Added custom exception and try-catch around the Decoding Part in get_…

…original_file_data() to provide the user with more helpful error messages as well as enabling easy catching of the exception in calling scripts

src/omero/util/populate_roi.py

@@ -142,6 +142,12 @@ class MeasurementError(Exception):
     """
     pass
 
+class DecodingError(Exception):
+
+    """
+    Raised if an error occurs during decoding original file data
+    """
+    pass
 
 class DownloadingOriginalFileProvider(object):
 
@@ -169,15 +175,22 @@ def get_original_file_data(self, original_file, encoding="utf-8"):
                                                      dir=str(self.dir))
 
         size = original_file.size.val
-        if encoding != "utf-8": size_new = 0 # Needed to keep track of reencoded file size if encoding is not utf-8 already
+        if encoding != "utf-8": size_new = 0 # Needed to keep track of re-encoded file size if encoding is not utf-8 already
         else: size_new = size # Else can be the same as the old data size
 
-        for i in range((old_div(size, self.BUFFER_SIZE)) + 1):
-            index = i * self.BUFFER_SIZE
-            data = self.raw_file_store.read(index, self.BUFFER_SIZE)
-            data_write = data.decode(encoding)
-            if encoding != "utf-8": size_new += len(data_write.encode("utf-8")) # Track total size
-            temporary_file.write(data_write)
+        try:
+            for i in range((old_div(size, self.BUFFER_SIZE)) + 1):
+                index = i * self.BUFFER_SIZE
+                data = self.raw_file_store.read(index, self.BUFFER_SIZE)
+                data_write = data.decode(encoding)
+                if encoding != "utf-8": size_new += len(data_write.encode("utf-8")) # Track total size
+                temporary_file.write(data_write)
+        except UnicodeDecodeError:
+            raise DecodingError("The original file data could not be decoded assuming unicode encoding. Please specify the correct encoding used for the file!")
+        except:
+            raise DecodingError("An unknown exception has occured during decoding of the orginal file data. Please specify the encoding used for the file!")
+        finally:
+            temporary_file.close()
         temporary_file.seek(0)
         temporary_file.truncate(size_new)