- Show the full stacktrace in the weird case of a "RestClientException" without an exception-message. Also, in this case, retry immediately, as there is no long-lasting network problem that requires some time between requests, but most probably a random interruption.

- Code polishing.

src/main/java/eu/openaire/urls_worker/components/AssignmentsHandler.java

@@ -108,11 +108,21 @@ public class AssignmentsHandler {
         try {   // Here, the HTTP-request is executed.
             assignmentRequest = restTemplate.getForObject(requestUrl, AssignmentsRequest.class);
         } catch (RestClientException rce) {
-            logger.error("Could not retrieve the assignments!\n" + rce.getMessage());   // It shows the response body (from Spring v.2.5.6 onwards).
-            hadConnectionErrorOnRequest = true;
+            final String errorMsg = "Could not retrieve the assignments! ";
+            String exceptionMsg = rce.getMessage(); // It also shows the response body of the response (from Spring v.2.5.6 onwards).
+            if ( (exceptionMsg != null) && !exceptionMsg.isEmpty() ) {
+                hadConnectionErrorOnRequest = true;
+                logger.error(errorMsg + exceptionMsg);
+            }
+            else {  // Otherwise, it's an undefined error, which occurs randomly
+                // and does not mean that the Controller has some problem, or the Worker requested something in a wrong way,
+                // or that the firewall disallow the connection (in this case we get "connection refused/timed out").
+                logger.error(errorMsg, rce);
+                // Try again immediately, do not wait 15 mins. The Controller will take some minutes to prepare the data, before it sends them anyway.
+            }
             return null;
         } catch (IllegalArgumentException iae) {
-            logger.error("Could not retrieve the assignments, as the provided Controller's url was malformed!\n" + iae.getMessage());
+            logger.error("Could not retrieve the assignments, as the provided Controller's url was malformed! " + iae.getMessage());
             // We do not need to send a "ShutdownReport" to the Controller, since this error will appear upon the Worker's initialization and the Controller will not have any information about this Worker's existence.
             UrlsWorkerApplication.gentleAppShutdown();
         }

src/main/java/eu/openaire/urls_worker/components/ScheduledTasks.java

@@ -61,18 +61,20 @@ public class ScheduledTasks {
     {
         if ( GeneralController.shouldShutdownWorker || AssignmentsHandler.shouldNotRequestMore ) {
             // Here we will be right after the Worker has posted its last report. It is guaranteed that the Controller will not have processed it and have not requested the full-text files.
-            // We do not want to shut down the controller.
+            // We do not want to shut down the Worker, until all files have been transferred to the Controller, or some time has passed.
             return;
         }
 
-        if ( rootPath.getFreeSpace() <= requiredFreeSpace ) {
+        // The user might have just requested the Worker to shut-down.
+        if ( GeneralController.shouldShutdownWorker ) { // Make sure the worker shuts-down, in case the user sends the relevant request, while the worker is stuck in a data-request error-loop.
+            AssignmentsHandler.shouldNotRequestMore = true;
+            return;
+        }
+
+        if ( rootPath.getFreeSpace() < requiredFreeSpace ) {
             // It's not safe to proceed with downloading more files and risk of "noSpaceLeft" error.
             // Wait for the Controller to take the full-texts and any remaining files to be deleted, so that more free-space becomes available.
             // We need to have some buffer zone for the ".tar" files which will be created from the already downloaded full-texts, when the Controller starts requesting them.
-            if ( GeneralController.shouldShutdownWorker ) { // Make sure the worker shuts-down, in case the user sends the relevant request, while the worker is stuck in a free-space check loop.
-                AssignmentsHandler.shouldNotRequestMore = true;
-                return;
-            }
             logger.warn("The free space is running out (less than " + (requiredFreeSpace / oneMb) + " Mb). The Worker will avoid getting new assignments for the next 15 minutes.");
             try {
                 Thread.sleep(900_000);  // Sleep for 15 mins to stall the scheduler from retrying right away, thus giving time to the disk-space to be freed.
@@ -83,10 +85,6 @@ public class ScheduledTasks {
         }
 
         if ( AssignmentsHandler.hadConnectionErrorOnRequest ) {
-            if ( GeneralController.shouldShutdownWorker ) { // Make sure the worker shuts-down, in case the user sends the relevant request, while the worker is stuck in a data-request error-loop.
-                AssignmentsHandler.shouldNotRequestMore = true;
-                return;
-            }
             try {
                 Thread.sleep(900_000);  // Sleep for 15 mins to stall the scheduler from retrying right away, thus giving time to the Controller to recover.
             } catch (InterruptedException ie) {