Tkinter and XML-RPC

[Roger Binns]

Etienne Posthumus wrote:
> That is a good tip, very interesting. Do you mind explaining what you
> did further?

My program (bitpim) manipulates the phonebook, wallpaper, ringtones
etc for US based CDMA cellphones (they behave very differently than
GSM phones used in the rest of the world :-).

I wanted the ability to have the program and the phone on different
machines, including over the Internet (which would make development
easier).

I wanted to use XML-RPC to remote the various methods used when
talking to a port (open, close, read, write) as well as some
others I have (list available devices, read until certain criteria
are met).  (Using XML-RPC meant I didn't have to reinvent the
wheel).

I wrote a program (named BitFling) that listens (by default on all
interfaces) for incoming connections and obeys commands sent by
XML-RPC.  The BitPim program then makes a connection to this and
issues commands.  Behind the scenes, everything is wrapped in
classes in BitPim so it can't tell the difference between a local
or remote port, and really doesn't need to care.

For this solution I obvious required security.  I use certificates
(self signed) for BitFling with access granted using username
and password combinations.  (You also have to list valid source
addresses).

You have to rework the existing XML-RPC client and server classes
to add the HTTP authentication.  I then wrapped it all in SSL
using M2Crypto.  Unfortunately the existing XML-RPC stuff goes
out of its way to do one transaction per connection.  Additionally
M2Crypto doesn't implement the makefile method, which internal
has the same effects as a dup.  I tried pretty hard to rework
the code to not rely on dup, not close connections etc, but
never could get everywhere.

Fortunately I found Paramiko and it was really easy to switch
to that.  I didn't both with the HTTP layer and just send
the raw output of the XML-RPC encoding.  SSH defines authentication
up front, rather than on every transaction like in HTTP.  It also
has the idea of multiple named channels.

So I just use a channel named "bitfling" and use regular old
SSH password authentication.

> Nie to know about Paramiko, it looks a little more lightweight than the
> SSH that comes with Twisted, if one does not want to go the whole
> Twisted route.

I really don't like Twisted anyway.  My code naturally is
threaded as the device access doesn't have the equivlent of
polling methods.  In theory I could run a background thread
that updates something else that emulates polling, but I
far prefer to just directly write the code I want executed
rather than the Twisted approach of giving a list of what
will be executed.

> Curious how much it could be sped up by using OpenSSL
> for the crypto operation in stead of PyCrypto.

You do know that pyCrypto uses native code?  Paramiko
is all Python however.  Consequently I don't think
there will be much performance difference between the
two.  Paramiko itself is being repeatedly improved and
I think that will give the biggest performance improvements.

Roger