Serialization - sample code in progress, clarifications

content/_code-samples/tx-serialization/base58/base58.py

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+'''Base58 encoding
+
+Implementations of Base58 and Base58Check endcodings that are compatible
+with the XRP Ledger.
+'''
+
+# This This code is adapted from the module by David Keijser at
+# <https://github.com/keis/base58>. - rome@ripple.com
+# His notes are preserved below:
+
+# This module is based upon base58 snippets found scattered over many bitcoin
+# tools written in python. From what I gather the original source is from a
+# forum post by Gavin Andresen, so direct your praise to him.
+# This module adds shiny packaging and support for python3.
+
+from hashlib import sha256
+
+__version__ = '1.0.3-xrp'
+
+# 58 character alphabet used
+# alphabet = b'123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz' # Bitcoin
+alphabet = b'rpshnaf39wBUDNEGHJKLM4PQRST7VWXYZ2bcdeCg65jkm8oFqi1tuvAxyz' # XRP Ledger
+
+
+if bytes == str:  # python2
+    iseq, bseq, buffer = (
+        lambda s: map(ord, s),
+        lambda s: ''.join(map(chr, s)),
+        lambda s: s,
+    )
+else:  # python3
+    iseq, bseq, buffer = (
+        lambda s: s,
+        bytes,
+        lambda s: s.buffer,
+    )
+
+
+def scrub_input(v):
+    if isinstance(v, str) and not isinstance(v, bytes):
+        v = v.encode('ascii')
+
+    if not isinstance(v, bytes):
+        raise TypeError(
+            "a bytes-like object is required (also str), not '%s'" %
+            type(v).__name__)
+
+    return v
+
+
+def b58encode_int(i, default_one=True):
+    '''Encode an integer using Base58'''
+    if not i and default_one:
+        return alphabet[0:1]
+    string = b""
+    while i:
+        i, idx = divmod(i, 58)
+        string = alphabet[idx:idx+1] + string
+    return string
+
+
+def b58encode(v):
+    '''Encode a string using Base58'''
+
+    v = scrub_input(v)
+
+    nPad = len(v)
+    v = v.lstrip(b'\0')
+    nPad -= len(v)
+
+    p, acc = 1, 0
+    for c in iseq(reversed(v)):
+        acc += p * c
+        p = p << 8
+
+    result = b58encode_int(acc, default_one=False)
+
+    return (alphabet[0:1] * nPad + result)
+
+
+def b58decode_int(v):
+    '''Decode a Base58 encoded string as an integer'''
+
+    v = scrub_input(v)
+
+    decimal = 0
+    for char in v:
+        decimal = decimal * 58 + alphabet.index(char)
+    return decimal
+
+
+def b58decode(v):
+    '''Decode a Base58 encoded string'''
+
+    v = scrub_input(v)
+
+    origlen = len(v)
+    v = v.lstrip(alphabet[0:1])
+    newlen = len(v)
+
+    acc = b58decode_int(v)
+
+    result = []
+    while acc > 0:
+        acc, mod = divmod(acc, 256)
+        result.append(mod)
+
+    return (b'\0' * (origlen - newlen) + bseq(reversed(result)))
+
+
+def b58encode_check(v):
+    '''Encode a string using Base58 with a 4 character checksum'''
+
+    digest = sha256(sha256(v).digest()).digest()
+    return b58encode(v + digest[:4])
+
+
+def b58decode_check(v):
+    '''Decode and verify the checksum of a Base58 encoded string'''
+
+    result = b58decode(v)
+    result, check = result[:-4], result[-4:]
+    digest = sha256(sha256(result).digest()).digest()
+
+    if check != digest[:4]:
+        raise ValueError("Invalid checksum")
+
+    return result
+
+
+def main():
+    '''Base58 encode or decode FILE, or standard input, to standard output.'''
+
+    import sys
+    import argparse
+
+    stdout = buffer(sys.stdout)
+
+    parser = argparse.ArgumentParser(description=main.__doc__)
+    parser.add_argument(
+        'file',
+        metavar='FILE',
+        nargs='?',
+        type=argparse.FileType('r'),
+        default='-')
+    parser.add_argument(
+        '-d', '--decode',
+        action='store_true',
+        help='decode data')
+    parser.add_argument(
+        '-c', '--check',
+        action='store_true',
+        help='append a checksum before encoding')
+
+    args = parser.parse_args()
+    fun = {
+        (False, False): b58encode,
+        (False, True): b58encode_check,
+        (True, False): b58decode,
+        (True, True): b58decode_check
+    }[(args.decode, args.check)]
+
+    data = buffer(args.file).read()
+
+    try:
+        result = fun(data)
+    except Exception as e:
+        sys.exit(e)
+
+    if not isinstance(result, bytes):
+        result = result.encode('ascii')
+
+    stdout.write(result)
+
+
+if __name__ == '__main__':
+    main()