[newbie] trying socket as a replacement for nc

[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.