display message when sdr unavailable

owrx/connection.py

@@ -142,6 +142,11 @@ class OpenWebRxReceiverClient(Client):
 
     def setSdr(self, id=None):
         next = SdrService.getSource(id)
+
+        if next is None:
+            self.handleSdrFailure("sdr device failed")
+            return
+
         if next == self.sdr:
             return
 
@@ -180,6 +185,9 @@ class OpenWebRxReceiverClient(Client):
 
         self.sdr.addSpectrumClient(self)
 
+    def handleSdrFailure(self, message):
+        self.write_sdr_error(message)
+
     def startDsp(self):
         if self.dsp is None:
             self.dsp = DspManager(self, self.sdr)

owrx/source.py

@@ -76,10 +76,14 @@ class SdrService(object):
     def getSource(id=None):
         SdrService.loadProps()
         sources = SdrService.getSources()
+        if not sources:
+            return None
         if id is None:
             # TODO: configure default sdr in config? right now it will pick the first one off the list.
             id = list(sources.keys())[0]
 
+        if not id in sources:
+            return None
         return sources[id]
 
     @staticmethod
@@ -654,7 +658,7 @@ class DspManager(csdr.output):
     def onSdrFailed(self):
         logger.debug("received onSdrFailed, shutting down DspSource")
         self.dsp.stop()
-        self.handler.write_sdr_error("sdr failed")
+        self.handler.handleSdrFailure("sdr device failed")
 
 
 class CpuUsageThread(threading.Thread):