On Dec 26, 2004, at 5:13 PM, Alex Tweedly wrote:
Server pseudo-code:
accept datagram connections on port "4567" with message "gotPacket"
on gotPacket pRemote, pData put pRemote into pRemote set the itemDel to ":" add 1 to item 2 of pRemote
There is a potential problem here. The socket designator might include a socket ID.
open datagram socket to pRemote write "reply with " & param(2) to socket pRemote close socket pRemote end gotPacket
Now the echo client version, using standard system calls, is simply
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) r = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
s.connect( (HOST,PORT) )
# get the source port allocated, and listen on adjacent one reply_host, reply_port = s.getsockname() reply_port += 1 r.bind( (reply_host, reply_port) )
while 1 : str = raw_input('type it') s.send(str) data = r.recv(1024) print "Back came ", data s.close()
Most of this translates simply into Rev - except I can't find the equivalent of getsockname(), which tells me the local IP address and port number which will be filled in as source addr, source port in the UDP packet.
A weakness, in my opinion.
But you can work around this.
The server uses this to determine where to send its reply; source addr is, of course, just the IP address of the client machine (which I can get from hostAddress() once I have connected the socket) - but I don't see a way to find which source port will be chosen. Without that, I don't know which port to bind to in order to receive the server responses.
Is there a way to find that ?
shell()?
Or, alternatively, is there a different way to set up a client-server UDP pair ? i.e. have a pre-defined port number used on the server, which is also configured in every client, but allocate the client ports dynamically.
If you must have the crossing pair, simply send data to the corresponding port on the other side. Both sides will have source ports that are not known, but the destination ports will be known.
But you don't need to use a crossing pair for a client server relationship.
The server knows the port on the other end (pRemote, in your example). Simply reply to that.
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http://www.swcp.com/dsc/
Programming Services and Software
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