Socket connection between python and C

[Dan Stromberg]

On Tue, Feb 8, 2011 at 5:41 PM, Roy Smith <roy at panix.com> wrote:
> In article <mailman.23.1297213437.1633.python-list at python.org>,
>  "Williamson, Ross X. (Guest)" <Ross.X.Williamson.Guest at usap.gov>
>  wrote:
>
>> Dear All,
>>
>> I'm trying to implement a server/client system where the server is written in
>> python and the client has to be written in c/c++.  I can happily send simple
>> text through the socket. Ideally I would like make say a struct (using python
>> struct library) - and then read that in using C. Is there a better way to
>> package data on the server in python to send down a socket to a C client?
>> XML? Pickle?
>
> Depends on what you are trying to accomplish.
>
> If your goal is for the communication to be as efficient as possible,
> sending raw packed binary with the struct module on the python side, and
> casting the i/o buffer pointer to a struct pointer on the C/C++ side
> probably can't be beat.  The downside is you need to worry about
> low-level things like padding, overflow, and endian-ness yourself.

Yes, this is fast, and yes, this likely won't be a good long-term
option if you envision someday using even slightly exotic (or new)
hardware - even using a different compiler on the same hardware could
lead to troubles with this approach.

However, socket.htons and related functions are a pretty good (and
somewhat similar, though without most of the problems) option.

> If you want to give up a little bit of efficiency in return for a huge
> amount of convenience, I'd go with JSON.  For the kinds of things you
> might be thinking about using the struct module for, it's just peachy.
> Hugely portable (libraries for every language imaginable), easy to use,
> and not grossly inefficient.  There's also BSON, which will be a bit
> more efficient at the cost of some portability.

JSON's cool.

> Based on your statement that you're thinking of using "struct", my guess
> is that XML would be overkill.

Yes, XML's a bit more heavyweight than JSON.

Also, if your data need not ever become hierarchical (which is another
architectural choice that could paint you into a corner a bit), or you
are prepared to add framing to your protocol if/when the time comes,
you can just use ASCII.  This has the benefit of allowing you to test
your server with telnet.

Actually, JSON and XML should preserve telnet-based server testing as
well, at least to some extent - you might have to cut and paste your
tests more though.