Fix a race condition

In the case that the remote token responds too quickly, the response will
be treated as output data and sent back to the token. We resolve this race
condition by clearly demarcating input and output chunks as separate
variables.

Author: npmccallum

u2f-ble-test-ios/Managers/DeviceManager.swift

@@ -29,7 +29,8 @@ final class DeviceManager: NSObject {
     var onAPDUReceived: ((DeviceManager, Data) -> Void)?
 
     fileprivate var chunksize = 0
-    fileprivate var pendingChunks: [Data] = []
+    fileprivate var pendingOutput: [Data] = []
+    fileprivate var pendingInput: [Data] = []
     fileprivate var writeCharacteristic: CBCharacteristic?
     fileprivate var notifyCharacteristic: CBCharacteristic?
     fileprivate var controlpointLengthCharacteristic: CBCharacteristic?
@@ -68,7 +69,7 @@ final class DeviceManager: NSObject {
         onDebugMessage?(self, "Trying to split APDU into chunks...")
         if let chunks = TransportHelper.split(data, command: .message, chuncksize: chunksize), chunks.count > 0 {
             onDebugMessage?(self, "Successfully split APDU into \(chunks.count) part(s)")
-            pendingChunks = chunks
+            pendingOutput = chunks
             writeNextPendingChunk()
         }
         else {
@@ -78,12 +79,12 @@ final class DeviceManager: NSObject {
     }
 
     fileprivate func writeNextPendingChunk() {
-        guard pendingChunks.count > 0 else {
+        guard pendingOutput.count > 0 else {
             onDebugMessage?(self, "Trying to write pending chunk but nothing left to write")
             return
         }
 
-        let chunk = pendingChunks.removeFirst()
+        let chunk = pendingOutput.removeFirst()
         onDebugMessage?(self, "Writing pending chunk = \(chunk)")
         peripheral.writeValue(chunk, for: writeCharacteristic!, type: .withResponse)
     }
@@ -109,10 +110,10 @@ final class DeviceManager: NSObject {
         }
 
         // join APDU
-        pendingChunks.append(chunk)
-        if let APDU = TransportHelper.join(pendingChunks, command: .message) {
+        pendingInput.append(chunk)
+        if let APDU = TransportHelper.join(pendingInput, command: .message) {
             onDebugMessage?(self, "Successfully joined APDU = \(APDU)")
-            pendingChunks.removeAll()
+            pendingInput.removeAll()
             onAPDUReceived?(self, APDU)
         }
     }