python · Marius-Juston · Apr 3, 2025 · Apr 3, 2025 · Apr 3, 2025 · Apr 3, 2025
@@ -39,8 +39,6 @@
     'unquote',
     ]
 
-import re
-
 from string import ascii_letters, digits, hexdigits
 
 CRLF = '\r\n'
@@ -281,12 +279,11 @@ def decode(encoded, eol=NL):
 decodestring = decode
 
 
-
-def _unquote_match(match):
-    """Turn a match in the form =AB to the ASCII character with value 0xab"""
-    s = match.group(0)
-    return unquote(s)
-
+_HEX_TO_CHAR = {}
+for i in range(256):
+    key_lower = f"{i:02x}"
+    char_val = chr(i)
+    _HEX_TO_CHAR[key_lower] = char_val
 
 # Header decoding is done a bit differently
 def header_decode(s):
@@ -296,5 +293,29 @@ def header_decode(s):
     quoted-printable (like =?iso-8859-1?q?Hello_World?=) -- please use
     the high level email.header class for that functionality.
     """
-    s = s.replace('_', ' ')
-    return re.sub(r'=[a-fA-F0-9]{2}', _unquote_match, s, flags=re.ASCII)
+    # Check for regex =[a-fA-F0-9]{2}
+    s = s.replace("_", " ")
+
+    if '=' not in s:
+        return s
+
+    result = []
+    s_len = len(s)
+    i = 0
+    last_append = 0
+
+    while i < s_len:
+        if s[i] == '=' and i + 2 < s_len:
+            if (hex_str := s[i + 1:i + 3].lower()) in _HEX_TO_CHAR:
+                if last_append < i:
+                    result.append(s[last_append:i])
+                result.append(_HEX_TO_CHAR[hex_str])
+                i += 3
+                last_append = i
+                continue
+        i += 1
+
+    if last_append < s_len:
+        result.append(s[last_append:])
+
+    return ''.join(result)