pdfminer.six/pdfminer/ascii85.py

""" Python implementation of ASCII85/ASCIIHex decoder (Adobe version).

This code is in the public domain.

"""

import re
import struct

import six  # Python 2+3 compatibility


# ascii85decode(data)
def ascii85decode(data):
    """
    In ASCII85 encoding, every four bytes are encoded with five ASCII
    letters, using 85 different types of characters (as 256**4 < 85**5).
    When the length of the original bytes is not a multiple of 4, a special
    rule is used for round up.

    The Adobe's ASCII85 implementation is slightly different from
    its original in handling the last characters.

    """
    n = b = 0
    out = b''
    for i in six.iterbytes(data):
        c = six.int2byte(i)
        if b'!' <= c and c <= b'u':
            n += 1
            b = b*85+(ord(c)-33)
            if n == 5:
                out += struct.pack('>L', b)
                n = b = 0
        elif c == b'z':
            assert n == 0, str(n)
            out += b'\0\0\0\0'
        elif c == b'~':
            if n:
                for _ in range(5-n):
                    b = b*85+84
                out += struct.pack('>L', b)[:n-1]
            break
    return out


# asciihexdecode(data)
hex_re = re.compile(b'([a-f0-9]{2})', re.IGNORECASE)
trail_re = re.compile(b'^(?:[a-f0-9]{2}|[ \t\n\r\f\v])*'
                      b'([a-f0-9])[ \t\n\r\f\v>]*$', re.IGNORECASE)


def asciihexdecode(data):
    """
    ASCIIHexDecode filter: PDFReference v1.4 section 3.3.1
    For each pair of ASCII hexadecimal digits (0-9 and A-F or a-f), the
    ASCIIHexDecode filter produces one byte of binary data. All white-space
    characters are ignored. A right angle bracket character (>) indicates
    EOD. Any other characters will cause an error. If the filter encounters
    the EOD marker after reading an odd number of hexadecimal digits, it
    will behave as if a 0 followed the last digit.
    """
    def decode(x):
        i = int(x, 16)
        return six.int2byte(i)

    out = b''
    for x in hex_re.findall(data):
        out += decode(x)

    m = trail_re.search(data)
    if m:
        out += decode(m.group(1)+b'0')
    return out