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# fat.py; ad-hoc fat16 reader
# by Bram Westerbaan <bram@westerbaan.name>
#
# references:
# http://en.wikipedia.org/wiki/File_Allocation_Table
# http://www.ecma-international.org/publications/standards/Ecma-107.htm
#
# example:
# with open("/dev/sdc1") as file:
# fs = FatFs(file)
# for rootdir in fs:
# print rootdir
import numbers
from io import BytesIO, BufferedReader
from construct import Struct, Byte, Bytes, ULInt16, ULInt32, Enum, \
Array, Padding, Embed, Pass, BitStruct, Flag, Const
def Fat16Header(name):
return Struct(name,
Bytes("jumpInstruction", 3),
Bytes("creatingSystemId", 8),
ULInt16("sectorSize"),
Byte("sectorsPerCluster"),
ULInt16("reservedSectorCount"),
Byte("fatCount"),
ULInt16("rootdirEntryCount"),
ULInt16("sectorCount_small"),
Byte("mediaId"),
ULInt16("sectorsPerFat"),
ULInt16("sectorsPerTrack"),
ULInt16("sideCount"),
ULInt32("hiddenSectorCount"),
ULInt32("sectorCount_large"),
Byte("physicalDriveNumber"),
Byte("currentHead"),
Byte("extendedBootSignature"),
Bytes("volumeId", 4),
Bytes("volumeLabel", 11),
Const(Bytes("fsType", 8), "FAT16 "),
Bytes("bootCode", 448),
Const(Bytes("bootSectorSignature", 2), "\x55\xaa"))
def BootSector(name):
header = Fat16Header("header")
return Struct(name,
Embed(header),
Padding(lambda ctx: ctx.sectorSize - header.sizeof()))
def FatEntry(name):
return Enum(ULInt16(name),
free_cluster = 0x0000,
bad_cluster = 0xfff7,
last_cluster = 0xffff,
_default_ = Pass)
def DirEntry(name):
return Struct(name,
Bytes("name", 8),
Bytes("extension", 3),
BitStruct("attributes",
Flag("unused"),
Flag("device"),
Flag("archive"),
Flag("subDirectory"),
Flag("volumeLabel"),
Flag("system"),
Flag("hidden"),
Flag("readonly")),
# reserved
Padding(10),
ULInt16("timeRecorded"),
ULInt16("dateRecorded"),
ULInt16("firstCluster"),
ULInt32("fileSize"))
def PreDataRegion(name):
rde = DirEntry("rootdirs")
fe = FatEntry("fats")
return Struct(name,
Embed(BootSector("bootSector")),
# the remaining reserved sectors
Padding(lambda ctx: (ctx.reservedSectorCount - 1)
* ctx.sectorSize),
# file allocation tables
Array(lambda ctx: (ctx.fatCount),
Array(lambda ctx: ctx.sectorsPerFat *
ctx.sectorSize / fe.sizeof(), fe)),
# root directories
Array(lambda ctx: (ctx.rootdirEntryCount*rde.sizeof())
/ ctx.sectorSize, rde))
class File(object):
def __init__(self, dirEntry, fs):
self.fs = fs
self.dirEntry = dirEntry
@classmethod
def fromDirEntry(cls, dirEntry, fs):
if dirEntry.name[0] in "\x00\xe5\x2e":
return None
a = dirEntry.attributes
#Long file name directory entry
if a.volumeLabel and a.system and a.hidden and a.readonly:
return None
if a.subDirectory:
return Directory(dirEntry, fs)
return File(dirEntry, fs)
@classmethod
def fromDirEntries(cls, dirEntries, fs):
return filter(None, [cls.fromDirEntry(de, fs)
for de in dirEntries])
def toStream(self, stream):
self.fs.fileToStream(self.dirEntry.firstCluster, stream)
@property
def name(self):
return "%s.%s" % (self.dirEntry.name.rstrip(),
self.dirEntry.extension)
def __str__(self):
return "&%s %s" % (self.dirEntry.firstCluster, self.name)
class Directory(File):
def __init__(self, dirEntry, fs, children=None):
File.__init__(self, dirEntry, fs)
self.children = children
if not self.children:
self.children = File.fromDirEntries(\
self.fs.getDirEntries(\
self.dirEntry.firstCluster), fs)
@property
def name(self):
return self.dirEntry.name.rstrip()
def __str__(self):
return "&%s %s/" % (self.dirEntry.firstCluster, self.name)
def __getitem__(self, name):
for file in self.children:
if file.name == name:
return file
def __iter__(self):
return iter(self.children)
class FatFs(Directory):
def __init__(self, stream):
self.stream = stream
self.pdr = PreDataRegion("pdr").parse_stream(stream)
Directory.__init__(self, dirEntry = None,
fs = self, children = File.fromDirEntries(
self.pdr.rootdirs, self))
def fileToStream(self, clidx, stream):
for clidx in self.getLinkedClusters(clidx):
self.clusterToStream(clidx, stream)
def clusterToStream(self, clidx, stream):
start, todo = self.getClusterSlice(clidx)
self.stream.seek(start)
while todo > 0:
read = self.stream.read(todo)
if not len(read):
print("failed to read %s bytes at %s" % (todo, self.stream.tell()))
raise EOFError()
todo -= len(read)
stream.write(read)
def getClusterSlice(self, clidx):
startSector = self.pdr.reservedSectorCount \
+ self.pdr.fatCount * self.pdr.sectorsPerFat \
+ (self.pdr.rootdirEntryCount * 32) \
/ self.pdr.sectorSize \
+ (clidx-2) * self.pdr.sectorsPerCluster
start = startSector * self.pdr.sectorSize
length = self.pdr.sectorSize * self.pdr.sectorsPerCluster
return (start, length)
def getLinkedClusters(self, clidx):
res = []
while clidx != "last_cluster":
if not isinstance(clidx, numbers.Real):
print(clidx)
assert False
assert 2 <= clidx <= 0xffef
res.append(clidx)
clidx = self.getNextCluster(clidx)
assert clidx not in res
return res
def getNextCluster(self, clidx):
ress = set([fat[clidx] for fat in self.pdr.fats])
if len(ress)==1:
return ress.pop()
print("inconsistencie between FATs: %s points to" % clidx)
for i,fat in enumerate(self.pdr.fats):
print("\t%s according to fat #%s" % (fat[clidx], i))
res = ress.pop()
print ("assuming %s" % res)
return res
def getDirEntries(self, clidx):
try:
for de in self._getDirEntries(clidx):
yield de
except IOError:
print("failed to read directory entries at %s" % clidx)
def _getDirEntries(self, clidx):
de = DirEntry("dirEntry")
with BytesIO() as mem:
self.fileToStream(clidx, mem)
mem.seek(0)
with BufferedReader(mem) as reader:
while reader.peek(1):
yield de.parse_stream(reader)
def __str__(self):
return "/"
@property
def name(self):
return ""
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