Differences between revisions 9 and 10

TCP Communication

Sending

(to be written)

Receiving

Here's simple code to serve TCP in Python:

   1 #!/usr/bin/env python
   2 
   3 import socket
   4 
   5 
   6 TCP_IP = '127.0.0.1'
   7 TCP_PORT = 5005
   8 
   9 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
  10 s.bind((TCP_IP, TCP_PORT))
  11 s.listen(1)
  12 
  13 conn, addr = s.accept()
  14 print 'Connection address:', addr
  15 while 1:
  16     data = conn.recv(10)  # buffer size is 10 bytes
  17     if not data: break
  18     print "received data:", data
  19     conn.send(data)  # echo
  20 conn.close()

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-  ⇤ ← Revision 9 as of 2005-01-20 08:06:32 → 
  Size: 3947
  Editor: NIVALI-IO10301289-macom
  Comment:
+   ← Revision 10 as of 2005-03-30 23:57:21 → ⇥
  Size: 651
  Editor: 168-103-146-113
  Comment: something to start with
-Deletions are marked like this.
+Additions are marked like this.
 Line 1:
-= UDP Communication =
+= TCP Communication =
 Line 7:
-Here's simple code to post a note by UDP in Python:
+(to be written)

== Receiving ==

Here's simple code to serve TCP in Python:
-Line 11:
+Line 15:
+#!/usr/bin/env python
-Line 13:
+Line 19:
-UDP_IP="127.0.0.1"
UDP_PORT=5005
MESSAGE="Hello, World!"
-Line 17:
+Line 20:
-print "UDP target IP:", UDP_IP
print "UDP target port:", UDP_PORT
print "message:", MESSAGE
+TCP_IP = '127.0.0.1'
TCP_PORT = 5005
-Line 21:
+Line 23:
-sock = socket.socket( socket.AF_INET, # Internet
                      socket.SOCK_DGRAM ) # UDP
sock.sendto( MESSAGE, (UDP_IP, UDP_PORT) )
+s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((TCP_IP, TCP_PORT))
s.listen(1)

conn, addr = s.accept()
print 'Connection address:', addr
while 1:
    data = conn.recv(10)  # buffer size is 10 bytes
    if not data: break
    print "received data:", data
    conn.send(data)  # echo
conn.close()
-Line 26:
+Line 37:
-== Receiving ==
+----
-Line 28:
+Line 39:
-Here's simple code to receive UDP messages in Python:

{{{
#!python
import socket

UDP_IP="127.0.0.1"
UDP_PORT=5005

sock = socket.socket( socket.AF_INET, # Internet
                      socket.SOCK_DGRAM ) # UDP
sock.bind( (UDP_IP,UDP_PORT) )

while True:
    data, addr = sock.recvfrom( 1024 ) # buffer size is 1024 bytes
    print "received message:", data
}}}
+See also: UdpCommunication
-Line 48:
+Line 43:
-*
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:
{{{
#!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.''"

  Are you running on Windows 2000/XP (pre-SP2)/Server 2003 with more than one network adapter? If so, the problem is Windows, not Python. The original code works for me on Windows 2000 (1 network adapter), but fails under XP Pro (pre-SP2, 3 adapters though 2 are disabled). Microsoft has a [http://support.microsoft.com/default.aspx?scid=kb;en-us;827536 support page] on the issue. The problem appears to be in the receiver: with both machines running the receiver, the Win2K machine sees packets sent from both machines, while the receiver on XP sees messages sent from the Win2K machine only. This, despite specifying the local IP address of the appropriate adapter in the second part of the mreq structure in the IP_ADD_MEMBERSHIP call. -- VinaySajip

  ''Hm, that's interesting. No, I'm not running on Windows; I'm running on FC3. That said, I hadn't considered the machine as a possible problem. What I'll do is this: I'll run this on my ''home'' FC3 computer, and on my ''home'' Redhat 9 computer, and see if I can get it to work on one of them.'' -- LionKimbro [[DateTime(2005-01-20T02:07:18Z)]]


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)]]
+  (none yet!)

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TCP Communication

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Receiving

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