Differences between revisions 2 and 4 (spanning 2 versions)

UDP Communication

Sending

Here's simple code to post a note by UDP in Python:

   1 import socket
   2 
   3 UDP_IP="127.0.0.1"
   4 UDP_PORT=5005
   5 MESSAGE="Hello, World!"
   6 
   7 print "UDP target IP:", UDP_IP
   8 print "UDP target port:", UDP_PORT
   9 print "message:", MESSAGE
  10 
  11 sock = socket.socket( socket.AF_INET, # Internet
  12                       socket.SOCK_DGRAM ) # UDP
  13 sock.sendto( MESSAGE, (UDP_IP, UDP_PORT) )

Receiving

Here's simple code to receive UDP messages in Python:

   1 import socket
   2 
   3 UDP_IP="127.0.0.1"
   4 UDP_PORT=5005
   5 
   6 sock = socket.socket( socket.AF_INET, # Internet
   7                       socket.SOCK_DGRAM ) # UDP
   8 sock.bind( (UDP_IP,UDP_PORT) )
   9 
  10 while True:
  11     data, addr = sock.recvfrom( 1024 ) # buffer size is 1024 bytes
  12     print "received message:", data

Discussion

* It would seem easy to extend this to a simple means to open a file on the sender side, send datagrams to the receiver side, and write those packets to a file there - I just wonder about synchronisation issues regarding the buffer...Anyone smart care to put something down, say as a simple practical extension of what is already here? (And if you do it pls delete this message) *

Multicasting?

I've been googling for some time now, and still have yet to find a working example of Python multicast listening.

Here's my own, non-functioning, effort:

   1 import socket
   2 import struct
   3 
   4 sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
   5 #sock.bind(('127.0.0.1', 1000))
   6 sock.bind(('', 1000))
   7 grpaddr = 0
   8 for byte in "239.192.0.100".split("."):
   9     grpaddr = (grpaddr << 8) | int(byte)
  10 mreq = struct.pack('ll', socket.htonl(grpaddr),
  11                    socket.htonl(socket.INADDR_ANY))
  12 sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
  13 print sock.recvfrom(100)

The mreq packing is based on [http://www.senux.com/linux/network/multicast/ some code that I found,] that does not work. On my computer, at least.

Sending to multicast groups is just fine; Here's some functional text:

   1 import socket
   2 
   3 sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
   4 sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 2)
   5 sock.sendto("robot", ("239.192.0.100", 1000))

At this point, I'm beginning to think: "Python multicast simply does not work."

It's too bad we don't have anything as simple as this:

   1 import UDP
   2 
   3 sock = UDP.MulticastListener("239.192.0.100", 1000)  # Listen on port 1000
   4 print sock.recv(100)

   1 import UDP
   2 
   3 UDP.send("Hello, world!", "239.192.0.100", 1000)

...or something like that.

-- LionKimbro DateTime(2005-01-19T19:54:19Z)

-  ⇤ ← Revision 2 as of 2004-08-04 23:29:15 → 
  Size: 1150
  Editor: 195
  Comment:
+   ← Revision 4 as of 2005-01-19 19:54:22 → ⇥
  Size: 2837
  Editor: 168-103-146-113
  Comment: Is there ANY working multicast Python code out there?
-Deletions are marked like this.
+Additions are marked like this.
 Line 46:
-== Discussion ==
+= Discussion =
 Line 48:
-I have two questions:
 * What is the 1024 in recvfrom?
   It is the buffer size.[[BR]]
   >>> help (sock.recvfrom)
 * How do you subscribe to a WikiPedia:Multicast_address ?
+*
It would seem easy to extend this to a simple means to open a file on the sender side, send datagrams to the receiver side, and write those packets to a file there - I just wonder about synchronisation issues regarding the buffer...Anyone smart care to put something down, say as a simple practical extension of what is already here?  (And if you do it pls delete this message)
*
-Line 54:
+Line 52:
-It seems that just setting UDP_IP to "224.0.0.250" (say) isn't quite good enough.
+== Multicasting? ==

I've been googling for some time now, and ''still'' have yet to find a ''working'' example of Python multicast listening.

Here's my own, non-functioning, effort:
{{{
#!python
import socket
import struct

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
#sock.bind(('127.0.0.1', 1000))
sock.bind(('', 1000))
grpaddr = 0
for byte in "239.192.0.100".split("."):
    grpaddr = (grpaddr << 8) | int(byte)
mreq = struct.pack('ll', socket.htonl(grpaddr),
                   socket.htonl(socket.INADDR_ANY))
sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
print sock.recvfrom(100)
}}}

The mreq packing is based on [http://www.senux.com/linux/network/multicast/ some code that I found,] ''that does not work.'' On my computer, at least.

Sending to multicast groups is just fine; Here's some functional text:
{{{
#!python
import socket

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 2)
sock.sendto("robot", ("239.192.0.100", 1000))
}}}

At this point, I'm beginning to think: "Python multicast simply ''does not work.''"

It's too bad we don't have anything as simple as this:

{{{
#!python
import UDP

sock = UDP.MulticastListener("239.192.0.100", 1000)  # Listen on port 1000
print sock.recv(100)
}}}

{{{
#!python
import UDP

UDP.send("Hello, world!", "239.192.0.100", 1000)
}}}

...or something like that.

-- LionKimbro [[DateTime(2005-01-19T19:54:19Z)]]

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User

UDP Communication

Sending

Receiving

Discussion

Multicasting?