read with timeout now throws error on connection lost, e.g. device disconnected

and similar connection lost detection for prolific input control lines

usbSerialForAndroid/src/androidTest/java/com/hoho/android/usbserial/DeviceTest.java

@@ -1660,18 +1660,27 @@ public class DeviceTest {
             purged = false;
         }
         usb.deviceConnection.close();
-        try {
+        try { // only Prolific driver has early exit if nothing changed
             usb.setParameters(115200, 8, 1, UsbSerialPort.PARITY_NONE);
             if(!(usb.serialDriver instanceof ProlificSerialDriver))
                 fail("setParameters error expected");
         } catch (IOException ignored) {
         }
+        try {
+            usb.setParameters(57600, 8, 1, UsbSerialPort.PARITY_NONE);
+            fail("setParameters error expected");
+        } catch (IOException ignored) {
+        }
         try {
             usb.write("x".getBytes());
             fail("write error expected");
         } catch (IOException ignored) {
         }
-        usb.serialPort.read(buf, 1000); // bulkTransfer returns -1 on timeout and error, so no exception thrown here
+        try {
+            usb.serialPort.read(buf, 1000);
+            fail("read error expected");
+        } catch (IOException ignored) {
+        }
         try {
             usb.serialPort.read(buf, 0);
             fail("read error expected");
@@ -1683,16 +1692,17 @@ public class DeviceTest {
         } catch (IOException ignored) {
         }
         try {
+            if(usb.serialDriver instanceof ProlificSerialDriver)
+                Thread.sleep(600); // wait for background thread
             usb.serialPort.getRI();
-            if(!(usb.serialDriver instanceof ProlificSerialDriver))
-                fail("getRI error expected");
+            fail("getRI error expected");
         } catch (IOException ignored) {
         } catch (UnsupportedOperationException ignored) {
         }
         if(purged) {
             try {
                 usb.serialPort.purgeHwBuffers(true, true);
-                fail("setRts error expected");
+                fail("purgeHwBuffers error expected");
             } catch (IOException ignored) {
             }
         }

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

@@ -129,13 +129,27 @@ public abstract class CommonUsbSerialPort implements UsbSerialPort {
 
     protected abstract void closeInt();
 
+    /**
+     * use simple USB request supported by all devices to test if connection is still valid
+     */
+    protected void testConnection() throws IOException {
+        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");
+    }
+
     @Override
     public int read(final byte[] dest, final int timeout) throws IOException {
+        return read(dest, timeout, true);
+    }
+
+    protected int read(final byte[] dest, final int timeout, boolean testConnection) throws IOException {
         if(mConnection == null) {
             throw new IOException("Connection closed");
         }
         if(dest.length <= 0) {
-            throw new IllegalArgumentException("read buffer to small");
+            throw new IllegalArgumentException("Read buffer to small");
         }
         final int nread;
         if (timeout != 0) {
@@ -147,8 +161,12 @@ public abstract class CommonUsbSerialPort implements UsbSerialPort {
             //     /system/lib64/libusbhost.so (usb_request_wait+192)
             //     /system/lib64/libandroid_runtime.so (android_hardware_UsbDeviceConnection_request_wait(_JNIEnv*, _jobject*, long)+84)
             // data loss / crashes were observed with timeout up to 200 msec
+            long endTime = testConnection ? System.currentTimeMillis() + 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, ...
+            if(nread == -1 && testConnection && System.currentTimeMillis() < endTime)
+                testConnection();
 
         } else {
             final ByteBuffer buf = ByteBuffer.wrap(dest);

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

@@ -138,7 +138,7 @@ public class FtdiSerialDriver implements UsbSerialDriver {
         @Override
         public int read(final byte[] dest, final int timeout) throws IOException {
             if(dest.length <= READ_HEADER_LENGTH) {
-                throw new IllegalArgumentException("read buffer to small");
+                throw new IllegalArgumentException("Read buffer to small");
                 // could allocate larger buffer, including space for 2 header bytes, but this would
                 // result in buffers not being 64 byte aligned any more, causing data loss at continuous
                 // data transfer at high baud rates when buffers are fully filled.
@@ -147,11 +147,13 @@ public class FtdiSerialDriver implements UsbSerialDriver {
             if (timeout != 0) {
                 long endTime = System.currentTimeMillis() + timeout;
                 do {
-                    nread = super.read(dest, Math.max(1, (int)(endTime - System.currentTimeMillis())));
+                    nread = super.read(dest, Math.max(1, (int)(endTime - System.currentTimeMillis())), false);
                 } while (nread == READ_HEADER_LENGTH && System.currentTimeMillis() < endTime);
+                if(nread <= 0 && System.currentTimeMillis() < endTime)
+                    testConnection();
             } else {
                 do {
-                    nread = super.read(dest, timeout);
+                    nread = super.read(dest, timeout, false);
                 } while (nread == READ_HEADER_LENGTH);
             }
             return readFilter(dest, nread);

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

@@ -184,10 +184,10 @@ public class ProlificSerialDriver implements UsbSerialDriver {
             try {
                 while (!mStopReadStatusThread) {
                     byte[] buffer = new byte[STATUS_BUFFER_SIZE];
-                    int readBytesCount = mConnection.bulkTransfer(mInterruptEndpoint,
-                            buffer,
-                            STATUS_BUFFER_SIZE,
-                            500);
+                    long endTime = System.currentTimeMillis() + 500;
+                    int readBytesCount = mConnection.bulkTransfer(mInterruptEndpoint, buffer, STATUS_BUFFER_SIZE, 500);
+                    if(readBytesCount == -1 && System.currentTimeMillis() < endTime)
+                        testConnection();
                     if (readBytesCount > 0) {
                         if (readBytesCount == STATUS_BUFFER_SIZE) {
                             mStatus = buffer[STATUS_BYTE_IDX] & 0xff;