Re: Python recv loop
Hi Roy,
On Feb 11, 2013, at 10:24 AM, Roy Smith r...@panix.com wrote:
Is this server that you're talking to something that you have control
over, i.e. are you stuck with this protocol? Given a choice, I'd go
with something like JSON, for which pre-existing libraries for every
language under the sun.
I'm running JSON for my application messaging protocol but with JSON and python
default unordered dict,
there's no guarantee if I put in the length key in the JSON message, it will be
placed on the first bytes hence
why it was designed for a fixed 4-byte at the start of the message to indicate
the message length.
Beyond the 4-bytes it is all JSON.
but if you have a better idea, i would certainly welcome it.
Do you actually *know* what the value of nbuf is? Is it possible that
(somehow) it's 0? You should print (log, whatever), the value of nbuf,
just to make sure.
nbuf is printing the right bytes amount, I removed the print statement before I
made the first post.
So to clarify, I added a print statement between the first recv and the second.
{msgver: 1.0, msgid: 200, subcode: 100, appver: 1.0, appid:
1.0, data: {1: igb0, 2: igb1, ifcnt: 2}}
connected to misty:8080
sending data
138 bytes sent: 0x86{msgver: 1.0, msgid: 200, subcode: 100,
appver: 1.0, appid: 1.0, data: {1: igb0, 2: igb1, ifcnt:
2}}
receiving data
message length is 188
0 bytes received:
So the subsequent recv() call will be readjusted with 188 bytes buffer size so
theoretically, recv shouldn't return 0.
The same logic that I used to send to the server from the python client that
the server will readjust the second recv() call based on the length
information. On this 2nd recv() call the server is able to obtain the rest of
the messages.
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Re: Python recv loop
Hi Dave,
On Feb 11, 2013, at 9:22 AM, Dave Angel da...@davea.name wrote:
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.)
They are ASCII stream, actually JSON with the exception of the first 4 bytes. I
avoided using struct class for this as it's overkill for my application.
So the idea is that i code the length to a max of 0xff (max length of 256
bytes), I would only have to assign 4 bytes to it. If i need 1k length, i just
need to increase it to 6 bytes or 4 if i decide to strip the 0x.
the code for the function is as follows:
def request_get_session(sock, jmsg):
# append message length
plen = hex(len(jmsg))
msg = '{0}{1}'.format(plen, jmsg)
print 'sending data'
n = sock.send(msg)
str = '{0} bytes sent: {1}'.format(n, msg)
print str
# receive message length
print 'receiving data'
mlen = sock.recv(4)
try:
nbuf = int(mlen, 16)
except ValueError as e:
print 'invalid length type'
return -1
print 'message length is {0}'.format(nbuf)
while True:
buf = sock.recv(nbuf)
if not buf:
break
slen = len(buf)
str = {0} bytes received: {1}.format(slen, buf)
print str
return 0
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.
That is what I meant. it just an ascii string.
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Re: Python recv loop
Hi MRAB,
My code now works thanks to your advice.
{msgver: 1.0, msgid: 200, subcode: 100, appver: 1.0, appid:
1.0, data: {1: igb0, 2: igb1, ifcnt: 2}}
connected to misty:8080
sending data
138 bytes sent: 0x86{msgver: 1.0, msgid: 200, subcode: 100,
appver: 1.0, appid: 1.0, data: {1: igb0, 2: igb1, ifcnt:
2}}
receiving data
message length is 188
188 bytes received: { msgver: 1.00, appver: 1.00, appid: 1000,
msgid: 10, subcode: 20, data: [ 110.159.183.16, 124.108.16.94,
2400:3700:50::2, 2400:3700:50::1, 2400:3700:51:: ] }
Many thanks.
On Feb 11, 2013, at 9:55 AM, MRAB pyt...@mrabarnett.plus.com wrote:
You should keep reading until you get all need or the connection is
closed:
buf = b''
while len(buf) nbuf:
chunk = sock.recv(nbuf - len(buf))
if not chunk:
break
buf += chunk
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Re: Python recv loop
On 2013-02-11 14:56, Ihsan Junaidi Ibrahim wrote:
Hi Roy,
On Feb 11, 2013, at 10:24 AM, Roy Smith r...@panix.com wrote:
Is this server that you're talking to something that you have control
over, i.e. are you stuck with this protocol? Given a choice, I'd go
with something like JSON, for which pre-existing libraries for every
language under the sun.
I'm running JSON for my application messaging protocol but with JSON and python
default unordered dict,
there's no guarantee if I put in the length key in the JSON message, it will be
placed on the first bytes hence
why it was designed for a fixed 4-byte at the start of the message to indicate
the message length.
Beyond the 4-bytes it is all JSON.
but if you have a better idea, i would certainly welcome it.
I probably wouldn't make it fixed length. I'd have the length in
decimal followed by, say, \n.
Do you actually *know* what the value of nbuf is? Is it possible that
(somehow) it's 0? You should print (log, whatever), the value of nbuf,
just to make sure.
nbuf is printing the right bytes amount, I removed the print statement before I
made the first post.
So to clarify, I added a print statement between the first recv and the second.
{msgver: 1.0, msgid: 200, subcode: 100, appver: 1.0, appid: 1.0, data: {1: igb0,
2: igb1, ifcnt: 2}}
connected to misty:8080
sending data
138 bytes sent: 0x86{msgver: 1.0, msgid: 200, subcode: 100, appver: 1.0, appid: 1.0, data: {1:
igb0, 2: igb1, ifcnt: 2}}
receiving data
message length is 188
0 bytes received:
So the subsequent recv() call will be readjusted with 188 bytes buffer size so
theoretically, recv shouldn't return 0.
The same logic that I used to send to the server from the python client that
the server will readjust the second recv() call based on the length
information. On this 2nd recv() call the server is able to obtain the rest of
the messages.
--
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Re: Python recv loop
On Tue, Feb 12, 2013 at 2:11 AM, MRAB pyt...@mrabarnett.plus.com wrote: I probably wouldn't make it fixed length. I'd have the length in decimal followed by, say, \n. Or even followed by any non-digit. Chances are your JSON data begins with a non-digit, so you'd just have to insert a space in the event that you're JSON-encoding a flat integer. (Which might not ever happen, if you know that your data will always be an object.) ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: Python recv loop
On 02/11/2013 10:02 AM, Ihsan Junaidi Ibrahim wrote:
snip
print 'message length is {0}'.format(nbuf)
while True:
buf = sock.recv(nbuf)
if not buf:
break
This loop doesn't terminate till buf is zero length, which it will be
eventually. At that point, you've overwritten the real data you may
have gotten. So the loop is just plain wrong.
Uwe MRAB's code, since there's no promise that all the data will be
returned in a single call. Keep accumulating it as you loop.
slen = len(buf)
str = {0} bytes received: {1}.format(slen, buf)
print str
return 0
--
DaveA
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Re: Python recv loop
On Feb 11, 2013, at 11:24 PM, Chris Angelico ros...@gmail.com wrote: On Tue, Feb 12, 2013 at 2:11 AM, MRAB pyt...@mrabarnett.plus.com wrote: I probably wouldn't make it fixed length. I'd have the length in decimal followed by, say, \n. Or even followed by any non-digit. Chances are your JSON data begins with a non-digit, so you'd just have to insert a space in the event that you're JSON-encoding a flat integer. (Which might not ever happen, if you know that your data will always be an object.) ChrisA So on the first recv() call, I set the buffer at 1 character and I iterate over single character until a non-digit character is encountered? -- http://mail.python.org/mailman/listinfo/python-list
Re: Python recv loop
On Tue, Feb 12, 2013 at 12:41 PM, Ihsan Junaidi Ibrahim ih...@grep.my wrote: On Feb 11, 2013, at 11:24 PM, Chris Angelico ros...@gmail.com wrote: On Tue, Feb 12, 2013 at 2:11 AM, MRAB pyt...@mrabarnett.plus.com wrote: I probably wouldn't make it fixed length. I'd have the length in decimal followed by, say, \n. Or even followed by any non-digit. Chances are your JSON data begins with a non-digit, so you'd just have to insert a space in the event that you're JSON-encoding a flat integer. (Which might not ever happen, if you know that your data will always be an object.) ChrisA So on the first recv() call, I set the buffer at 1 character and I iterate over single character until a non-digit character is encountered? More efficient would be to guess that it'll be, say, 10 bytes, and then retain any excess for your JSON read loop. But you'd need to sort that out between the halves of your code. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: Python recv loop
In article mailman.1655.1360594595.2939.python-l...@python.org, Ihsan Junaidi Ibrahim ih...@grep.my wrote: I'm running JSON for my application messaging protocol but with JSON and python default unordered dict, there's no guarantee if I put in the length key in the JSON message, it will be placed on the first bytes hence why it was designed for a fixed 4-byte at the start of the message to indicate the message length. Beyond the 4-bytes it is all JSON. I'm confused. It sounds like you're making things way more complicated than they have to be. Can you give us an example of an actual data message? -- http://mail.python.org/mailman/listinfo/python-list
Re: Python recv loop
On 2013-02-12 02:20, Chris Angelico wrote: On Tue, Feb 12, 2013 at 12:41 PM, Ihsan Junaidi Ibrahim ih...@grep.my wrote: On Feb 11, 2013, at 11:24 PM, Chris Angelico ros...@gmail.com wrote: On Tue, Feb 12, 2013 at 2:11 AM, MRAB pyt...@mrabarnett.plus.com wrote: I probably wouldn't make it fixed length. I'd have the length in decimal followed by, say, \n. Or even followed by any non-digit. Chances are your JSON data begins with a non-digit, so you'd just have to insert a space in the event that you're JSON-encoding a flat integer. (Which might not ever happen, if you know that your data will always be an object.) ChrisA So on the first recv() call, I set the buffer at 1 character and I iterate over single character until a non-digit character is encountered? More efficient would be to guess that it'll be, say, 10 bytes, and then retain any excess for your JSON read loop. But you'd need to sort that out between the halves of your code. If the length is always followed by a space then it's easier to split it off the input: buf = sock.recv(10) space_pos = buf.find(b ) nbuf = int(buf[ : space_pos]) buf = buf[space_pos+ 1 : ] while len(buf) nbuf: chunk = sock.recv(nbuf - len(buf)) if not chunk: break buf += chunk I'm assuming that: 1. The initial recv returns the length followed by a space. It could, of course, return fewer bytes (space_pos == -1), so you may need to recv some more bytes, like what's done later on. 2. At least 10 bytes were sent. Imagine what would happen if the sender sent b2 [] immediately followed by b2 []. The initial recv could return all of it. In that case you could save the excess until next time. Alternatively, the sender could guarantee that it would never send fewer than the 10 bytes, padding with several b if necessary. -- http://mail.python.org/mailman/listinfo/python-list
Python recv loop
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{...}
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)
except ValueError as e:
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
--
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Re: Python recv loop
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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Re: Python recv loop
On 2013-02-11 00:48, 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{...}
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)
except ValueError as e:
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 should keep reading until you get all need or the connection is
closed:
buf = b''
while len(buf) nbuf:
chunk = sock.recv(nbuf - len(buf))
if not chunk:
break
buf += chunk
--
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Re: Python recv loop
In article mailman.1612.1360544258.2939.python-l...@python.org,
Ihsan Junaidi Ibrahim ih...@grep.my wrote:
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{...}
Is this server that you're talking to something that you have control
over, i.e. are you stuck with this protocol? Given a choice, I'd go
with something like JSON, for which pre-existing libraries for every
language under the sun.
But, let's assume for the moment that you're stuck with this
length-value encoding. OK, but it's going to be more complicated than
you think. [I assume we're talking TCP here?]
Carefully read the documentation for socket.recv():
socket.recv(bufsize[, flags]) [...] The maximum amount of data to be received
at once is specified by bufsize.
Linger on the word maximum, and try to grok the fullness of of how
annoying that can be. What it means is that if the other side sent 120
bytes (octets), recv() might return all 120 at once, or it might return
them one at a time, or anything in between.
So, what you need to do is call recv() repeatedly in a loop, each time
passing it a value for bufsize which represents the amount left in the
message (i.e. the original message length parsed earlier minus all the
little bits and pieces that have been read so far).
Keep in mind, you also need to do this when you recv() the first 4
octets, which make up the length field. What you've got, recv(4), will
work MOST of the time, but it's perfectly legal for recv() to return a
short read. You can't predict how fragmentation and retry timeouts and
all sorts of low-level crud will cause your message boundaries to get
scrambled.
# receive message length
print 'receiving data'
mlen = sock.recv(4)
try:
nbuf = int(mlen, 16)
except ValueError as e:
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
Do you actually *know* what the value of nbuf is? Is it possible that
(somehow) it's 0? You should print (log, whatever), the value of nbuf,
just to make sure.
And, once you'e got all this working, tear it all out and convert to
using something sane like JSON. Let somebody else worry about all the
horrible details.
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