageReceived(), to prevent the app from crashing if another NFC tag is read while the decoded screen of the previous certificate is still up on the screen.

* All the NDEF messages and all the records contained on an NFC tag are parsed, and those of type urn:nfc:wkt:T containing a text record starting with "HC1:" are decoded.
This allows a mixed usage of the NFC tag - for example formatted as a smart poster containing the bearer's information in plain text and a PNG image of the COVID certificate's QR code, readable by any cellphone without the verifier app, as well as the COVID certificate string that can be read and decoded by the verifier app natively.
Previously, the NFC tag had contain only a single message with a single urn:nfc:wkt:T text record containing the COVID certificate string, and was not usable in any other fashion.

Co-authored-by: Giraut <>

app/src/main/java/dgca/verifier/app/android/MainActivity.kt

@@ -113,25 +113,24 @@ class MainActivity : AppCompatActivity() {
             return
         }
 
-        val builder = StringBuilder()
-        val records = NdefParser.parse(messages[0])
-        val size = records.size
-
-        for (i in 0 until size) {
-            val record = records[i]
-            val str = record.str()
-            builder.append(str)
-        }
-
-        val qrCodeText = builder.toString()
-        if (qrCodeText.isNotEmpty()) {
-            navHostFragment.childFragmentManager.primaryNavigationFragment?.let { fragment ->
-                if (fragment is CodeReaderFragment && fragment.isVisible) {
-                    fragment.onNdefMessageReceived(qrCodeText)
+        val itr = messages.listIterator()
+
+        while (itr.hasNext()) {
+            val records = NdefParser.parse(itr.next())
+
+            for (i in 0 until records.size) {
+                if (records[i] != null) {
+                    val record = records[i].str()
+
+                    if (record.length >= 5 && record.substring(0, 4) == "HC1:") {
+                       navHostFragment.childFragmentManager.primaryNavigationFragment?.let { fragment ->
+                            if (fragment is CodeReaderFragment && fragment.isVisible) {
+                                fragment.onNdefMessageReceived(record)
+                            }
+                        }
+                    }
                 }
             }
-        } else {
-            Timber.d("Received empty NDEFMessage")
         }
     }
 }

app/src/main/java/dgca/verifier/app/android/nfc/NdefParser.kt

@@ -65,7 +65,9 @@ fun NdefRecord.parse(): ParsedNdefRecord? {
                 Charsets.UTF_16
             }
 
-            val text = String(recordPayload, textEncoding)
+            val langCodeLen = (recordPayload[0] and 63.toByte()).toInt()
+            val text = String(recordPayload, textEncoding).substring(1 + langCodeLen)
+
             return TextRecord(text)
         } catch (e: UnsupportedEncodingException) {
             Timber.w("We got a malformed tag.")

app/src/main/java/dgca/verifier/app/android/reader/CodeReaderFragment.kt

@@ -267,21 +267,15 @@ class CodeReaderFragment : BindingFragment<FragmentCodeReaderBinding>(), NavCont
     }
 
     fun onNdefMessageReceived(qrCodeText: String) {
-        val position = binding.countrySelector.selectedItemPosition
-        if (position == -1 || refinedCountries.isEmpty()) {
-            return
-        }
-
         try {
-            val countryCode = refinedCountries[position].toLowerCase(Locale.ROOT)
             val action =
                 CodeReaderFragmentDirections.actionCodeReaderFragmentToVerificationDialogFragment(
-                    qrCodeText,
-                    countryCode
+                qrCodeText,
+                binding.countrySelector.selectedItem?.toString() ?: ""
                 )
             findNavController().navigate(action)
         } catch (ex: Exception) {
-            Timber.d("Cannot get iso country code for position.")
+            Timber.d("action_codeReaderFragment_to_verificationDialogFragment cannot be found from the current destination Destination.")
         }
     }
-}
+}