Fix Bug #1228905 Calibre does not create a valid .bib file

src/calibre/library/catalogs/bibtex.py

@@ -179,6 +179,8 @@ class BIBTEX(CatalogPlugin):
                     #\n removal
                     item = item.replace(u'\r\n',u' ')
                     item = item.replace(u'\n',u' ')
+                    # unmatched brace removal (users should use \leftbrace or \rightbrace for single braces)
+                    item = bibtexdict.stripUnmatchedSyntax(item, u'{', u'}')
                     #html to text
                     try:
                         item = html2text(item)

src/calibre/utils/bibtex.py

@@ -2902,3 +2902,31 @@ class BibTeX:
         """
         return self.utf8ToBibtex(u' and '.join([author for author in item]))
 
+    def stripUnmatchedSyntax(self, text, open_character, close_character):
+        """ 
+        Strips unmatched BibTeX syntax
+        """
+        stack = list()
+    
+        if len(open_character) > 1 or len(close_character) > 1:
+            raise ValueError("Only single characters accepted")
+        
+        for i in text:
+            if i == open_character: 
+                stack.append(open_character)
+            # if there is already an orphan closing character strip everything
+            elif i == close_character and not stack:
+                text = text.replace(open_character, u'')
+                text = text.replace(close_character, u'')
+                return text 
+            elif i == close_character and stack:
+                    stack.pop()
+                    
+        # if there are still open_tokens on the stack they have not been closed strip everything
+        if stack:
+            text = text.replace(open_character, u'')
+            text = text.replace(close_character, u'')
+            return text
+        # if nothing left on stack all characters matched and do nothing
+        else:
+            return text