Restore base64.py

python · serhiy-storchaka · Feb 6, 2026 · Mar 8, 2023 · Apr 26, 2025 · Apr 26, 2025
commit aa06c5dcfcab69e5e6f618d346b9531145e5c2c8
diff --git a/Lib/base64.py b/Lib/base64.py
@@ -290,6 +290,36 @@ def b16decode(s, casefold=False):
 #
 # Ascii85 encoding/decoding
 #
+
+_a85chars = None
+_a85chars2 = None
+_A85START = b"<~"
+_A85END = b"~>"
+
+def _85encode(b, chars, chars2, pad=False, foldnuls=False, foldspaces=False):
+    # Helper function for a85encode and b85encode
+    if not isinstance(b, bytes_types):
+        b = memoryview(b).tobytes()
+
+    padding = (-len(b)) % 4
+    if padding:
+        b = b + b'\0' * padding
+    words = struct.Struct('!%dI' % (len(b) // 4)).unpack(b)
+
+    chunks = [b'z' if foldnuls and not word else
+              b'y' if foldspaces and word == 0x20202020 else
+              (chars2[word // 614125] +
+               chars2[word // 85 % 7225] +
+               chars[word % 85])
+              for word in words]
+
+    if padding and not pad:
+        if chunks[-1] == b'z':
+            chunks[-1] = chars[0] * 5
+        chunks[-1] = chunks[-1][:-padding]
+
+    return b''.join(chunks)
+
 def a85encode(b, *, foldspaces=False, wrapcol=0, pad=False, adobe=False):
     """Encode bytes-like object b using Ascii85 and return a bytes object.
 
@@ -307,8 +337,29 @@ def a85encode(b, *, foldspaces=False, wrapcol=0, pad=False, adobe=False):
     adobe controls whether the encoded byte sequence is framed with <~ and ~>,
     which is used by the Adobe implementation.
     """
-    return binascii.b2a_ascii85(b, fold_spaces=foldspaces,
-                                wrap=adobe, width=wrapcol, pad=pad)
+    global _a85chars, _a85chars2
+    # Delay the initialization of tables to not waste memory
+    # if the function is never called
+    if _a85chars2 is None:
+        _a85chars = [bytes((i,)) for i in range(33, 118)]
+        _a85chars2 = [(a + b) for a in _a85chars for b in _a85chars]
+
+    result = _85encode(b, _a85chars, _a85chars2, pad, True, foldspaces)
+
+    if adobe:
+        result = _A85START + result
+    if wrapcol:
+        wrapcol = max(2 if adobe else 1, wrapcol)
+        chunks = [result[i: i + wrapcol]
+                  for i in range(0, len(result), wrapcol)]
+        if adobe:
+            if len(chunks[-1]) + 2 > wrapcol:
+                chunks.append(b'')
+        result = b'\n'.join(chunks)
+    if adobe:
+        result += _A85END
+
+    return result
 
 def a85decode(b, *, foldspaces=False, adobe=False, ignorechars=b' \t\n\r\v'):
     """Decode the Ascii85 encoded bytes-like object or ASCII string b.
@@ -327,36 +378,148 @@ def a85decode(b, *, foldspaces=False, adobe=False, ignorechars=b' \t\n\r\v'):
     The result is returned as a bytes object.
     """
     b = _bytes_from_decode_data(b)
-    return binascii.a2b_ascii85(b, fold_spaces=foldspaces,
-                                wrap=adobe, ignore=ignorechars)
+    if adobe:
+        if not b.endswith(_A85END):
+            raise ValueError(
+                "Ascii85 encoded byte sequences must end "
+                "with {!r}".format(_A85END)
+                )
+        if b.startswith(_A85START):
+            b = b[2:-2]  # Strip off start/end markers
+        else:
+            b = b[:-2]
+    #
+    # We have to go through this stepwise, so as to ignore spaces and handle
+    # special short sequences
+    #
+    packI = struct.Struct('!I').pack
+    decoded = []
+    decoded_append = decoded.append
+    curr = []
+    curr_append = curr.append
+    curr_clear = curr.clear
+    for x in b + b'u' * 4:
+        if b'!'[0] <= x <= b'u'[0]:
+            curr_append(x)
+            if len(curr) == 5:
+                acc = 0
+                for x in curr:
+                    acc = 85 * acc + (x - 33)
+                try:
+                    decoded_append(packI(acc))
+                except struct.error:
+                    raise ValueError('Ascii85 overflow') from None
+                curr_clear()
+        elif x == b'z'[0]:
+            if curr:
+                raise ValueError('z inside Ascii85 5-tuple')
+            decoded_append(b'\0\0\0\0')
+        elif foldspaces and x == b'y'[0]:
+            if curr:
+                raise ValueError('y inside Ascii85 5-tuple')
+            decoded_append(b'\x20\x20\x20\x20')
+        elif x in ignorechars:
+            # Skip whitespace
+            continue
+        else:
+            raise ValueError('Non-Ascii85 digit found: %c' % x)
+
+    result = b''.join(decoded)
+    padding = 4 - len(curr)
+    if padding:
+        # Throw away the extra padding
+        result = result[:-padding]
+    return result
+
+# The following code is originally taken (with permission) from Mercurial
+
+_b85alphabet = (b"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+                b"abcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~")
+_b85chars = None
+_b85chars2 = None
+_b85dec = None
 
 def b85encode(b, pad=False):
     """Encode bytes-like object b in base85 format and return a bytes object.
 
     If pad is true, the input is padded with b'\\0' so its length is a multiple of
     4 bytes before encoding.
     """
-    return binascii.b2a_base85(b, pad=pad, newline=False)
+    global _b85chars, _b85chars2
+    # Delay the initialization of tables to not waste memory
+    # if the function is never called
+    if _b85chars2 is None:
+        _b85chars = [bytes((i,)) for i in _b85alphabet]
+        _b85chars2 = [(a + b) for a in _b85chars for b in _b85chars]
+    return _85encode(b, _b85chars, _b85chars2, pad)
 
 def b85decode(b):
     """Decode the base85-encoded bytes-like object or ASCII string b
 
     The result is returned as a bytes object.
     """
+    global _b85dec
+    # Delay the initialization of tables to not waste memory
+    # if the function is never called
+    if _b85dec is None:
+        _b85dec = [None] * 256
+        for i, c in enumerate(_b85alphabet):
+            _b85dec[c] = i
+
     b = _bytes_from_decode_data(b)
-    return binascii.a2b_base85(b, strict_mode=True)
+    padding = (-len(b)) % 5
+    b = b + b'~' * padding
+    out = []
+    packI = struct.Struct('!I').pack
+    for i in range(0, len(b), 5):
+        chunk = b[i:i + 5]
+        acc = 0
+        try:
+            for c in chunk:
+                acc = acc * 85 + _b85dec[c]
+        except TypeError:
+            for j, c in enumerate(chunk):
+                if _b85dec[c] is None:
+                    raise ValueError('bad base85 character at position %d'
+                                    % (i + j)) from None
+            raise
+        try:
+            out.append(packI(acc))
+        except struct.error:
+            raise ValueError('base85 overflow in hunk starting at byte %d'
+                             % i) from None
+
+    result = b''.join(out)
+    if padding:
+        result = result[:-padding]
+    return result
+
+_z85alphabet = (b'0123456789abcdefghijklmnopqrstuvwxyz'
+                b'ABCDEFGHIJKLMNOPQRSTUVWXYZ.-:+=^!/*?&<>()[]{}@%$#')
+# Translating b85 valid but z85 invalid chars to b'\x00' is required
+# to prevent them from being decoded as b85 valid chars.
+_z85_b85_decode_diff = b';_`|~'
+_z85_decode_translation = bytes.maketrans(
+    _z85alphabet + _z85_b85_decode_diff,
+    _b85alphabet + b'\x00' * len(_z85_b85_decode_diff)
+)
+_z85_encode_translation = bytes.maketrans(_b85alphabet, _z85alphabet)
 
 def z85encode(s):
     """Encode bytes-like object b in z85 format and return a bytes object."""
-    return binascii.b2a_base85(s, newline=False, z85=True)
+    return b85encode(s).translate(_z85_encode_translation)
 
 def z85decode(s):
     """Decode the z85-encoded bytes-like object or ASCII string b
 
     The result is returned as a bytes object.
     """
     s = _bytes_from_decode_data(s)
-    return binascii.a2b_base85(s, strict_mode=True, z85=True)
+    s = s.translate(_z85_decode_translation)
+    try:
+        return b85decode(s)
+    except ValueError as e:
+        raise ValueError(e.args[0].replace('base85', 'z85')) from None
 
 # Legacy interface.  This code could be cleaned up since I don't believe
 # binascii has any line length limitations.  It just doesn't seem worth it