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

Removed the custom error class again, since decoders that can fail decoding will always raise a UnicodeDecodeError according to
https://docs.python.org/3/library/codecs.html.
Modified try-catch to add a more specific note to the UnicodeError for better user information.

src/omero/util/populate_roi.py

@@ -142,7 +142,6 @@ class MeasurementError(Exception):
     """
     pass
 
-
 class DownloadingOriginalFileProvider(object):
 
     """
@@ -169,15 +168,21 @@ 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 as e:
+            e.add_note("The original file data could not be decoded assuming unicode encoding. Please specify the correct encoding used for the file!")
+            raise
+        finally:
+            temporary_file.close()
         temporary_file.seek(0)
         temporary_file.truncate(size_new)