[newbie] trying socket as a replacement for nc

Jean Dubois jeandubois314 at gmail.com
Fri Dec 13 04:23:18 CET 2013


Op donderdag 12 december 2013 22:23:22 UTC+1 schreef Dan Stromberg:
> On Thu, Dec 12, 2013 at 12:28 AM, Jean Dubois <jeandubois314 at gmail.com> wrote:
> 
> > On Thursday, December 12, 2013 12:20:36 AM UTC+1, Dan Stromberg wrote:
> 
> >> On Wed, Dec 11, 2013 at 3:08 PM, Jean Dubois <jeandu... at gmail.com> wrote:
> 
> >>
> 
> >> I have an ethernet-rs232 adapter which allows me to connect to a measurement instrument by means of netcat on a linux system.
> 
> >>
> 
> >>
> 
> >> e.g. entering nc 10.128.59.63 7000
> 
> >>
> 
> >> allows me to enter e.g.
> 
> >>
> 
> >> *IDN?
> 
> >>
> 
> >> after which I get an identification string of the measurement instrument back.
> 
> >>
> 
> >> I thought I could accomplish the same using the python module "socket"
> 
> >>
> 
> >> and tried out the sample program below which doesn't work however:
> 
> >>
> 
> >>
> 
> >>
> 
> >> Sockets reserve the right to split one socket.send() into multiple socket.recv()'s on the other end of the communication, or to aggregate multiple socket.send()'s into a single socket.recv() - pretty much any way the relevant IP stacks and communications equipment feel like for the sake of performance or reliability.
> 
> >>
> 
> >>
> 
> >> The confusing thing about this is, it won't be done on every transmission - in fact, it'll probably happen rather seldom unless you're on a heavy loaded network or have some MTU issues (see Path MTU Discovery, and bear in mind that paths can change during a TCP session).  But writing your code assuming it will never happen is a bad idea.
> 
> >>
> 
> >>
> 
> >>
> 
> >> For this reason, I wrote http://stromberg.dnsalias.org/~strombrg/bufsock.html , which abstracts away these complications, and actually makes things pretty simple.  There are examples on the web page.
> 
> >>
> 
> >>
> 
> >>
> 
> >> HTH
> 
> >
> 
> > Dear Dan,
> 
> > Could you copy paste here the code for your function I have to add to my "program"?
> 
> 
> 
> This is untested, but it should be something like the following:
> 
> 
> 
> #!/usr/bin/env python
> 
> 
> 
> """
> 
> A simple echo client
> 
> """
> 
> import socket as socket_mod
> 
> import bufsock as bufsock_mod
> 
> host = '10.128.59.63'
> 
> port = 7000
> 
> size = 10
> 
> socket = socket_mod.socket(socket.AF_INET, socket.SOCK_STREAM)
> 
> socket.connect((host,port))
> 
> bufsock = bufsock_mod.bufsock(socket)
> 
> bufsock.send('*IDN?')
> 
> data = bufsock.recv(size)
> 
> bufsock.close()
> 
> print 'Received:', data
> 
> 
> 
> You might look over
> 
> http://stackoverflow.com/questions/19918307/retrieve-file-information-located-on-a-different-application-server-using-python/19918706#19918706
> 
> for a more complete example.

Thank you very much for the example, the only trouble I'm having now is installing the bufsock module:
wget http://dcs.nac.uci.edu/~strombrg/bufsock.tar.gz 
results in The requested URL /~strombrg/bufsock.tar.gz was not found on this server.
Could you supply me the necessary installation instructions?

kind regards,
jean
p.s. I'm using Linux/Kubuntu 11.04



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