PDF Output: Fix balanced parentheses in the text of items in the Table of Contents not being rendered properly by some PDF viewers. Fixes #1358443 [PDF ToC omitting entries in parentheses](https://bugs.launchpad.net/calibre/+bug/1358443)

src/calibre/ebooks/pdf/render/common.py

@@ -93,24 +93,44 @@ class Name(unicode):
                in raw]
         stream.write(b'/'+b''.join(buf))
 
+def escape_unbalanced_parantheses(bytestring):
+    indices = []
+    bad = []
+    ba = bytearray(bytestring)
+    for i, num in enumerate(ba):
+        if num == 40:  # (
+            indices.append(i)
+        elif num == 41:  # )
+            if indices:
+                indices.pop()
+            else:
+                bad.append(i)
+    bad = sorted(list(indices) + bad, reverse=True)
+    if not bad:
+        return bytestring
+    for i in bad:
+        ba.insert(i, 92)  # \
+    return bytes(ba)
+
+
 class String(unicode):
 
     def pdf_serialize(self, stream):
-        s = self.replace('\\', '\\\\').replace('(', r'\(').replace(')', r'\)')
+        s = self.replace('\\', '\\\\')
         try:
             raw = s.encode('latin1')
             if raw.startswith(codecs.BOM_UTF16_BE):
                 raw = codecs.BOM_UTF16_BE + s.encode('utf-16-be')
         except UnicodeEncodeError:
             raw = codecs.BOM_UTF16_BE + s.encode('utf-16-be')
-        stream.write(b'('+raw+b')')
+        stream.write(b'('+escape_unbalanced_parantheses(raw)+b')')
 
 class UTF16String(unicode):
 
     def pdf_serialize(self, stream):
-        s = self.replace('\\', '\\\\').replace('(', r'\(').replace(')', r'\)')
+        s = self.replace('\\', '\\\\')
         raw = codecs.BOM_UTF16_BE + s.encode('utf-16-be')
-        stream.write(b'('+raw+b')')
+        stream.write(b'('+escape_unbalanced_parantheses(raw)+b')')
 
 class Dictionary(dict):