Present desktop OTP and sensitive outputs

crates/storage/src/presentation.rs

@@ -198,6 +198,9 @@ impl NativeClipboardManager {
 pub enum QrError {
     EmptyPayload,
     PayloadTooLarge,
+    InvalidImage,
+    NotFound,
+    InvalidPayload,
 }
 
 impl fmt::Display for QrError {
@@ -205,6 +208,9 @@ impl fmt::Display for QrError {
         match self {
             Self::EmptyPayload => formatter.write_str("empty data cannot be encoded as a QR code"),
             Self::PayloadTooLarge => formatter.write_str("the QR payload is too large"),
+            Self::InvalidImage => formatter.write_str("the selected file is not a supported image"),
+            Self::NotFound => formatter.write_str("the image does not contain a QR code"),
+            Self::InvalidPayload => formatter.write_str("the QR code contains invalid text"),
         }
     }
 }
@@ -233,6 +239,26 @@ impl QrMatrix {
         Ok(Self { width, modules })
     }
 
+    /// Decode the first QR symbol from an encoded image without exposing the
+    /// secret-derived payload to a presentation adapter.
+    pub fn decode_image(image: &SecretBytes) -> Result<SecretBytes, QrError> {
+        let grayscale = image::load_from_memory(image.expose())
+            .map_err(|_| QrError::InvalidImage)?
+            .into_luma8();
+        let mut prepared = rqrr::PreparedImage::prepare_from_greyscale(
+            grayscale.width() as usize,
+            grayscale.height() as usize,
+            |x, y| grayscale.get_pixel(x as u32, y as u32).0[0],
+        );
+        let grid = prepared
+            .detect_grids()
+            .into_iter()
+            .next()
+            .ok_or(QrError::NotFound)?;
+        let (_, payload) = grid.decode().map_err(|_| QrError::InvalidPayload)?;
+        Ok(SecretBytes::new(payload.into_bytes()))
+    }
+
     pub fn width(&self) -> usize {
         self.width
     }