[Twisted-Python] txThings - simple library for CoAP protocol

[Maciej Wasilak]

Ron,

Following with interest.  Seeking a CoAP Python client capability that
> includes:
> - Support for IPV6 to talk directly to server motes in constrained 6LoWPAN
> WSNs. (the large IPV6 address space is for me intrinsic to the IoT concept)
> - Security for the same, so presumably DTLS.
> Both of these needed and particularly security, for any serious monitoring
> and control applications.
>

IPv6 is my target too. In general I've managed to run some tests with
txThings and Contiki powered 6LoWPAN motes. My points below:

1. Twisted doesn't officially support UDP IPv6 yet - however there was
great progress lately - see ticket #5086 (
http://twistedmatrix.com/trac/ticket/5086). Someone else should probably
comment on that, but it seems to be close to the finish line

2. You can easily add unofficial IPv6 support (basic unicast) by modifying
twisted/internet/udp.py. I'll email you the details.

3. There is a problem with txThings IPv6 server, because in most operating
systems source address of datagram is determined in round robin fashion. It
may cause the source address of the response to be different than
destination address of the request. CoAP client drops such responses and
sends RST. I haven't solved the problem yet. However if you need only
client you should be okay for now.

4. DTLS is currently not supported. I agree it's a must for any real life
application. There are some Python DTLS implementations out there, but I
haven't tried to use them with Twisted yet.

5. I don't know of any non-Twisted Python CoAP libraries with full IPv6 and
DTLS support. This week there was CoAP Plugtest event in Las Vegas (ended
yesterday) - when IETF Core working group publishes some report, it might
be a good summary of existing CoAP implementations. According to the first
summary DTLS plugtest had 66% success rate - which means it's a though
topic.

Best regards
Maciej Wasilak
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