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filters.py

# vim: sw=4:expandtab:foldmethod=marker
#
# Copyright (c) 2006, Mathieu Fenniak
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
#
# * Redistributions of source code must retain the above copyright notice,
# this list of conditions and the following disclaimer.
# * Redistributions in binary form must reproduce the above copyright notice,
# this list of conditions and the following disclaimer in the documentation
# and/or other materials provided with the distribution.
# * The name of the author may not be used to endorse or promote products
# derived from this software without specific prior written permission.
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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"""
Implementation of stream filters for PDF.
"""
__author__ = "Mathieu Fenniak"
__author_email__ = "biziqe@mathieu.fenniak.net"

from utils import PdfReadError
try:
    from cStringIO import StringIO
except ImportError:
    from StringIO import StringIO

try:
    import zlib
    def decompress(data):
        return zlib.decompress(data)
    def compress(data):
        return zlib.compress(data)
except ImportError:
    # Unable to import zlib.  Attempt to use the System.IO.Compression
    # library from the .NET framework. (IronPython only)
    import System
    from System import IO, Collections, Array
    def _string_to_bytearr(buf):
        retval = Array.CreateInstance(System.Byte, len(buf))
        for i in range(len(buf)):
            retval[i] = ord(buf[i])
        return retval
    def _bytearr_to_string(bytes):
        retval = ""
        for i in range(bytes.Length):
            retval += chr(bytes[i])
        return retval
    def _read_bytes(stream):
        ms = IO.MemoryStream()
        buf = Array.CreateInstance(System.Byte, 2048)
        while True:
            bytes = stream.Read(buf, 0, buf.Length)
            if bytes == 0:
                break
            else:
                ms.Write(buf, 0, bytes)
        retval = ms.ToArray()
        ms.Close()
        return retval
    def decompress(data):
        bytes = _string_to_bytearr(data)
        ms = IO.MemoryStream()
        ms.Write(bytes, 0, bytes.Length)
        ms.Position = 0  # fseek 0
        gz = IO.Compression.DeflateStream(ms, IO.Compression.CompressionMode.Decompress)
        bytes = _read_bytes(gz)
        retval = _bytearr_to_string(bytes)
        gz.Close()
        return retval
    def compress(data):
        bytes = _string_to_bytearr(data)
        ms = IO.MemoryStream()
        gz = IO.Compression.DeflateStream(ms, IO.Compression.CompressionMode.Compress, True)
        gz.Write(bytes, 0, bytes.Length)
        gz.Close()
        ms.Position = 0 # fseek 0
        bytes = ms.ToArray()
        retval = _bytearr_to_string(bytes)
        ms.Close()
        return retval


class FlateDecode(object):
    def decode(data, decodeParms):
        data = decompress(data)
        predictor = 1
        if decodeParms:
            predictor = decodeParms.get("/Predictor", 1)
        # predictor 1 == no predictor
        if predictor != 1:
            columns = decodeParms["/Columns"]
            # PNG prediction:
            if predictor >= 10 and predictor <= 15:
                output = StringIO()
                # PNG prediction can vary from row to row
                rowlength = columns + 1
                assert len(data) % rowlength == 0
                prev_rowdata = (0,) * rowlength
                for row in xrange(len(data) / rowlength):
                    rowdata = [ord(x) for x in data[(row*rowlength):((row+1)*rowlength)]]
                    filterByte = rowdata[0]
                    if filterByte == 0:
                        pass
                    elif filterByte == 1:
                        for i in range(2, rowlength):
                            rowdata[i] = (rowdata[i] + rowdata[i-1]) % 256
                    elif filterByte == 2:
                        for i in range(1, rowlength):
                            rowdata[i] = (rowdata[i] + prev_rowdata[i]) % 256
                    else:
                        # unsupported PNG filter
                        raise PdfReadError("Unsupported PNG filter %r" % filterByte)
                    prev_rowdata = rowdata
                    output.write(''.join([chr(x) for x in rowdata[1:]]))
                data = output.getvalue()
            else:
                # unsupported predictor
                raise PdfReadError("Unsupported flatedecode predictor %r" % predictor)
        return data
    decode = staticmethod(decode)

    def encode(data):
        return compress(data)
    encode = staticmethod(encode)

class ASCIIHexDecode(object):
    def decode(data, decodeParms=None):
        retval = ""
        char = ""
        x = 0
        while True:
            c = data[x]
            if c == ">":
                break
            elif c.isspace():
                x += 1
                continue
            char += c
            if len(char) == 2:
                retval += chr(int(char, base=16))
                char = ""
            x += 1
        assert char == ""
        return retval
    decode = staticmethod(decode)

class ASCII85Decode(object):
    def decode(data, decodeParms=None):
        retval = ""
        group = []
        x = 0
        hitEod = False
        # remove all whitespace from data
        data = [y for y in data if not (y in ' \n\r\t')]
        while not hitEod:
            c = data[x]
            if len(retval) == 0 and c == "<" and data[x+1] == "~":
                x += 2
                continue
            #elif c.isspace():
            #    x += 1
            #    continue
            elif c == 'z':
                assert len(group) == 0
                retval += '\x00\x00\x00\x00'
                continue
            elif c == "~" and data[x+1] == ">":
                if len(group) != 0:
                    # cannot have a final group of just 1 char
                    assert len(group) > 1
                    cnt = len(group) - 1
                    group += [ 85, 85, 85 ]
                    hitEod = cnt
                else:
                    break
            else:
                c = ord(c) - 33
                assert c >= 0 and c < 85
                group += [ c ]
            if len(group) >= 5:
                b = group[0] * (85**4) + \
                    group[1] * (85**3) + \
                    group[2] * (85**2) + \
                    group[3] * 85 + \
                    group[4]
                assert b < (2**32 - 1)
                c4 = chr((b >> 0) % 256)
                c3 = chr((b >> 8) % 256)
                c2 = chr((b >> 16) % 256)
                c1 = chr(b >> 24)
                retval += (c1 + c2 + c3 + c4)
                if hitEod:
                    retval = retval[:-4+hitEod]
                group = []
            x += 1
        return retval
    decode = staticmethod(decode)

def decodeStreamData(stream):
    from generic import NameObject
    filters = stream.get("/Filter", ())
    if len(filters) and not isinstance(filters[0], NameObject):
        # we have a single filter instance
        filters = (filters,)
    data = stream._data
    for filterType in filters:
        if filterType == "/FlateDecode":
            data = FlateDecode.decode(data, stream.get("/DecodeParms"))
        elif filterType == "/ASCIIHexDecode":
            data = ASCIIHexDecode.decode(data)
        elif filterType == "/ASCII85Decode":
            data = ASCII85Decode.decode(data)
        elif filterType == "/Crypt":
            decodeParams = stream.get("/DecodeParams", {})
            if "/Name" not in decodeParams and "/Type" not in decodeParams:
                pass
            else:
                raise NotImplementedError("/Crypt filter with /Name or /Type not supported yet")
        else:
            # unsupported filter
            raise NotImplementedError("unsupported filter %s" % filterType)
    return data

if __name__ == "__main__":
    assert "abc" == ASCIIHexDecode.decode('61\n626\n3>')

    ascii85Test = """
     <~9jqo^BlbD-BleB1DJ+*+F(f,q/0JhKF<GL>Cj@.4Gp$d7F!,L7@<6@)/0JDEF<G%<+EV:2F!,
     O<DJ+*.@<*K0@<6L(Df-\\0Ec5e;DffZ(EZee.Bl.9pF"AGXBPCsi+DGm>@3BB/F*&OCAfu2/AKY
     i(DIb:@FD,*)+C]U=@3BN#EcYf8ATD3s@q?d$AftVqCh[NqF<G:8+EV:.+Cf>-FD5W8ARlolDIa
     l(DId<j@<?3r@:F%a+D58'ATD4$Bl@l3De:,-DJs`8ARoFb/0JMK@qB4^F!,R<AKZ&-DfTqBG%G
     >uD.RTpAKYo'+CT/5+Cei#DII?(E,9)oF*2M7/c~>
    """
    ascii85_originalText="Man is distinguished, not only by his reason, but by this singular passion from other animals, which is a lust of the mind, that by a perseverance of delight in the continued and indefatigable generation of knowledge, exceeds the short vehemence of any carnal pleasure."
    assert ASCII85Decode.decode(ascii85Test) == ascii85_originalText


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