802 lines
26 KiB
Python
802 lines
26 KiB
Python
#!/usr/bin/env python
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import re
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import struct
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import logging
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import six # Python 2+3 compatibility
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try:
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import hashlib as md5
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except ImportError:
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import md5
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try:
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from Crypto.Cipher import ARC4
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from Crypto.Cipher import AES
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from Crypto.Hash import SHA256
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except ImportError:
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AES = SHA256 = None
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from . import arcfour as ARC4
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from .psparser import PSEOF
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from .psparser import literal_name
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from .psparser import LIT
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from .psparser import KWD
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from .psparser import STRICT
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from .pdftypes import PDFException
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from .pdftypes import PDFTypeError
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from .pdftypes import PDFStream
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from .pdftypes import PDFObjectNotFound
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from .pdftypes import decipher_all
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from .pdftypes import int_value
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from .pdftypes import str_value
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from .pdftypes import list_value
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from .pdftypes import dict_value
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from .pdftypes import stream_value
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from .pdfparser import PDFSyntaxError
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from .pdfparser import PDFStreamParser
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from .utils import choplist
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from .utils import nunpack
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from .utils import decode_text
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## Exceptions
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##
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class PDFNoValidXRef(PDFSyntaxError):
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pass
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class PDFNoOutlines(PDFException):
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pass
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class PDFDestinationNotFound(PDFException):
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pass
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class PDFEncryptionError(PDFException):
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pass
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class PDFPasswordIncorrect(PDFEncryptionError):
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pass
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class PDFTextExtractionNotAllowed(PDFEncryptionError):
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pass
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# some predefined literals and keywords.
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LITERAL_OBJSTM = LIT('ObjStm')
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LITERAL_XREF = LIT('XRef')
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LITERAL_CATALOG = LIT('Catalog')
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## XRefs
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##
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class PDFBaseXRef(object):
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def get_trailer(self):
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raise NotImplementedError
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def get_objids(self):
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return []
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# Must return
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# (strmid, index, genno)
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# or (None, pos, genno)
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def get_pos(self, objid):
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raise KeyError(objid)
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## PDFXRef
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##
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class PDFXRef(PDFBaseXRef):
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def __init__(self):
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self.offsets = {}
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self.trailer = {}
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return
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def __repr__(self):
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return '<PDFXRef: offsets=%r>' % (self.offsets.keys())
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def load(self, parser):
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while 1:
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try:
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(pos, line) = parser.nextline()
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if not line.strip():
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continue
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except PSEOF:
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raise PDFNoValidXRef('Unexpected EOF - file corrupted?')
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if not line:
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raise PDFNoValidXRef('Premature eof: %r' % parser)
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if line.startswith(b'trailer'):
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parser.seek(pos)
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break
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f = line.strip().split(b' ')
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if len(f) != 2:
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raise PDFNoValidXRef('Trailer not found: %r: line=%r' % (parser, line))
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try:
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if six.PY2:
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(start, nobjs) = map(long, f)
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else:
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(start, nobjs) = map(int, f)
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except ValueError:
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raise PDFNoValidXRef('Invalid line: %r: line=%r' % (parser, line))
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for objid in range(start, start+nobjs):
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try:
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(_, line) = parser.nextline()
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except PSEOF:
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raise PDFNoValidXRef('Unexpected EOF - file corrupted?')
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f = line.strip().split(b' ')
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if len(f) != 3:
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raise PDFNoValidXRef('Invalid XRef format: %r, line=%r' % (parser, line))
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(pos, genno, use) = f
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if use != b'n':
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continue
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self.offsets[objid] = (None, long(pos) if six.PY2 else int(pos), int(genno))
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logging.info('xref objects: %r' % self.offsets)
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self.load_trailer(parser)
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return
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def load_trailer(self, parser):
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try:
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(_, kwd) = parser.nexttoken()
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assert kwd.name == 'trailer'
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(_, dic) = parser.nextobject()
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except PSEOF:
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x = parser.pop(1)
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if not x:
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raise PDFNoValidXRef('Unexpected EOF - file corrupted')
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(_, dic) = x[0]
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self.trailer.update(dict_value(dic))
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return
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def get_trailer(self):
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return self.trailer
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def get_objids(self):
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return six.iterkeys(self.offsets)
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def get_pos(self, objid):
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try:
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return self.offsets[objid]
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except KeyError:
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raise
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## PDFXRefFallback
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##
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class PDFXRefFallback(PDFXRef):
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def __repr__(self):
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return '<PDFXRefFallback: offsets=%r>' % (self.offsets.keys())
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PDFOBJ_CUE = re.compile(r'^(\d+)\s+(\d+)\s+obj\b')
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def load(self, parser):
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parser.seek(0)
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while 1:
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try:
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(pos, line) = parser.nextline()
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except PSEOF:
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break
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if line.startswith(b'trailer'):
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parser.seek(pos)
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self.load_trailer(parser)
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logging.info('trailer: %r' % self.get_trailer())
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break
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if six.PY3:
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line=line.decode('utf-8')
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m = self.PDFOBJ_CUE.match(line)
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if not m:
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continue
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(objid, genno) = m.groups()
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objid = int(objid)
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genno = int(genno)
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self.offsets[objid] = (None, pos, genno)
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# expand ObjStm.
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parser.seek(pos)
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(_, obj) = parser.nextobject()
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if isinstance(obj, PDFStream) and obj.get('Type') is LITERAL_OBJSTM:
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stream = stream_value(obj)
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try:
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n = stream['N']
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except KeyError:
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if STRICT:
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raise PDFSyntaxError('N is not defined: %r' % stream)
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n = 0
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parser1 = PDFStreamParser(stream.get_data())
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objs = []
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try:
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while 1:
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(_, obj) = parser1.nextobject()
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objs.append(obj)
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except PSEOF:
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pass
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n = min(n, len(objs)//2)
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for index in xrange(n):
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objid1 = objs[index*2]
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self.offsets[objid1] = (objid, index, 0)
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return
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## PDFXRefStream
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##
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class PDFXRefStream(PDFBaseXRef):
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def __init__(self):
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self.data = None
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self.entlen = None
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self.fl1 = self.fl2 = self.fl3 = None
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self.ranges = []
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return
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def __repr__(self):
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return '<PDFXRefStream: ranges=%r>' % (self.ranges)
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def load(self, parser):
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(_, objid) = parser.nexttoken() # ignored
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(_, genno) = parser.nexttoken() # ignored
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(_, kwd) = parser.nexttoken()
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(_, stream) = parser.nextobject()
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if not isinstance(stream, PDFStream) or stream['Type'] is not LITERAL_XREF:
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raise PDFNoValidXRef('Invalid PDF stream spec.')
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size = stream['Size']
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index_array = stream.get('Index', (0, size))
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if len(index_array) % 2 != 0:
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raise PDFSyntaxError('Invalid index number')
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self.ranges.extend(choplist(2, index_array))
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(self.fl1, self.fl2, self.fl3) = stream['W']
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self.data = stream.get_data()
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self.entlen = self.fl1+self.fl2+self.fl3
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self.trailer = stream.attrs
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logging.info('xref stream: objid=%s, fields=%d,%d,%d' %
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(', '.join(map(repr, self.ranges)),
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self.fl1, self.fl2, self.fl3))
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return
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def get_trailer(self):
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return self.trailer
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def get_objids(self):
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for (start, nobjs) in self.ranges:
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for i in xrange(nobjs):
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offset = self.entlen * i
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ent = self.data[offset:offset+self.entlen]
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f1 = nunpack(ent[:self.fl1], 1)
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if f1 == 1 or f1 == 2:
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yield start+i
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return
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def get_pos(self, objid):
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index = 0
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for (start, nobjs) in self.ranges:
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if start <= objid and objid < start+nobjs:
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index += objid - start
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break
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else:
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index += nobjs
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else:
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raise KeyError(objid)
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offset = self.entlen * index
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ent = self.data[offset:offset+self.entlen]
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f1 = nunpack(ent[:self.fl1], 1)
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f2 = nunpack(ent[self.fl1:self.fl1+self.fl2])
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f3 = nunpack(ent[self.fl1+self.fl2:])
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if f1 == 1:
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return (None, f2, f3)
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elif f1 == 2:
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return (f2, f3, 0)
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else:
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# this is a free object
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raise KeyError(objid)
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## PDFSecurityHandler
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##
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class PDFStandardSecurityHandler(object):
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PASSWORD_PADDING = (b'(\xbfN^Nu\x8aAd\x00NV\xff\xfa\x01\x08'
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b'..\x00\xb6\xd0h>\x80/\x0c\xa9\xfedSiz')
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supported_revisions = (2, 3)
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def __init__(self, docid, param, password=b''):
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self.docid = docid
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self.param = param
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self.password = password
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self.init()
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return
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def init(self):
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self.init_params()
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if self.r not in self.supported_revisions:
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raise PDFEncryptionError('Unsupported revision: param=%r' % self.param)
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self.init_key()
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return
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def init_params(self):
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self.v = int_value(self.param.get('V', 0))
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self.r = int_value(self.param['R'])
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self.p = int_value(self.param['P'])
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self.o = str_value(self.param['O'])
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self.u = str_value(self.param['U'])
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self.length = int_value(self.param.get('Length', 40))
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return
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def init_key(self):
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self.key = self.authenticate(self.password)
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if self.key is None:
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raise PDFPasswordIncorrect
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return
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def is_printable(self):
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return bool(self.p & 4)
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def is_modifiable(self):
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return bool(self.p & 8)
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def is_extractable(self):
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return bool(self.p & 16)
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def compute_u(self, key):
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if self.r == 2:
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# Algorithm 3.4
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return ARC4.new(key).encrypt(self.PASSWORD_PADDING) # 2
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else:
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# Algorithm 3.5
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hash = md5.md5(self.PASSWORD_PADDING) # 2
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hash.update(self.docid[0]) # 3
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result = ARC4.new(key).encrypt(hash.digest()) # 4
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for i in range(1, 20): # 5
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k = b''.join(chr(ord(c) ^ i) for c in key)
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result = ARC4.new(k).encrypt(result)
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result += result # 6
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return result
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def compute_encryption_key(self, password):
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# Algorithm 3.2
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password = (password + self.PASSWORD_PADDING)[:32] # 1
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hash = md5.md5(password) # 2
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hash.update(self.o) # 3
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hash.update(struct.pack('<l', self.p)) # 4
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hash.update(self.docid[0]) # 5
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if self.r >= 4:
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if not self.encrypt_metadata:
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hash.update(b'\xff\xff\xff\xff')
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result = hash.digest()
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n = 5
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if self.r >= 3:
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n = self.length // 8
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for _ in range(50):
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result = md5.md5(result[:n]).digest()
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return result[:n]
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def authenticate(self, password):
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key = self.authenticate_user_password(password)
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if key is None:
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key = self.authenticate_owner_password(password)
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return key
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def authenticate_user_password(self, password):
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key = self.compute_encryption_key(password)
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if self.verify_encryption_key(key):
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return key
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else:
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return None
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def verify_encryption_key(self, key):
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# Algorithm 3.6
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u = self.compute_u(key)
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if self.r == 2:
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return u == self.u
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return u[:16] == self.u[:16]
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def authenticate_owner_password(self, password):
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# Algorithm 3.7
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password = (password + self.PASSWORD_PADDING)[:32]
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hash = md5.md5(password)
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if self.r >= 3:
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for _ in range(50):
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hash = md5.md5(hash.digest())
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n = 5
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if self.r >= 3:
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n = self.length // 8
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key = hash.digest()[:n]
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if self.r == 2:
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user_password = ARC4.new(key).decrypt(self.o)
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else:
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user_password = self.o
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for i in range(19, -1, -1):
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k = b''.join(chr(ord(c) ^ i) for c in key)
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user_password = ARC4.new(k).decrypt(user_password)
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return self.authenticate_user_password(user_password)
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def decrypt(self, objid, genno, data, attrs=None):
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return self.decrypt_rc4(objid, genno, data)
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def decrypt_rc4(self, objid, genno, data):
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key = self.key + struct.pack('<L', objid)[:3] + struct.pack('<L', genno)[:2]
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hash = md5.md5(key)
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key = hash.digest()[:min(len(key), 16)]
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return ARC4.new(key).decrypt(data)
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class PDFStandardSecurityHandlerV4(PDFStandardSecurityHandler):
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supported_revisions = (4,)
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def init_params(self):
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super(PDFStandardSecurityHandlerV4, self).init_params()
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self.length = 128
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self.cf = dict_value(self.param.get('CF'))
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self.stmf = literal_name(self.param['StmF'])
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self.strf = literal_name(self.param['StrF'])
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self.encrypt_metadata = bool(self.param.get('EncryptMetadata', True))
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if self.stmf != self.strf:
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raise PDFEncryptionError('Unsupported crypt filter: param=%r' % self.param)
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self.cfm = {}
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for k, v in self.cf.items():
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f = self.get_cfm(literal_name(v['CFM']))
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if f is None:
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raise PDFEncryptionError('Unknown crypt filter method: param=%r' % self.param)
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self.cfm[k] = f
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self.cfm['Identity'] = self.decrypt_identity
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if self.strf not in self.cfm:
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raise PDFEncryptionError('Undefined crypt filter: param=%r' % self.param)
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return
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def get_cfm(self, name):
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if name == 'V2':
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return self.decrypt_rc4
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elif name == 'AESV2':
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return self.decrypt_aes128
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else:
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return None
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def decrypt(self, objid, genno, data, attrs=None, name=None):
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if not self.encrypt_metadata and attrs is not None:
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t = attrs.get('Type')
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if t is not None and literal_name(t) == 'Metadata':
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return data
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if name is None:
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name = self.strf
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return self.cfm[name](objid, genno, data)
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def decrypt_identity(self, objid, genno, data):
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return data
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def decrypt_aes128(self, objid, genno, data):
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key = self.key + struct.pack('<L', objid)[:3] + struct.pack('<L', genno)[:2] + b'sAlT'
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hash = md5.md5(key)
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key = hash.digest()[:min(len(key), 16)]
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return AES.new(key, mode=AES.MODE_CBC, IV=data[:16]).decrypt(data[16:])
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class PDFStandardSecurityHandlerV5(PDFStandardSecurityHandlerV4):
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supported_revisions = (5,)
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def init_params(self):
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super(PDFStandardSecurityHandlerV5, self).init_params()
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self.length = 256
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self.oe = str_value(self.param['OE'])
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self.ue = str_value(self.param['UE'])
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self.o_hash = self.o[:32]
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self.o_validation_salt = self.o[32:40]
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self.o_key_salt = self.o[40:]
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self.u_hash = self.u[:32]
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self.u_validation_salt = self.u[32:40]
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self.u_key_salt = self.u[40:]
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return
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def get_cfm(self, name):
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if name == 'AESV3':
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return self.decrypt_aes256
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else:
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return None
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def authenticate(self, password):
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password = password.encode('utf-8')[:127]
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hash = SHA256.new(password)
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hash.update(self.o_validation_salt)
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hash.update(self.u)
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if hash.digest() == self.o_hash:
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hash = SHA256.new(password)
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hash.update(self.o_key_salt)
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hash.update(self.u)
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return AES.new(hash.digest(), mode=AES.MODE_CBC, IV=b'\x00' * 16).decrypt(self.oe)
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hash = SHA256.new(password)
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hash.update(self.u_validation_salt)
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if hash.digest() == self.u_hash:
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hash = SHA256.new(password)
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hash.update(self.u_key_salt)
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return AES.new(hash.digest(), mode=AES.MODE_CBC, IV=b'\x00' * 16).decrypt(self.ue)
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return None
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def decrypt_aes256(self, objid, genno, data):
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return AES.new(self.key, mode=AES.MODE_CBC, IV=data[:16]).decrypt(data[16:])
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## PDFDocument
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##
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class PDFDocument(object):
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"""PDFDocument object represents a PDF document.
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Since a PDF file can be very big, normally it is not loaded at
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once. So PDF document has to cooperate with a PDF parser in order to
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dynamically import the data as processing goes.
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Typical usage:
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doc = PDFDocument(parser, password)
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obj = doc.getobj(objid)
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"""
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security_handler_registry = {
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1: PDFStandardSecurityHandler,
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2: PDFStandardSecurityHandler,
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}
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if AES is not None:
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security_handler_registry[4] = PDFStandardSecurityHandlerV4
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if SHA256 is not None:
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security_handler_registry[5] = PDFStandardSecurityHandlerV5
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debug = 0
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def __init__(self, parser, password=b'', caching=True, fallback=True):
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"Set the document to use a given PDFParser object."
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self.caching = caching
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self.xrefs = []
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self.info = []
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self.catalog = None
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self.encryption = None
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self.decipher = None
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self._parser = None
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self._cached_objs = {}
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self._parsed_objs = {}
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self._parser = parser
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self._parser.set_document(self)
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self.is_printable = self.is_modifiable = self.is_extractable = True
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# Retrieve the information of each header that was appended
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# (maybe multiple times) at the end of the document.
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try:
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pos = self.find_xref(parser)
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self.read_xref_from(parser, pos, self.xrefs)
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except PDFNoValidXRef:
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fallback = True
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if fallback:
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parser.fallback = True
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xref = PDFXRefFallback()
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xref.load(parser)
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self.xrefs.append(xref)
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for xref in self.xrefs:
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trailer = xref.get_trailer()
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if not trailer:
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continue
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# If there's an encryption info, remember it.
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if 'Encrypt' in trailer:
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#assert not self.encryption
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self.encryption = (list_value(trailer['ID']),
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dict_value(trailer['Encrypt']))
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self._initialize_password(password)
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if 'Info' in trailer:
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self.info.append(dict_value(trailer['Info']))
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if 'Root' in trailer:
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# Every PDF file must have exactly one /Root dictionary.
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self.catalog = dict_value(trailer['Root'])
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break
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else:
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raise PDFSyntaxError('No /Root object! - Is this really a PDF?')
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if self.catalog.get('Type') is not LITERAL_CATALOG:
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if STRICT:
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raise PDFSyntaxError('Catalog not found!')
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return
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# _initialize_password(password=b'')
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# Perform the initialization with a given password.
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def _initialize_password(self, password=b''):
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(docid, param) = self.encryption
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if literal_name(param.get('Filter')) != 'Standard':
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raise PDFEncryptionError('Unknown filter: param=%r' % param)
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v = int_value(param.get('V', 0))
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factory = self.security_handler_registry.get(v)
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if factory is None:
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raise PDFEncryptionError('Unknown algorithm: param=%r' % param)
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handler = factory(docid, param, password)
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self.decipher = handler.decrypt
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self.is_printable = handler.is_printable()
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self.is_modifiable = handler.is_modifiable()
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self.is_extractable = handler.is_extractable()
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self._parser.fallback = False # need to read streams with exact length
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return
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def _getobj_objstm(self, stream, index, objid):
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if stream.objid in self._parsed_objs:
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(objs, n) = self._parsed_objs[stream.objid]
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else:
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(objs, n) = self._get_objects(stream)
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if self.caching:
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self._parsed_objs[stream.objid] = (objs, n)
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i = n*2+index
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try:
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obj = objs[i]
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except IndexError:
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raise PDFSyntaxError('index too big: %r' % index)
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return obj
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def _get_objects(self, stream):
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if stream.get('Type') is not LITERAL_OBJSTM:
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if STRICT:
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raise PDFSyntaxError('Not a stream object: %r' % stream)
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try:
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n = stream['N']
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except KeyError:
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if STRICT:
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raise PDFSyntaxError('N is not defined: %r' % stream)
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n = 0
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parser = PDFStreamParser(stream.get_data())
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parser.set_document(self)
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objs = []
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try:
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while 1:
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(_, obj) = parser.nextobject()
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objs.append(obj)
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except PSEOF:
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pass
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return (objs, n)
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def _getobj_parse(self, pos, objid):
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self._parser.seek(pos)
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(_, objid1) = self._parser.nexttoken() # objid
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if objid1 != objid:
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raise PDFSyntaxError('objid mismatch: %r=%r' % (objid1, objid))
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(_, genno) = self._parser.nexttoken() # genno
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(_, kwd) = self._parser.nexttoken()
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if kwd.name !='obj':
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raise PDFSyntaxError('Invalid object spec: offset=%r' % pos)
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(_, obj) = self._parser.nextobject()
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return obj
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# can raise PDFObjectNotFound
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def getobj(self, objid):
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assert objid != 0
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if not self.xrefs:
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raise PDFException('PDFDocument is not initialized')
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if self.debug:
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logging.debug('getobj: objid=%r' % objid)
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if objid in self._cached_objs:
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(obj, genno) = self._cached_objs[objid]
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else:
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for xref in self.xrefs:
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try:
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(strmid, index, genno) = xref.get_pos(objid)
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except KeyError:
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continue
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try:
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if strmid is not None:
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stream = stream_value(self.getobj(strmid))
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obj = self._getobj_objstm(stream, index, objid)
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else:
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obj = self._getobj_parse(index, objid)
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if self.decipher:
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obj = decipher_all(self.decipher, objid, genno, obj)
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if isinstance(obj, PDFStream):
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obj.set_objid(objid, genno)
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break
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except (PSEOF, PDFSyntaxError):
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continue
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else:
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raise PDFObjectNotFound(objid)
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if self.debug:
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logging.debug('register: objid=%r: %r' % (objid, obj))
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if self.caching:
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self._cached_objs[objid] = (obj, genno)
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return obj
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def get_outlines(self):
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if 'Outlines' not in self.catalog:
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raise PDFNoOutlines
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def search(entry, level):
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entry = dict_value(entry)
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if 'Title' in entry:
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if 'A' in entry or 'Dest' in entry:
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title = decode_text(str_value(entry['Title']))
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dest = entry.get('Dest')
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action = entry.get('A')
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se = entry.get('SE')
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yield (level, title, dest, action, se)
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if 'First' in entry and 'Last' in entry:
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for x in search(entry['First'], level+1):
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yield x
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if 'Next' in entry:
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for x in search(entry['Next'], level):
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yield x
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return
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return search(self.catalog['Outlines'], 0)
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def lookup_name(self, cat, key):
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try:
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names = dict_value(self.catalog['Names'])
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except (PDFTypeError, KeyError):
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raise KeyError((cat, key))
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# may raise KeyError
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d0 = dict_value(names[cat])
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def lookup(d):
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if 'Limits' in d:
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(k1, k2) = list_value(d['Limits'])
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if key < k1 or k2 < key:
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return None
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if 'Names' in d:
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objs = list_value(d['Names'])
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names = dict(choplist(2, objs))
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return names[key]
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if 'Kids' in d:
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for c in list_value(d['Kids']):
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v = lookup(dict_value(c))
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if v:
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return v
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raise KeyError((cat, key))
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return lookup(d0)
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def get_dest(self, name):
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try:
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# PDF-1.2 or later
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obj = self.lookup_name('Dests', name)
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except KeyError:
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# PDF-1.1 or prior
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if 'Dests' not in self.catalog:
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raise PDFDestinationNotFound(name)
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d0 = dict_value(self.catalog['Dests'])
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if name not in d0:
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raise PDFDestinationNotFound(name)
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obj = d0[name]
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return obj
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# find_xref
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def find_xref(self, parser):
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"""Internal function used to locate the first XRef."""
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# search the last xref table by scanning the file backwards.
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prev = None
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for line in parser.revreadlines():
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line = line.strip()
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if self.debug:
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logging.debug('find_xref: %r' % line)
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if line == b'startxref':
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break
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if line:
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prev = line
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else:
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raise PDFNoValidXRef('Unexpected EOF')
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logging.info('xref found: pos=%r' % prev)
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return long(prev) if six.PY2 else int(prev)
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# read xref table
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def read_xref_from(self, parser, start, xrefs):
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"""Reads XRefs from the given location."""
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parser.seek(start)
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parser.reset()
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try:
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(pos, token) = parser.nexttoken()
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except PSEOF:
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raise PDFNoValidXRef('Unexpected EOF')
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logging.info('read_xref_from: start=%d, token=%r' % (start, token))
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if isinstance(token, int):
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# XRefStream: PDF-1.5
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parser.seek(pos)
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parser.reset()
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xref = PDFXRefStream()
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xref.load(parser)
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else:
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if token is parser.KEYWORD_XREF:
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parser.nextline()
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xref = PDFXRef()
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xref.load(parser)
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xrefs.append(xref)
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trailer = xref.get_trailer()
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logging.info('trailer: %r' % trailer)
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if 'XRefStm' in trailer:
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pos = int_value(trailer['XRefStm'])
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self.read_xref_from(parser, pos, xrefs)
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if 'Prev' in trailer:
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# find previous xref
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pos = int_value(trailer['Prev'])
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self.read_xref_from(parser, pos, xrefs)
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return
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