On 02/10/2013 07:48 PM, Ihsan Junaidi Ibrahim wrote:
Hi,
I'm implementing a python client connecting to a C-backend server and am
currently stuck to as to how to proceed with receiving variable-length byte
stream coming in from the server.
I have coded the first 4 bytes (in hexadecimal) of message coming in from the
server to specify the length of the message payload i.e. 0xad{...}
Exactly how are you sending "hexadecimal" ? If that 0xad (which is only
one byte, what about the other 3 ?) is intended to be a C description,
then it's certainly not hex, it's binary. And probably little-endian,
to boot. That's a mistake, as network protocols almost always use
big-endian.
So what is the range of values for the length, and how are they actually
encoded? Are they uint32 in native binary format? And are you
permitted to change the encoding, to fix it? (If it were my choice, I'd
make it a printable decimal value, first choice, or printable hex,
second choice.)
I've managed to receive and translate the message length until I reach my
second recv which I readjusted the buffer size to include the new message
length.
However that failed and recv received 0 bytes. I implemented the same algorithm
on the server side using C and it work so appreciate if you can help me on this.
# receive message length
print 'receiving data'
mlen = sock.recv(4)
try:
nbuf = int(mlen, 16)
That supposes the count is being sent as a printable string of hex
digits. That's not what I concluded above.
except ValueError as e:
If the count starts as 0xad, I can't imagine why this exception wasn't
thrown.
print 'invalid length type'
return -1
while True:
buf = sock.recv(nbuf)
if not buf:
break
slen = len(buf)
str = "{0} bytes received: {1}".format(slen, buf)
print str
You might need to play with hexlify, if you persist in sending the count
in binary.
--
DaveA
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