read w/o timeout now throws exception on connection lost or buffer to small

SerialInputOutputManager already returned connection lost exception, as the next read failed

usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/CommonUsbSerialPort.java

@@ -155,7 +155,7 @@ public abstract class CommonUsbSerialPort implements UsbSerialPort {
         byte[] buf = new byte[2];
         int len = mConnection.controlTransfer(0x80 /*DEVICE*/, 0 /*GET_STATUS*/, 0, 0, buf, buf.length, 200);
         if(len < 0)
-            throw new IOException("USB get_status request failed");
+            throw new IOException("Connection lost, USB get_status request failed");
     }
 
     @Override
@@ -183,7 +183,7 @@ public abstract class CommonUsbSerialPort implements UsbSerialPort {
             long endTime = testConnection ? MonotonicClock.millis() + timeout : 0;
             int readMax = Math.min(dest.length, MAX_READ_SIZE);
             nread = mConnection.bulkTransfer(mReadEndpoint, dest, readMax, timeout);
-            // Android error propagation is improvable, nread == -1 can be: timeout, connection lost, buffer undersized, ...
+            // Android error propagation is improvable, nread == -1 can be: timeout, connection lost, buffer to small
             if(nread == -1 && testConnection && MonotonicClock.millis() < endTime)
                 testConnection();
 
@@ -197,11 +197,15 @@ public abstract class CommonUsbSerialPort implements UsbSerialPort {
                 throw new IOException("Waiting for USB request failed");
             }
             nread = buf.position();
+            if(nread == 0) {
+                if(dest.length % mReadEndpoint.getMaxPacketSize() != 0) {
+                    throw new IOException("Connection lost or buffer to small");
+                } else {
+                    throw new IOException("Connection lost");
+                }
+            }
         }
-        if (nread > 0)
-            return nread;
-        else
-            return 0;
+        return Math.max(nread, 0);
     }
 
     @Override

usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/FtdiSerialDriver.java

@@ -162,7 +162,7 @@ public class FtdiSerialDriver implements UsbSerialDriver {
             return readFilter(dest, nread);
         }
 
-        private int readFilter(byte[] buffer, int totalBytesRead) throws IOException {
+        protected int readFilter(byte[] buffer, int totalBytesRead) throws IOException {
             final int maxPacketSize = mReadEndpoint.getMaxPacketSize();
             int destPos = 0;
             for(int srcPos = 0; srcPos < totalBytesRead; srcPos += maxPacketSize) {

usbSerialForAndroid/src/main/java/com/hoho/android/usbserial/driver/ProlificSerialDriver.java

@@ -217,7 +217,7 @@ public class ProlificSerialDriver implements UsbSerialDriver {
             IOException readStatusException = mReadStatusException;
             if (mReadStatusException != null) {
                 mReadStatusException = null;
-                throw readStatusException;
+                throw new IOException(readStatusException);
             }
 
             return mStatus;