Fix StatusWords::code output for StatusWords::VerifyFailError (#479)

* Fix `StatusWords::code` output for `StatusWords::VerifyFailError`

Closes iqlusioninc/yubikey.rs#473.

* Refactor `Transaction::transfer_data` to match on `StatusWords`

This makes the code more reliable, such that it would have avoided
the bug in iqlusioninc/yubikey.rs#473.

src/apdu.rs

@@ -353,6 +353,12 @@ pub(crate) enum StatusWords {
     /// Successful execution
     Success,
 
+    /// The requested data was too large for the response, and there is data remaining.
+    BytesRemaining {
+        /// The number of bytes remaining, as indicated in the response.
+        len: u8,
+    },
+
     /// https://github.com/Yubico/yubikey-manager/blob/1f22620b623c6b345dd9f9193ec765a542dddc80/ykman/driver_ccid.py#L53
     NoInputDataError,
 
@@ -410,8 +416,9 @@ impl StatusWords {
     pub fn code(self) -> u16 {
         match self {
             StatusWords::None => 0,
+            StatusWords::BytesRemaining { len } => 0x6100 | len as u16,
             StatusWords::NoInputDataError => 0x6285,
-            StatusWords::VerifyFailError { tries } => 0x63c0 & tries as u16,
+            StatusWords::VerifyFailError { tries } => 0x63c0 | tries as u16,
             StatusWords::WrongLengthError => 0x6700,
             StatusWords::SecurityStatusError => 0x6982,
             StatusWords::AuthBlockedError => 0x6983,
@@ -439,6 +446,9 @@ impl From<u16> for StatusWords {
     fn from(sw: u16) -> Self {
         match sw {
             0x0000 => StatusWords::None,
+            sw if sw & 0xff00 == 0x6100 => Self::BytesRemaining {
+                len: (sw & 0x00ff) as u8,
+            },
             0x6285 => StatusWords::NoInputDataError,
             sw if sw & 0xfff0 == 0x63c0 => StatusWords::VerifyFailError {
                 tries: (sw & 0x000f) as u8,
@@ -466,3 +476,40 @@ impl From<StatusWords> for u16 {
         sw.code()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::StatusWords;
+
+    #[test]
+    fn status_words_round_trip() {
+        let round_trip = |sw: StatusWords| {
+            assert_eq!(StatusWords::from(sw.code()), sw);
+        };
+
+        round_trip(StatusWords::None);
+        round_trip(StatusWords::BytesRemaining { len: 1 });
+        round_trip(StatusWords::BytesRemaining { len: 10 });
+        round_trip(StatusWords::BytesRemaining { len: 0xFF });
+        round_trip(StatusWords::Success);
+        round_trip(StatusWords::NoInputDataError);
+        round_trip(StatusWords::VerifyFailError { tries: 0x0F });
+        round_trip(StatusWords::VerifyFailError { tries: 3 });
+        round_trip(StatusWords::VerifyFailError { tries: 2 });
+        round_trip(StatusWords::VerifyFailError { tries: 1 });
+        round_trip(StatusWords::VerifyFailError { tries: 0 });
+        round_trip(StatusWords::WrongLengthError);
+        round_trip(StatusWords::SecurityStatusError);
+        round_trip(StatusWords::AuthBlockedError);
+        round_trip(StatusWords::DataInvalidError);
+        round_trip(StatusWords::ConditionsNotSatisfiedError);
+        round_trip(StatusWords::CommandNotAllowedError);
+        round_trip(StatusWords::IncorrectParamError);
+        round_trip(StatusWords::NotFoundError);
+        round_trip(StatusWords::NoSpaceError);
+        round_trip(StatusWords::IncorrectSlotError);
+        round_trip(StatusWords::NotSupportedError);
+        round_trip(StatusWords::CommandAbortedError);
+        round_trip(StatusWords::Other(0x1337));
+    }
+}

src/transaction.rs

@@ -400,11 +400,12 @@ impl<'tx> Transaction<'tx> {
                 .data(&in_data[in_offset..(in_offset + this_size)])
                 .transmit(self, 261)?;
 
-            sw = response.status_words().code();
+            sw = response.status_words();
 
-            if !response.is_success() && (sw >> 8 != 0x61) {
+            match sw {
+                StatusWords::Success | StatusWords::BytesRemaining { .. } => (),
                 // TODO(tarcieri): is this really OK?
-                return Ok(Response::new(sw.into(), out_data));
+                _ => return Ok(Response::new(sw, out_data)),
             }
 
             if !out_data.is_empty() && (out_data.len() - response.data().len() > max_out) {
@@ -425,17 +426,15 @@ impl<'tx> Transaction<'tx> {
             }
         }
 
-        while sw >> 8 == 0x61 {
-            trace!(
-                "The card indicates there is {} bytes more data for us",
-                sw & 0xff
-            );
+        while let StatusWords::BytesRemaining { len } = sw {
+            trace!("The card indicates there is {} bytes more data for us", len);
 
             let response = Apdu::new(Ins::GetResponseApdu).transmit(self, 261)?;
-            sw = response.status_words().code();
+            sw = response.status_words();
 
-            if sw != StatusWords::Success.code() && (sw >> 8 != 0x61) {
-                return Ok(Response::new(sw.into(), vec![]));
+            match sw {
+                StatusWords::Success | StatusWords::BytesRemaining { .. } => (),
+                _ => return Ok(Response::new(sw, vec![])),
             }
 
             if out_data.len() + response.data().len() > max_out {
@@ -451,7 +450,7 @@ impl<'tx> Transaction<'tx> {
             out_data.extend_from_slice(&response.data()[..response.data().len()]);
         }
 
-        Ok(Response::new(sw.into(), out_data))
+        Ok(Response::new(sw, out_data))
     }
 
     /// Fetch an object.