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Explore the source code of the class compdoc.py


# -*- coding: cp1252 -*-

##
# Implements the minimal functionality required
# to extract a "Workbook" or "Book" stream (as one big string)
# from an OLE2 Compound Document file.
# 

Copyright � 2005-2012 Stephen John Machin, Lingfo Pty Ltd

#

This module is part of the xlrd package, which is released under a BSD-style licence.

## # No part of the content of this file was derived from the works of David Giffin. # 2008-11-04 SJM Avoid assertion error when -1 used instead of -2 for first_SID of empty SCSS [Frank Hoffsuemmer] # 2007-09-08 SJM Warning message if sector sizes are extremely large. # 2007-05-07 SJM Meaningful exception instead of IndexError if a SAT (sector allocation table) is corrupted. # 2007-04-22 SJM Missing "<" in a struct.unpack call => can't open files on bigendian platforms. from __future__ import print_function import sys from struct import unpack from .timemachine import * import array ## # Magic cookie that should appear in the first 8 bytes of the file. SIGNATURE = b"\xD0\xCF\x11\xE0\xA1\xB1\x1A\xE1" EOCSID = -2 FREESID = -1 SATSID = -3 MSATSID = -4 EVILSID = -5 class CompDocError(Exception): pass class DirNode(object): def __init__(self, DID, dent, DEBUG=0, logfile=sys.stdout): # dent is the 128-byte directory entry self.DID = DID self.logfile = logfile (cbufsize, self.etype, self.colour, self.left_DID, self.right_DID, self.root_DID) = \ unpack(' 20: # allows for 2**20 bytes i.e. 1MB print("WARNING: sector size (2**%d) is preposterous; assuming 512 and continuing ..." \ % ssz, file=logfile) ssz = 9 if sssz > ssz: print("WARNING: short stream sector size (2**%d) is preposterous; assuming 64 and continuing ..." \ % sssz, file=logfile) sssz = 6 self.sec_size = sec_size = 1 << ssz self.short_sec_size = 1 << sssz if self.sec_size != 512 or self.short_sec_size != 64: print("@@@@ sec_size=%d short_sec_size=%d" % (self.sec_size, self.short_sec_size), file=logfile) ( SAT_tot_secs, self.dir_first_sec_sid, _unused, self.min_size_std_stream, SSAT_first_sec_sid, SSAT_tot_secs, MSATX_first_sec_sid, MSATX_tot_secs, # ) = unpack(' 1: print('MSATX: sid=%d (0x%08X)' % (sid, sid), file=logfile) if sid >= mem_data_secs: msg = "MSAT extension: accessing sector %d but only %d in file" % (sid, mem_data_secs) if DEBUG > 1: print(msg, file=logfile) break raise CompDocError(msg) elif sid < 0: raise CompDocError("MSAT extension: invalid sector id: %d" % sid) if seen[sid]: raise CompDocError("MSAT corruption: seen[%d] == %d" % (sid, seen[sid])) seen[sid] = 1 actual_MSATX_sectors += 1 if DEBUG and actual_MSATX_sectors > expected_MSATX_sectors: print("[1]===>>>", mem_data_secs, nent, SAT_sectors_reqd, expected_MSATX_sectors, actual_MSATX_sectors, file=logfile) offset = 512 + sec_size * sid MSAT.extend(unpack(fmt, mem[offset:offset+sec_size])) sid = MSAT.pop() # last sector id is sid of next sector in the chain if DEBUG and actual_MSATX_sectors != expected_MSATX_sectors: print("[2]===>>>", mem_data_secs, nent, SAT_sectors_reqd, expected_MSATX_sectors, actual_MSATX_sectors, file=logfile) if DEBUG: print("MSAT: len =", len(MSAT), file=logfile) dump_list(MSAT, 10, logfile) # # === build the SAT === # self.SAT = [] actual_SAT_sectors = 0 dump_again = 0 for msidx in xrange(len(MSAT)): msid = MSAT[msidx] if msid in (FREESID, EOCSID): # Specification: the MSAT array may be padded with trailing FREESID entries. # Toleration: a FREESID or EOCSID entry anywhere in the MSAT array will be ignored. continue if msid >= mem_data_secs: if not trunc_warned: print("WARNING *** File is truncated, or OLE2 MSAT is corrupt!!", file=logfile) print("INFO: Trying to access sector %d but only %d available" \ % (msid, mem_data_secs), file=logfile) trunc_warned = 1 MSAT[msidx] = EVILSID dump_again = 1 continue elif msid < -2: raise CompDocError("MSAT: invalid sector id: %d" % msid) if seen[msid]: raise CompDocError("MSAT extension corruption: seen[%d] == %d" % (msid, seen[msid])) seen[msid] = 2 actual_SAT_sectors += 1 if DEBUG and actual_SAT_sectors > SAT_sectors_reqd: print("[3]===>>>", mem_data_secs, nent, SAT_sectors_reqd, expected_MSATX_sectors, actual_MSATX_sectors, actual_SAT_sectors, msid, file=logfile) offset = 512 + sec_size * msid self.SAT.extend(unpack(fmt, mem[offset:offset+sec_size])) if DEBUG: print("SAT: len =", len(self.SAT), file=logfile) dump_list(self.SAT, 10, logfile) # print >> logfile, "SAT ", # for i, s in enumerate(self.SAT): # print >> logfile, "entry: %4d offset: %6d, next entry: %4d" % (i, 512 + sec_size * i, s) # print >> logfile, "%d:%d " % (i, s), print(file=logfile) if DEBUG and dump_again: print("MSAT: len =", len(MSAT), file=logfile) dump_list(MSAT, 10, logfile) for satx in xrange(mem_data_secs, len(self.SAT)): self.SAT[satx] = EVILSID print("SAT: len =", len(self.SAT), file=logfile) dump_list(self.SAT, 10, logfile) # # === build the directory === # dbytes = self._get_stream( self.mem, 512, self.SAT, self.sec_size, self.dir_first_sec_sid, name="directory", seen_id=3) dirlist = [] did = -1 for pos in xrange(0, len(dbytes), 128): did += 1 dirlist.append(DirNode(did, dbytes[pos:pos+128], 0, logfile)) self.dirlist = dirlist _build_family_tree(dirlist, 0, dirlist[0].root_DID) # and stand well back ... if DEBUG: for d in dirlist: d.dump(DEBUG) # # === get the SSCS === # sscs_dir = self.dirlist[0] assert sscs_dir.etype == 5 # root entry if sscs_dir.first_SID < 0 or sscs_dir.tot_size == 0: # Problem reported by Frank Hoffsuemmer: some software was # writing -1 instead of -2 (EOCSID) for the first_SID # when the SCCS was empty. Not having EOCSID caused assertion # failure in _get_stream. # Solution: avoid calling _get_stream in any case when the # SCSS appears to be empty. self.SSCS = "" else: self.SSCS = self._get_stream( self.mem, 512, self.SAT, sec_size, sscs_dir.first_SID, sscs_dir.tot_size, name="SSCS", seen_id=4) # if DEBUG: print >> logfile, "SSCS", repr(self.SSCS) # # === build the SSAT === # self.SSAT = [] if SSAT_tot_secs > 0 and sscs_dir.tot_size == 0: print("WARNING *** OLE2 inconsistency: SSCS size is 0 but SSAT size is non-zero", file=logfile) if sscs_dir.tot_size > 0: sid = SSAT_first_sec_sid nsecs = SSAT_tot_secs while sid >= 0 and nsecs > 0: if seen[sid]: raise CompDocError("SSAT corruption: seen[%d] == %d" % (sid, seen[sid])) seen[sid] = 5 nsecs -= 1 start_pos = 512 + sid * sec_size news = list(unpack(fmt, mem[start_pos:start_pos+sec_size])) self.SSAT.extend(news) sid = self.SAT[sid] if DEBUG: print("SSAT last sid %d; remaining sectors %d" % (sid, nsecs), file=logfile) assert nsecs == 0 and sid == EOCSID if DEBUG: print("SSAT", file=logfile) dump_list(self.SSAT, 10, logfile) if DEBUG: print("seen", file=logfile) dump_list(seen, 20, logfile) def _get_stream(self, mem, base, sat, sec_size, start_sid, size=None, name='', seen_id=None): # print >> self.logfile, "_get_stream", base, sec_size, start_sid, size sectors = [] s = start_sid if size is None: # nothing to check against while s >= 0: if seen_id is not None: if self.seen[s]: raise CompDocError("%s corruption: seen[%d] == %d" % (name, s, self.seen[s])) self.seen[s] = seen_id start_pos = base + s * sec_size sectors.append(mem[start_pos:start_pos+sec_size]) try: s = sat[s] except IndexError: raise CompDocError( "OLE2 stream %r: sector allocation table invalid entry (%d)" % (name, s) ) assert s == EOCSID else: todo = size while s >= 0: if seen_id is not None: if self.seen[s]: raise CompDocError("%s corruption: seen[%d] == %d" % (name, s, self.seen[s])) self.seen[s] = seen_id start_pos = base + s * sec_size grab = sec_size if grab > todo: grab = todo todo -= grab sectors.append(mem[start_pos:start_pos+grab]) try: s = sat[s] except IndexError: raise CompDocError( "OLE2 stream %r: sector allocation table invalid entry (%d)" % (name, s) ) assert s == EOCSID if todo != 0: fprintf(self.logfile, "WARNING *** OLE2 stream %r: expected size %d, actual size %d\n", name, size, size - todo) return b''.join(sectors) def _dir_search(self, path, storage_DID=0): # Return matching DirNode instance, or None head = path[0] tail = path[1:] dl = self.dirlist for child in dl[storage_DID].children: if dl[child].name.lower() == head.lower(): et = dl[child].etype if et == 2: return dl[child] if et == 1: if not tail: raise CompDocError("Requested component is a 'storage'") return self._dir_search(tail, child) dl[child].dump(1) raise CompDocError("Requested stream is not a 'user stream'") return None ## # Interrogate the compound document's directory; return the stream as a string if found, otherwise # return None. # @param qname Name of the desired stream e.g. u'Workbook'. Should be in Unicode or convertible thereto. def get_named_stream(self, qname): d = self._dir_search(qname.split("/")) if d is None: return None if d.tot_size >= self.min_size_std_stream: return self._get_stream( self.mem, 512, self.SAT, self.sec_size, d.first_SID, d.tot_size, name=qname, seen_id=d.DID+6) else: return self._get_stream( self.SSCS, 0, self.SSAT, self.short_sec_size, d.first_SID, d.tot_size, name=qname + " (from SSCS)", seen_id=None) ## # Interrogate the compound document's directory. # If the named stream is not found, (None, 0, 0) will be returned. # If the named stream is found and is contiguous within the original byte sequence ("mem") # used when the document was opened, # then (mem, offset_to_start_of_stream, length_of_stream) is returned. # Otherwise a new string is built from the fragments and (new_string, 0, length_of_stream) is returned. # @param qname Name of the desired stream e.g. u'Workbook'. Should be in Unicode or convertible thereto. def locate_named_stream(self, qname): d = self._dir_search(qname.split("/")) if d is None: return (None, 0, 0) if d.tot_size > self.mem_data_len: raise CompDocError("%r stream length (%d bytes) > file data size (%d bytes)" % (qname, d.tot_size, self.mem_data_len)) if d.tot_size >= self.min_size_std_stream: result = self._locate_stream( self.mem, 512, self.SAT, self.sec_size, d.first_SID, d.tot_size, qname, d.DID+6) if self.DEBUG: print("\nseen", file=self.logfile) dump_list(self.seen, 20, self.logfile) return result else: return ( self._get_stream( self.SSCS, 0, self.SSAT, self.short_sec_size, d.first_SID, d.tot_size, qname + " (from SSCS)", None), 0, d.tot_size ) def _locate_stream(self, mem, base, sat, sec_size, start_sid, expected_stream_size, qname, seen_id): # print >> self.logfile, "_locate_stream", base, sec_size, start_sid, expected_stream_size s = start_sid if s < 0: raise CompDocError("_locate_stream: start_sid (%d) is -ve" % start_sid) p = -99 # dummy previous SID start_pos = -9999 end_pos = -8888 slices = [] tot_found = 0 found_limit = (expected_stream_size + sec_size - 1) // sec_size while s >= 0: if self.seen[s]: print("_locate_stream(%s): seen" % qname, file=self.logfile); dump_list(self.seen, 20, self.logfile) raise CompDocError("%s corruption: seen[%d] == %d" % (qname, s, self.seen[s])) self.seen[s] = seen_id tot_found += 1 if tot_found > found_limit: raise CompDocError( "%s: size exceeds expected %d bytes; corrupt?" % (qname, found_limit * sec_size) ) # Note: expected size rounded up to higher sector if s == p+1: # contiguous sectors end_pos += sec_size else: # start new slice if p >= 0: # not first time slices.append((start_pos, end_pos)) start_pos = base + s * sec_size end_pos = start_pos + sec_size p = s s = sat[s] assert s == EOCSID assert tot_found == found_limit # print >> self.logfile, "_locate_stream(%s): seen" % qname; dump_list(self.seen, 20, self.logfile) if not slices: # The stream is contiguous ... just what we like! return (mem, start_pos, expected_stream_size) slices.append((start_pos, end_pos)) # print >> self.logfile, "+++>>> %d fragments" % len(slices) return (b''.join([mem[start_pos:end_pos] for start_pos, end_pos in slices]), 0, expected_stream_size) # ========================================================================================== def x_dump_line(alist, stride, f, dpos, equal=0): print("%5d%s" % (dpos, " ="[equal]), end=' ', file=f) for value in alist[dpos:dpos + stride]: print(str(value), end=' ', file=f) print(file=f) def dump_list(alist, stride, f=sys.stdout): def _dump_line(dpos, equal=0): print("%5d%s" % (dpos, " ="[equal]), end=' ', file=f) for value in alist[dpos:dpos + stride]: print(str(value), end=' ', file=f) print(file=f) pos = None oldpos = None for pos in xrange(0, len(alist), stride): if oldpos is None: _dump_line(pos) oldpos = pos elif alist[pos:pos+stride] != alist[oldpos:oldpos+stride]: if pos - oldpos > stride: _dump_line(pos - stride, equal=1) _dump_line(pos) oldpos = pos if oldpos is not None and pos is not None and pos != oldpos: _dump_line(pos, equal=1)