Minor fixes

ugs-core/src/com/willwinder/universalgcodesender/connection/JSerialCommConnection.java

@@ -21,7 +21,9 @@ This file is part of Universal Gcode Sender (UGS).
 import com.fazecast.jSerialComm.SerialPort;
 import com.fazecast.jSerialComm.SerialPortDataListener;
 import org.apache.commons.lang3.StringUtils;
+import org.apache.commons.lang3.SystemUtils;
 
+import java.io.File;
 import java.util.Arrays;
 import java.util.List;
 
@@ -48,6 +50,8 @@ public void setUri(String uri) {
             String portName = StringUtils.substringBetween(uri, ConnectionDriver.JSERIALCOMM.getProtocol(), ":");
             int baudRate = Integer.parseInt(StringUtils.substringAfterLast(uri, ":"));
             initSerialPort(portName, baudRate);
+        } catch (ConnectionException e) {
+            throw e;
         } catch (Exception e) {
             throw new ConnectionException("Couldn't parse connection string " + uri, e);
         }
@@ -72,13 +76,26 @@ private void initSerialPort(String name, int baud) throws Exception {
         }
 
         serialPort = SerialPort.getCommPort(name);
+        checkPermissions();
+
         serialPort.setParity(SerialPort.NO_PARITY);
         serialPort.setNumStopBits(SerialPort.ONE_STOP_BIT);
         serialPort.setNumDataBits(8);
         serialPort.addDataListener(this);
         serialPort.setBaudRate(baud);
     }
 
+    private void checkPermissions() {
+        if (!SystemUtils.IS_OS_LINUX) {
+            return;
+        }
+
+        File port = new File(serialPort.getSystemPortPath());
+        if (!port.canWrite() || !port.canRead() ) {
+            throw new ConnectionException("Do not have required permissions to open the device on " + serialPort.getSystemPortPath());
+        }
+    }
+
     @Override
     public void closePort() throws Exception {
         if (serialPort != null) {

ugs-core/src/com/willwinder/universalgcodesender/model/GUIBackend.java

@@ -617,7 +617,8 @@ public boolean canCancel() {
     @Override
     public boolean canSend() {
         return isIdle() &&
-                this.gcodeFile != null;
+                this.gcodeFile != null &&
+                (controller != null && !controller.isStreaming());
     }
 
     @Override
@@ -762,7 +763,7 @@ private boolean openCommConnection(String port, int baudRate) throws Exception {
             disconnect();
             logger.log(Level.INFO, "Exception in openCommConnection.", e);
             throw new Exception(Localization.getString("mainWindow.error.connection")
-                    + ": " + e.getMessage());
+                    + ": " + e.getMessage(), e);
         }
         return connected;
     }