Edit Book: When editing HTML files that have charset encoding declarations, automatically change the declared encoding (if any) to UTF-8 on save, since the editor always saves files in the UTF-8 encoding.

This prevents a mismatch between the declared encoding and the actual
encoding if the HTML file was originally in an encoding other than
UTF-8.

src/calibre/ebooks/chardet.py

@@ -19,15 +19,31 @@ ENCODING_PATS = [
 ]
 ENTITY_PATTERN = re.compile(r'&(\S+?);')
 
-def strip_encoding_declarations(raw):
-    limit = 50*1024
+def strip_encoding_declarations(raw, limit=50*1024):
+    prefix = raw[:limit]
+    suffix = raw[limit:]
     for pat in ENCODING_PATS:
-        prefix = raw[:limit]
-        suffix = raw[limit:]
         prefix = pat.sub('', prefix)
-        raw = prefix + suffix
+    raw = prefix + suffix
     return raw
 
+def replace_encoding_declarations(raw, enc='utf-8', limit=50*1024):
+    prefix = raw[:limit]
+    suffix = raw[limit:]
+    changed = [False]
+    def sub(m):
+        ans = m.group()
+        if m.group(1).lower() != enc.lower():
+            changed[0] = True
+            start, end = m.start(1) - m.start(0), m.end(1) - m.end(0)
+            ans = ans[:start] + enc + ans[end:]
+        return ans
+
+    for pat in ENCODING_PATS:
+        prefix = pat.sub(sub, prefix)
+    raw = prefix + suffix
+    return raw, changed[0]
+
 def substitute_entites(raw):
     from calibre import xml_entity_to_unicode
     return ENTITY_PATTERN.sub(xml_entity_to_unicode, raw)

src/calibre/gui2/tweak_book/editor/widget.py

@@ -15,6 +15,7 @@ from PyQt4.Qt import (
 
 from calibre import prints
 from calibre.constants import DEBUG
+from calibre.ebooks.chardet import replace_encoding_declarations
 from calibre.gui2 import error_dialog
 from calibre.gui2.tweak_book import actions, current_container, tprefs, dictionaries, editor_toolbar_actions
 from calibre.gui2.tweak_book.editor import SPELL_PROPERTY
@@ -136,6 +137,9 @@ class Editor(QMainWindow):
     def data(self):
         def fget(self):
             ans = self.get_raw_data()
+            ans, changed = replace_encoding_declarations(ans, enc='utf-8', limit=4*1024)
+            if changed:
+                self.data = ans
             return ans.encode('utf-8')
         def fset(self, val):
             self.editor.load_text(val, syntax=self.syntax)