Re: Binary data transfer issue



Jordan Apgar wrote:
Hi all,

I'm trying to transfer a binary file over xmlrpclib. My test file is
a .jpeg file. I can transfer all the data over but when I go to open
the .jpeg I get "Error interpreting JPEG image file (Invalid JPEG file
structure: SOS before SOF)"

here's the code:

===========Various Shared Functions========
#EncodeAES takes a Cipher c and encrypts a String s
EncodeAES = lambda c, s: base64.b64encode(c.encrypt(pad(s)))

#DecodeAES takes a Cipher C and decrypts the cyphertext e
#then removes the padding from the decrypted string
DecodeAES = lambda c, e:
c.decrypt(base64.b64decode(e)).rstrip(PADDING)


CIPHER = AES.new("KEY")


# method to change strings back into tuples
def stringToTuple(string):
if string[0] + string[-1] == "()":
items = string[1:-1]
items = items.split(',')
return items
else:
raise ValueError("Badly formatted string (missing brackets).")

======client=================
def Download(self, FileName, Data_Size=1024):
ErrorCount = 0
Pkt_Num = -1
OldPkt_Num = Pkt_Num
localFile = open("files/"+FileName, "wb")
print
print "Requesting First Packet"
packet = self.client.download(EncodeAES(CIPHER, str(Pkt_Num)))
if packet[0] == "False":
print packet[1]
return False
packet = stringToTuple(DecodeAES(CIPHER, packet))
if int(packet[0]) == -3:
print "Received Error Packet"
else:
print "Received Packet: ", int(packet[0])

print "packet[1], ", packet[2:-1]

Pkt_Num = int(packet[0])

while Pkt_Num >= 0 and ErrorCount <= 10:
if (OldPkt_Num +1) == Pkt_Num:
OldPkt_Num = OldPkt_Num +1
localFile.write(binascii.
a2b_base64(packet[1][2:-1]))
#<<<<!!!!!<<< writing to the file on the client
ErrorCount == 0
else:
ErrorCount = ErrorCount +1
Pkt_Num = OldPkt_Num

print "Requesting Packet: ", Pkt_Num +1
packet = self.client.download(EncodeAES(CIPHER,
str(Pkt_Num)))
packet = stringToTuple(DecodeAES(CIPHER, packet))
Pkt_Num = int(packet[0])
if int(packet[0]) == -3:
print "Received Error Packet"
elif int(packet[0]) == -2:
print "Received EOF"
else:
print "Received Packet: ", int(packet[0])

localFile.close()

if Pkt_Num == -2:
print packet[1][2:-1]
return True
elif Pkt_Num == -3:
os.remove("files/"+FileName)
print packet[1][2:-1]
return False
else:
os.remove("files/"+FileName)
print "Unexpected Packet: File Transfer Stopped"
return False


==========Server Method=============
def download(self, Pkt_Num):

Old_Pkt_Num = self.PKT
DataRate = self.DATA
Pkt_Num = int(DecodeAES(CIPHER,Pkt_Num))
if Pkt_Num == -1 and Old_Pkt_Num == -1:
Pkt_Num = 0
try:
f = open("files/"+self.usr_dict[client][FILENAME],
"rb")
except IOError:
return EncodeAES(CIPHER,
str((-3, "File Could Not be
opened")))
data = binascii.b2a_base64(f.read((Pkt_Num+1 *
DataRate))) #<<<<<<!!!!!!!<<<<<<<< reading from file

I don't understand what you're trying to do when you're reading from
the file. For a start:

Pkt_Num+1 * DataRate

is the same as:

Pkt_Num + (1 * DataRate)

or:

Pkt_Num + DataRate

and that's how many bytes you're reading.

f.close()
self.usr_dict[client][PKT] = Pkt_Num
return EncodeAES(CIPHER,
str((Pkt_Num, data)))

elif Pkt_Num == Old_Pkt_Num:
if Pkt_Num * DataRate >=
os.path.getsize("files/"+self.usr_dict[client][FILENAME]):
return EncodeAES(CIPHER,
str((-2, "File Transfer Complete")))
try:
f = open("files/"+self.usr_dict[client][FILENAME],
"rb")
except IOError:
return EncodeAES(CIPHER,
str((-3, "File Could Not be opened")))
data = f.read((Pkt_Num+1 * DataRate))

Here you're reading:

Pkt_Num + DataRate

bytes again,

data = None

discarding what you've just read,

data = binascii.b2a_base64(f.read(DataRate))
#<<<<<<<<!!!!!!!<<<<<<< reading from file

and then reading:

DataRate

more bytes.

I think what you meant to do is .seek to the position in the file and
then read some bytes:

f.seek(Pkt_Num * DataRate)
data = f.read(DataRate)

ie, send the contents of the file in chunks which are DataRate bytes
long (the last chunk will be shorter if the file size isn't a multiple
of DataRate bytes).

f.close()
self.usr_dict[client][PKT] = Pkt_Num +1

return EncodeAES(CIPHER,
str((Pkt_Num+1, data)))

else:

return EncodeAES(CIPHER,
str((-3, "Incorrect Packet Requested")))



Thank you all for the help, I know there are better ways and transfer
protocol modules to but I'd like to do this without them.

I'm not surprised that the transfer is failing! :-)
.