[Twisted-Python] Serial interface for software program

[Laurens Van Houtven]

Hi Anatoly,


Do you know about manhole? I made a video that also demos axiom, but it
should show you what manhole does :)

https://www.youtube.com/watch?v=3-UZiO-AnLc

Essentially it's "repl in a running process".


hth
lvh


On Mon, May 5, 2014 at 4:43 AM, anatoly techtonik <techtonik at gmail.com>wrote:

> Hello, network hackers,
>
> Recently I've got a Raspberry Pi and a friend showed me its serial
> interface and helped to setup it. I was stunned. What I saw - you open
> serial terminal, and you jump in into the middle of boot section. Just
> open a terminal and you see what's going on inside of R.Pi. Any time.
> That's was an intro. =)
>
> For a long time I wanted the same interface for debugging software
> programs. When I was hacking on Spyder I found that my human brain is
> too limited to squeeze details of dynamic of interaction of objects at
> run-time. Spyder is written in Python with Qt, and it is a parallel
> application much like any Twisted app is. But I wanted to push the
> progress, I have to deal with complexity, so I badly needed to be able
> to draw a video of interaction at run-time. That was the problem I
> tried to solve.
>
> And for the first step I needed a way to connect to Spyder at run-time
> and see what's going on. I didn't know how to call that way before,
> but now I have a rather accurate wording - "a serial interface for an
> application". That is the background for the question I am trying to
> ask.
>
> What is the best way to implement such interface considering the
> following properties:
> 1. it needs to be simple (so that you can quickly create python script
> that reads the info)
> 2. it needs to be universal (so that script for one app worked for other)
> 3. it should be asynchronous (connected terminal should not degrade
> performance)
> 4. it needs to be reliable (at least detecting missing packets)
> 5. and cross-platform (and pure python)
>
> Why Twisted? For the first I think that this problem is actual for
> people who are dealing with complexity of dynamic and interconnected
> systems built with the help of Twisted. For the second I believe it
> can only be solved or analyzed by people skilled in interprocess and
> internetwork communications.
>
> One button test:
> 1. program behaves weird
> 2. user hits the button
> 3. terminal pops up
> 4. shows a lot of data for a running program
>
> I am interested to know.
> 1. how the button should discover the program
> network port seems cool, but what about two parallel programs? what
> about different programs that provide this interface?
>
> 2. how terminal receives the data
> i see it as line based - one line - one event, everything is text
>
> 3. how to make it fast
> TCP clearly won't here
>
> 4. how to send the data
> what if two threads (or parallel code) produce serial data? who should
> run the server that serves connected terminals, and how other thread
> will send message to this server? you can not run two TCP servers on
> the same port on the app side, so is there an alternative? how to
> detect missing data in a stream? how to avoid dealing with incomplete
> packets and low level network details?
>
> Thanks. I'd like to get back to hacking on Spyder one day, but this is
> a stumbling block for me every time I think about it or any program of
> compared complexity.
> --
> anatoly t.
>
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