Split error message in toUser and toDeveloper. Add error code. Fixes #8558.

extension/Source/core/Constants.php

@@ -300,6 +300,7 @@ const ERROR_DOWNLOAD_UNEXPECTED_NUMBER_OF_SOURCES = 1704;
 const ERROR_DOWNLOAD_FILE_NOT_READABLE = 1705;
 const ERROR_DOWNLOAD_FOPEN_BLOCKED = 1706;
 const ERROR_DOWNLOAD_JSON_CONVERT = 1707;
+const ERROR_DOWNLOAD_MERGE_FAILED = 1708;
 
 // Excel
 const ERROR_EXCEL_POSITION_ARGUMENT_EMPTY = 1800;

extension/Source/core/report/Download.php

@@ -157,7 +157,9 @@ class Download {
         exec($cmd, $output, $rc);
 
         if ($rc != 0) {
-            throw new DownloadException ("<p>Failed: RC=$rc   $cmd</p>" . implode("<br>", $output));
+            throw new DownloadException (json_encode([ERROR_MESSAGE_TO_USER => "Failed to merge PDF file",
+                    ERROR_MESSAGE_TO_DEVELOPER => "CMD: " . $cmd . "<br>RC: $rc<br>Output: " . implode("<br>", $output)])
+                , ERROR_DOWNLOAD_MERGE_FAILED);
         }
 
         return $concatFile;