ISSUE-4106: Fix NFC read stuck on Mifare Ultralight when signature read fails (fi…

lib/nfc/protocols/mf_ultralight/mf_ultralight_poller.c

@@ -305,22 +305,34 @@ static NfcCommand mf_ultralight_poller_handler_get_feature_set(MfUltralightPolle
 }
 
 static NfcCommand mf_ultralight_poller_handler_read_signature(MfUltralightPoller* instance) {
-    MfUltralightPollerState next_state = MfUltralightPollerStateAuth;
+    bool signature_read_ok = false;
+
     if(mf_ultralight_support_feature(
            instance->feature_set, MfUltralightFeatureSupportReadSignature)) {
         FURI_LOG_D(TAG, "Reading signature");
         instance->error =
             mf_ultralight_poller_read_signature(instance, &instance->data->signature);
-        if(instance->error != MfUltralightErrorNone) {
-            FURI_LOG_D(TAG, "Read signature failed");
-            next_state = MfUltralightPollerStateReadFailed;
+        if(instance->error == MfUltralightErrorNone) {
+            signature_read_ok = true;
+        } else {
+            FURI_LOG_D(TAG, "Read signature failed, continuing without signature");
+            memset(
+                instance->data->signature.data,
+                0,
+                sizeof(instance->data->signature.data));
         }
     } else {
         FURI_LOG_D(TAG, "Skip reading signature");
-        if(mf_ultralight_support_feature(
-               instance->feature_set, MfUltralightFeatureSupportAuthenticate)) {
-            next_state = MfUltralightPollerStateAuthMfulC;
-        }
+    }
+
+    MfUltralightPollerState next_state;
+    if(signature_read_ok) {
+        next_state = MfUltralightPollerStateAuth;
+    } else if(mf_ultralight_support_feature(
+                  instance->feature_set, MfUltralightFeatureSupportAuthenticate)) {
+        next_state = MfUltralightPollerStateAuthMfulC;
+    } else {
+        next_state = MfUltralightPollerStateAuth;
     }
     instance->state = next_state;
 

test-with-nfc-hardware.md

@@ -0,0 +1,53 @@
+## 1. Build and flash this branch
+On your machine (with the repo and this branch checked out):
+```bash
+cd /Users/jclaus/dev/flipperzero-firmware
+git checkout ISSUE-4106/fix-nfc-mifare-ultralight-card   # if not already
+./fbt
+Connect the Flipper over USB (powered on, normal firmware running), then:
+
+./fbt flash_usb
+Wait until the Flipper reboots. You're now running the fixed firmware.
+
+2. Test with NFC app (normal read)
+Open NFC — Main menu → NFC.
+Start a read — Read (or Scan / Detect, depending on menu wording).
+Hold the card — Put the Mifare Ultralight or NTAG213 flat on the back of the Flipper and keep it still.
+Expected with the fix — After a short "Don't move" phase, you get a success (and optionally "Save"). No endless "Don't move" even if the card is one that used to get stuck (e.g. signature read failing).
+If you have a card that used to get stuck on official/unfixed firmware, that's the main case to retest: it should now complete instead of hanging.
+
+3. What to check
+Behavior — Read finishes and shows success (and you can save the dump). No infinite "Don't move".
+Saved dump — Open the saved file: UID, type (e.g. NTAG213), and page data should look correct. Signature may be all zeros if that read failed (that's expected with the fix).
+Optional – debug log — If you use ./fbt debug or a serial/debug console and enable debug logs, you may see:
+Read signature failed, continuing without signature when the fix path is used.
+Then the read continues and completes instead of going to "Read Failed".
+4. Optional: compare with unfixed firmware
+To see the old bug and confirm the fix:
+
+Flash stock/unfixed firmware (e.g. dev or latest release):
+
+git stash
+git checkout dev
+./fbt flash_usb
+Try the same card that used to get stuck: run NFC → Read, hold card. If it still reproduces, you'll see it hang on "Don't move".
+
+Flash your branch again:
+
+git checkout ISSUE-4106/fix-nfc-mifare-ultralight-card
+git stash pop   # if you stashed
+./fbt flash_usb
+Retest the same card — read should now complete.
+
+5. Testing multiple devices/cards
+Several Flippers — Repeat "build once → ./fbt flash_usb" for each device (plug one at a time, or use ./fbt flash_usb -p /dev/cu.usbmodem* to pick a port if needed).
+Several cards — Use at least:
+One Mifare Ultralight (or compatible).
+One NTAG213 (or NTAG215/216).
+If you have one that used to get stuck (e.g. ATQA 0x0044, SAK 0x00), that's the most important to test.
+6. Quick checklist
+Step	Action
+1	./fbt then ./fbt flash_usb on branch ISSUE-4106/fix-nfc-mifare-ultralight-card
+2	NFC → Read, hold Ultralight/NTAG213 until read finishes
+3	Confirm success (no endless "Don't move"), save and open dump
+4	(Optional) Flash dev, reproduce hang, then re-flash branch and confirm fix